cassini mission plan (pdf) - caps

C A S S I N I

MISSION PLAN

REVISION O, Change 1

August 2005

J

Jet Propulsion Laboratory California Institute of Technology PD 699-100, Rev O, chg 1 JPL D-5564, Rev O, chg 1

1.0 MISSION OVERVIEW..................................................................................................... 1-11.1 Interplanetary Trajectory ............................................................................................... 1-41.2 Tour Overview ................................................................................................................ 1-41.3 Reference Figures and Tables........................................................................................ 1-4

2.0 OPERATIONS OVERVIEW ............................................................................................ 2-12.1 Ground Planning & Coordination................................................................................ 2-12.2 Spacecraft Description.................................................................................................... 2-3

2.2.1 Science Instruments ............................................................................................ 2-42.2.2 The Huygens Probe System............................................................................... 2-4

2.3 Tour Description & Strategies..................................................................................... 2-102.4 Telecommunications..................................................................................................... 2-20

2.4.1 Playback.............................................................................................................. 2-222.4.2 DSN Lockup....................................................................................................... 2-232.4.3 Maintenance....................................................................................................... 2-232.4.4 Probe Relay Problem ........................................................................................ 2-27

2.5 Data Routing and Storage............................................................................................ 2-272.5.1 Orbiter Telemetry Modes................................................................................. 2-282.5.2 SSR Usage........................................................................................................... 2-322.5.3 Data policing...................................................................................................... 2-362.5.4 Carryover............................................................................................................ 2-37

2.6 Navigation and maneuvers ......................................................................................... 2-372.6.1 Tracking.............................................................................................................. 2-372.6.2 Maneuvers.......................................................................................................... 2-392.6.3 Main Engine usage............................................................................................ 2-43

2.7 Attitude Control ............................................................................................................ 2-452.7.1 S/C Attitude Definition ................................................................................... 2-452.7.2 Attitude Commanding..................................................................................... 2-462.7.3 Inertial Vector Propagation ............................................................................. 2-472.7.4 Turning the Spacecraft ..................................................................................... 2-482.7.5 Target Motion Compensation ......................................................................... 2-492.7.6 Titan atmospheric model ................................................................................. 2-492.7.7 Minimum Flyby Altitudes ............................................................................... 2-492.7.8 Hydrazine usage ............................................................................................... 2-502.7.9 Complications with Reaction Wheel Control................................................ 2-52

2.8 Environmental hazards & control .............................................................................. 2-532.8.1 Radiation ............................................................................................................ 2-532.8.2 Thermal Control and Sun Exposure............................................................... 2-532.8.3 Dust ..................................................................................................................... 2-54

2.9 Periodic Activities ......................................................................................................... 2-542.9.1 Engineering Maintenance ................................................................................ 2-542.9.2 Huygens Probe Checkouts............................................................................... 2-552.9.3 Periodic Instrument Maintenance .................................................................. 2-56

2.10 Contingency Plans .................................................................................................... 2-562.10.1 When to halt the background sequence......................................................... 2-562.10.2 When to declare a spacecraft emergency....................................................... 2-572.10.3 High-Level Contingency Plans ....................................................................... 2-57

3.0 OPERATIONAL MODES, GUIDELINES AND CONSTRAINTS, ANDCONTROLLED SCENARIO TIMELINES................................................................................ 3-1

3.1 Operational Mode Definition........................................................................................ 3-13.2 Sequence Constructs Definition.................................................................................... 3-13.3 Requirements on the Design of Operational Modes.................................................. 3-33.4 Requirements on the Design of Modules .................................................................... 3-33.5 Mission Design Guidelines & Constraints ................................................................ 3-12

3.5.1 Operational Modes and Sequence Constructs.............................................. 3-123.5.2 Sequence Development.................................................................................... 3-133.5.3 Spacecraft Pointing ........................................................................................... 3-173.5.4 Telecommunications......................................................................................... 3-173.5.5 Management of On-Board Data...................................................................... 3-193.5.6 Pre-Saturn Science Activities........................................................................... 3-203.5.7 Saturn Tour & SOI............................................................................................. 3-203.5.8 Miscellaneous .................................................................................................... 3-21

3.6 Controlled Scenario Timelines .................................................................................... 3-224.0 SELECTED REFERENCE PROJECT POLICY REQUIREMENTS (FROM 004)5.0 MISSION PLANNING PROCEDURES

1-1

1.0 MISSION OVERVIEWThe Cassini spacecraft is a combined Saturn orbiter and Titan atmospheric probe (to bedelivered on the first or second flyby of Titan). It is a three-axis stabilized spacecraft equippedfor 27 diverse science investigations with 12 orbiter and 6 Huygens probe instruments, onehigh gain and two low gain antennas, three Radioisotope Thermal Generators (RTGs) forpower, main engines, attitude thrusters, and reaction wheels.Cassini was successfully launched on 15 October 1997 using the Titan IV/Centaur launchvehicle with Solid Rocket Motor Upgrade (SRMU) strap-ons and a Centaur upper stage. Thespacecraft is flying a 6.7-year Venus-Venus-Earth-Jupiter Gravity Assist (VVEJGA) trajectoryto Saturn, during which cruise science is planned to checkout, calibrate, and maintain theinstruments as well as characterize the instruments and perform limited science observations.Cruise science is limited by flight software available on the spacecraft as well as cost,scheduling and workforce constraints. Limited science data collection occurred during theVenus flybys and science and calibration occurred during the Earth flyby. As the spacecraftapproached Jupiter, science activities picked up as Jupiter observations served as preparationfor the four-year tour of the Saturnian system.During most of the early portion of cruise, the High Gain Antenna (HGA) was required toshield most of the spacecraft from the Sun and only low-rate communications via thespacecraft’s Low Gain Antennas (LGAs) was possible. Six months after the Earth flyby, thespacecraft was far enough from the Sun to orient the High Gain Antenna (HGA) to Earthenabling much faster communications. Following the Jupiter flyby, the spacecraft attempts todetect gravitational waves using its Ka-band and X-band radio equipment. Instrumentcalibrations, checkout, and other tour preparations are also conducted during the cruisebetween Jupiter and Saturn. In the six months preceding its arrival at Saturn, the spacecraftwill conduct more intensive science activities, including observations of Phoebe immediatelybefore arrival on 11 June 2004.During Saturn Orbit Insertion (SOI) on 1 July 2004, the spacecraft makes its closest approach tothe planet’s surface during the entire mission at an altitude of only 0.3 Saturn radii (18,000km). Due to this unique opportunity, the approximately 100-minute SOI burn required toplace Cassini in orbit around Saturn executes sooner than its optimal point centered aroundperiapsis, and instead ends at periapsis, allowing science observations immediately afterclosest approach.At the third targeted Titan flyby, the ESA Huygens probe descends through the atmosphere ofTitan to its surface. This probe is released from the orbiter 20 days before entry to Titan. Twodays after probe release, the orbiter performs a deflection maneuver to place itself on theproper trajectory for the encounter. The probe flies directly into Titan's atmosphere, where itrelays data to the orbiter for up to 2.5 hours during its descent to the surface.The orbiter then continues on a 74-orbit tour of the Saturnian system, including 45 close Titanflybys for gravity assist and science acquisition. The Titan flybys and Saturn orbits have beendesigned to maximize science coverage while meeting resource and operations limitations.Eight targeted and dozens of non-targeted flybys of selected icy satellites have also beenincluded to determine icy satellite surface compositions and geologic histories. Cassini’sorbital inclination varies widely to investigate the field, particle, and wave environment athigh latitudes, including the hypothesized source of the unique Saturn kilometric radiation.High inclinations also permit high-latitude Saturn radio occultations, viewing of Saturn polarregions, and more nearly vertical viewing of Saturn's rings. The baseline mission ends in mid-2008, for a total mission duration of 10.7 years.

Jupit

er

Venus

1

Venus

2

Earth

Launch

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400DAYS FROM LAUNCH

PHASES

DSN COVERAGE REQUESTED(passes/week)

EVENTS

MANEUVERS

c c c c c

EARTH

CONJUNCTION OPPOSITION

POINTING

ANTENNA

c

HGA HGA

SUN

Laun

ch

Scienc

e

On

EARTH#

HGA#

Inf Inf

PERIHELION/ APHELION

A P A P

Refer to Appendix J for more information about data rate capability.*

1.02 AU 0.68 AU 1.58 AU 0.72 AU

c

LGA LGA

SUN EARTH

Superior Conjunction causes degradation of telemetry and radiometric tracking data.†

Figure 1: Cassini Cruise Segment Timeline

Sup†

SOI

Sup† Sup† Sup†

EARTH/SCIENCE TARGET

DSM SOI

Initial Orbit

Sup†

HGA

SUBPHASES ICO #1

Inner Cruise Outer Cruise Science Cruise

Launch Sequence

TCM1Venus 1 Venus 2 - Earth Jupiter Quiet Cruise Space Science

ApproachScience

Phoebeflyby

GWEopp GWE GWE GWE

Conj.Experiment

Conj.Experiment

c

Indicates actual instrument checkout window.#

21

0

7

14

DOWNLINKDATA RATECAPABILITY(Ranging ON)

high

rat

es

M AFJDNOSAJJMAMFJDNOSAJJMAMFJDNOSAJJMAMFJDNOSAJJMAMFJDNOSAJJMAMFJDNOSAJJMAMFJDN MO

1997 1998 1999 2000 2001 2002 2003 2004AJJ

bps(log scale)

4 0

200948

142 k248 k

HGATransition ICO #2

LGA HGA

22 k

82 k35 k

1-4

1.1 Interplanetary TrajectoryCassini's baseline trajectory is a VVEJGA (flybys of Venus twice, Earth and Jupiter) trajectory.This multiple gravity-assist trajectory is necessary because no existing launch vehicle/upperstage combination can place a spacecraft of Cassini's mass on a direct trajectory to Saturn. Theminimum C3 (or launch energy) required for a direct trajectory in 1997 is 108 km2/s2. A JGAtrajectory, with a single gravity-assist at Jupiter, would require a C3 of 83 km2/s2. Themaximum C3 achievable by the Titan IV (SRMU)/Centaur for the launch mass of Cassini was34 km2/sec2.This trajectory starts the spacecraft inward from the Earth’s orbit, toward Venus, where thefirst Venus gravity assist places the spacecraft on a nearly resonant Venus-to-Venus transfer. Amaneuver at aphelion of this loop lowers perihelion, allowing the trajectory to intersect Venusearlier, and with a greater flight path angle. The second flyby at Venus targets the spacecraftfor a very quick transfer (approximately eight weeks) to Earth. This extremely fortuitousplanetary phasing eliminates the need for an additional trajectory loop in the inner solarsystem. The spacecraft grazes Mars’ orbit on the Venus 1 - Venus 2 leg, and passes through theasteroid belt on the Earth - Jupiter leg of the trajectory. No asteroid flyby is included in thebaseline due to a combination of ground system resource constraints and the high ∆V cost totarget to even the closest asteroid encounter. The Jupiter flyby imparts the remaining velocityrequired to reach Saturn, where arrival occurs on 1 July 2004. Figures 2.3 and 2.4 show thespacecraft interplanetary trajectory.1.2 Tour OverviewThe reference tour consists of 74 orbits of Saturn with various orientations, orbital periodsranging from 7 to 118 days, and Saturn-centered periapsis radii ranging from about 2.7 to 15.6RS (Saturn radii). Orbital inclination with respect to Saturn's equator ranges from 0 – 75.6 ϒ,providing opportunities for ring imaging, magnetospheric coverage, and radio (Earth), solar,and stellar occultations of Saturn, Titan, and the ring system. A total of 45 targeted Titan flybysoccur during the reference tour. Of these, 41 have flyby altitudes less than 2800 km and twohave flyby altitudes greater than 10,000 km. Titan flybys are used to control the spacecraft'sorbit about Saturn as well as for Titan science acquisition. The tour also contains 7 close flybysof icy satellites, and 30 additional distant flybys of icy satellites within 100,000 km.Close Titan flybys are capable of making large changes in the orbiter’s trajectory. A single closeflyby of Titan can change the orbiter’s Saturn-relative velocity by more than 800 m/s.However, Titan is the only satellite of Saturn which is massive enough to use for orbit controlduring a tour. The masses of the others are so small that even close flybys (within severalhundred km) only change the orbiter’s trajectory slightly. Consequently, the Cassini tourconsists mostly of Titan flybys. This places a restriction that each Titan flyby must place theorbiter on a trajectory leading back to Titan. The orbiter cannot be targeted to a flyby of asatellite other than Titan unless the flyby lies almost along a return path to Titan. The largenumber of Titan flybys does result in extensive coverage of Titan.Figure 2.5 shows a view from above Saturn's north pole of all tour orbits in a rotatingcoordinate system in which the Sun direction is fixed. This type of figure is often referred to asa "petal plot" due to the resemblance of the orbits to petals of a flower. The broad range of orbitorientations allows detailed survey of the magnetosphere and atmosphere of Saturn. Figure 1.6shows a "side view", from a direction perpendicular to the plane formed by the Saturn-Sun lineand Saturn’s north pole, in which the inclination of the orbits is apparent. The tour is describedin detail in the following subsections.1.3 Reference Figures and TablesThe following figures and tables provide reference data for the Cassini mission. Trajectoryplots, encounters during the nominal tour and all events during the tour are given, as well asutility tables showing calendar date, one-way light time, weekday and day of year.

Figure 3 CASSINI CRUISE TRAJECTORY

VENUS 1 SWINGBY26 APR 1998

VENUS 2 SWINGBY24 JUN 1999

EARTH SWINGBY18 AUG 1999

DEEP SPACEMANEUVER3 DEC 1998

LAUNCH15 OCT 1997

JUPITER FLYBY30 DEC 2000

PERIHELIA27 MAR 1998 0.67 AU29 JUN 1999 0.72 AU

SATURN ARRIVAL1 JUL 2004

VENUS 2 FLYBY24 JUN 1999

DEEP-SPACE MANEUVERDEC 1998

EARTH FLYBY18 AUG 1999

VENUS 1 FLYBY26 APR 1998

LAUNCH15 OCT 1997

Figure 4 Cassini Cruise Trajectory

TICKS EVERY 30 DAYSTO

JUPITER

PERIHELIA27 MAR 1998 0.67 AU29 JUN 1999 0.72 AU

Saturn Approach through Probe Mission

-40.0

-20.0

0.0

20.0

40.0

60.0

-20.0 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0

Range from Saturn (along Saturn’s direction of motion), Rs

Rang

e fr

om S

atur

n (s

unw

ard)

, Rs

Rev 0 Rev A Rev B Rev C Time ticks

Ta: 2004 Oct 26 @ 1200 kmTb: 2004 Dec 13 @ 2336 kmTc: 2005 Jan 14 @ 60,000 km (Probe Descent)

Time ticks every 2 days

2004 Jun 15

SOI: 2004 Jul 01626 m/s, 96 min

OTM-1: SOI c/u2004 Jul 03

OTM1A: SOI c/u2004 Jul 17

OTM-2: PRM2004 Aug 23392 m/s

OTM-3: PRM c/u2004 Sep 07

OTM-4: Ta-3d 2004 Oct 23OTM-7: Tb-3d 2004 Dec 10

OTM-5: Ta+3d2004 Oct 29

2003 Jul 30

T0: 2004 Jul 02 @ 339,000 km

OTM-6: Apo2004 Nov 21

OTM-8: PTM2004 Dec 1716 m/s

Probe Release2004 Dec 24

OTM-10: ODM2004 Dec 2824 m/s

OTM-10A: ODM c/u2005 Jan 04

OTM-9: PTM c/u2004 Dec 23

1-7

Figure 1.5 Tour Petal Plot-North Pole View(+X parallel to Saturn to Sun direction, +Z Saturn N. Pole)

Figure 1.6 Tour Petal Plot - Side View

Name Epoch CAL DOW CommentLaunch 1997-288 Oct15 Wed C3 = 16.6 km2/sec2APHELION 1997-310 Nov06 Thu Sun range = 1.01 AUTCM-1 1997-313 Nov09 Sun ∆V = 2.7 m/sec on MEo Conjunction 1998-040 Feb09 Mon Inferior conjunctionTCM-2 1998-056 Feb25 Wed ∆V = 0.2 m/sec on RCSPERIHELION 1998-086 Mar27 Fri Sun range = 0.67 AU(TCM-3) 1998-098 Apr08 Wed CanceledVenus flyby 1998-116 Apr26 Sun Altitude = 284 km; Speed = 11.8 km/sec(TCM-4) 1998-134 May14 Thu CanceledDSM 1998-337 Dec03 Thu ∆V = 450 m/secDSM-5 1998-337 Dec03 Thu ∆V = 450.2 m/sec on MEAPHELION 1998-341 Dec07 Mon Sun range = 1.58 AUHGA 1998-362 Dec28 Mon 25 day checkout periodo Opposition 1999-009 Jan09 SatLGA 1999-021 Jan21 Thu Probe thermal constraints restrict HGA usageTCM-6 1999-035 Feb04 Thu ∆V = 11.6 m/sec on METCM-7 1999-138 May18 Tue ∆V = 0.2 m/sec on RCS(TCM-8) 1999-154 Jun03 Thu CanceledVenus flyby 1999-175 Jun24 Thu Altitude = 603 km; Speed = 13.6 km/secPERIHELION 1999-180 Jun29 Tue Sun range = 0.72 AUTCM-9 1999-187 Jul06 Tue ∆V = 43.5 m/sec on METCM-10 1999-200 Jul19 Mon ∆V = 5.1 m/sec on METCM-11 1999-214 Aug02 Mon ∆V = 36.3 m/sec on METCM-12 1999-223 Aug11 Wed ∆V = 12.3 m/sec on MEo Conjunction 1999-229 Aug17 Tue Inferior conjunctionEarth flyby 1999-230 Aug18 Wed Altitude = 1175 km; Speed = 19.0 km/secTCM-13 1999-243 Aug31 Tue ∆V = 6.7 m/sec on MEo Opposition 1999-256 Sep13 MonEnter Asteroid Belt 1999-345 Dec11 Sat Sun range = 2.2 AUHGA 2000-032 Feb01 Tue HGA is Earth-pointed; use after this dateExit Asteroid Belt 2000-103 Apr12 Wed Sun range = 3.3 AUo Conjunction 2000-134 May13 Sat Superior ConjunctionTCM-14 2000-166 Jun14 Wed ∆V = 0.6 m/sec on METCM-15 2000-258 Sep14 Thu ∆V = 0.2 m/sec on RCSo Opposition 2000-333 Nov28 Tue Gravity Wave Opportunity(TCM-16) 2000-342 Dec07 Thu CancelledJupiter flyby 2000-365 Dec30 Sat Altitude = 9,723,890 km; Speed = 11.6 km/secTCM-17 2001-059 Feb28 Wed ∆V = 1.0 m/sec on MEo Conjunction 2001-158 Jun07 Thu Superior Conjunctiono Opposition 2001-350 Dec16 Sun Gravity Wave Experiment - opp±20 daysTCM-18 2002-093 Apr03 Wed ∆V = 1.2 m/sec on MEo Conjunction 2002-172 Jun21 Fri Conjunction Experiment - conj±15 dayso Opposition 2002-361 Dec27 Fri Gravity Wave Experiment - opp±20 daysTCM-19 2003-121 May01 Thu ∆V = 1.6 m/sec on MEo Conjunction 2003-182 Jul01 Tue Conjunction Experiment - conj±15 daysTCM-19A 2003-253 Sep10 Wed Test of tour RCS maneuver blockTCM-19B 2003-274 Oct01 Wed Test of yaw steering, energy cutoff for SOIo Opposition 2004-004 Jan04 Sun Early Gravity Wave Experiment - Oct-Nov 2003Start of tour 2004-136 May15 Sat Start of first tour sequence S1TCM-20 2004-148 May27 Thu ∆V = 34 m/sec on MEPhoebe flyby 2004-163 Jun11 Fri Altitude = 2000 km; Speed = 6.4 km/secTCM-21 2004-168 Jun16 Wed ∆V = 4 m/sec on METCM-22 2004-173 Jun21 Mon Emergency TCM window if neededSOI 2004-183 Jul01 Thu ∆V = 626 m/secEOM 2008-187 Jul05 Sat End of nominal tour sequences

CASSINI CRUISE EVENT SUMMARY

Seq Rev Name Event Epoch (SCET) Date DOW Comment

S1 0 0PH (t) Phoebe 2004-163T19:33 Jun11 Fri Was P1; inbound 1997 km flyby, v=6.4 km/s, Phase=25 degS5 a aTI (t) Titan 2004-300T15:30 Oct26 Tue T N/A; inbound 1,200 km flyby, v=6.1 km/s, phase=91 degS6 b bTI (t) Titan 2004-348T11:36 Dec13 Mon T N/A; inbound 2,336 km flyby, v=6.0 km/s, phase=98 degS7 c cTI (t) Titan 2005-014T11:04 Jan14 Fri T N/A; inbound 60,000 km flyby, v=5.4 km/s, phase=93 degS8 3 3TI (t) Titan 2005-046T06:54 Feb15 Tue T3; inbound 950 km flyby, v=6.0 km/s, phase=102 degS9 4 4EN (t) Enceladus 2005-068T09:06 Mar09 Wed was E1; inbound 499 km flyby, v=6.6 km/s, phase=43 degS9 5 5TI (t) Titan 2005-090T19:55 Mar31 Thu T4; outbound 2,523 km flyby, v=5.9 km/s, phase=65 degS10 6 6TI (t) Titan 2005-106T19:05 Apr16 Sat T5; outbound 950 km flyby, v=6.1 km/s, phase=127 degS12 11 11EN (t) Enceladus 2005-195T19:57 Jul14 Thu was E2; inbound 1000 km flyby, v=8.1 km/s, phase=43 degS13 13 13TI (t) Titan 2005-234T08:40 Aug22 Mon T6; outbound 4,015 km flyby, v=5.8 km/s, phase=42 degS14 14 14TI (t) Titan 2005-250T07:50 Sep07 Wed T7; outbound 950 km flyby, v=6.1 km/s, phase=84 degS14 15 15HY (t) Hyperion 2005-269T01:41 Sep26 Mon was H1; outbound 990 km flyby, v=5.6 km/s, phase=45 degS15 16 16DI (t) Dione 2005-284T17:58 Oct11 Tue was D1; inbound 500 km flyby, v=9.0 km/s, phase=66 degS15 17 17TI (t) Titan 2005-301T03:58 Oct28 Fri T8; inbound 1,446 km flyby, v=5.9 km/s, phase=105 degS16 18 18RH (t) Rhea 2005-330T22:35 Nov26 Sat was R1; inbound 500 km flyby, v=7.3 km/s, phase=87 degS17 19 19TI (t) Titan 2005-360T18:54 Dec26 Mon T9; outbound 10,429 km flyby, v=5.6 km/s, phase=67 degS17 20 20TI (t) Titan 2006-015T11:36 Jan15 Sun T10; inbound 2,042 km flyby, v=5.8 km/s, phase=121 degS18 21 21TI (t) Titan 2006-058T08:20 Feb27 Mon T11; outbound 1,812 km flyby, v=5.9 km/s, phase=93 degS19 22 22TI (t) Titan 2006-077T23:58 Mar18 Sat T12; inbound 1,947 km flyby, v=5.8 km/s, phase=148 degS20 23 23TI (t) Titan 2006-120T20:53 Apr30 Sun T13; outbound 1,853 km flyby, v=5.8 km/s, phase=121 degS20 24 24TI (t) Titan 2006-140T12:13 May20 Sat T14; inbound 1,879 km flyby, v=5.8 km/s, phase=163 degS21 25 25TI (t) Titan 2006-183T09:12 Jul02 Sun T15; outbound 1,911 km flyby, v=5.8 km/s, phase=148 degS22 26 26TI (t) Titan 2006-203T00:25 Jul22 Sat T16; inbound 950 km flyby, v=6.0 km/s, phase=105 degS23 28 28TI (t) Titan 2006-250T20:12 Sep07 Thu T17; inbound 950 km flyby, v=6.0 km/s, phase=45 degS24 29 29TI (t) Titan 2006-266T18:52 Sep23 Sat T18; inbound 950 km flyby, v=6.0 km/s, phase=90 degS24 30 30TI (t) Titan 2006-282T17:23 Oct09 Mon T19; inbound 950 km flyby, v=6.0 km/s, phase=81 degS25 31 31TI (t) Titan 2006-298T15:51 Oct25 Wed T20; inbound 950 km flyby, v=6.0 km/s, phase=25 degS26 35 35TI (t) Titan 2006-346T11:35 Dec12 Tue T21; inbound 950 km flyby, v=6.0 km/s, phase=124 degS26 36 36TI (t) Titan 2006-362T10:00 Dec28 Thu T22; inbound 1,500 km flyby, v=5.9 km/s, phase=62 degS27 37 37TI (t) Titan 2007-013T08:34 Jan13 Sat T23; inbound 950 km flyby, v=6.0 km/s, phase=53 degS27 38 38TI (t) Titan 2007-029T07:12 Jan29 Mon T24; inbound 2,776 km flyby, v=5.8 km/s, phase=73 degS28 39 39TI (t) Titan 2007-053T03:10 Feb22 Thu T25; outbound 953 km flyby, v=6.3 km/s, phase=161 degS28 40 40TI (t) Titan 2007-069T01:47 Mar10 Sat T26; outbound 956 km flyby, v=6.3 km/s, phase=149 degS28 41 41TI (t) Titan 2007-085T00:21 Mar26 Mon T27; outbound 953 km flyby, v=6.3 km/s, phase=144 degS29 42 42TI (t) Titan 2007-100T22:57 Apr10 Tue T28; outbound 951 km flyby, v=6.3 km/s, phase=137 degS29 43 43TI (t) Titan 2007-116T21:32 Apr26 Thu T29; outbound 951 km flyby, v=6.3 km/s, phase=130 degS30 44 44TI (t) Titan 2007-132T20:08 May12 Sat T30; outbound 950 km flyby, v=6.3 km/s, phase=121 degS30 45 45TI (t) Titan 2007-148T18:51 May28 Mon T31; outbound 2,425 km flyby, v=6.1 km/s, phase=114 degS31 46 46TI (t) Titan 2007-164T17:46 Jun13 Wed T32; outbound 950 km flyby, v=6.3 km/s, phase=107 degS31 47 47TI (t) Titan 2007-180T17:05 Jun29 Fri T33; outbound 1,942 km flyby, v=6.2 km/s, phase=96 degS32 48 48TI (t) Titan 2007-200T00:39 Jul19 Thu T34; inbound 1,302 km flyby, v=6.2 km/s, phase=34 degS33 49 49TI (t) Titan 2007-243T06:34 Aug31 Fri T35; outbound 3,227 km flyby, v=6.1 km/s, phase=87 degS33 49 49IA (t) Iapetus 2007-253T12:33 Sep10 Mon was I1; outbound 1000 km flyby, v=2.4 km/s, phase=65 degS34 50 50TI (t) Titan 2007-275T04:48 Oct02 Tue T36; outbound 950 km flyby, v=6.3 km/s, phase=67 degS35 52 52TI (t) Titan 2007-323T00:52 Nov19 Mon T37; outbound 950 km flyby, v=6.3 km/s, phase=51 degS35 53 53TI (t) Titan 2007-339T00:06 Dec05 Wed T38; outbound 1,300 km flyby, v=6.3 km/s, phase=70 degS36 54 54TI (t) Titan 2007-354T22:56 Dec20 Thu T39; outbound 953 km flyby, v=6.3 km/s, phase=61 degS36 55 55TI (t) Titan 2008-005T21:26 Jan05 Sat T40; outbound 949 km flyby, v=6.3 km/s, phase=37 degS38 59 59TI (t) Titan 2008-053T17:39 Feb22 Fri T41; outbound 959 km flyby, v=6.4 km/s, phase=30 degS38 61 61EN (t) Enceladus 2008-072T19:05 Mar12 Wed was E3; inbound 995 km flyby, v=14.6 km/s, phase=56 degS39 62 62TI (t) Titan 2008-085T14:35 Mar25 Tue T42; outbound 950 km flyby, v=6.4 km/s, phase=21 degS40 67 67TI (t) Titan 2008-133T10:09 May12 Mon T43; outbound 950 km flyby, v=6.4 km/s, phase=35 degS40 69 69TI (t) Titan 2008-149T08:33 May28 Wed T44; outbound 1,316 km flyby, v=6.3 km/s, phase=23 degEM 78 78TI (t) Titan 2008-213T02:20 Jul31 Thu T45; outbound 3,980 km flyby, v=6.1 km/s, phase=7 deg

CASSINI TOUR ENCOUNTERS All times are in SCET. For events with nonzero duration, epoch given is start.

LengthName Date (SCET) CAL DOW Date (SCET) CAL DOW (days)C42 2004-009T12:25 Jan09 Fri 2004-051T00:27 Feb20 Fri 42C43 2004-051T00:27 Feb20 Fri 2004-092T21:28 Apr01 Thu 42C44 2004-092T21:28 Apr01 Thu 2004-135T18:40 May14 Fri 43S1 2004-135T18:40 May14 Fri 2004-171T21:52 Jun19 Sat 36S2 2004-171T21:52 Jun19 Sat 2004-212T21:32 Jul30 Fri 41S3 2004-212T21:32 Jul30 Fri 2004-256T11:35 Sep12 Sun 44S4 2004-256T11:35 Sep12 Sun 2004-292T09:30 Oct18 Mon 36S5 2004-292T09:30 Oct18 Mon 2004-320T07:49 Nov15 Mon 28S6 2004-320T07:49 Nov15 Mon 2004-351T13:22 Dec16 Thu 31S7 2004-351T13:22 Dec16 Thu 2005-022T10:38 Jan22 Sat 37S8 2005-022T10:38 Jan22 Sat 2005-058T00:36 Feb27 Sun 36S9 2005-058T00:36 Feb27 Sun 2005-099T05:15 Apr09 Sat 41S10 2005-099T05:15 Apr09 Sat 2005-134T02:50 May14 Sat 35S11 2005-134T02:50 May14 Sat 2005-169T01:34 Jun18 Sat 35S12 2005-169T01:34 Jun18 Sat 2005-212T22:00 Jul31 Sun 44S13 2005-212T22:00 Jul31 Sun 2005-242T21:43 Aug30 Tue 30S14 2005-242T21:43 Aug30 Tue 2005-281T15:57 Oct08 Sat 39S15 2005-281T15:57 Oct08 Sat 2005-316T17:01 Nov12 Sat 35S16 2005-316T17:01 Nov12 Sat 2005-351T14:21 Dec17 Sat 35S17 2005-351T14:21 Dec17 Sat 2006-027T04:03 Jan27 Fri 41S18 2006-027T04:03 Jan27 Fri 2006-070T00:35 Mar11 Sat 43S19 2006-070T00:35 Mar11 Sat 2006-112T05:15 Apr22 Sat 42S20 2006-112T05:15 Apr22 Sat 2006-154T02:39 Jun03 Sat 42S21 2006-154T02:39 Jun03 Sat 2006-198T00:06 Jul17 Mon 44S22 2006-198T00:06 Jul17 Mon 2006-231T22:06 Aug19 Sat 34S23 2006-231T22:06 Aug19 Sat 2006-263T20:22 Sep20 Wed 32S24 2006-263T20:22 Sep20 Wed 2006-295T18:26 Oct22 Sun 32S25 2006-295T18:26 Oct22 Sun 2006-328T16:30 Nov24 Fri 33S26 2006-328T16:30 Nov24 Fri 2007-005T13:50 Jan05 Fri 42S27 2007-005T13:50 Jan05 Fri 2007-048T10:52 Feb17 Sat 43S28 2007-048T10:52 Feb17 Sat 2007-087T08:04 Mar28 Wed 39S29 2007-087T08:04 Mar28 Wed 2007-124T22:00 May04 Fri 38S30 2007-124T22:00 May04 Fri 2007-162T03:10 Jun11 Mon 37S31 2007-162T03:10 Jun11 Mon 2007-195T01:06 Jul14 Sat 33S32 2007-195T01:06 Jul14 Sat 2007-223T23:20 Aug11 Sat 29S33 2007-223T23:20 Aug11 Sat 2007-265T20:51 Sep22 Sat 42S34 2007-265T20:51 Sep22 Sat 2007-304T18:40 Oct31 Wed 39S35 2007-304T18:40 Oct31 Wed 2007-348T16:00 Dec14 Fri 44S36 2007-348T16:00 Dec14 Fri 2008-022T13:35 Jan22 Tue 39S37 2008-022T13:35 Jan22 Tue 2008-047T11:51 Feb16 Sat 25S38 2008-047T11:51 Feb16 Sat 2008-083T01:50 Mar23 Sun 36S39 2008-083T01:50 Mar23 Sun 2008-110T07:18 Apr19 Sat 27S40 2008-110T07:18 Apr19 Sat 2008-152T04:27 May31 Sat 42S41 2008-152T04:27 May31 Sat 2008-187T00:00 Jul05 Sat 35*Note that S1 begins before the "official" start of the tour at SOI on July 1, 2004.

CASSINI LOAD BOUNDARIES (APPROACH / TOUR)*Start End

Day of Year, Week of Year, and OWLT Calendar for Cassini:

January 2005 February 2005 March 2005Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su

1 2 1 2 3 4 5 6 5 1 2 3 4 5 6 91 2 32 33 34 35 36 37 60 61 62 63 64 651:07 1:07 1:08 1:08 1:08 1:08 1:08 1:08 1:10 1:10 1:10 1:10 1:10 1:10

3 4 5 6 7 8 9 1 7 8 9 10 11 12 13 6 7 8 9 10 11 12 13 103 4 5 6 7 8 9 38 39 40 41 42 43 44 66 67 68 69 70 71 721:07 1:07 1:07 1:07 1:07 1:07 1:07 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:10 1:11 1:11 1:11 1:11 1:11 1:11

10 11 12 13 14 15 16 2 14 15 16 17 18 19 20 7 14 15 16 17 18 19 20 1110 11 12 13 14 15 16 45 46 47 48 49 50 51 73 74 75 76 77 78 791:07 1:07 1:07 1:07 1:07 1:07 1:07 1:08 1:08 1:09 1:09 1:09 1:09 1:09 1:11 1:11 1:11 1:12 1:12 1:12 1:12

17 18 19 20 21 22 23 3 21 22 23 24 25 26 27 8 21 22 23 24 25 26 27 1217 18 19 20 21 22 23 52 53 54 55 56 57 58 80 81 82 83 84 85 861:07 1:07 1:07 1:07 1:07 1:07 1:07 1:09 1:09 1:09 1:09 1:09 1:09 1:10 1:12 1:12 1:12 1:12 1:13 1:13 1:13

24 25 26 27 28 29 30 4 28 9 28 29 30 31 1324 25 26 27 28 29 30 59 87 88 89 901:07 1:07 1:07 1:07 1:07 1:07 1:07 1:10 1:13 1:13 1:13 1:14

31 5311:07

April 2005 May 2005 June 2005Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su

1 2 3 13 1 17 1 2 3 4 5 2291 92 93 121 152 153 154 155 1561:14 1:14 1:14 1:18 1:21 1:21 1:21 1:22 1:22

4 5 6 7 8 9 10 14 2 3 4 5 6 7 8 18 6 7 8 9 10 11 12 2394 95 96 97 98 99 100 122 123 124 125 126 127 128 157 158 159 160 161 162 1631:14 1:14 1:14 1:14 1:15 1:15 1:15 1:18 1:18 1:18 1:18 1:18 1:18 1:19 1:22 1:22 1:22 1:22 1:22 1:22 1:22

11 12 13 14 15 16 17 15 9 10 11 12 13 14 15 19 13 14 15 16 17 18 19 24101 102 103 104 105 106 107 129 130 131 132 133 134 135 164 165 166 167 168 169 1701:15 1:15 1:15 1:15 1:16 1:16 1:16 1:19 1:19 1:19 1:19 1:19 1:19 1:19 1:22 1:22 1:22 1:23 1:23 1:23 1:23

18 19 20 21 22 23 24 16 16 17 18 19 20 21 22 20 20 21 22 23 24 25 26 25108 109 110 111 112 113 114 136 137 138 139 140 141 142 171 172 173 174 175 176 1771:16 1:16 1:16 1:16 1:16 1:17 1:17 1:20 1:20 1:20 1:20 1:20 1:20 1:20 1:23 1:23 1:23 1:23 1:23 1:23 1:23

25 26 27 28 29 30 17 23 24 25 26 27 28 29 21 27 28 29 30 26115 116 117 118 119 120 143 144 145 146 147 148 149 178 179 180 1811:17 1:17 1:17 1:17 1:17 1:18 1:20 1:21 1:21 1:21 1:21 1:21 1:21 1:23 1:23 1:23 1:23

30 31 22150 1511:21 1:21

July 2005 August 2005 September 2005Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su

1 2 3 26 1 2 3 4 5 6 7 31 1 2 3 4 35182 183 184 213 214 215 216 217 218 219 244 245 246 2471:23 1:23 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:22 1:22 1:22 1:22

4 5 6 7 8 9 10 27 8 9 10 11 12 13 14 32 5 6 7 8 9 10 11 36185 186 187 188 189 190 191 220 221 222 223 224 225 226 248 249 250 251 252 253 2541:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:23 1:22 1:22 1:22 1:22 1:22 1:22 1:22

11 12 13 14 15 16 17 28 15 16 17 18 19 20 21 33 12 13 14 15 16 17 18 37192 193 194 195 196 197 198 227 228 229 230 231 232 233 255 256 257 258 259 260 2611:24 1:24 1:24 1:24 1:24 1:24 1:24 1:23 1:23 1:23 1:23 1:23 1:23 1:23 1:22 1:21 1:21 1:21 1:21 1:21 1:21

18 19 20 21 22 23 24 29 22 23 24 25 26 27 28 34 19 20 21 22 23 24 25 38199 200 201 202 203 204 205 234 235 236 237 238 239 240 262 263 264 265 266 267 2681:24 1:24 1:24 1:24 1:24 1:24 1:24 1:23 1:23 1:23 1:23 1:23 1:23 1:23 1:21 1:21 1:21 1:21 1:20 1:20 1:20

25 26 27 28 29 30 31 30 29 30 31 35 26 27 28 29 30 39206 207 208 209 210 211 212 241 242 243 269 270 271 272 2731:24 1:24 1:24 1:24 1:24 1:24 1:24 1:23 1:23 1:23 1:20 1:20 1:20 1:20 1:20

October 2005 November 2005 December 2005Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su

1 2 39 1 2 3 4 5 6 44 1 2 3 4 48274 275 305 306 307 308 309 310 335 336 337 3381:20 1:19 1:16 1:15 1:15 1:15 1:15 1:15 1:12 1:11 1:11 1:11

3 4 5 6 7 8 9 40 7 8 9 10 11 12 13 45 5 6 7 8 9 10 11 49276 277 278 279 280 281 282 311 312 313 314 315 316 317 339 340 341 342 343 344 3451:19 1:19 1:19 1:19 1:19 1:19 1:19 1:15 1:15 1:14 1:14 1:14 1:14 1:14 1:11 1:11 1:11 1:11 1:11 1:11 1:10

10 11 12 13 14 15 16 41 14 15 16 17 18 19 20 46 12 13 14 15 16 17 18 50283 284 285 286 287 288 289 318 319 320 321 322 323 324 346 347 348 349 350 351 3521:18 1:18 1:18 1:18 1:18 1:18 1:18 1:14 1:14 1:13 1:13 1:13 1:13 1:13 1:10 1:10 1:10 1:10 1:10 1:10 1:10

17 18 19 20 21 22 23 42 21 22 23 24 25 26 27 47 19 20 21 22 23 24 25 51290 291 292 293 294 295 296 325 326 327 328 329 330 331 353 354 355 356 357 358 3591:18 1:17 1:17 1:17 1:17 1:17 1:17 1:13 1:13 1:13 1:12 1:12 1:12 1:12 1:10 1:09 1:09 1:09 1:09 1:09 1:09

24 25 26 27 28 29 30 43 28 29 30 48 26 27 28 29 30 31 52297 298 299 300 301 302 303 332 333 334 360 361 362 363 364 3651:17 1:16 1:16 1:16 1:16 1:16 1:16 1:12 1:12 1:12 1:09 1:09 1:09 1:09 1:09 1:09

31 44304

2005



1 1 2 3 4 5 5 1 2 3 4 5 91 32 33 34 35 36 60 61 62 63 641:09 1:08 1:08 1:08 1:08 1:08 1:09 1:09 1:09 1:09 1:09

2 3 4 5 6 7 8 1 6 7 8 9 10 11 12 6 6 7 8 9 10 11 12 102 3 4 5 6 7 8 37 38 39 40 41 42 43 65 66 67 68 69 70 711:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:09 1:10 1:10 1:10 1:10 1:10 1:10

9 10 11 12 13 14 15 2 13 14 15 16 17 18 19 7 13 14 15 16 17 18 19 119 10 11 12 13 14 15 44 45 46 47 48 49 50 72 73 74 75 76 77 781:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:10 1:10 1:10 1:10 1:10 1:11 1:11

16 17 18 19 20 21 22 3 20 21 22 23 24 25 26 8 20 21 22 23 24 25 26 1216 17 18 19 20 21 22 51 52 53 54 55 56 57 79 80 81 82 83 84 851:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:09 1:09 1:09 1:11 1:11 1:11 1:11 1:11 1:11 1:12

23 24 25 26 27 28 29 4 27 28 9 27 28 29 30 31 1323 24 25 26 27 28 29 58 59 86 87 88 89 901:08 1:08 1:08 1:08 1:08 1:08 1:08 1:09 1:09 1:12 1:12 1:12 1:12 1:12

30 31 530 311:08 1:08


1 2 13 1 2 3 4 5 6 7 18 1 2 3 4 2291 92 121 122 123 124 125 126 127 152 153 154 1551:12 1:12 1:16 1:16 1:17 1:17 1:17 1:17 1:17 1:20 1:21 1:21 1:21

3 4 5 6 7 8 9 14 8 9 10 11 12 13 14 19 5 6 7 8 9 10 11 2393 94 95 96 97 98 99 128 129 130 131 132 133 134 156 157 158 159 160 161 1621:13 1:13 1:13 1:13 1:13 1:13 1:13 1:17 1:17 1:18 1:18 1:18 1:18 1:18 1:21 1:21 1:21 1:21 1:21 1:21 1:22

10 11 12 13 14 15 16 15 15 16 17 18 19 20 21 20 12 13 14 15 16 17 18 24100 101 102 103 104 105 106 135 136 137 138 139 140 141 163 164 165 166 167 168 1691:14 1:14 1:14 1:14 1:14 1:14 1:14 1:18 1:18 1:18 1:19 1:19 1:19 1:19 1:22 1:22 1:22 1:22 1:22 1:22 1:22

17 18 19 20 21 22 23 16 22 23 24 25 26 27 28 21 19 20 21 22 23 24 25 25107 108 109 110 111 112 113 142 143 144 145 146 147 148 170 171 172 173 174 175 1761:14 1:15 1:15 1:15 1:15 1:15 1:15 1:19 1:19 1:19 1:20 1:20 1:20 1:20 1:22 1:22 1:22 1:23 1:23 1:23 1:23

24 25 26 27 28 29 30 17 29 30 31 22 26 27 28 29 30 26114 115 116 117 118 119 120 149 150 151 177 178 179 180 1811:15 1:15 1:16 1:16 1:16 1:16 1:16 1:20 1:20 1:20 1:23 1:23 1:23 1:23 1:23


1 2 26 1 2 3 4 5 6 31 1 2 3 35182 183 213 214 215 216 217 218 244 245 2461:23 1:23 1:25 1:25 1:25 1:25 1:25 1:25 1:24 1:24 1:24

3 4 5 6 7 8 9 27 7 8 9 10 11 12 13 32 4 5 6 7 8 9 10 36184 185 186 187 188 189 190 219 220 221 222 223 224 225 247 248 249 250 251 252 2531:23 1:23 1:24 1:24 1:24 1:24 1:24 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:24 1:24 1:24 1:24 1:24 1:23 1:23

10 11 12 13 14 15 16 28 14 15 16 17 18 19 20 33 11 12 13 14 15 16 17 37191 192 193 194 195 196 197 226 227 228 229 230 231 232 254 255 256 257 258 259 2601:24 1:24 1:24 1:24 1:24 1:24 1:24 1:25 1:25 1:24 1:24 1:24 1:24 1:24 1:23 1:23 1:23 1:23 1:23 1:23 1:23

17 18 19 20 21 22 23 29 21 22 23 24 25 26 27 34 18 19 20 21 22 23 24 38198 199 200 201 202 203 204 233 234 235 236 237 238 239 261 262 263 264 265 266 2671:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:24 1:23 1:23 1:23 1:23 1:23 1:23 1:22

24 25 26 27 28 29 30 30 28 29 30 31 35 25 26 27 28 29 30 39205 206 207 208 209 210 211 240 241 242 243 268 269 270 271 272 2731:24 1:24 1:24 1:24 1:24 1:25 1:25 1:24 1:24 1:24 1:24 1:22 1:22 1:22 1:22 1:22 1:22

31 312121:25


1 39 1 2 3 4 5 44 1 2 3 48274 305 306 307 308 309 335 336 3371:22 1:18 1:18 1:18 1:18 1:18 1:14 1:14 1:14

2 3 4 5 6 7 8 40 6 7 8 9 10 11 12 45 4 5 6 7 8 9 10 49275 276 277 278 279 280 281 310 311 312 313 314 315 316 338 339 340 341 342 343 3441:22 1:22 1:21 1:21 1:21 1:21 1:21 1:17 1:17 1:17 1:17 1:17 1:17 1:17 1:14 1:13 1:13 1:13 1:13 1:13 1:13

9 10 11 12 13 14 15 41 13 14 15 16 17 18 19 46 11 12 13 14 15 16 17 50282 283 284 285 286 287 288 317 318 319 320 321 322 323 345 346 347 348 349 350 3511:21 1:21 1:21 1:20 1:20 1:20 1:20 1:16 1:16 1:16 1:16 1:16 1:16 1:16 1:13 1:13 1:12 1:12 1:12 1:12 1:12

16 17 18 19 20 21 22 42 20 21 22 23 24 25 26 47 18 19 20 21 22 23 24 51289 290 291 292 293 294 295 324 325 326 327 328 329 330 352 353 354 355 356 357 3581:20 1:20 1:20 1:20 1:20 1:20 1:19 1:15 1:15 1:15 1:15 1:15 1:15 1:15 1:12 1:12 1:12 1:12 1:11 1:11 1:11

23 24 25 26 27 28 29 43 27 28 29 30 48 25 26 27 28 29 30 31 52296 297 298 299 300 301 302 331 332 333 334 359 360 361 362 363 364 3651:19 1:19 1:19 1:19 1:19 1:19 1:18 1:15 1:14 1:14 1:14 1:11 1:11 1:11 1:11 1:11 1:10 1:10

30 31 44303 304

2006


January 2007 February 2007 March 2007Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su1 2 3 4 5 6 7 1 1 2 3 4 5 1 2 3 4 91 2 3 4 5 6 7 32 33 34 35 60 61 62 631:10 1:10 1:10 1:10 1:10 1:10 1:10 1:08 1:08 1:08 1:08 1:09 1:09 1:09 1:09

8 9 10 11 12 13 14 2 5 6 7 8 9 10 11 6 5 6 7 8 9 10 11 108 9 10 11 12 13 14 36 37 38 39 40 41 42 64 65 66 67 68 69 701:10 1:10 1:10 1:09 1:09 1:09 1:09 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:09 1:09 1:09 1:09 1:09 1:09 1:09

15 16 17 18 19 20 21 3 12 13 14 15 16 17 18 7 12 13 14 15 16 17 18 1115 16 17 18 19 20 21 43 44 45 46 47 48 49 71 72 73 74 75 76 771:09 1:09 1:09 1:09 1:09 1:09 1:09 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:09 1:09 1:09 1:10 1:10 1:10 1:10

22 23 24 25 26 27 28 4 19 20 21 22 23 24 25 8 19 20 21 22 23 24 25 1222 23 24 25 26 27 28 50 51 52 53 54 55 56 78 79 80 81 82 83 841:09 1:09 1:09 1:09 1:09 1:09 1:09 1:08 1:08 1:08 1:08 1:08 1:08 1:08 1:10 1:10 1:10 1:10 1:10 1:10 1:10

29 30 31 5 26 27 28 9 26 27 28 29 30 31 1329 30 31 57 58 59 85 86 87 88 89 901:08 1:08 1:08 1:09 1:09 1:09 1:10 1:11 1:11 1:11 1:11 1:11


1 13 1 2 3 4 5 6 18 1 2 3 2291 121 122 123 124 125 126 152 153 1541:11 1:15 1:15 1:15 1:15 1:15 1:16 1:19 1:19 1:19

2 3 4 5 6 7 8 14 7 8 9 10 11 12 13 19 4 5 6 7 8 9 10 2392 93 94 95 96 97 98 127 128 129 130 131 132 133 155 156 157 158 159 160 1611:11 1:11 1:12 1:12 1:12 1:12 1:12 1:16 1:16 1:16 1:16 1:16 1:16 1:17 1:19 1:20 1:20 1:20 1:20 1:20 1:20

9 10 11 12 13 14 15 15 14 15 16 17 18 19 20 20 11 12 13 14 15 16 17 2499 100 101 102 103 104 105 134 135 136 137 138 139 140 162 163 164 165 166 167 1681:12 1:12 1:12 1:12 1:13 1:13 1:13 1:17 1:17 1:17 1:17 1:17 1:17 1:18 1:20 1:21 1:21 1:21 1:21 1:21 1:21

16 17 18 19 20 21 22 16 21 22 23 24 25 26 27 21 18 19 20 21 22 23 24 25106 107 108 109 110 111 112 141 142 143 144 145 146 147 169 170 171 172 173 174 1751:13 1:13 1:13 1:13 1:13 1:14 1:14 1:18 1:18 1:18 1:18 1:18 1:18 1:19 1:21 1:21 1:21 1:22 1:22 1:22 1:22

23 24 25 26 27 28 29 17 28 29 30 31 22 25 26 27 28 29 30 26113 114 115 116 117 118 119 148 149 150 151 176 177 178 179 180 1811:14 1:14 1:14 1:14 1:14 1:14 1:15 1:19 1:19 1:19 1:19 1:22 1:22 1:22 1:22 1:22 1:22

30 181201:15


1 26 1 2 3 4 5 31 1 2 35182 213 214 215 216 217 244 2451:23 1:25 1:25 1:25 1:25 1:25 1:25 1:25

2 3 4 5 6 7 8 27 6 7 8 9 10 11 12 32 3 4 5 6 7 8 9 36183 184 185 186 187 188 189 218 219 220 221 222 223 224 246 247 248 249 250 251 2521:23 1:23 1:23 1:23 1:23 1:23 1:23 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25

9 10 11 12 13 14 15 28 13 14 15 16 17 18 19 33 10 11 12 13 14 15 16 37190 191 192 193 194 195 196 225 226 227 228 229 230 231 253 254 255 256 257 258 2591:23 1:23 1:23 1:23 1:24 1:24 1:24 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:24 1:24

16 17 18 19 20 21 22 29 20 21 22 23 24 25 26 34 17 18 19 20 21 22 23 38197 198 199 200 201 202 203 232 233 234 235 236 237 238 260 261 262 263 264 265 2661:24 1:24 1:24 1:24 1:24 1:24 1:24 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:24 1:24 1:24 1:24 1:24 1:24 1:24

23 24 25 26 27 28 29 30 27 28 29 30 31 35 24 25 26 27 28 29 30 39204 205 206 207 208 209 210 239 240 241 242 243 267 268 269 270 271 272 2731:24 1:24 1:24 1:24 1:24 1:24 1:24 1:25 1:25 1:25 1:25 1:25 1:24 1:24 1:24 1:24 1:24 1:24 1:24

30 31 31211 2121:25 1:25

October 2007 November 2007 December 2007Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su1 2 3 4 5 6 7 40 1 2 3 4 44 1 2 48274 275 276 277 278 279 280 305 306 307 308 335 3361:24 1:23 1:23 1:23 1:23 1:23 1:23 1:20 1:20 1:20 1:20 1:16 1:16

8 9 10 11 12 13 14 41 5 6 7 8 9 10 11 45 3 4 5 6 7 8 9 49281 282 283 284 285 286 287 309 310 311 312 313 314 315 337 338 339 340 341 342 3431:23 1:23 1:23 1:23 1:23 1:22 1:22 1:20 1:20 1:20 1:19 1:19 1:19 1:19 1:16 1:16 1:16 1:16 1:16 1:15 1:15

15 16 17 18 19 20 21 42 12 13 14 15 16 17 18 46 10 11 12 13 14 15 16 50288 289 290 291 292 293 294 316 317 318 319 320 321 322 344 345 346 347 348 349 3501:22 1:22 1:22 1:22 1:22 1:22 1:22 1:19 1:19 1:19 1:19 1:19 1:18 1:18 1:15 1:15 1:15 1:15 1:15 1:15 1:14

22 23 24 25 26 27 28 43 19 20 21 22 23 24 25 47 17 18 19 20 21 22 23 51295 296 297 298 299 300 301 323 324 325 326 327 328 329 351 352 353 354 355 356 3571:22 1:22 1:21 1:21 1:21 1:21 1:21 1:18 1:18 1:18 1:18 1:18 1:17 1:17 1:14 1:14 1:14 1:14 1:14 1:14 1:13

29 30 31 44 26 27 28 29 30 48 24 25 26 27 28 29 30 52302 303 304 330 331 332 333 334 358 359 360 361 362 363 3641:21 1:21 1:20 1:17 1:17 1:17 1:17 1:17 1:13 1:13 1:13 1:13 1:13 1:13 1:13

31365

2007



1 2 3 4 5 6 1 1 2 3 5 1 2 91 2 3 4 5 6 32 33 34 61 621:12 1:12 1:12 1:12 1:12 1:12 1:10 1:10 1:09 1:09 1:09

7 8 9 10 11 12 13 2 4 5 6 7 8 9 10 6 3 4 5 6 7 8 9 107 8 9 10 11 12 13 35 36 37 38 39 40 41 63 64 65 66 67 68 691:12 1:12 1:11 1:11 1:11 1:11 1:11 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09

14 15 16 17 18 19 20 3 11 12 13 14 15 16 17 7 10 11 12 13 14 15 16 1114 15 16 17 18 19 20 42 43 44 45 46 47 48 70 71 72 73 74 75 761:11 1:11 1:11 1:11 1:11 1:11 1:10 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09

21 22 23 24 25 26 27 4 18 19 20 21 22 23 24 8 17 18 19 20 21 22 23 1221 22 23 24 25 26 27 49 50 51 52 53 54 55 77 78 79 80 81 82 831:10 1:10 1:10 1:10 1:10 1:10 1:10 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:09 1:10 1:10 1:10 1:10 1:10 1:10

28 29 30 31 5 25 26 27 28 29 9 24 25 26 27 28 29 30 1328 29 30 31 56 57 58 59 60 84 85 86 87 88 89 901:10 1:10 1:10 1:10 1:09 1:09 1:09 1:09 1:09 1:10 1:10 1:10 1:10 1:10 1:10 1:10

31 14911:11


1 2 3 4 5 6 14 1 2 3 4 18 1 2292 93 94 95 96 97 122 123 124 125 1531:11 1:11 1:11 1:11 1:11 1:11 1:14 1:14 1:14 1:14 1:18

7 8 9 10 11 12 13 15 5 6 7 8 9 10 11 19 2 3 4 5 6 7 8 2398 99 100 101 102 103 104 126 127 128 129 130 131 132 154 155 156 157 158 159 1601:11 1:11 1:11 1:11 1:12 1:12 1:12 1:14 1:15 1:15 1:15 1:15 1:15 1:15 1:18 1:18 1:19 1:19 1:19 1:19 1:19

14 15 16 17 18 19 20 16 12 13 14 15 16 17 18 20 9 10 11 12 13 14 15 24105 106 107 108 109 110 111 133 134 135 136 137 138 139 161 162 163 164 165 166 1671:12 1:12 1:12 1:12 1:12 1:12 1:13 1:15 1:16 1:16 1:16 1:16 1:16 1:16 1:19 1:19 1:19 1:20 1:20 1:20 1:20

21 22 23 24 25 26 27 17 19 20 21 22 23 24 25 21 16 17 18 19 20 21 22 25112 113 114 115 116 117 118 140 141 142 143 144 145 146 168 169 170 171 172 173 1741:13 1:13 1:13 1:13 1:13 1:13 1:13 1:16 1:16 1:17 1:17 1:17 1:17 1:17 1:20 1:20 1:20 1:21 1:21 1:21 1:21

28 29 30 18 26 27 28 29 30 31 22 23 24 25 26 27 28 29 26119 120 121 147 148 149 150 151 152 175 176 177 178 179 180 1811:14 1:14 1:14 1:17 1:17 1:18 1:18 1:18 1:18 1:21 1:21 1:21 1:21 1:21 1:22 1:22

30 271821:22


1 2 3 4 5 6 27 1 2 3 31 1 2 3 4 5 6 7 36183 184 185 186 187 188 214 215 216 245 246 247 248 249 250 2511:22 1:22 1:22 1:22 1:22 1:23 1:25 1:25 1:25 1:26 1:26 1:26 1:26 1:26 1:26 1:26

7 8 9 10 11 12 13 28 4 5 6 7 8 9 10 32 8 9 10 11 12 13 14 37189 190 191 192 193 194 195 217 218 219 220 221 222 223 252 253 254 255 256 257 2581:23 1:23 1:23 1:23 1:23 1:23 1:23 1:25 1:25 1:25 1:25 1:25 1:25 1:25 1:26 1:26 1:26 1:26 1:26 1:26 1:26

14 15 16 17 18 19 20 29 11 12 13 14 15 16 17 33 15 16 17 18 19 20 21 38196 197 198 199 200 201 202 224 225 226 227 228 229 230 259 260 261 262 263 264 2651:23 1:23 1:24 1:24 1:24 1:24 1:24 1:25 1:25 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26

21 22 23 24 25 26 27 30 18 19 20 21 22 23 24 34 22 23 24 25 26 27 28 39203 204 205 206 207 208 209 231 232 233 234 235 236 237 266 267 268 269 270 271 2721:24 1:24 1:24 1:24 1:24 1:24 1:24 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:25 1:25

28 29 30 31 31 25 26 27 28 29 30 31 35 29 30 40210 211 212 213 238 239 240 241 242 243 244 273 2741:25 1:25 1:25 1:25 1:26 1:26 1:26 1:26 1:26 1:26 1:26 1:25 1:25


1 2 3 4 5 40 1 2 44 1 2 3 4 5 6 7 49275 276 277 278 279 306 307 336 337 338 339 340 341 3421:25 1:25 1:25 1:25 1:25 1:23 1:23 1:19 1:19 1:19 1:19 1:19 1:18 1:18

6 7 8 9 10 11 12 41 3 4 5 6 7 8 9 45 8 9 10 11 12 13 14 50280 281 282 283 284 285 286 308 309 310 311 312 313 314 343 344 345 346 347 348 3491:25 1:25 1:25 1:25 1:25 1:25 1:25 1:23 1:22 1:22 1:22 1:22 1:22 1:22 1:18 1:18 1:18 1:18 1:18 1:17 1:17

13 14 15 16 17 18 19 42 10 11 12 13 14 15 16 46 15 16 17 18 19 20 21 51287 288 289 290 291 292 293 315 316 317 318 319 320 321 350 351 352 353 354 355 3561:25 1:24 1:24 1:24 1:24 1:24 1:24 1:22 1:22 1:22 1:21 1:21 1:21 1:21 1:17 1:17 1:17 1:17 1:17 1:16 1:16

20 21 22 23 24 25 26 43 17 18 19 20 21 22 23 47 22 23 24 25 26 27 28 52294 295 296 297 298 299 300 322 323 324 325 326 327 328 357 358 359 360 361 362 3631:24 1:24 1:24 1:24 1:24 1:23 1:23 1:21 1:21 1:21 1:21 1:20 1:20 1:20 1:16 1:16 1:16 1:16 1:16 1:16 1:15

27 28 29 30 31 44 24 25 26 27 28 29 30 48 29 30 31301 302 303 304 305 329 330 331 332 333 334 335 364 365 3661:23 1:23 1:23 1:23 1:23 1:20 1:20 1:20 1:20 1:19 1:19 1:19 1:15 1:15 1:15

2008

Table B.1: Saturn Geometric QuantitiesQuantity Value UnitsSolar distance, mean 1430 million km

9.56 AUSolar distance, min 1350 million km

9.02 AUOrbital Solar distance, max 1510 million kmQuantities 10.09 AU

Siderial orbit period 10760 days29.46 years

Mean orbital velocity 9.64 km/sOrbital eccentricity 0.056Inclination to ecliptic 2.49 degreesEquatorial radius at 100 mbar =Rs 60330 kmPolar radius at 100 mbar 54180 kmEquatorial radius at 1 bar 60268 kmPolar radius at 1 bar 54364 kmJ2 (unnormalized) 0.016298Mass 5.69E+26 kg

95.2 Earth massesGM (planet centered) 37931267.73 km^3/s^2Volume 8.25E+23 cubic meters

Planetary 764 Earth volumesQuantities Rotation period, kilometric 10.66 hours

Rotation period, equatorial 10.17 hoursAxial tilt 26.73 degreesAtmospheric temp. at 1 bar 134 degrees KelvinEffective temperature 95 degrees KelvinVisual geometric albedo 0.47Bolometric Bond albedo 0.34Mean density 0.688 g/cm3Mean gravity at 1 bar 10.46 m/s2

1.07 Earth gravitiesConstituent gases H2, He, CH4, NH3Magnetic dipole moment 0.218 gauss Rs3

Field 4.70E+28 gauss cm3Quantities Magnetic dipole tilt < 1 degrees

Magnetic dipole offset 0.04 Rs

Distance Distance Orbital Mean Orbital Orbital Orbital

Satellite or Ring from Saturn from Saturn Period Velocity Inclination Eccentricity

Name (km x 1000)(Saturn radii

of 60330 km)(days) (km/sec) (degrees)

D RING (inner edge) 66.97 1.11 0.20 23.81 0 0

C RING (inner edge) (D ring outer edge) 74.51 1.24 0.24 22.57 0 0

Maxwell Gap 87.64 1.45 0.31 20.81 0 0B RING (inner edge) (C ring outer edge) 92.00 1.52 0.33 20.31 0 0

CASSINI div. (inner edge) B ring (outer edge) 117.58 1.95 0.48 17.97 0 0

A RING (inner edge) (Cassini div. outer edge) 122.17 2.03 0.50 17.63 0 0

Encke Division (inner edge) 133.41 2.21 0.58 16.87 0 0

Pan 133.58 2.21 0.58 16.86 0 0

Encke Division (outer edge) 133.73 2.22 0.58 16.85 0 0

Keeler Gap 136.53 2.26 0.58 16.67 0 0(A ring outer edge) 136.78 2.27 0.60 16.66 0 0

Atlas 137.64 2.28 0.60 16.61 0.3 0.0030

Prometheus 139.35 2.31 0.61 16.50 0 0.0024

F RING (inner edge) 140.18 2.32 0.62 16.46 0 0

F RING (outer edge) 140.27 2.33 0.62 16.45 0 0

Pandora 141.70 2.35 0.63 16.37 0.1 0.0042

Epimetheus 151.42 2.51 0.69 15.83 0.34 (var.) 0.0090

Janus 151.47 2.51 0.69 15.83 0.14 (var.) 0.0070

G RING (inner edge) 165.00 2.73 0.79 15.17 0 0

G RING (outer edge) 176.00 2.92 0.87 14.69 0 0

Mimas 185.52 3.08 0.94 14.30 1.53 0.0202

E RING (approximate inner edge) 189.87 3.15 0.98 14.14 0 0

Enceladus 238.02 3.95 1.37 12.63 0.02 0.0045

Tethys 294.66 4.88 1.89 11.35 1.09 0

Telesto 294.66 4.88 1.89 11.35 0 0

Calypso 294.66 4.88 1.89 11.35 0 0

Dione 377.40 6.26 2.74 10.03 0.02 0.0022

Helene 378.40 6.27 2.74 10.02 0.20 0.0050

(E ring approx. outer edge) 420.00 6.96 3.21 9.51 0.00 0

Rhea 527.04 8.74 4.52 8.49 0.35 0.0010

Titan 1221.90 20.25 15.95 5.57 0.33 0.0292

Hyperion 1481.10 24.55 21.28 5.06 0.43 0.1042

Iapetus 3561.30 59.03 79.33 3.26 14.72 0.0283

Phoebe 12952.00 214.69 550.48 1.71 175.30 0.1633

Table B.2A: Saturnian Satellites - Orbital Geometry

Mean Alternate

Satellite or Ring Radius* GM Density Observed Features Names Discovery

Name (km) (km^3/s^2) (g/cm3)

D RING (inner edge) 7540 ---- ---- D: very thin, not well defined; seen best in forward-scattered light Pioneer 11 1979

C RING (inner edge) (D ring outer edge) 17490 ---- ---- C: very complicated grooved region; many ringlets

of regular ordering Crepe ring C ring: W.C. & G.P Bond & C. W. Tuttle 1850

Maxwell Gap 270 ---- ---- ----B RING (inner edge) (C ring outer edge) 25580 ---- ---- B: brightest ring; highly complex; thousands of

ringlets; ring spokes; redder particlesB ring:

C. Huygens 1659*CASSINI div. (inner edge) B ring (outer edge) 4590 ---- ---- Cassini division: most prominent gap; caused by

half-period resonance with Mimas; faint ringletsdivision:

G. D. Cassini 1675A RING (inner edge) (Cassini div. outer edge) 14610 ---- ---- A: many ringlets & minor gaps; darker & more

transparent than BA ring:

C. Huygens 1659*Encke Division (inner edge) 325 ---- ---- has faint ringlets J. F. Encke 1837

Pan 10 0.00018 ---- ---- 1981 S13 S18

Voyager 2 1981 (Showalter)

Encke Division (outer edge) ---- ---- ----

Keeler Gap 35 ---- ---- ----(A ring outer edge) ---- ---- ---- ---- ----

Atlas 18.5 x 17.2 x 13.5 0.00072 ---- elongated; may control A ring outer edge 1980 S28

S17Voyager 1 1980

(Terrile)

Prometheus 74 x 50 x 34 0.022 ~0.70 shepherd satellite to F ring with Pandora 1980 S27 S16

Voyager 1 1980 (Collins & Carlson)

F RING (inner edge) 90 ---- ---- "braided" ring with separate strands; shepherded by Prometheus and Pandora Pioneer 11 1979

F RING (outer edge) ---- ---- ----

Pandora 55 x 44 x 31 0.013 ~0.70 shepherd satellite to F ring with Prometheus 1980 S26 S15

Voyager 1 1980 (Collins & Carlson)

Epimetheus 69 x 55 x 55 0.0357 ~0.70 irregular; may have been joined with Janus 1980 S3 S11 Fountain & Larson 1978

Janus 97 x 95 x 77 0.1284 ~0.67 irregular; trades orbits with Epimetheus 1980 S1 S10 Fountain & Larson 1978

G RING (inner edge) 11000 ---- ---- extremely tenuous & optically thin; seen best with forward-scattered light; has denser core

detected Pioneer 11 1979 confirmed Voyager 1 1980

G RING (outer edge) ---- ---- ---- extremely tenuous & optically thin; seen best with forward-scattered light; has denser core

detected Pioneer 11 1979 confirmed Voyager 1 1980

Mimas 209 x 196 x 191 2.5 1.17 giant crater Herschel on leading hemisphere; icy

surface; may be covered with water frost S1 Herschel 1789

E RING (approximate inner edge) 230130 ---- ---- E: thought to be sustained by Enceladus; density

peaks at Enceladus' orbit Voyager 1 1980

Enceladus 256 x 247 x 245 4.9 1.24 complex & varied geological evolution; craters;

plains; crustal movements; may be E ring source S2 Herschel 1789

Tethys 536 x 528 x 526 41.808 1.21 almost pure ice; large trench Ithaca Chasma (4-5km

deep); large 400km crater Odysseus S3 G. D. Cassini 1684

Telesto 15 x 12.5 x 7.5 0.00048 ---- co-orbital with Tethys, 60° ahead (L4) 1980 S13 S13 Smith et al 1980

Calypso 15 x 8 x 8 0.00024 ---- co-orbital with Tethys, 60° behind (L5) 1980 S25 S14 Smith et al 1980

Dione 560 73.156 1.43 cratered leading hemisphere; wispy features on trailing hemisphere S4 G. D. Cassini 1684

Helene 16 0.0017 ---- co-orbital with Dione 60° ahead (L4) Dione B 1980S6 S12

Lacques & Lecacheaux 1980

(E ring approx. outer edge) ---- ---- ---- ---- ----

Rhea 764 154 1.33 largest icy satellite; dark trailing hemisphere; densely cratered equator S5 Cassini 1672

Titan 2575 8978.2 1.88largest of the satellites; N2, He atmosphere; aerosols, hydrocarbons; surface temp. = 92°K; orangish disk; darker n. hemisphere; H2 torus

S6 Huygens 1655

Hyperion 180 x 140 x 113 0.99 1.40

irregular shape; long axis not pointed at Saturn (perhaps due to recent collision); dark surface; chaotic orbit

S7 Bond 1848

Iapetus 718 106 1.21 MUCH darker leading hemisphere; ring of dark material near division S8 G. D. Cassini 1671

Phoebe 115 x 110 x 105 0.48 0.70

retrograde orbit; only satellite not tidally locked; ~9hr rotation; dark surface; roughly spherical; may be captured body

S9 Pickering 1898

Table B.2B: Saturnian Satellites - Body Characteristics

*Some bodies list 3-axis radii when available corresponding to sub-Saturn equatorial radius, along orbit eq. radius, and polar radius.

Ring values indicate width ( R) of ring.

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2.0 OPERATIONS OVERVIEWThe mission design has a long (almost 7 year) cruise to get the spacecraft to Saturn and a 4 yeartour in orbit around Saturn. During the cruise phase, the priority is placed on essentialengineering, navigation, and science instrument maintenance, calibrations, and checkout.Some limited science collection is conducted, but is generally constrained to those activitiesrequired for tour readiness, or unique science opportunities that are in line with the programscience objectives. A typical week in cruise would contain two downlink passes and have ahandful of engineering activities as well as a low level of science observations. During earlycruise, the spacecraft stayed on Earth-point most of the time due to thermal constraints; in latercruise, the spacecraft occasionally articlates to collect data from a particular target. Duringapproach science, beginning in January 2004, intensive tour-like science observations begin.On a typical day in the Cassini tour, the spacecraft collects science data for 15 hours byorienting the spacecraft at a variety of targets. One instrument at a time controls the pointingof the spacecraft, and other instruments may “ride along” and collect data at the same time.Ride-alongs or collaborative data collection is often negotiated between the science teams.The remaining 9 hours is spent in one block on Earth-point, downlinking (or playing back) thedata. During downlink – since one axis of the spacecraft must be fixed to Earth - the spacecraftcan only spin about the Z axis and collect fields, particles & waves data. This sweeping duringplayback allows three dimensional and temporal variations in the fields and particlesenvironment to be measured.Control of the spacecraft is done, for the most part, from autonomous sequences stored on-board the spacecraft. Spacecraft sequencing uses a combination of centralized commands (forcontrol of the system level resources) and instrument commands issued by the Command andData Subsystem (CDS) and the instrument microprocessors to conduct activities and maintainthe health and safety of the spacraft. Instrument data is formatted (including editing orcompression) within the instrument microprocessor, and then collected on the spacecraft busby the CDS on a schedule determined by the active telemetry mode. Packets from theengineering subsystems and instruments are assembled into frames and stored on the SolidState Recorder or inserted directly into the downlink telemetry stream.The spacecraft provides system level services for each of the twelve science investigations.These services include instrument command delivery, telemetry collection and transmission,spacecraft pointing and attitude stability, power, and thermal control. The spacecraft is flownwith sufficient margins to allow the instruments to operate fairly independently from eachother, and with a minimum of real-time ground intervention, but still allow for collaborative,synergistic collection of data.The Cassini spacecraft operates in a series of standard well-characterized configurations,referred to as "operational modes," and transitions between them use "fixed sequences." Sincethere is insufficient power to operate all instruments simultaneously, operational modes havebeen defined to balance the science return with the need to constrain operational complexityand cost in the planning and sequencing of science observations. Within an operational mode,any science and spacecraft activities are allowed that do not violate either the mode definitionor other applicable constraints. The definition of each mode mirrors a common category ofactivities (such as maneuvers, or downlink to Earth) that are expected to be done often duringthe mission. Certain non-repetitive activities will be done with unique sequences of commandsrather than operational modes. Non-variable but repetitive activities that are not done withinan operational mode are called fixed sequences. These sequences are developed and validatedonce for use multiple times.2.1 Ground Planning & CoordinationSpacecraft operations will be centralized at JPL. The science teams are led using a distributedoperations structure to allow scientists to operate their instruments from their home

2-2

institutions with the minimum interaction necessary to collect their data. Specific functionsprovided centrally by JPL for the scientists include mission planning, sequence integration,sequence and command radiation, spacecraft telemetry data collection/processing (packetextraction)/storage, spacecraft monitoring and performance maintenance, Facility Instrumenthealth and safety monitoring, and spacecraft navigation.The sequencing process is a hierarchical step-wise refinement process, starting with generalgoals, to high-level sequence components, and ends with low-level commanding. Sequenceplanning begins with long-range plans generated by the mission planners. Consumableallocations, margin policy, long-range DSN agreements, guidelines & constraints, and theoperational strategies documented in this section guide the initial sequence design. The scienceplanning team works with the mission planning, spacecraft and other offices to generate aconflict-free activity plan of integrated science and engineering activities. Both the distributedscience teams and engineering subsystem representatives submit activity requests which areintegrated by the science planning team. Conflicts between science activities are resolvedwithin the science planning team, and conflicts between engineering activities are resolvedwithin the spacecraft office, with help from the science planning team. Conflicts betweenscience and engineering activities are resolved with participation from all elementrepresentatives, with the mission planning office as the liaison when necessary.Once the conflict-free activity plan is completed, with scheduled activities, DSN passes,instrument pointing, and data allocations, the sequence virtual team integrates the plan into aconflict-free sequence and generates, verifies and validates all related commands to be sent tothe spacecraft, except for instrument internal commands. The sequence virtual team is alsoresponsible for all system-level real-time commands associated with the sequence, andmonitors the progress of the activities until the sequence is complete.During cruise, sequences largely make use of commands and scripts inherited from spacecrafttesting during the Assembly, Test, and Launch Operations (ATLO) phase. Repeatablesequence components (i.e. modules) are developed slowly as experience is gained in operatingthe spacecraft. Some science is collected during cruise in order to gain experience withinstrument operations and prepare the instrument and instrument teams for tour. During thelater portions of cruise, the Science Operations Plan (SOP) is developed as the detailed plan oftour activities. The SOP is a conflict-free listing of all observations and engineering activities, aconstraint-checked pointing profile, and data volume allocations that would provide anacceptable level of science required to meet the primary mission objectives. As tourapproaches, any high-level trade studies and changes in operations strategy are incorporatedvia an SOP aftermarket process, which is also used for further science optimization. In the fewmonths before execution, the SOP sequences are refined as necessary via a short-term updateprocess and final constraint checking, integration, validation, and command generation areperformed. Figure 2-1 illustrates the processes for sequence generation for tour.The flight team is sized for nominal operations, and anomaly staffing is done by augmentationwith personnel (with spacecraft expertise) from the JPL technical divisions. Only a few specificcontingency plans are developed (mostly dealing with launch and Earth flyby events).Identification and prioritization of these plans has been done as needed to reduce the risk tothe mission within the cost constraints. This effort is documented in the Risk ManagementPlan.Updates to a sequence after it has been validated are limited. Changes to an instrument’sinternal commands or instrument memory may be accomplished via the instrument-internalreal-time command process and can range from the replacement of an entire block ofinstructions to the update of a few words in instrument memory. Updates to the tables whichstore the locations of various mission targets may also be uplinked if the spacecraft or targetephemeris has changed to refine pointing for planned observations. Tweaks to the storedsequence for other observation timing changes are also possible. These changes should be

2-3

limited as much as possible, and must be approved by the sequence teams and/or the projectmanager.

Figure 2-1 Planning Processes for Tour2.2 Spacecraft DescriptionThe Cassini spacecraft is a three-axis-stabilized spacecraft, depicted in figure 2-2. The origin ofthe Orbiter coordinate system lies at the center of the field joint between the Bus and theUpper Equipment Module Upper Shell Structure Assembly. The Z-axis emanates from theorigin and is perpendicular to a plane generated by the mating surfaces of the Bus. The +Z-axisis on the propulsion module side of the interface. The –Z axis is aligned with the mechanicalboresight fo the high gain antenna. The X-axis emanates from the origin The -X-axis pointstoward the Huygens Probe. The Y-axis is mutually perpendicular to the X and Z axes, with the+Y axis oriented along the magnetometer boom.The remote sensing pallet is mounted on the +X side of the spacecraft, the mag boom extendsin the +Y direction, and the +Z axis completes the orthogonal body axes in the direction of themain engine. The primary remote sensing boresights view in the -Y direction, the probe willbe ejected in the -X direction, the HGA boresight is in the -Z direction, the main engine exhaustis in the +Z direction with the thrust in the -Z direction. Two important directions to bear inmind are the HGA placement in the minus Z direction and the remote sensing instrumentboresights along the minus Y direction.The rotational motion of the spacecraft about the coordinate system axes is commonly calledsimply a “turn.” The terms roll, pitch and yaw are generally discouraged because of possibleambiguity of the axis specified. However, roll, pitch and yaw are defined about the +Z, +Y,and +X directions respectively. The right-hand rule is used as to directions, e.g. during apositive roll while on Earth-line, the spacecraft will be spinning clockwise as seen from theEarth. (Point the right thumb along the +Z direction, i.e. along the main engines – in this caseaway from the Earth. The fingers of the right hand indicate the direction of rotation as theycurl closed – in this case, clockwise looking from the Earth.)The main body of the spacecraft is formed by a stack consisting of the lower equipmentmodule, the propulsion module, the upper equipment module, and the HGA. Attached to thisstack are the remote sensing pallet, the fields and particles pallet, and the Huygens Probesystem. The two equipment modules are also used for external mounting of the magnetometerboom and the three radioisotope thermoelectric generators (RTGs) which supply the spacecraftpower. Measurements of the output of the radioisotope thermoelectric generators indicate abeginning-of-life power of 876 ± 6 Watts and estimates of 740 Watts at SOI and 692 Watts atend of mission. The spacecraft electronics bus is part of the upper equipment module and

2-4

carries the electronics to support the spacecraft data handling, including the command anddata subsystem and the radio frequency subsystem.The Spacecraft stands 6.8 meters (22.3 ft) high. Its maximum diameter, the diameter of theHGA, is 4 meters (13.1 ft). Therefore, the HGA can fully shield the rest of the spacecraft(except the deployed MAG boom and RPWS antennas) from sunlight when the HGA ispointed within ±2.5° of the Sun. The dry mass of the spacecraft is 2523 kg, including theHuygens Probe system and the science instruments. The best estimate of the actual spacecraftmass at separation from the Centaur was 5573.8 kg. The spacecraft mass properties are listedin Table 1.2.2.1 Science InstrumentsThere are 12 science instrument subsystems grouped into three larger groups: Optical RemoteSensing, Fields/Particles/Waves and Microwave Remote Sensing. The Optical RemoteSensing instruments are mounted on the Remote Sensing Pallet (RSP) rigidly attached to theUEM.The Fields, Particles, and Waves (FPW) instruments are mounted in several locations on thespacecraft. The MAG sensors are located on the extensible MAG boom, attached to the top ofthe UEM. A small pallet, also mounted on the UEM, carries INMS, MIMI LEMMS andCHEMS, and CAPS. MIMI INCA, CDA, and the RPWS antennas and Magnetic Search Coils(MSC) are attached elsewhere on the UEM. (Note that the MIMI INCA is a remote sensinginstrument with the capability of imaging the charged particle population of Saturn'smagnetosphere.There are two microwave sensing instruments: RADAR and the Radio Science Subsystem(RSS). The RADAR Flight Instrument System consists of the following subsystems: the RadioFrequency Electronics Subsystem (RFES), the Digital Subsystem (DSS), the Energy StorageSubsystem (ESS), and the Antenna Subsystem. DSS and ESS are located in one of theequipment bays below the HGA. RFES is in a penthouse-like attachment over the bay. Theprincipal component of the Antenna Subsystem is the five-beam Ku-band HGA feed. RADARshares the HGA with the RSS for both its active (Synthetic Aperture RADAR imaging andaltimetry) and passive (radiometry) operations.The Radio Science instrument is composed of elements located in the DSN and onboard thespacecraft. The flight Radio Science instrument consists of the Radio Frequency InstrumentSubsystem (RFIS) and elements of the RFS. The main assemblies of the RFIS are the Ka-bandExciter, the Ka-band TWTA, the Ka-band Translator, and the S-band transmitter. In addition,the HGA is used as part of the Radio Science Instrument to receive the X- and Ka-band signalsand to transmit at X-, Ka-, and S-bands.2.2.2 The Huygens Probe SystemThe Probe System consists of two elements:• the Huygens Probe itself, which enters the Titan atmosphere near the beginning of the

tour 22 days after separation from the Orbiter; and• the Probe Support Equipment (PSE) consisting of those parts of the System which

remain attached to the Orbiter in support of the Probe Mission.

2-6

Figure 2.3 Remote Sensing Pallet

Figure 2.4 Fields & Particle Pallet

2-7

FIGURE 2.5 Fields of View for Cassini Science Instruments

2-8

UVIS narrow (0.75 mrad by 61 mrad)

UVIS wide (6 mrad by 61 mrad)

ISS NAC* (6.1 mrad)

ISS WAC (61.2 mrad)

CIRS (4.3 mrad, center offset from optical axis by 4 mrad)

VIMS Visible & IR Frame (32 mrad)

CIRS (2 at 2.9 x 0.3 mrad, 0.67 mrad separation between inside edges)

PROJECTION ON SKY (ALONG Y-AXIS)

+X

+Z

+Y

Spacecraft Axes

UVIS medium (1.5 mrad by 61 mrad)

Figure 4.8 Fields of view for the Optical Remote Sensing Instruments.

*ISS NAC calibration shows offset by +0.822 mrad in X and -0.426 mrad from in Z from the -Y axis. Other instruments are shown in their nominal positions.

2-9

Figure 4.9 Huygens Probe Composition

2-10

2.3 Tour Description & StrategiesEach orbit about Saturn is assigned a rev number from 1 to N incrementing at apoapsis (whereone orbit ends, and the next begins). The partial orbit from SOI to the first apoapsis is orbit 0.Each satellite encounter is assigned a unique satellite encounter label consisting of a threedigit rev number on which the encounter occurs followed by a two character body indicator.For the major nine satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus,and Phoebe), the first two letters are unique and are used as the body indicator. Encounters ofsatellites occur either inbound (before Saturn periapsis) or outbound (after Saturn periapsis).Orbit orientation defines the location of apoapsis of the Saturn centered orbit with respect tothe Sun direction which is an important consideration for observations of Saturn’smagnetosphere and atmosphere. Orbit orientation may be defined by an angle or a local truesolar time (LTST) as depicted in Figure 2.8. The orbit orientation angle is measured clockwisein the Saturn equatorial plane from the projection of the Saturn–Sun line in the equatorialplane to the projection of the Saturn-apoapsis line. The local true solar time (LTST), measuredin hours (or hh:mm:ss), is obtained by scaling the orbit orientation angle by (24 hours/360ϒ).

DAWNDUSK

SUN

MIDNIGHT / TAIL

S/C Orbit

View From Saturn North Pole

Saturn

Orbit Orientation Angle = 90ϒ,Local True Solar Time (LTST)= 6 AM

LTST = 06:00= 6 AM

LTST = 0:00= 12 AM

LTST =18:00= 6 PM

Figure 2.8 Definition of Orbit Orientation

NOONLTST = 12:00 = 12 PM

Projection of Saturn-SunDirection in SaturnEquatorial Plane

Projection of Saturn-Apoapsis Direction inSaturn Equatorial Plane

The time available for observations of Saturn’s lit side decreases as the orbit rotates toward theanti-sun direction. Arrival conditions at Saturn fix the initial orientation at about 90ϒ which isequivalent to 6 AM LTST. Due to the motion of Saturn around the Sun, the orbit orientationincreases with time, at a rate of orientation of about 1ϒ/month, which over the four-year tour

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results in a total rotation of about 48ϒ (3.2 hours) in the clockwise direction (as seen from aboveSaturn’s north pole). Period-changing targeted flybys that rotate the line of apsides may beused to add to or subtract from this drift in orbit orientation. The petal plot shows howtargeted flybys combine with orbit drift to rotate the orbit from the initial orientation clockwisemost of the way around Saturn to near the Sun line. In the coordinate system used in thisfigure, the direction to the Sun is fixed.A targeted flyby is one where the orbiter’s trajectory has been designed to pass through aspecified aimpoint (latitude, longitude, and altitude) at closest approach. At Titan, theaimpoint is selected to produce a desired change in the trajectory using the satellite’sgravitational influence. Flybys within a few thousand km of Titan must be targeted due to thelarge ΔV imparted by Titan. At targeted flybys of icy satellites, the aimpoint is generallyselected to optimize the opportunities for scientific observations, since the gravitationalinfluence of those satellites is small. However, in some cases the satellite’s gravitationalinfluence is great enough to cause unacceptably large ΔV penalties for some aimpoints, whichmakes it necessary to constrain the range of allowable aimpoints to avoid this penalty.If the closest approach aimpoint during a flyby is not controlled, the flyby is referred to as anon-targeted flyby. Flybys of Titan at distances greater than 11,000 km (with the notableexception of the Probe Titan flyby 003Tc) are non-targeted flybys. Flybys of satellites otherthan Titan at distances greater than a few thousand kilometers are usually non-targeted flybys.If the closest approach point is far from the satellite, or if the satellite’s mass is small, thegravitational effect of the flyby can be small enough that the aimpoint at the flyby need not betightly controlled in order to ensure a return path to Titan. However, the gravitationalinfluence of the flyby is not the sole criteria for distinguishing between targeted and non-targeted flybys. Operations constraints on satellite encounter frequency may force some closeicy satellite flybys(usually within a few days of a Titan flyby) to be non-targeted.Opportunities to achieve non-targeted flybys of smaller satellites occur frequently during thetour. These are important for global imaging.If the transfer angle between two Titan flybys is an integer multiple of 360ϒ (i.e., the two flybysencounter Titan at the same place in its orbit), the orbit connecting the two flybys is called aresonant orbit. The period of a Titan-resonant orbit is an integer multiple of Titan's 16 d orbitalperiod. The plane of the transfer orbit between any two flybys is formed by the positionvectors of the flybys with respect to Saturn. In this case, an infinite number of orbital planesconnect the flybys; therefore, for resonant orbits, the plane of the transfer orbit can be inclinedsignificantly to Saturn’s equator. The Titan flyby altitude for resonant transfers is often theminimum permitted value of 950 km since maximum inclination change per flyby is usuallydesired.If two successive flybys encounter Titan at a different place in its orbit, the orbit connecting thetwo flybys called a non-resonant orbit. Non-resonant orbits have orbital periods which are notinteger multiples of Titan's period. Non-resonant transfer orbits connect inbound Titan flybysto outbound Titan flybys, or visa versa. Except for the special case of a 180ϒ transfer, the Titanposition vectors at successive encounters are not parallel (i.e., Titan is encountered at differentlocations in its orbit), and therefore the orbital plane formed by the position vectors of the twoflybys is unique and lies close to Titan’s orbital plane (which lies close to Saturn’s equatorialplane). Nonresonant transfers therefore have near zero orbit inclination. The Titan flybyaltitude for nonresonant transfers is usually much greater than the minimum flyby altitudevalue of 950 km since inclination is constrained to be near zero and thus the Titan gravityassist must be used solely to obtain a return trajectory to Titan.A 180ϒ transfer is a very special case of a Titan nonresonant transfer. In a 180ϒ transfer, thetransfer angle between two Titan flybys is an odd multiple of 180ϒ. In this case, successiveTitan encounters occur first at the ascending node of Titan’s orbit and then the descendingnode, or visa versa. Only one 180ϒ transfer occurs in the tour. Significant inclination and orbit

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orientation change are accomplished during a sequence of flybys which includes a 180ϒtransfer.

RESONANT TRANSFER

DEFINITION: Next Titan encounter occurs at SAME place in Titan's orbit as current encounter, i.e.s/c orbit is in resonance with Titan orbit. Used primarily for changing s/c orbit inclination or whenalready in an inclined orbit, changing s/c orbit period.

Titan at current encounter

Titan at next encounter

Saturn

S/C OrbitTitan Orbit

n complete Titan revs per m complete s/c revs

where n, m = 1, 2, 3, ...

Line of Nodes

Figure 2.9 Definition of Resonant Transfer

NONRESONANT TRANSFER

DEFINITION: Next Titan encounter occurs at a DIFFERENT place in Titan's orbit as current encounter, i.e. s/c orbit is NOT in resonance with Titan orbit. Used primarily for changing s/c orbit orientation(local solar time of s/c orbit apoapsis).

Titan at current encounter

Titan at next encounter.8 revs later

Saturn

S/C OrbitTitan Orbit

Transfers are from Titan outbound from Saturn to Titan inbound to Saturn or visa versa. S/C orbit planemust contain Titan at current encounter, Titan at next encounter, and Saturn. Therefore, s/c orbitinclination must be near zero unless Titan encountered at opposite sides of its orbit (i.e., 180 deg. transfer).

Outbound

Inbound

Titan at currentencounter

Titan at nextencounter 1.1 revslater

Saturn

S/C Orbit

Titan OrbitOutbound

InboundLine of S/CNodes =Saturn toTitanDirection

Sample Low Inclination Transfer Sample Inclined 180 deg. Transfer

Figure 2.10 Definition of Nonresonant and 180ϒ Transfer

Table 2 shows a breakdown of the tour into segments and shows the main characteristics ofeach segment. Segments are delineated by Titan encounters since only at Titan encounters isthe orbital geometry significantly altered. An expanded description of each segment follows.Recall that the first 3 digits of the encounter label are the rev number and that encounter labelsin parentheses use the navigation encounter numbering scheme (1 to n).

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Table 2.1 Tour Segment CharacteristicsEncounte

rs

Dates Figure Comments

SOI-Tc(SOI-Tc)

Jul 2004 –Jan 2005

2.11,2.12

SOI, PRM, target for Probe mission at Tc, reduce period & inclination

Tc-14TI(Tc-T7)

Jan 2005 –Sep 2005

2.13,2.14

Reduce inclination to enable nonresonant transfer to establish optimal occultationgeometry, raise inclination for Saturn/ring occultations and lower again to equator.Two targeted Enceladus flybys.

14TI-26TI(T7-T16)

Sep 2005– Jul 2006

2.15 Rotate clockwise toward anti-sun direction to establish optimal magnetotailgeometry. Targeted Hyperion, Dione, and Rhea flybys.

26TI-47TI(T16-T33)

Jul 2006 –Jun 2007

2.16,2.17

Deep magnetotail passage initiating 180-deg. transfer sequence (includingseveral revs for ring observations)

47TI-49TI(T33-T35)

Jun 2007 –Oct 2007

2.18 Rotate clockwise to optimize atmospheric observation and Saturn/ring occultationgeometries

49TI-End(T35-T44)

Oct 2007 –Jul 2008

2.19,2.20

Increase inclination to 75.6ϒ (maximum value in tour). Targeted Iapetus andEnceladus flyby. Last Titan flyby is 69TI (T44).

SOI-TcThis tour segment has been significantly redesigned since the last Mission Plan release dueProbe mission considerations. The remaining tour segments only contain a few tweaks to thelatest T18-5 reference tour and will be described in subsequent segments. The spacecraftapproaches Saturn from below the ring plane on a trajectory inclined about 17° with respect toSaturn’s equator [ Saturn’s equatorial plane is inclined 26.7° with respect to it’s orbit aroundthe Sun. Saturn’s orbit is itself inclined 2.49° with respect to the ecliptic.]. The first Titan flybyis inbound due to Probe delivery considerations.In February 2000, it was discovered that the bit synchronizer of the Huygens receiver on theorbiter has a bandwidth that is too small to accommodate the Doppler shift of the relay signal.In order to recover the Probe mission, the redesign reduces the Doppler shift between theProbe and orbiter. To reduce the relay Doppler shift, the closest approach altitude of theorbiter at the Probe relay encounter (Tc) was raised to 60000 km which reduces the radialcomponent of the orbiter’s velocity relative to the Probe and hence the Doppler shift of therelay signalThree new Titan encounters: Ta, Tb, and Tc have been designed with a distant flyby duringProbe delivery on Tc. These three initial Titan encounters replace the first two Titanencounters of the T18-5 tour. The new tour therefore contains an additional Titan flyby albeitat very high altitude. Following Tc, the trajectory rejoins the T18-5 tour at the 3TI (T3)encounter. After the 3TI encounter, the encounter times differ from those in T18-5 by less than4 hours and the geometry of the encounters and occultations remain essentially the same.The orbiter’s inclination is gradually reduced to enable a nonresonant transfer in the next toursegment needed to establish optimum Saturn/ring occultation geometry. Therefore, the initialseries of Titan flybys must all take place at the same place in Titan’s orbit (i.e. they all must beresonant, inbound flybys). The initial flybys quickly reduce period, as well as inclination, tomaximize the number of Titan flybys in the tour. These three inbound, period-reducing flybysrotate the line of apsides counterclockwise (Figure 2.11). This moves the apoapse toward theSun line which provides time for observations of Saturn’s atmosphere and helps establish thegeometry needed for near equatorial Saturn/ring occultations later in the tour.If the Probe cannot be delivered at the Tc flyby, a contingency trajectory exists that allows asecond chance to deliver the Probe. This contingency retargets Tc to a lower altitude andintroduces a new distant flyby, Td, for Probe delivery. However, this contingency causesCassini to fall off of the tour and it doesn't return to the T18-5 tour until the 13TI (T6) flyby. Inthis case, the first two targeted Enceladus flybys will be lost as well as 3 of the 7 diametricSaturn/ring occultations. Due to the severe science impact of this contingency, every effortwill be made to deliver the Probe on the nominal Tc encounter.

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Tc-14TI (Tc-T7) (Figures 2.13 and 2.14)The 3TI (T3) flyby initiates a nonresonant inbound to outbound transfer that orients the line ofnodes nearly normal to the Saturn-Earth line. This orientation minimizes the inclinationrequired to achieve an occultation of Saturn and results in Saturn/ring occultations which arecharacterized by ingress and egress close to Saturn’s equatorial plane (i.e., near-equatorial).The use of outbound flybys for the early tour dawn orbit orientation minimizes the Saturn-spacecraft distance during these occultations which improves science return since the“footprint" projected on the rings is minimized, improving the spatial resolution of the"scattered" radio signal observations. This is an important influence on the design of the tour.A targeted Enceladus (4EN, (E1)) flyby is obtained during the 3TI-5TI (T3-T4) nonresonanttranfer. Note that targeted flybys of the icy satellites such as 4EN are usually obtained onorbits which are also used to establish desired Saturn-relative geometries.The resonant outbound flybys 5TI (T4) and 6TI (T5) increase inclination to ~22ϒ to set up theSaturn/ring equatorial occultations. During the 6TI (T5) to 13TI (T6) segment, seven near-equatorial occultations of Earth and Sun by Saturn and its rings (one on each 18.2 d periodorbit) occur. During these seven orbits, the orbiter crosses Saturn’s equator near Enceladus’orbit; on the fourth orbit, Enceladus and the spacecraft both arrive at nearly the same point inEnceladus’ orbit at the same time, and the second targeted flyby of Enceladus (11EN, (E2))occurs. Enceladus’ gravity is too weak to displace inclination significantly from the valuerequired to achieve occultations.The 13TI (T6) flyby decreases inclination once again to near Saturn's equator to enable anonresonant transfer in order to begin the next tour segment. Unlike the last officially releasedtour, the 13TI (T6) flyby altitude was raised from 950 to ~4000 km in order to avoid a G ringcrossing but the 14TI (T7) altitude was lowered from ~4000 to 950 km. These two Titan flybystherefore do not change the distribution of Titan flyby altitudes.14TI-26TI (T7-T16) (Figure 2.15)The 14TI-17TI (T7-T8) nonresonant transfer initiates a series of alternating outbound/period-reducing and inbound/period-increasing flybys lasting about 10 months. These flybys areused to rotate the orbit apoapsis clockwise toward the magnetotail to establish the geometryrequired for a deep magnetotail passage. The period typically alternates between 23 d(outbound) and 39 d (inbound) with .8 to 1.1 revs between flybys since this sequence results inthe most rapid change in orbit orientation. The only exceptions to this pattern were orbitsused to obtain targeted icy satellites during these nonresonant transfers.Following the 14TI (T7) flyby, a 19 d period, 2.8 rev nonresonant transfer is used in order toachieve the first targeted flybys of Hyperion (15HY, (H1)) and Dione (16DI, (D1)) along theway. Compared to the last officially released tour, the Dione flyby aimpoint has been loweredin altitude (to 500 km) and changed in B-plane angle per PSG request. Similarly, following the17TI (T8) flyby, a 28 d, 2.1 rev nonresonant transfer is utilized to obtain the first targeted Rhea(18RH, R1) flyby.26TI-47TI (T16-T33) (Figures 2.16, 2.17)The 26TI (T16) flyby places apoapsis near the anti-Sun line at an inclination of ~15ϒ to achievepassage through the current sheet in the magnetotail region. Apoapsis distance is about 49 RS,exceeding the 40 RS MAPS requirement associated with magnetotail passage. At distances thisfar from Saturn, the current sheet is assumed to be swept away from Saturn’s equatorial planeby the solar wind. This flyby also initiates the 180ϒ transfer sequence.A series of 17 Titan flybys comprise the 180ϒ transfer sequence. A series of 9 resonanttransfers, usually with period of 16 d, increases inclination and decreases orbit eccentricity to apoint at which both the ascending and descending nodes of the spacecraft orbit are at Titan’sorbital radius. At an inclination of ~59ϒ, a nonresonant 180ϒ transfer is then performed (the

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orbit shown in bold in Figures 16 and 17), i.e., the true anomaly of Titan in its orbit at which itis encountered by the spacecraft on successive flybys differs by 180ϒ (actually 540ϒ). A series of8 16 day period orbits then decreases inclination back to near zero and increases eccentricityback to its original value. Orbit orientation is changed by ~135ϒ to ~8 PM LTST over the 11month sequence duration.Most Titan flyby altitudes are at the minimum permitted value of 950 km in order to maximizethe inclination and eccentricity change at each flyby. Such low altitude Titan flybys arepreferred for many science observations. The 31TI (T20) flyby reduces period to 12 daysresulting in 4 revs over an interval of 48 d between Titan flybys in order to provide additionalORS observations of the rings at a time of favorable observational geometry. This 48-dayinterval also serves to reduce operational stress on the ground system.47TI-49TI (T33-T35) (Figure 2.18)The 47TI (T33) and 48TI (T34) nonresonant transfers rotate the orbit petal further clockwise(toward noon) to enable Saturn atmospheric observations at both great distance (> 40 Rs) andlow phase angle. This tour segment provides much of the long integration time daytimeatmospheric observation opportunities. The nonresonant transfers also move the line of nodescloser to the Sun line in order to establish the geometry needed for near polar Saturn/ringoccultations in the next tour segment.49TI-End Baseline Mission (post 69TI) on Rev 74 (T35-post T44) (Figures 2.19 and 2.20)This segment is comprised solely of resonant transfers which gradually raise inclination to themaximum value attained in the tour. The first targeted Iapetus encounter (49IA (I1)) isobtained on the 49TI-50TI (T35-T36) resonant transfer at an inclination of ~6ϒ. Note that theascending node on which this targeted Iapetus encounter is obtained differs ~180ϒ from theascending node desired for the maximum inclination sequence. The desired ascending nodefor the maximum inclination segment places periapsis below the ring plane such that thespacecraft can view the illuminated side of the rings at Saturn periapsis (note Solar declinationis negative during this time period). The third targeted Enceladus (61EN, (E3)) encounter isobtained on the 59TI-62TI (T41-T42) transfer. Note that this Enceladus flyby is occulted fromthe Sun at closest approach.Following the targeted 49IA (I1) Iapetus flyby, starting at 50TI (T36), a series of 10 outboundTitan resonant transfers are used increase inclination as much as possible for ring observationsand in-situ fields and particles measurements. These resonant transfers continue until the endof the baseline tour on July 1, 2008 (rev 74) four years after insertion into orbit about Saturn.The LTST of these orbits is near noon to enable near polar Saturn/ring occultations at closedistances.The maximum inclination possible is dictated primarily by the Titan-relative V-infinity (fixed),orbital period (free), and the number of Titan flybys (constrained by time left in tour) devotedto increasing inclination. The closest approach altitudes during this segment are kept at theminimum allowed value of 950 km to maximize inclination change at each flyby. The orbitalperiod must be gradually reduced in order to further increase inclination which decreases thedescending node crossing distance to the point where ring hazard avoidance becomes alimiting constraint. The orbital characteristics after the last Titan flyby in the tour, 69TI (T44),are a period of 7.1 d, inclination of 75.6ϒ, and descending node distance of 2.7 Rs. Fiveperiapses are completed at this maximum inclination before the end of the baseline tour.The aimpoint at the last Titan flyby is chosen to target the orbiter to a Titan flyby on 7/31/08(64 days and 9 revs after the 69TI (T44) flyby), providing the opportunity to proceed with moreflybys during an extended mission, if resources allow. Nothing in the design of the tourprecludes an extended mission.

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Figure 2.11 Tour Segment SOI-Tc– Side View

Figure 2.12 Tour Segment Tc-14TI (Tc-T7)(+X parallel to Saturn to Sun direction, +Z Saturn N. Pole)

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Figure 2.13 Tour Segment Tc-14TI (Tc-T7) – Side View

Figure 2.14 Tour Segment 14TI-26TI (T7-T16) [~Zero Inclination](+X parallel to Saturn to Sun direction, +Z Saturn N. Pole)

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Figure 2.15 Tour Segment 26TI-47TI (T16-T33)(+X parallel to Saturn to Sun direction, +Z Saturn N. Pole)

180ϒ Transfer Orbiti=59ϒ

Figure 2.16 Tour Segment 26TI-47TI (T16-T33) – Side View

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Figure 2.17 Tour Segment 47TI-49TI (T33-T35) [~Zero Inclination](+X parallel to Saturn to Sun direction, +Z Saturn N. Pole)

Figure 2.18 Tour Segment 49TI-End Baseline Mission (post 69TI) on Rev 74 (T35-post T44)(+X parallel to Saturn to Sun direction, +Z Saturn N. Pole)

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Figure 2.19 Tour Segment 49TI-End Baseline Mission (post 69TI)on Rev 74 (T35-post T44) – Side View

2.4 TelecommunicationsThe Radio Frequency Subsystem (RFS) provides the telecommunications facilities for thespacecraft and is used as part of the radio science instrument. For telecommunications, itproduces an X-band carrier at 8.4 GHz, modulates it with data received from CDS, amplifiesthe X-band carrier power to produce 20 W from the Traveling Wave Tube Amplifiers (TWTA),and delivers it to the Antenna Subsystem (ANT). (The 20W is expected to degrade to about19W by the start of the tour.) From ANT, RFS accepts X-band ground command/data signalsat 7.2 GHz, demodulates them, and delivers the commands/data to CDS for storage and/orexecution.The Ultra Stable Oscillator (USO), the Deep Space Transponder (DST), the X-band TravelingWave Tube Amplifier (TWTA), and the X-band Diplexer are those elements of the RFS whichare used as part of the radio science instrument. The DST can phase-lock to an X-band uplinkand generate a coherent downlink carrier with a frequency translation adequate fortransmission at X-, S-, or Ka-band. The DST has the capability of detecting a rangingmodulation and of modulating the X-band downlink carrier with the detected rangingmodulation. Differenced one-way ranging (DOR) tones can also be modulated onto thedownlink. The DST can also accept the reference signal from the USO and generate a non-coherent downlink carrier. However, there are currently no plans to use the DOR tones fornavigation.The ANTenna subsystem (ANT) provides a directional high gain antenna (HGA) for X-, Ka-, S-and Ku-band for transmitting and receiving on all four bands. Because of its narrow half-power beam width of 0.14 deg for Ka-band, it must be accurately pointed. The HGA, and thelow gain antenna 1 (LGA1) located on the HGA feed structure, are provided by the Italian

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Space Agency. Another LGA (LGA2) is located below the Probe pointing in the -X direction.During the inner solar system cruise, the HGA is Sun-pointed to provide shade for thespacecraft. ANT provides two LGAs which allow one or the other to receive/transmit X-bandfrom/to the Earth when the spacecraft is Sun-pointed. The LGAs also provide an emergencyuplink/downlink capability while Cassini is at Saturn. The HGA downlink gain at X-band is47dBi and the LGA1 peak downlink gain is 8.9 dBi. The X-band TWTA power is 20 watts.Telecommunications strategies are developed to use the three antennas (the HGA and twoLGAs) to maximize science data return and visibility of the ground teams within the projectand DSN constraints.Telecommunications with Cassini for the first 800-plus days of the mission is generallyrestricted to the spacecraft's low gain antennas (LGAs). During this time, it is necessary to usethe high gain antenna (HGA) as a sunshade. Telemetry mode RTE-40 is used for most cruisedownlink since it is generally the highest data rate achievable. Where advantageous, othermodes such as PB&RTE-40, PB&RTE-200, RTE-948, RTE-158, or PB&RTE-948 are used whenavailable and if Earth range and trajectory geometry permit. RTE-20 is the lowest data rate thatthe spacecraft will use for downlink in a non-emergency situation, whereas PB&RTE-40 is thelowest data rate available for playback of data from the SSR.The spacecraft transmits and receive through Low Gain Antenna 1 (LGA1) for the majority ofthe early cruise periods. LGA1 is preferred since the spacecraft does not have to be constrainedin roll attitude as with LGA2, although the Earth-Spacecraft-Sun angle generally dictateswhich LGA is required. There is a 25 day period at launch plus 14 months when the Earth-Spacecraft-Sun (EPS) angle is sufficiently small to allow use of the HGA fortelecommunications. This is the first post-launch functional checkout of the scienceinstruments. After the 25 days until early 2000, telecommunications must again use the LGAsat low rates (except very near Earth).Following the switch to the HGA in February 2000, the telecommunications link capability isimproved significantly and much higher rates are possible, allowing more data-intensiveengineering and science activities throughout the rest of the mission.The normal DSN coverage for cruise is two passes per week, for spacecraft monitoring, datareturn and navigation. During the tour the Cassini telecommunications support requirement isone pass per day due to the high level of science activity expected. These basic coveragesrepresent a general commitment of DSN loading. Radio science measurements (e.g.,occultations) will be accommodated on an occasional basis and will generally be added on topof the one pass per day schedule. The specific site used is chosen based on DSN workload,maximum downlink rate, conflicts with other missions, or other issues. Typically, however,the project will select Goldstone regularly since it has good downlink capability and using thesame station allows for repeated activities (e.g. 15 hours collect, 9 hours downlink). Madridalso has good downlink rate and is desired by navigation to check for station-specific trackingbiases. Canberra is undesirable due to its poor geometry and downlink rate.Antenna switch times are based on Earth range and on Earth-Spacecraft-Sun (EPS) geometry.If the EPS angle is greater than 44 degrees, LGA2 offers better downlink performance.However, if the EPS angle is less than 44 degrees, LGA1 should be used. LGA2 must not beused during probe checkouts due to its proximity to the probe and resulting interference.Table 5.1 defines the antenna usage periods for early cruise.

Table 2.2 Antenna Usages (Year - Day Of Year)LGA1 Periods LGA2 Periods HGA Periods97-290 to 97-29998-175 to 98-36199-022 to 99-06399-231 to 00-031

97-300 to 98-17499-063 to 99-230

98-362 to 99-02100-032 to EOM

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During the tour uplink is typically performed at 500 bps. The confidence level for uplinktransmission is 99% or better. Generally speaking, the uplink signal is much stronger due tothe much higher radiating power of the ground antenna.2.4.1 PlaybackDuring cruise, telemetry is returned to the ground according to the (often limited) downlinkcapability, and is generally not heavily optimized due in part to a limited set of telemetrymodes and tour capabilities which are still in development. During tour, however, much efforthas been spent in selecting the data rates and DSN pass configurations to maximize the datareturn related to the project’s primary science objectives.For the purposes of operational simplicity, the Tour DSN coverage has been classified into twocategories: "high activity," presumably when the science opportunities are most intensive andrequire the most data to be collected, and "low activity," when the opportunities are morescarce or permit low data return. The science community has indicated that 1.0 Gbit per dayfor low activity periods and 4.0 Gbit per day for the high activity periods is adequate toachieve their science goals.To accomplish this, high activity periods are concentrated at targeted flybys and Saturnperiapses, and take up about one quarter to one third of each orbit. These passes are 9 hours inlength and use a northern-hemisphere 70 meter station or 70/34 array. Communications is 2-way coherent at a 90% confidence level with ranging on. Low activity passes are also 9 hoursin length and use northern hemishere 34 meter stations. Communications is also 2-waycoherent at a 90% confidence level, ranging on.During the tour, expected data rates for the spacecraft's HGA and 19W X-band transmitterrange from 14 kbps to 166 kbps. These rates vary due to the assumed telecom confidence level,the ground station configuration and the Earth's motion around the Sun, which affects thetransmission range, and Saturn's motion around the Sun, which affects the declination of thespacecraft as seen from Earth. Earth's motion is by far the dominant geometric factor and isevident in the sinusoidal nature of the link performance. Since the link performance variessignificantly with time, multiple data rates must be used as the performance changes orsignificant data return capability will be lost. In addition, the performance varies during a passand multiple data rates per pass also increases telecom performance significantly as show infigure 2.20.

Time

Telemetry PassData Rate

Ratio of Time Used

1/61/6 2/3

Figure 2.20 Multiple Data Rate StrategyFourteen data rates compatible with the spacecraft information system have been chosen forthe tour as listed in Table 4. These rates cover all expected ground apertures with a minimumof lost data return capability.Higher rates of 199.08 and 248.85 kbps are available, but are not used because either theycannot be supported by the telecom link or because they are not needed to achieve the 4.0 Gbitdaily return. Any slot that would be occupied by a high data rate would be better appliedtowards the lower data rate region to increase performance during low activity days.

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Table 2.3 Tour Data Rates (kb/s)14.22 66.3622.12 82.9527.65 99.5433.18 110.6535.55 124.42541.475 142.2047.40 165.9

If a DSN pass is lost too late in the planning or execution process to alter the sequence safely,no steps will be taken to recover the data recorded on the SSR and the sequence is allowed toproceed as planned. The spacecraft continues operation as if the data are being receivedsuccessfully, resulting in loss of these data as they are overwritten during the downlink periodand the following observing period.The following figures show the downlink science data return in Gbit over the tour forGoldstone, Madrid, and Canberra (occasional Canberra passes may be required to resolveDSN conflicts). Nine hour passes are assumed, causing the jagged data returns, especially forarrayed antennas, since occasionally the top two data rates are not available for a full 9 hours,and occasionally the lower data rate is used less than the minimum of 45 minutes. In thesecases, additional data return could be achieved by lengthening the duration of the pass beyond9 hours, or reducing the time you collect data in the highest rate. Note that there are periodswhen 4 Gb of science is not achievable even at arrayed stations, ant there are periods of lowactivity when 1 Gb is not available from 34 m HEF antennas.2.4.2 DSN LockupDSN lockup during tour is theoretically predicted to be on the order of seconds; however,during cruise lockup has typically taken several minutes. In order to prevent data loss, theplayback of data at the beginning of a pass (as well as during data rate or coherency changes)should be avoided.During cruise, the technique for preventing data loss is to snap and restore the pointer after 15minutes of playback to the start of the partition. This duplicates the playback of the first 15minutes of data and accommodates an equivalent lockup time. The tour flight software hasimplemented a playback pause capability which halts SSR playback for a fixed amount of timewhenever a new telemetry mode is activated. This time can be uploaded as a parameter andcan be used to accommodate DSN lockup, data rate, or coherency changes. During playbackpause, the transmitter still sends data to the ground at the expected rate, but only real-timeengineering and fill frames; no data from the SSR is sent to the ground. For tour, 5 minutes oflockup and 1 minute of pause at each data rate are the baseline2.4.3 MaintenancePreventive Maintenance (PM) is scheduled to occur during weekly maintenance downtimes.The major goal of PM is to minimize the likelihood of a sudden loss of an asset requiringcorrective maintenance. The maintenance teams perform hundreds of maintenance procedureseach month on the antennas. Most of these can only be conducted during daylight hoursduring the standard workweek (M-F at CDSCC & GDSCC, Tu-F at MDSCC).Typically, each 26-meter, BWG, HEF, and HSB antenna is taken down for maintenance for a 6 -8 hour period each week. It is not uncommon for maintenance time to be reduced on theseantennas to as low as 4 hours in a week when special support is requested by a flight project.The 70-meter antennas are taken down for maintenance 8 - 16 hours each week, depending onthe complex. When one 70-meter antenna is down for an extended period of time because ofan implementation, the maintenance hours are reduced on the other two 70-meter antennas. Itis extremely rare for maintenance to be reduced by more than 50%.

Bits to Ground - Goldstone

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

2004-Jul 2004-Dec 2005-Jul 2006-Jan 2006-Jul 2007-Jan 2007-Jul 2008-Jan 2008-Jul

HEF

BWG

70ARR

70MET

34ARR

Bits to Ground - Madrid

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000


HEFBWG

70ARR

70MET

34ARR

Bits to Ground - Canberra

0

500

1000

1500

2000

2500

3000

3500


HEF

BWG

70MET

34ARR

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The project policy is to adhere to weekly maintenance requirements whenever possible,especially during implementation. An attempt to waive maintenance will only be pursued inthe most extreme cases where maintenance degrades high value science and all other avenueshave been exhausted.2.4.4 Probe Relay ProblemThe receivers in the Huygens Probe support equipment on board the Cassini spacecraft haveexhibited a performance anomaly under the conditions expected during the nominal Probemission.There is sufficient margin to maintain both carrier and sub-carrier lock throughout the Probemission. However, at the link levels expected, the digital circuitry which decodes the datafrom the sub-carrier does not have sufficient bandwidth to properly process the data from asub-carrier which has been Doppler shifted by the nominal 5.6 km/s velocity differencebetween the Cassini orbiter and the Huygens Probe. The initial assessment of the affect of thisanomaly is that it will lead to unacceptable data losses during the Probe descent to Titan.This anomaly was addressed by redesigning the orbiter trajectory at the time of the probemission in order to minimize the Doppler on the received probe signal. In addition to this, itmay be possible to preheat the probe transmitters for four hours before the probe mission toimprove data performance and to insert zero packets into the probe data stream minimizingthe expected cycle slips. However these latter two options are still being investigated.2.5 Data Routing and StorageData control on board the spacecraft is controlled by the Command and Data Subsystem (CDS)which controls two Solid State Recorders (SSRs). Cassini’s two SSRs are the primary memorystorage and retrieval devices for the orbiter. Each SSR contains 128 submodules, of which 8 areused for flight software and 120 are useable for telemetry. Each submodule has 16,777,200 bitsfor data, so the total data available for telemetry for each SSR is 2.013 Gbit. Expressed in termsof 8800-bit telemetry frames, this is 228,780 frames per SSR. Accounting for effects of solar andcosmic radiation, the end of mission capacity is expected to be no less than 1.800 Gbit per SSR.There are currently no bad blocks on either SSR, so the total start of mission capacity is stillavailable.Spacecraft telemetry and AACS, CDS, and instrument memory loads can be stored in separatefiles, or partitions, on board the SSR routed through virtual channels. Three telemetrypartitions have been defined on each SSR, numbered 4, 5 and 6. Partition 4 is the generalscience partition, whereas partition 6 is for engineering data. Partition 5 is used to store opticalnavigation images. In order to support science both the AACS prime engineering packets andthe RFS packets are duplicated and recorded to Partition 4 for downlink to ground.There are three different SSR modes in which the SSR can function: Read-Write to End,Circular FIFO, and Ring Buffer. There is also a record pointer and a playback pointer, whichmark the memory addresses at which the SSR will write or read, respectively. In Read-Writeto End, there is a logical beginning and end to the SSR. Recording begins at this logicalbeginning and continues until either the SSR is reset (the record and playback pointers arereturned to the logical beginning) or until the record pointer reaches the end. If the recordpointer does reach the end, recording is halted until the SSR is reset. In Circular FIFO, there isno logical end to the SSR. The data is continuously recorded until the record pointer reachesthe playback pointer. The Ring Buffer mode behaves exactly like Circular FIFO, with oneexception. Recording will not stop if the record pointer reaches the playback pointer.The principal purpose of the Solid State Recorders (SSRs) is to store science and engineeringdata during observation periods for playback during DSN passes, and to buffer FPW andengineering data during DSN passes for downlink during those same passes. The amount of

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data which can be recorded per period is primarily limited by the downlink capability of DSNstations.During most of cruise, only one SSR is needed primarily for engineering, but also to recordmaintenance, calibration, and checkout data, as well as limited cruise science. The other SSRmay be turned off. During approach and tour, however, both SSRs are on. Even though amajority of days during tour are expected to be low activity, requiring only one SSR, both SSRsare kept on to maintain a 4.0 Gbit storage and downlink capacity. Activity levels changeseveral times per orbit, and cycling the SSRs on and off increases the ground workload andmay impact the reliability of the SSRs.Each CDS is attached to the two SSRs such that each CDS can communicate (read, write) withone SSR or the other SSR but not simultaneously. The ground has the capability to control howthe SSR attachments are configured via real-time command or a stored sequence. Under faultresponse conditions FSW can switch SSR attachment from CDS A to CDS B.The CDS receives the uplink command stream via the RFS and decodes this stream whichincludes timing (immediate or sequence), routing, action, and parameter information. The CDSthen distributes commands designated for other subsystems or instruments, executes thosecommands which are decoded as CDS commands, and stores sequence commands for laterexecution. The CDS has a capacity of 153,600 words. One CDS word equals 16 bits. Thefollowing table shows the allocation for the CDS words.

Table 2.4 CDS Words AllocationsSequence Memory CDS WordsOn-board modules 12,288Background sequence 111,808Live Movable Blocks 10,240TCM 2,048IVP Update 10,240Mini-sequence 4,096IDAPs 1,856Global Variables 1,024

Total: 153,600The CDS receives data destined for the ground on the data bus from other on-boardsubsystems, processes it, formats it for telemetry and delivers it to RFS for transmission toEarth. Each subsystem interfaces with the data bus through a standard Bus Interface Unit(BIU) or a Remote Engineering Unit (REU). Data is collected in 8800 - bit frames, and Reed-Soloman Encoded on downlink. A 32 framesync marker along with the encoding increasesthese frames to 10,112 bits.CDS software contains algorithms that provide protection for the spacecraft and the mission inthe event of a fault. Fault protection software ensures that, in the case of a serious fault, thespacecraft will be placed into a safe, stable, commandable state (without ground intervention)for a period of at least two weeks to give the ground time to solve the problem and send thespacecraft a new command sequence. It also autonomously responds to a predefined set offaults needing immediate action.2.5.1 Orbiter Telemetry ModesA set of telemetry modes has been defined to accommodate different engineering and scienceactivities and the changing telecommunications capability during the Cassini mission. Eleventelemetry modes were implemented before launch to accommodate pre-launch and early post-launch operations. The remaining modes are being developed and tested during cruise.Thirty modes can be stored on-board the spacecraft at any one time; more may exist on the

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ground, and various modes may be updated or replaced as the telemetry needs of the missionchange. Refer to CAS-3-281 for more information on orbiter telemetry modes.Each telemetry mode represents a unique configuration of data sources, rates, and destinationsfor telemetry data gathered and distributed by the CDS. Data are routed either to the SSR fortemporary storage or to the RFS for transmission to the ground or both. There are five sourcesof telemetry data:1) Engineering data from the spacecraft subsystems is gathered in every telemetry mode

and sent to the SSR for recording. Realtime engineering data are also included in thedownlink data stream in most of the telemetry modes. For some of the telemetry modesused during the early part of the cruise phase, when the downlink data are transmittedvia the LGAs, the engineering data rate could drop to 0 or 20 bps for SSR playback and20 bps in real-time.

2) Science housekeeping data are gathered from the instruments when they are operatingand are either sent to the SSR or routed into the downlink data stream. The peak ratefor science housekeeping data are predicted to not exceed 275 bps.

3) Scientific data from the instruments is always routed to the SSR in the telemetry modesthat include science data collection. Data rates in these modes can be up to 410 kbps,however, the actual data rate into the SSR during science data collection in a giventelemetry mode can vary up to this maximum. This is because there is insufficientstorage and downlink data volume to collect data continuously at this rate, and some ofthe higher rate instruments will have to vary their data collection rates to fit within theavailable downlink data volume.

4) Playback data from the SSR is routed into the downlink data stream to the RFS, atspeeds depending on the downlink data rate.

5) Probe data are included in two of the telemetry modes to allow for Probe checkout andProbe relay operations. These data will be collected at a rate of about 20 kbps.

Tables 6-7 describes the telemetry modes used for tour, which have been grouped intofunctional categories, which are:

Realtime Engineering (RTE)Probe Checkout (PCHK)Probe Operations (PRLY)Science and Engineering Record (S&ER)Realtime Engineering plus Science Playback (RTE&SPB)SAF Instrument Checkout (SAF)

TELEMETRY MODES - RECORD & REAL-TIME DOWNLINKRECORD TO SSR DOWNLINK

SCIENCE HOUSEKEEPING ENG ENG ENG TOTAL

Telemetry Mode

CAPS

CDA

INMS

MAG

MIMI

RPWS

CIRS

ISS

ISS

UVIS

VIMS

RADA

PSA

CAPS

CDA

INMS

MAG

MIMI

RPWS

CIRS

ISSn

ISSw

UVIS

VIMS

RADR

PSA

Total rate (bps)

P4 Rate (bps)

P6 Rate (bps)

(bps) Downlink (bps)

S&ER-1 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-2 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-3 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-4 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-5 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-5a √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 241 724 1638 1650 1896S&ER-6 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-7 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-8 √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 241 724 1638 1650 1896S&ER-10 (prime)* √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 220 724 1638 1650 1896S&ER-10 (online)* 579 1225 1650 1896

RTE-5 √ 1638 1638 4 5

RTE-10 √ √ √ √ √ √ √ √ √ √ √ √ √ √ 3180 1638 1638 9 10

RTE-20 √ √ √ √ √ √ √ √ √ √ √ √ √ √ 3180 1638 1638 17 20

RTE-1896 √ √ √ √ √ √ √ √ √ √ √ √ √ √ 3180 1638 1638 1650 1896

PCHK √ √ 2939 1638 2054 24885PRLY (prime) √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ 6097 724 1638 1650 1896PRLY (online) √ √ 5877 579 1225 1650 1896* S&ER-10 is the telemetry mode used during SOI.

TELEMETRY MODES - PLAYBACKRECORD TO SSR DOWNLINK

SCIENCE ENG SSR HOUSEKEEPING ENG TOTAL

Telemetry ModeCAP

CDA

INM

MAG

MIM

RPW

CIR

ISS

ISS

UVI

VIM

RAD

PSA

(bps) Playback (bps)

CAP

CDA

INM

MAG

MIM

RPW

CIR

ISS

ISS

UVI

VIM

RAD

PSA

Total rate (bps)

R-T ENG (bps)

Downlink (bps)

RTE&SPB-14220 √ √ √ √ √ √ √ √ 1638 10515 √ √ √ √ √ √ √ √ √ √ √ 220 1640 14220RTE&SPB-22120 √ √ √ √ √ √ √ √ 1638 17382 √ √ √ √ √ √ √ √ √ √ √ 220 1648 22120RTE&SPB-27650 √ √ √ √ √ √ √ √ 1638 22202 √ √ √ √ √ √ √ √ √ √ √ 220 1640 27650RTE&SPB-33180 √ √ √ √ √ √ √ √ 1638 27012 √ √ √ √ √ √ √ √ √ √ √ 220 1643 33180RTE&SPB-35550 √ √ √ √ √ √ √ √ 1638 29077 √ √ √ √ √ √ √ √ √ √ √ 220 1640 35550RTE&SPB-41475 √ √ √ √ √ √ √ √ 1638 34235 √ √ √ √ √ √ √ √ √ √ √ 220 1639 41475RTE&SPB-47400 √ √ √ √ √ √ √ √ 1638 39382 √ √ √ √ √ √ √ √ √ √ √ 220 1648 47400RTE&SPB-66360 √ √ √ √ √ √ √ √ 1638 55882 √ √ √ √ √ √ √ √ √ √ √ 220 1648 66360RTE&SPB-82950 √ √ √ √ √ √ √ √ 1638 70327 √ √ √ √ √ √ √ √ √ √ √ 220 1640 82950RTE&SPB-99540 √ √ √ √ √ √ √ √ 1638 84762 √ √ √ √ √ √ √ √ √ √ √ 220 1643 99540RTE&SPB-110600 √ √ √ √ √ √ √ √ 1638 94382 √ √ √ √ √ √ √ √ √ √ √ 220 1648 110600RTE&SPB-124425 √ √ √ √ √ √ √ √ 1638 106422 √ √ √ √ √ √ √ √ √ √ √ 220 1639 124425RTE&SPB-142200 √ √ √ √ √ √ √ √ 1638 121882 √ √ √ √ √ √ √ √ √ √ √ 220 1648 142200RTE&SPB-165900 √ √ √ √ √ √ √ √ 1638 142512 √ √ √ √ √ √ √ √ √ √ √ 220 1643 165900

SAF-142.2 √ √ √ √ √ √ √ √ √ √ √ √ 1638 121861 √ √ √ √ √ √ √ √ √ √ √ √ 241 1648 142200

SAF-248.85(2) √ √ √ √ √ √ √ √ √ √ √ √ 1638 214681 √ √ √ √ √ √ √ √ √ √ √ √ 241 1640 248850

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2.5.2 SSR UsagePartitions 0-3 on each SSR are memory load partitions containing flight software. Each SSR canhave up to 3 additional partitions used for telemetry. A CDS command edits partitions in thebackground sequence, enabling the number and size of telemetry partitions to be changed on adaily basis if needed. The minimum size of a partition in order for it to exist is one frame, or8800 bits.The exception is the recording of Huygens data, which is duplicated on each SSR using aunique partitioning strategy. During cruise, typically one SSR with a single telemetry partitionin circular FIFO mode is used to store and downlink all data collected, mixing engineering,housekeeping, maintenance, checkout and science data collected. Engineering is recordedcontinuously at a rate of 1638 bps. At this rate, one SSR can store up to 14 days of data(assuming a capacity of 2.0 Gbit). During cruise, the least frequent DSN passes occur once perweek. The SSR therefore would record up to 7 days of data between the least frequentdownlinks, filling half of its capacity. During a DSN pass at greater than 20 bps downlink rate,along with real-time engineering, selected data from the SSR can be played back if desired. At20 bps (the minimum planned downlink rate) only real-time engineering can be sent to Earth.At the end of the pass, the pointers are not reset and the SSR continues to record where it leftoff.

Figure 2.24 Cruise One-Partition SSR ManagementWhen a fault has occurred, at least 7 days (which is also the maximum time between passes) ofdata collection is guaranteed. This strategy allows time for the ground to make arrangementsto receive fault protection data and engineering data before or after the fault to analyze theproblem. If the spacecraft is not directed otherwise, it stops recording data once the recordpointer hits the playback pointer.During the later portion of cruise and tour, once the final flight software is uploaded, the SSRsare configured to use multiple partitions. Engineering data, optical navigation images, and/orhigh value science data can be routed to specific partitions and preserved separate fromgeneral science data for priority or multiple playbacks.For tour, partition 4 is used as the primary day-to-day telemetry partition. Engineering datastored during observation periods does not need to be downlinked every day, so it is routed topartition 6 at 1638 bps. Some engineering, however, is required to reconstruct pointing, etc.,and this data is duplicated in partition 4 during observation periods at a lower rate of 724 bps.

A5

OPNAV

LOW ACTIVITY DAY (1 SSR)

R

P

RPA5

A5

1

RP

ENG

A6

CIRCFIFO

D. Seal 10 May 2002

OPNAV

OPNAV

ENG

A6 P

R

RINGBUFFER

START EMPTY

A4 = science partition with duplicated subset of engineering data (e.g. AACS, RFS) required for playback. Circular FIFO allows free recording up to data played back and is required if any data is to be held over to next pass.

A5 = OPNAV partition. Circular FIFO allows for MAPS data to use up OPNAV space after playback. Sized to volume of contents plus playback buffer for data recorded in A5 for each downlink. 4.26 Mb each OPNAV (484 frames) which assumes compression of 4:1 or better (>7:1 performance has been observed in flight on OPNAV-like images).

A6 = engineering partition. Sized to hold 39.5 hours, needed for anomaly recovery. Ring buffer allows engineering to be recorded without pointer management. After safing, fault protection may route post-fault engineering to A4.

RECORD

All engineering in A6 at 1623 bps and science & a duplicated subset of engineering in A4 at 718 bps, plus HK at up to 239 bps. OPNAVs are routed to A5 by telemetry mode overlay command.

PLAYBACK

In order as shown. A6 is never played back unless needed for anomaly diagnosis. All data collected during playback (including ENG at 1623 bps) must be recorded in active partition ONLY. Therefore, playback buffer in A5 must be bookkept for each downlink as illustrated to prevent data loss. Playback pointer is paused at start of downlink and at data rate changes for DSN lockup; record pointer is free to continue.

POST-PLAYBACK

Resize partitions if needed (and no carryover). Reset partition 4 and 5 pointers to start of partition.

R

ENG

A6

RP

2

A4

SCI +AACSR

P

RP

RPA4

SCI +AACS

A4

SCI +AACS

CIRCFIFO

2

P

B5

R

OPNAV

ENG

P

R

HIGH ACTIVITY DAY (2 SSRs)

RPA5

P

RPB5

B5

A6

RP

ENG

A6

R

B6

RP

ENG

B6

1

D. Seal 10 May 2002

B6

ENG

A6 P

R

OPNAV

OPNAV

OPNAV

START EMPTY

Parition map for each SSR must always be identical in case of unexpected SSR swaps. Also, size partitions on each SSR to equal volumes whenever possible for ops simplicity. Stochastic compression or unforseen problems makes SSR swaps variable, so A5 or B5 must be able to contain entire volume of OPNAVs (plus playback buffers). Paying twice in storage capacity only limits science if SSRs would otherwise be completely filled; this is unlikely since OPNAVs will almost always be recorded on low activity days.

RECORD

SSR swap is triggered when one identified partition becomes full. This partition should always be A4/B4. If A5/B5 are sized to each contain the full volume of OPNAVs (plus playback buffers), they will never fill up before the swap. Otherwise, data will be discarded.

PLAYBACK

In order as shown. If A5/B5 are not used, the record pointers and playback pointers will be at partition start and the partition will just be skipped. High-rate MAPS data collection must wait until after start of A4 playback so there will be SSR space for the data. Pause of playback pointer for DSN lockup occurs before playback order is asserted, so downlink starts on last partition B4 with room to record and only switches to filled A4 when playback resumes.

POST-PLAYBACK

Resize partitions if needed (and no carryover). Reset partition 4 and 5 pointers to start of partition.

ENG

R

ENG

P

R

P

Note: the1-SSR strategy can be implemented identical to this one; some partitions would just not be used. Only day-to-day variations in OPNAV volume require special handling.

A5

OPNAV

R

PA5

OPNAV

RP

A4

SCI +AACS

RP

RPA4

SCI +AACS

A4

SCI +AACS

B4

SCI +AACS

P

RP

RPB4

SCI +AACS

B4

SCI +AACS

RP

3 4

R

A5

OPNAV

2 LOW ACTIVITY DAYS (1 SSR) WITH CARRYOVER

R

P

RPA5

A5

1

RP

ENG

A6

CIRCFIFO

D. Seal 10 May 2002

OPNAV

OPNAV

ENG

A6 P

R

RINGBUFFER

R

ENG

A6

RP

ENG

A6 P

R

A5

OPNAV

1

RP

A5

OPNAV

R

A5

OPNAV

ENG

A6 PR

START EMPTY

As usual:A4 = science + some engineering.

A5 = OPNAVS.

A6 = all engineering.

RECORD #1

As usual, record pointers move ahead.

PLAYBACK #1

As usual, in order shown, except data left on A4. Downlink capability must be adequate to downlink all of A5. All data recorded during downlink is stored in active partition as usual.

P

POST-PLAYBACK

Usual is reset pointers in partitions 4 & 5. If carryover, do not reset any pointers. This is the only change in operations needed to acommodate carryover!

RECORD #2

As usual. Data carried over in A4 + new data recorded must not exceed partition capacity (of A4 + B4, really).

PLAYBACK #2

As usual, in order shown. All data on A4 & A5 downlinked.

POST-PLAYBACK

Resize partitions if needed. Reset partition 4 and 5 pointers to start of partition.

2

A4

SCI +AACSR

P

R

P

RPA4

SCI +AACS

A4

SCI +AACS

CIRCFIFO

R

P

A4

SCI +AACS

2

R

P

A4

SCI +AACS

R

P

A4

SCI +AACS P

P

R

ENG

A6 P

R

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Partition 6 is sized to hold 25,596 frames of engineering data (225 Mbit). This size guaranteesthat no engineering data is overwritten as long as there is one pass per day (at any complex). Ifpasses are skipped, the duration of recording to any one SSR must not exceed 39.5 hours overtwo consecutive observations periods in order for engineering data to be preserved for faultdiagnosis. For example, if both SSRs are filled at an even rate during a 48-hour observationperiod, each SSR is only used for 24 hours. If the subsequent observation period only uses oneSSR, and the duration of that observation period exceeds 15.5 hours, some engineering datamay be unrecoverable if a fault should occur during these two days.Note that the size of partitions 4 and 6 total 2013 Mbit, the total volume on each SSR usable fortelemetry.Partition 5 is set aside for optical navigation. This data is routed via a telemetry mode overlaycommand. Once the OPNAV data is complete, an additional telemetry mode overlaycommand is sent to restore the data flow to its original form. New telemetry modes for eachpermutation of data routing are not required; the overlay command is sufficient to reroutespecific instrument’s data to the appropriate partition. If partition 5 is used, its volume must betaken from partition4.OPNAVs are taken with the ISS NAC, using lossless compression and no encoding. ach NACfile is 1027 rows x 1036 columns x 16 bits (the first three rows, and the first 12 columns of allsubsequent rows contain header data). Therefore, the maximum file size for these images is17.0 Mbit. Recent in-flight performance of the lossless compressor on OPNAV-like images hasbeen estimated at over 7:1.Refer to the guidelines & constraints in section 8 for some details on how SSR management isimplemented.

Table 2.7 Tour SSR Partitioning# FUNCTION SIZE0 DEFAULT MEM. LOAD 1 30 Mbit1 DEFAULT MEM. LOAD 2 30 Mbit2 NEW MEMORY LOAD 1 30 Mbit3 NEW MEMORY LOAD 2 30 Mbit4 TELEMETRY (SCIENCE & ENGINEERING) 1788 Mbit5 TELEMETRY (OPNAVS FOR TOUR ONLY) 0 unless needed (tour only)6 TELEMETRY (ENGINEERING FOR TOUR ONLY) 225 Mbit (tour only)

During downlink, all data recorded can only be written to the active partition being playedback. This is required in order for the CDS to retrieve data from the SSR as quickly as possible(i.e. from only one partition at a time) to support the high downlink rates during playback.When more than one SSR is required (e.g. high activity day), data recording will switch fromone SSR to the other only when partition 4 becomes full. The sizing of the other partitions, ifused, should be done to ensure that they do not fill up before partition 4 (or data will be lost).Optimizing partition sizing should be avoided whenever possible to minimize operationscomplexity; instead, partitions should be sized the same on each SSR and with sufficientmargin to allow for stochastic data collection.2.5.3 Data policingThe limitations on downlink capability and SSR volume, as well as the non-deterministicnature of many of the instruments' data collection rates implies the need for control over theamount of data each instrument can place on the SSR. Data volume is set aside each day forOPNAVs, when needed, and engineering, and whatever remains of the downlink capabilitycan be determined and allocated among the science instruments. The science office determinesthe allocation process and assigns volume on a per-instrument basis as a function of time,including instrument housekeeping data. Once these allocations are uploaded to the

2-37

spacecraft, they are activated in a background sequence when observations start, and are thenenforced by CDS. The CDS is responsible for protection of instrument data and ceases torecord data from an instrument which has exceeded its allocation. Navigation OPNAVs, whentaken, are implemented as supplements to the ISS data allocation.The CDS has room for 90 data allocation tables, allowing for 44 days of SSR management withone uplink of these tables. (Separate tables are used for both observation and downlinkperiods, and two tables are set aside for support imaging and OPNAVs.)2.5.4 CarryoverDuring low-activity periods, there will occasionally be a need to collect more data than can bedownlinked in a single low-activity pass. This option is desirable during extended low-activityperiods when prime science opportunities are unevenly spaced. The amount of data which canbe taken during the observation period immediately preceding a given downlink period isusually assumed to be equal to the downlink capability of the pass minus the FPW andengineering data collected during the pass (after accounting for R-S encoding). However, if itis desirable to take more data during a particular observing period, this can be done by“borrowing” data from subsequent observing period(s). The total amount of data which can betaken over these multiple observing periods is still fixed, and limited to the total capability ofthe multiple downlink periods minus the FPW and engineering data collected during thosedownlink periods.Data storage must meet two key requirements: data collected during observations periodsmust not exceed the volume that the SSR can store, and data collected during the observation+ downlink period that is intended for playback must not exceed the downlink capability ofthe DSN pass (unless data is carried over).2.6 Navigation and maneuversThe main objective of navigation is to maintain the spacecraft on the planned trajectory for theduration of the nominal mission. Secondary objectives of the navigation effort includeminimizing the operational complexity of its related activities and the delta-vee required tomaintain the correct trajectory. Unlike other missions, the trajectory design will not be re-optimized continuously. Every effort will be made to maintain that trajectory and not replan anew path.While Cassini is in the inner solar system, the focus is on achieving the three planetary flybysand satisfying the Earth swingby requirements. The Earth impact probability, required to beless than one in a million, is controlled by biasing the trajectory away from the Earth until thefinal pre-Earth maneuver. After the Earth flyby, the long Earth to Jupiter and Jupiter to Saturnlegs are rather uneventful. During the Saturn approach phase, the nav team calibrates andunderstands the optical portion of the navigation system and places the spacecraft on theproper trajectory for the Phoebe encounter and SOI. In tour, the nav system controls thespacecraft trajectory on the nominal tour, and updates the tour trajectory only to account forexpected variations in parameters such as satellite ephemerides and the Titan atmosphericdensity. Also during tour, the nav team is responsible for providing accurate predicted andreconstructed spacecraft and satellite ephemerides.2.6.1 TrackingNavigation primarily uses DSN tracking during cruise and tour to collect two separate typesof tracking data as follows.

∞ Ranging is derived from a modulation on the uplink which is processed by thespacecraft and remodulated onto the downlink carrier. The ranging channel competeswith the telemetry channel for power and in intervals of low telecom performance,telemetry modulation must be turned off in order to achieve satisfactory rangingperformance.

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∞ Coherent Doppler requires a 2-way coherent X-band link and is a measure of the totalfrequency shift of the up- and downlink carriers. The spacecraft receives the carrierfrom the ground and multiplies that frequency by a fixed ratio to derive the downlinkcarrier frequency.

In addition to DSN tracking, optical navigation is used during approach and tour andprovides a measurement of a satellite against a fixed stellar background. The images taken bythe imaging cameras directly support the estimation of not only the Cassini spacecraftephemeris but also the positions of the satellites, particularly early in the tour. OPNAVscomplement the radiometric doppler and ranging measurements in orbit determination.Operational measurements begin during Saturn approach and continue throughout theduration of the mission, but are needed less often after the first year of the tour. Initially,between 4 and 8 images per day are taken for the first few Titan flybys with the number ofimages decreasing as the ephemerides converge. The number of images increase whenapproaching icy satellites for the first time.During the first two years of the mission, DSN tracking can always obtain the Doppler data,but obtaining the ranging data is complicated by a number of competing requirements.

∞ The spacecraft is normally sun pointed which requires that the communications beaccomplished using the low gain antennas (LGAs). The performance characteristics ofthe LGAs create problems with the acquisition of range data.

∞ Navigation requires Doppler and ranging data from both northern and southernhemisphere tracking stations.

∞ The spacecraft analysis team requires telemetry at least once per week.During this portion of early cruise, there are several periods where telemetry both types oftracking data are not achievable and must be accounted for.During later cruise, the spacecraft geometry is changing more slowly and HGAcommunication is possible. Tracking 1-2 times per week is sufficient to maintain acceptableknowledge of the spacecraft trajectory. On the long Jupiter-Saturn leg (the quiet and sciencecruise phases), orbit determination is only needed on a quarterly basis.During tour, most navigation tracking is tied to the schedule of close satellite encounters. Pre-encounter tracking in part supports the flyby targeting maneuver which places the spacecraftin the final flyby trajectory. Post-encounter maneuvers are required only for Titan as a result ofits gravitational effect on the trajectory. Since the nominal DSN coverage is one pass per dayduring tour, tracking that rides along whenever these passes are desired by science may beacceptable.For optical navigation during approach and tour, once the overall requirements for opticalnavigation are known, a “super set” of opportunities is generated that pass all of the pointingand timing constraints. Each opportunity is a unique image and specifies the time of theimage, its target (typically a star) and the satellite also being imaged. The super set containsextra images (e.g. 25%) in order to allow flexibility in the science planning process. Requestsfor OPNAVs are submitted through the Cassini Information Management System (CIMS) asengineering activities. The narrow angle camera is the primary instrument for OPNAVsalthough the wide angle camera can also be used.Navigation then participates in the planning process and is responsible for assuring that theimages approved in the final sequence meet the nav requirements, and that the details of eachobservation – start/end times, turns, camera parameters, etc. – are properly included. Pointingconstraints are checked and ride-alongs are coordinated. The real-time execution of theOPNAVs is monitored and the images are acquired at the beginning of the next downlink passfor processing.

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2.6.2 ManeuversDuring the inner solar system cruise, typically three maneuvers are required betweenconsecutive encounters; the first to clean up the dispersions caused by the first flyby, and thenext two to assure accurate delivery to the next encounter. In the later portions of cruise, thetrajectory requires very infrequent maneuvers. However, “flushing maneuvers” of at least 5seconds in duration are required to flush the wet portion of the propellant valves of the mainengine every 400 days. To maintain at least one maneuver every 400 days, several maneuvershave been added to the schedule and are accommodated in the navigation plan. Theseflushing maneuvers ensure that oxidization of iron alloys in the bipropellant feed system donot build up long enough to plug the small orifices of the valves.Maneuvers have two components of delta-vee: a deterministic (or pre-planned) component,and a statistical component required to clean up dispersions to maintain the correct trajectory.Cassini can execute maneuvers using either the main engines or the Reaction Control System(RCS) thrusters. Generally, delta-vees larger than a crossover point, currently at 0.5 m/s, aredone with the main engine since the main engines have a higher thrust than the RCS thrustersand can impart higher ∆V in a shorter period of time. The crossover point is selected – withinlimits – to share the delta-vee burden between the bipropellant and monopropellant systemsand to take advantage of the improved accuracy with the RCS. Ideally, Cassini should run outof each propellant at the same time in the extended mission (save for any hydrazine left overfor continued attitude control).Main engine maneuvers require REA heaters on for 6 hours before the burn (from TCM 18onward). During each main engine burn, the main engine nozzle gimbals control the engine toapply thrust as closely as possible in the direction of the center of mass of the spacecraft. TheEGAs are stowed in the same position every time. For each main-engine maneuver that occursnear the ring plane, the MEA cover must also be opened before the maneuver and closedafterward in order to minimize micrometeoroid exposure of the sensitive engine nozzles. Themaneuver will not proceed unless this is verified on the ground and a ‘go’ command is sent toexecute the maneuver block. The cover is closed after the engine burn, following anappropriate cooling period. The total open time is usually six to seven hours per main enginemaneuver. Both types of burns must be at least one second in duration; the minimumresolution for a main engine burn is 8-12 cm/s.During cruise, all maneuvers have continuous coverage for three DSN passes centered on theburn. The SSR will record maneuver data during the time the spacecraft is off-Sun (or off-Earthfor TCM 18 onward). During early cruise where HGA communication is not possible, up toseven passes at 40 bps downlink (20 bps SSR playback) are required to play back all recordedTCM data. As a result, only the off-Sun data is played back (off-Earth for TCM 18 onward).Sprint turns may be used when they are necessary to meet the thermal constraints. A sprintturn to the burn attitude can take as long as 7 minutes each way. The total off-Sun time for aburn includes the turn to the burn attitude, a settling period of approximately 5 minutes, theactual burn time, a burn settling of 2 minutes, and the turn back to Sun-point. During cruise,maneuver backup dates are typically 14 days after the scheduled maneuver when time allows.Beginning with TCM 19a, in September 2003, RCS TCM turns to and from the burn attitudewill be done on reaction wheels. Control during the RCS TCM burns will still be on RCS butthe RWAs will be left ON during the burn in their RATE mode. For ME TCMs, RWAs areused for the roll turns, RCS for the yaw turns. RWAs are OFF during the actual ME burn, thenturned back ON afterward. This operational strategy will save significant hydrazine.The tour selected for the Cassini mission places new and significant requirements on theexecution of maneuvers. Control of the trajectory requires at least three maneuvers bescheduled between each targeted encounter of Titan or an icy satellite. The scheduled dates, asfollows, were chosen to balance the ∆V budget with operational constraints on placingmaneuvers close to flybys.

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∞ Encounter Cleanup - scheduled at each targeted Titan encounter + 3 days . Thismaneuver corrects for most errors in the flyby and may provide some or all of thechanges required to achieve the next flyby. Generally these are statistical maneuvers.

∞ Near Apoapsis - scheduled near apoapsis on the orbit between the targeted encounters.This maneuver sets up the trajectory to achieve the next targeted encounter. In manycases this maneuver has a significant deterministic component.

∞ Approach Targeting – scheduled at each targeted encounter – 3 days. This maneuver isstatistical and cleans up any residual errors from the apoapsis maneuver in order toachieve an accurate delivery to the next encounter.

In order to maintain the spacecraft on the tour within the available propellant, it is necessaryto execute both the cleanup maneuver and the near-apoapsis maneuver. The maneuvers maybe delayed by a day or two with only a modest increase in the propellant cost, but skipping amaneuver could required a tour redesign due to propellant availability. The criticality of theapproach targeting maneuvers depends upon the achieved accuracy of the near apoapsismaneuver.Also, the reference tour includes a significant number of 16 day orbits. With only 16 daysbetween targeted encounters, a maneuver must be accomplished, on average, every 5.3 days.This maneuver frequency implies that maneuvers can occur on any day of the week and at anytime of day. With only a few days between maneuvers, the time to evaluate the results of amaneuver, determine the post-maneuver trajectory and plan the next maneuver is at premium.With more than 160 TCMs planned for the tour, efficient and consistent planning andexecution is necessary.All maneuvers will be executed during a single DSN tracking pass with the maneuver mini-sequence uplinked twice at the beginning of the pass. If, because of DSN problems at thebeginning of the OTM pass, either 1) the health status of the spacecraft cannot be verified, or2) the maneuver cannot be successfully uplinked there is insufficient time to retry themaneuver and the backup pass must be used. In this case, the OD solution will not berecalculated, but the maneuver will simply be replanned for the following day using the sametrajectory. Two-way Doppler tracking data is collected before and after the maneuver (ingeneral 2-way tracking will be lost during the maneuver). The engineering telemetry recordedduring the maneuver is played back immediately after the maneuver.For icy satellite flybys, targeting maneuvers before the flyby are also required but typicallycleanup maneuvers after the encounter are not required, since the satellite’s gravitational effecton the trajectory is negligible. Occasionally there are maneuvers scheduled on the day after icysatellite flybys. These maneuvers are primarily deterministic and are implemented as cannedmaneuvers.The maneuver parameters and mini-sequence is automatically generated by the ManeuverTeam. This team has the responsibility for generation of the final orbit determination solution,generation and validation of the mini-sequence and transmission of the command file to theACE for uplink. The generation and validation of the input files and parameters necessary forthe execution of the automatic maneuver generation software is usually accomplished duringstandard working hours.A typical maneuver timeline is shown in the following figure. In addition, requirements forhandover passes (two-station passes) are given for maneuver support.

Example Nine Hour OTM PassManeuver block*

Op Mode transition

6 hours

DFWP-TCM, Spin DFWP-TCM No Spin

“off-Earth”

1:30 hrOWLT

Op Mode transition

SpacecraftEvent

EarthReceive

A 9-hour OTM pass gives:• > 1:41 hr for verifying s/c health & safety

and uplinking the maneuver• > 7:33 hr science downlink• ! 2:20 hr two-way Doppler before and after

maneuver• 15 min OTM engineering data playback

A 9-hour OTM pass gives:• > 1:41 hr for verifying s/c health & safety

and uplinking the maneuver• > 7:33 hr science downlink• ! 2:20 hr two-way Doppler before and after

maneuver• 15 min OTM engineering data playback

BOT EOT

* = assuming “worst case” (longest) maneuverblock length of 2:44 hr.

= Health & safety check + maneuver uplink

= Two-way Doppler

= Science downlink

= Engineering downlink

24 Apr 02

2

Ref *

OTM Split-Pass Rules

Pass 2

EOTBOT

EOTBOT

Pass 1

EOTBOT

EOTBOT

X

≥ 8:37 hr

≤ REF – TWLT + 8:05

≥ TWLT + 2:10 hr

≥ TWLT + 2:10 hr

≥ TWLT + 2:10 hr

≥ TWLT + 2:10 hr

= one-way= two-way= three-way

= downlink only= transmitter on

= transmitter off

≥ REF + 4 hr

* = Reference line. OWLT after beginningof 9-hour OTM window request in CIMS.

Latest

Pre-maneuvertwo-way

Earliest

Latest

Post-maneuvertwo-way

Earliest

1

1

1

1

2 ≤ REF

3

4

5

1. All passes must be ≥ TWLT + 2:10 hr long.

2. Pass 1 BOT must be ≤ REF.

3. Pass 1 EOT must be ≥ REF + 4:00 hr.

4. Pass 2 BOT must be ≤ REF - TWLT + 8:05 hr.


1. All passes must be ≥ TWLT + 2:10 hr long.

2. Pass 1 BOT must be ≤ REF.


4. Pass 2 BOT must be ≤ REF - TWLT + 8:05 hr.


1

2

3

4

5

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RCS thrusters provide ∆V for small maneuvers. For larger ∆Vs, PMS has a primary andredundant pressure-regulated main rocket engine. Each engine is capable of a thrust ofapproximately 445 N when regulated. The bipropellant main engines burn nitrogen tetroxide(N2O4) and monomethylhydrazine (N2H3CH3) producing an expected specific impulse of upto 308s. These engines are gimbaled so that, under AACS control during burns, the thrustvector can be maintained through the shifting center of mass of the spacecraft. AACS-provided valve drivers for all the engines/thrusters operate in response to commands receivedfrom AACS via the CDS data bus. While the gimbals or the valve drive electronics are active --be it during a burn or spacecraft checkout -- there is some effect to the Radio and Plasma WaveSpectrometer due to electromagnetic interference. Since maneuvers and checkout occur soinfrequently, and usually during periods where little or no science is collected, this is not aproblem, but RPWS planning staff must be aware of this.During a main engine burn, RCS thrusters, controlled by AACS, maintain the spacecraftattitude about the roll axis. The main rocket engine performs most large maneuvers with thepressure regulated; however, it performs maneuvers in the blowdown mode during portionsof the mission when the pressurization system is pyro-isolated. Only one of the two mainengines is permitted to operate at a time, whether pressurized or in blowdown mode.Mounted below the main engines is a retractable cover which is used during cruise to protectthe main engines from micrometeoroids. The thin coating on the inside of the engines isespecially vulnerable to micrometeoroid damage, and if this coating is damaged it can lead tothe loss of the engine. The main engine cover can be extended and retracted multiple times (atleast 25 times), and has a pyro ejection mechanism to jettison the cover should there be amechanical problem with the cover that interferes with main engine operation. During cruisethe cover will remain closed when the main engines are not in use.2.6.3 Main Engine usageThis subsection discusses main engine burn profiles for the Cassini mission set. ∆V estimatesare expressed in terms of mean ∆V. The navigation staff recommends that suballocated ∆Vestimates be used for statistical maneuvers on a maneuver-to-maneuver basis. Thesuballocations are computed so that when added together, the net budget is equal to a 50%confidence ΔV estimate. However, this section considers the most realistic ΔV budget as awhole and therefore uses current best estimates.The launch delay to the tenth day of the primary launch period resulted in a near-optimallaunch date and reduced the ∆V requirements for reaching Saturn. Current estimates by theNavigation Team forecast the ∆V available for the tour as 520 m/s from the bipropellantengines and 37 m/s from the monopropellant thrusters with a 95% confidence. An additional70 m/s is held as end-of-mission margin. 2.7% of the bipropellant is considered unusablebecause it will be left over in the tank/lines and loading uncertainty.During testing, the MEA developed an oscillation (i.e., “chugging”) when operated belowcertain pressure levels. In order to minimize the possibility of damage to the MEA or thespacecraft, the amount of time that the MEA is allowed to operate in the “chugging” regimewill be limited to a total of 60 minutes.Figure 2.30 shows the predicted progression of the mean values of the bipropellant fuel andoxidizer pressures for the interplanetary portion of the mission. The circles on the figuredenote the coast periods between events. The figure begins with TCM-1 which wasaccomplished in blow-down mode after the pressurization of the fuel and oxidizer tanks. Thepressures before and after TCM-1 were obtained from telemetry data. Following TCM-1 thepressures varied as a results of helium absorption and temperature changes. TCM-2 wasaccomplished using the RCS thrusters and, therefore, is not reflected in the bipropellantpressure history.

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160 180 200 220 240 260 280160

180

200

220

240

260

280

Fuel Tank Pressure, psia

REA Operating Boundary

Chugging Boundary

DSM SOI

TCM 9

Earth Swingby

Saturn Approach

Figure 6: Biprop Tank Pressure History - Mean - Post-TCM 2 Trajectory Redesign

Post-TCM-1 He Absorption

TCM 1

Figure 2.30 Biprop Tank Pressure History - Mean - Post-TCM-2 Trajectory RedesignThe fuel and oxidizer tanks will be pressurized and regulated for the DSM. Following the DSMthe oxidizer tank is isolated with a pyro valve and the fuel tank is isolated with a high pressurelatch valve. Except for TCM-9, the plan is to remain isolated until just prior to SOI andaccomplish all of the bipropellant maneuvers in "blow down” mode. In order to precludecrossing the "chugging" boundary, it is necessary to pressurize the fuel tank during theexecution of TCM-9. The history assumes that the fuel tank achieves the regulated pressureafter the end of TCM-9 (the variations in the fuel pressure during the maneuver are notmodeled). The figures assume that all maneuvers under 0.7 m/s are accomplished using theRCS system. (The actual value for choosing RCS or ME will be between 0.5 and 1.0 m/s).Regulator Leak Problem: As the initial pressurization was being performed just prior toTCM1, an unexpectedly high leak rate, 1700 sccm (standard cubic centimeters per minute),was noticed from the primary regulator (PR1). The specified rate for leakage from thisregulator was supposed to be ≤ 0.6 sccm. High pressure latch valve LV10 was closed inresponse. The incident was addressed in ISA Z44505.While regulator leakage is a well known phenomenon, the magnitude of this leak wassurprising, especially given the leakage characteristics demonstrated by PR1 during groundtesting. Analysis demonstrated that particulate contamination could very easily explain theobserved regulator leakage, since the requisite particle size that causes a 1700 sccm leak is twoorders of magnitude smaller than the filter capacity between pyro valve PV1 and PR1. That is,a particle that just fits and passes through the filter upstream of PR1 could actually cause aleak a hundred times larger than the leak observed at initial pressurization.Recommendation has been made to the project to continue to use PR1 unless the leakagereaches 20000 sccm. The PR1 regulation function is considered excellent despite high leakage

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during DSM and TCM13, and procedures have been identified, specifically for the coordinateduse of LV10, that can be employed at the next regulated maneuvers, Phoebe and SOI.2.7 Attitude ControlThe Attitude and Articulation Control Subsystem (AACS) provides dynamic control of thespacecraft in rotation and translation. It provides fixed-target staring for HGA and remotesensing pointing and performs target relative pointing using inertial vector propagation aswell as repetitive subroutines such as scans and mosaics. Rotational motion during the Saturntour that requires high pointing stability is normally controlled by the three main ReactionWheel Assemblies (RWAs), although modes requiring faster rates or accelerations may usethrusters. The additional fourth reaction wheel can articulate to replace any single failedwheel.Each RWA has a mass of 14.53 kg. The largest reaction torque for each RWA is 0.13Nm. Noneof the three RWAs can absorb an angular momentum that is larger than 34Nms (approx. 2000rpm). All RWAs have their spin axes at 54.7356o from the spacecraft Z-axis.Gyros are used primarily during the four year tour of the Saturnian system but will have somepre-Saturn use as well. If, upon evaluation after SOI, the IRUs show no signs of performancedegradation, they will be used continuously for the full tour. The IRUs will be re-evaluatedwhenever a life limiting characteristic becomes evident. In the event of IRU failure or loss ofperformance, IRU use during the tour can be restricted to periods of high science activity.AACS contains a suite of sensors that includes redundant Sun Sensor Assemblies (SSA),redundant Stellar Reference Units (SRU, also called star trackers), a Z-axis accelerometer, andtwo 3-axis gyro Inertial Reference Units (IRU).Each IRU consists of four gyros, three orthogonal to each other and the fourth skewedequidistant to the other three. AACS also controls actuators for the main rocket enginegimbals. With two redundant MIL-STD-1750A AACS Flight Computers (AFC) running flightsoftware programmed in Ada, AACS processes commands from CDS via the CDS data busand produces commands to be delivered to AACS actuators and/or PMS ME and RCS valvesfor spacecraft attitude and ∆V control. AACS provides heartbeat, telemetry and fault responseinformation to the CDS.For attitude control, PMS has a Reaction Control Subsystem (RCS) consisting of four thrusterclusters mounted off the PMS core structure adjacent to the LEM at the base of the spacecraft.Each of the clusters contain 4 hydrazine thrusters. The thrusters are oriented to provide thrustalong the spacecraft ±Y and -Z axes. RCS thrusters also provide ∆V for small maneuvers. Theapproximate ISP for the RCS is 180s for turns, 140s for RWA unloads, 120s for limit cycling, andthe theoretical max is 217s.

Table 2.8 Thruster Cluster Mass ProperitesThrusterCluster #

Mass(kg)

Xcm(m)

Ycm(m)

Zcm(m)

1 5.91 1.24 1.59 2.882 5.91 -1.24 1.59 2.883 5.91 -1.24 -1.59 2.884 5.91 1.24 -1.59 2.88

2.7.1 S/C Attitude DefinitionThe spacecraft orientation in inertial space is always defined with respect to the basebodyattitude. All changes to the attitude are referenced with respect to the basebody attitude.The base attitude is specified by defining two pairs of vectors; two local vectors in the S/Cbody coordinate system and two inertial vectors in the J2000 inertial system. From each of

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these pairs, one of the vectors is termed the primary vector and the other is termed thesecondary vector.

Table 2.9 Spacecraft Mass ProperitesMissionphase

S/C Information Mass(kg)

Xcm(m)

Ycm(m)

Zcm(m)

IXX(kg-m2)

IYY(kg-m2)

IZZ(kg-m2)

BOM Huygens attached, Magboom stowed, RPWSantennas stowed.

5573.8 -0.02 -0.01 1.33 8553.0 8846.8 3820.3

BeforeSOI

Huygens attached, Magboom deployed, 2 RPWSantennas deployed.

4640.8 -0.03 0.02 1.36 8758.9 8128.2 4650.9

BeforeProbeRelease

Huygens attached, Magboom deployed, 2 RPWSantennas deployed.

3306.8 -0.04 0.03 1.30 7669.2 7045.0 4383.3

AfterProbeRelease

Huygens released, Magboom deployed, 2 RPWSantennas deployed.

2986.8 0.11 0.03 1.27 7505.5 6288.5 3665.9

EOM Huygens released, Magboom deployed, all RPWSantennas deployed.

2452.8 0.13 0.06 1.14 6864.4 5719.5 3553.5

The base attitude shall be that attitude which satisfies the following two relationships:The primary body vector is pointing in the same direction as the primary inertial vector;The angle between the secondary body vector and the secondary inertial vector isminimized.

Typically the primary body vector will be an instrument boresight and the primary inertialvector will be observation target. The secondary vectors are chosen to provide a preferertialattitude for satisfying (thermal) constraints or optimizing other aspects of the investigation.For example, the NAC boresight and the Z-axis could be the primary and secondary bodyvectors, respectively, while the S/C to Titan vector and the normal to the Titan flyby trajectoryplane could be the primary and secondary inertial vectors, respectively. This would produce acontinually changing attitude that points the NAC at Titan by rotating about the Z-axis.The "base" attitude is the spacecraft attitude that aligns one body vector with one inertialvector and places a second body vector as close as possible in alignment to a second inertialvector. The unit vectors XBASE, YBASE and ZBASE are fixed in the base coordinate frame. Thespacecraft X, Y and Z axes are parallel to XBASE, YBASE and ZBASE, respectively, when thespacecraft is at the base attitude with zero offset. The user-selected body vectors must bemembers of the Body Vector Table (BVT). The user-selected inertial vectors must all bemembers of the Inertial Vector Table (IVT). If the chosen body vector does not exist in the BVTor the chosen inertial vector can not be constructed from entries in the IVT, the command tospecify the base attitude is rejected. The base attitude is specified by the 7TARGET command.The 7TARGET command basically answers the question: "What do you want to point andwhere ?"2.7.2 Attitude CommandingAttitude offset shall be commanded by specifying a 'rotation' vector in base attitudecoordinates or in the S/C basebody coordinates which determines the axis (vector direction)and angle (vector magnitude) of rotation necessary to achieve the offset. The commandedoffset rotation axis may be specified in the base attitude or the body attitude coordinates.Attitude Commander allows for both types of offsets. Primary and secondary inertial vectorsshall be selected by name from Inertial Vector Propagator entries. Commanded changes to theselection of basebody and/or inertial vectors (not the vector values) shall not be effective until

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the first subsequent offset rotation command. That offset command shall be with respect to themost recently selected basebody and inertial vectors.The basebody commander shall accept absolute and relative turn commands. For absolutecommands, the basebody commander shall generate the shortest vector turn between thecurrent attitude and a newly commanded offset with respect to the base attitude such thatconditions 1, 2, and 3 below are met during the transition. For relative commands, such as spinor turns that are larger than half a revolution, the basebody commander shall accept a turn (orspin) vector, consisting of a turn axis and a turn angle. It will then generate a turn profilebetween the current attitude and a newly computed offset (with respect to the base attitude)such that the following conditions during the turn are met:

(1) The attitude offset with respect to the base attitude (not the attitude with respect toinertial space) rotates predictably about an axis relative to the base attitude;(2) The commanded attitude offset profile is composed of an acceleration phase, anoptional constant rate coast phase (if coast rate is reached), and a deceleration phase;and(3) The offset rotation rate with respect to the base attitude reaches zero when the newlycommanded offset is achieved.

The peak acceleration/deceleration and coast rate of such a turn profile shall be commandableparameters and shall take effect only at the initiation of the next turn profile.Updates to basebody, inertial, and offset vectors, changes in the selections of basebody andinertial vectors, and changes in turn rate profile parameters shall be independentlycommandable. Other than the inertial and basebody vectors, all other updates shall take effectonly at the initiation of the next turn profile.2.7.3 Inertial Vector PropagationThe Inertial Vector Propagator (IVP) propagates relative inertial positions and velocitiesbetween two objects (which may be spacecraft or inertial), e.g. Sun and Earth, Earth and Moon,Sun and Saturn, Saturn and Titan, Titan and spacecraft etc. The propagated vectors aremaintained in the Inertial Vector Table (IVT). This table can simultaneously maintain severalinertial vectors, a subset of which is generally required to support science instrument pointing,antenna pointing, star tracker pointing, thrust vector pointing, constraint enforcement etc.Although there is no algorithmic restriction, the users (other AACS software objects) generallyask IVP for spacecraft-relative position and velocity vectors. The user may ask IVP for vectorsbetween any two distinct objects propagated by IVP. The Inertial Vector Propagator will addor subtract the required relative vectors (components) to calculate the position and velocityvectors between the user-specified end points. The component vectors are propagatedseparately and one component may figure in several user requests. The component vectorsform a tree, termed the inertial vector "tree".Three types of vector propagation are possible in IVP -- Fixed (time-invariant), Conic (time-varying) and Polynomial (time-varying). The determination of which type is suited best for aparticular vector is based on fits carried out on the ground. The Inertial Vector Propagatormust be provided with either fixed vectors or sets of propagation constants, each setdescribing the time-dependent motion of a single component vector. Component vectors neednot all be based at the spacecraft. For instance, one set of propagation constants might specifythe motion of Saturn with respect to the Sun while other defines the motion of Titan aroundSaturn.The Body Vector Table (BVT) resident in IVP stores various spacecraft boresights in the AACSbody-fixed reference coordinate frame. Entries in the Body Vector Table are not propagatedwith respect to spacecraft time but are fixed according to user-specified command parameters.

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The Body Vector Table allows the user to explicitly accommodate in-flight identification ofend-to-end structural and/or electrical misalignments. The vectors are stored as unit vectors.2.7.4 Turning the SpacecraftAttitude control of the spacecraft is maintained through the use of the RCS thrusters and thereaction wheel assmblies (RWAs), while attitude determination is controlled through the startrackers, inertial reference units and sun sensors.Most of the attitude control resources are used merely to maintain a constant attitude, limitcycling between the bounds of the pointing requirements. External influences also requireattitude control, and the two largest contributors are RTG radiation and solar radiationtorques.Turns during cruise are typically done using the RCS system to save the reaction wheellifetime for the tour period and to allow faster turns to minimize thermal exposure whenturning off the Sun line. In situations where the fastest possible turns are required (e.g. forthermal constraints), sprint turns are available at higher rates with degraded pointingaccuracy. Turns on thrusters generally take minutes, while turns on wheels can take up to anhour. Finer pointing control is possible with wheels, however, so the need for fast turn timesand fine control must be balanced on a case by case basis. Care must be taken to ensure thatorientations during turns do not violate thermal constraints or place the Sun, planets orsatellites in the boresights of the star trackers and, in some cases, instrument fields of view.Spacecraft resources which are used for turns, mosaics, and target body motion are dividedinto two groups: torque, which determines the angular acceleration of the spacecraft; andmomentum, which determines the maximum rate achievable by the spacecraft. Either resourcecan limit spacecraft capabilities. For the reaction wheels, the power allocated and some relativebalance determines the maximum torque and momentum; for thrusters, the torque is a fixedquantity determined by the thrust provided by the RCS. Momentum (maximum rate) availableon the thrusters is tied to the star tracker limits, and to a lesser extent, the propellant requiredto stabilize the spacecraft during its rotation.Reaction wheels require unloading due to external torques applied to the spacecraft by solarpressure, RTG pressure, etc. During unloads, the thrusters control the spacecraft attitude whilethe wheels are spun up or down to the desired rate. The reaction wheels must be unloaded (orre-biased) every 15 days, during a tracking pass so the activity can be monitored in real timeand the resulting delta-vee measured via navigation tracking. In addition, a re-bias should beplaced on the last pass of each sequence to set the wheel speeds properly for the nextsequence. The time required to unload the reaction wheels is approximately 15 minutes.For the reaction wheels, mosaics typically use very small turns between frames that neverreach the maximum spin rate of either the spacecraft or reaction wheels. Therefore, most of thepower can be allocated to torque (i.e., acceleration) to minimize the time required for eachmosaic. On the other hand, target turns (e.g. Saturn to Earth) usually spend a lot of timecoasting at the maximum rate (determined by momentum).Reaction wheel capabilities are further complicated by variances between wheels, the fact thatthey are canted with respect to the body axes of the spacecraft, and they operate at variousspeeds depending on the orientation, biasing at the last reaction wheel unload, and externaltorques placed on the spacecraft. Each wheel has slight differences in its operating conditions;turns about different axes burden the wheels in different proportions; and the moment-to-moment spin rates of the reaction wheels – which indicate how much authority each hasavailable – varies with time and the past conditions. For these reasons, articulation capabilitiesfor planning must be selected carefully with an appropriate across-the board margin policy sothat the science observations are not too limited, but the risk of not completing a turn isminimal.

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Typically, turns about the Z axis provide the best performance. This is due mainly to the factthat the spacecraft moment of inertia is lowest about Z. For reaction wheels, Z axis turns areshared equally between all three wheels which also provides some advantage.2.7.5 Target Motion CompensationTarget motion compensation is required for some of the highest value science near close flybyswhen satellites and features must be tracked as they move across the sky quickly. WithoutTMC, images would be smeared and data corrupted unacceptably. Naturally, the closestencounters can provide the highest potential resolution for images and the strongestmeasurements of fields, particles and waves, but these flybys also have the highest targetmotion.During a flyby, each of the two available resources (torque and momentum) must be dividedbetween TMC and any science articulation. As the satellite rate or acceleration increases, moremomentum and torque must be devoted to TMC, and less is available for other science turns.If the maximum rate or acceleration limits are reached, no resources are left for science turns. Ifrate or acceleration limits are exceeded, the target body may move too fast for the scienceinstruments to take advantage of the close encounter.When the spacecraft is engaged in target motion compensation, well-planned science turns canbe oriented so they subtract rather than add to the target body rates. In other words, if thetarget motion should be used to turn from one position to another, rather than requiring thewheels to fight against the target motion. For example, a row of images starting on the leadingedge (as seen from the spacecraft) and finishing at the trailing edge will allow the spacecraft toslew from frame to frame by simply compensating less for the target body motion.2.7.6 Titan atmospheric modelTitan's atmosphere is primarily comprised of a handful of constituents, each of which can bemodeled in a formula which approximates the atmospheric density as a function of heightfrom the surface. This formula contains several terms, one for each main constituent, and isbased on the PSG endorsed atmospheric model developed by Yelle in 1993-94. A relativelysimple formula is possible because Titan's atmosphere is close to isothermic in the Yelle modelat the altitudes of interest for this problem (i.e., 800 - 3000 km).At these altitudes of interest, Titan's atmosphere is comprised mainly of nitrogen, methane andargon. Therefore, there are three terms in the equation, as follows:

ρ(z) = 6.35x10−6 e11400(z−76)T(z+2575) + 5.13 x10−7 e

8030(z+429)T(z+2575) + 7.35x10−5 e

15000(z−44)T(z+2575)

− − −

where ρ(z) is the atmospheric density in g/cm3, z is the altitude in km, and T is thestratospheric temperature in Kelvin. Note that this formula is only valid for altitudes between800km and 3000km. The formula is accurate to within 1% of the altitude in this region. Thefirst term is for nitrogen, the second for methane, and the third for argon.The temperature variation arises only with different confidence levels; again, Titan'satmosphere is isothermic at these altitudes, but what temperature it is fixed at is uncertain. Todetermine the temperature, the formula

T = 175 + 10 γis used, where γ is the gaussian variable; i.e., γ = ± 1 equals a 1-sigma uncertainty (T = 165K or185K). Gamma is greater than zero for denser atmospheres, and less than zero for sparseatmospheres.2.7.7 Minimum Flyby AltitudesMany of the low (< 4000 km) Titan flybys will be allocated to RADAR, when the thrusters willcontrol the spacecraft attitude; most of the remainder will require reaction wheels, particularly

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for remote sensing. Both target motion compensation (TMC) and maintaining attitude underatmospheric torque must be possible for the flyby to be useful to the science investigations.Since target motion compensation is required for smear-free imaging of Titan, the reactionwheel or thruster capabilities must be split between atmospheric compensation and TMC. Theminimum flyby altitude can therefore be constrained by either of two formulae: that fortorque, which has contributions from both TMC and the atmosphere; and that for momentum,which affects the spin rates of the wheels, and has a transient contribution from TMC and alasting one from the atmosphere.RADAR passes currently use the reaction control thrusters which, compared with the reactionwheels, exerts a strong control over the spacecraft attitude and can rotate it rapidly. However,at the lowest planned altitudes (950 km) Titan's atmosphere becomes a significant source ofspacecraft torque. Minimum altitude limits must be set based on the atmospheric model andthruster torque capability. Violating these altitudes will place the spacecraft in an environmentwhere it cannot control its attitude to the desired target(s) for RADAR science. Significantdeviations lower than the altitude limits will jeopardize the safety of the spacecraft.Titan's atmosphere, like any, is exponential in nature and has a scale height of about 70 km atthe altitudes of interest (this is the ∆ altitude required to see a change in density of a factor of e,or 2.7x). Therefore, limit violations as low as tens of kilometers can require significantly highercontrol torques.One option, besides changing the ORS balance between torque and momentum, which mightincrease the available momentum is "biasing" the wheels. The momentum available is a vectorand not a scalar value. In other words, any momentum limit is defined from 0 Nms in eitherdirection. Since the momentum that the wheels will compensate for is predictable in directionit may be possible to "bias," or pre-spin the wheels in the opposite direction to compensate.This strategy could potentially double the available momentum.The project has adopted a strategy for selecting a minimum altitude for Titan flybys andconsidering redesign of flyby aimpoints. This strategy is needed to assure efficient use ofpropellant and to address the potential need to raise or lower the closest approach altitude atseveral flybys for spacecraft safety and/or INMS science. The design minimum Titan flybyaltitude on thrusters is 950 km. This altitude is selected such that the chance of the atmospherebeing too dense for the thrusters to maintain attitude control is 5%. If the atmospheric model ismore dense than expected, and is refuted by in-situ measurement of the Titan atmosphereduring early, higher flybys, then this altitude will have to be increased.For the first 950 km altitude flyby of Titan, two trajectories and sequence plans are developedin parallel, one at 950 km (the baseline) and one at a higher altitude of 1065 km guaranteed tobe safe under any possible atmospheric conditions. Both trajectories and sequence plans arecanned long before the encounter; after the atmospheric density is measured on the first Titanflyby, a decision is made on which plan is used. If the atmosphere is found to be less densethan expected, future encounters may be lowered to meet INMS science objectives.2.7.8 Hydrazine usageThe hydrazine tank will be fully loaded at launch to maximize the propellant available at theend of the tour and for any extended mission. 1% of the hydrazine is considered unusablebecause it may be left over in the tank/lines and loading uncertainty. The CassiniConsumables document, PD 699-523, details the expected hydrazine usage during tour.Advance planning and tracking of hydrazine usage should allow for a healthy margin to bemaintained. The margin will be available for unexpected occurances during tour should theyarise. Any unused hydrazine remaining after tour will be available for use in an extendedmission.As propellant is used, the helium pressurant expands to fill the space used by the expendedpropellant, thereby decreasing the pressure in the tank. When the tank pressure reaches some

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minimum level, a second tank containing additional helium pressurant is connected to thehydrazine tank by firing a pyro valve. This effectively raises the pressure of the hydrazinetank. This one-time recharge will likely be used after the probe mission is complete to raise thethrust level for the tour portion of the mission.At launch, the initial pressure of the hydrazine tank is determined by the maximum allowablepressure and temperature of the tank and by the propellant load. The planned propellant loadfor the Cassini hydrazine tank is 132 kg, which is the maximum allowable load for the tankdesign. This value represents the maximum pressure at which the thruster is qualified tooperate. The maximum flight allowable temperature of the hydrazine tank is 45°C. With thecurrent constraints, the maximum allowable initial pressure of the tank has been calculated tobe 370 psia, at an initial tank pressure of 21°C.The pressure after recharge can be calculated in a similar fashion as above. In this case, thepropellant load can vary, depending on when in the mission the tank is re-pressurized. Theblowdown curve in Figure 2.31 assumes that the recharge occurs when 100 kg of propellantremains in the tank. Given a 100 kg load, and the previous pressure and temperatureconstraints, the maximum recharge pressure is calculated to be 380 psia.The hydrazine tank pressure needs to be above 250 psia to maintain turn times in thethermally constrained environment inside one AU. The minimum pressure needed during“low” (950 km altitude) Titan flybys is also 250 psia. Figure 2.31 shows the hydrazineblowdown curve with the recharge after SOI, when approximately 100 kg of hydrazineremains. The range of fuel remaining for SOI and EOM are estimates based on expectedvalues and 50% greater use (AACS) or allocation (Nav). The recharge point may be moved intime depending on whether hydrazine usage is more or less than expected and when higherturn performance is desired. However, there is a pressure which must be reached before thetank can safely be recharged. In the example shown in Figure 2.31, that pressure is 237 psia,based on a recharge with 100 kg of hydrazine in the tank. The maximum allowable pressureprior to recharge is a function of the recharge tank helium load and is fixed at PMS loading,months before launch.The tour will have a series of low Titan flybys. The majority of these low flybys will mostlikely occur late in the tour. As a result, the hydrazine tank pressure may be allowed to dipbelow 250 psia early in the tour if there are no Titan low flybys scheduled. However, if thetour has low Titan flybys scheduled early, the tank recharge may need to occur early after theprobe mission.

Figure 2.31 Hydrazine Tank Pressure (psi) vs. Remaining Fuel

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2.7.9 Complications with Reaction Wheel ControlA problem with the RWAs occurred on 16 December 2000. Increased friction on one of thewheels, operating near zero rpm, caused the spacecraft to autonomously switch to the RCS forattitude control. With the switch to RCS, hydrazine usage increased. Two of the four jointCAPS-HST observations, a Jupiter North-South map, the Himalia "flyby", and a UVIS torusobservation were all executed on RCS before the sequence was terminated on 19 December2000. MAPS data continued to be recorded at a reduced rate. All other planned scienceactivities were cancelled until 29 December, when they were resumed.RWA operation was resumed for attitude control on 22 December, with constraints imposed toavoid low RPM regions. This was accomplished by biasing the wheels. Continued testing byAACS personnel suggested the anomaly was a transient event so the sequence was restartedon December 29. Since the anomalous behavior in December 2000, tests and studies led to aProgram decision to use RCS as the primary attitude control system whenever possible duringcruise. RWA usage has been allowed for certain activities that require increased stability orpointing accuracy, e.g., GWE and RSS tests, and for limited cruise science. For ApproachScience starting January 2004, RWA control is the baseline.In order to avoid such anomalies in the future, the low rpm dwell time must be minimized,and continued trending of the RWA performance is required. The low-rpm optimization isperformed as a regular step in the sequencing process, by biasing the wheels at speeds whichshould ensure that they are spinning at moderate to high rpm for most of the sequence, andhas not significantly impacted science collections to date.In the later stages of cruise, notably in late 2002 – early 2003, another reaction wheel problemwas identified as a “cage instability” on wheel 3. Its symptoms include intermittent dragtorque transients and a significant increase in the bearing drag torque. The consequences arelarge unstable oscillations in the cage, leading to premature bearing failure, and severetransient forces that can cause high wear or fracture which may eventually disable the bearing.Based on project, division, and manufacturer recommendations, the project chose to activatethe redundant wheel RWA-4 in July of 2003 and articulate it to the RWA3 position, and use itas a primary wheel together with RWA-1 and 2. It is believed that the RWA-3 cage instabilitywill stay with RWA-3 for its remaining life, and continued operation would increase both thefrequency of occurrence and the size of the drag torque “steps”. Since clearly the twoconsumable specifications of RWA-3 (total revolutions and total low-rpm dwell time) havebeen compromised, it is prudent to cut RWA3 usage for the remainder of mission.One of the pointing requests that have been made of the project, in particular by the CDAinstrument, is to “rock” back and forth about a specific attitude during some downlink passes.This enables CDA to collect data that can be used to distinguish dust impacts from variousdirections, which is a key measurement to their science objectives.Unfortunately, this “rocking” significantly complicates the low RPM management, dependingon number of discrete orientations used, particularly when rocking is required about a largeangle (as is the case most of the time). This operation also requires constant commandingduring downlink, which would prevent the ground from being able to command anunexpected OTM or RWA unload.However, assuming that the number of “rocking” passes is on the order of 10-20 total passesduring the tour, the spacecraft office (specifically the attitude control team) and the projecthave agreed to accommodate the CDA request. The CDA team shall develop a pointing designfor such downlinks to be reviewed by the project, and if the RWA management is not toocumbersome, rocking downlinks will be implemented as requested. (For CDA observationswhich require “rocking” that do not occur during downlinks, there are no unique restrictionson CDA’s pointing designs, just as with any prime instrument planning pointing during anobservation period.)

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2.8 Environmental hazards & controlDuring the mission, the spacecraft is exposed to a variety of potentially hazardousenvironments. Careful planning is required to not only ensure that spacecraft health and safetyis not compromised, but that creative solutions are developed to balance the risk from thesehazards against the scientific objectives when they conflict.2.8.1 RadiationRadiation design for the Cassini spacecraft was created using the back-up mission trajectory(March 1999 VEEGA- Venus-Earth-Earth Gravity Assist), because the radiation environmentfor this mission is the most severe of any of the possible interplanetary trajectories. A radiationdesign margin of ≥ 2 for ionization dose, displacement damage and integrated peak flux wastherefore used for all engineering subsystems, bus science electronics, imaging scienceinstruments and the Huygens probe. Science instruments were required to operate with aradiation exposure of 100 krad.2.8.2 Thermal Control and Sun ExposureThere are several general pointing orientations which expose sensitive components of thespacecraft to undesirable thermal input. This radiative heating can potentially degradeperformance or violate safety constraints. The primary source of thermal input at Saturn is theSun; however, heating from Saturn and its rings, particularly when lit, and the satellitesduring close approaches are of concern as well.To maintain thermal control during cruise, the spacecraft HGA must remain Sun-pointed forvirtually all of its travels in the inner solar system. Off-Sun orientations are possible for shortperiods of time, as listed in table 5.4, and these durations can be scaled with the square of theSun range. For example, at 0.61 AU the spacecraft could withstand a transient off-Sun durationof 0.5 hours/day. At 0.8 AU, however, the spacecraft could turn 180° off-Sun for a scaledduration of about 0.9 hours once/day. For all these off-sun events, the roll angle is restricted sothat the sun line lies in the -X (Probe) side of the X-Z plane. For more information aboutallowable off-Sun durations, consult CAS-3-210.

Table 2.10 Thermal CapabilitiesContinuous off-sun: Transient off-sun exposure at rangeContinuous off-Sun Transient off-Sun exposure at range

Sun Range Off-sun angle Range Off-sun angle Duration0.61-2.7 AU** 2.5° 0.61 AU ≤180° 0.5 hours* 1/day2.7-5.0 AU Earth point OK 1.0 AU ≤180° 1.35 hours* 1/day>5.0 AU (unrestricted) 1.0 AU <60° 4.0 hours* 1/day*Durations include turn times.**Earth-point OK for 25-day Instrument Checkout.

During the later portions of cruise and tour, however, there are performance implications ofsun exposure which must be considered. There are three major "exclusion zones" whichthermal energy sources should be kept from: the SRU boresights (+X direction), the opticalremote sensing instrument boresights (- Y direction), and the cryogenic instrument radiatorshemisphere (also centered along +X).First, the SRU performance can be seriously degraded from thermal input within a 30° cone. Agyro-only mode, in which the spacecraft calculates its attitude without the SRU, may beavailable for short periods of time. Second, most of the remote sensing instruments reportsome performance degradation from thermal input within a ~15° cone.Third, the cryogenic instrument radiators have hemispherical fields of view and share theirexclusion zone with the SRU boresight zone (actually encompassing it completely). Of course,the more vertical the thermal input, the greater the effect on the instruments. Drivers in thiszone include VIMS IR and CIRS. Performance, not safety, is the primary concern. Overheating

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renders instrument data first degraded, then useless. Overheating for the VIMS IR instrumentcan be rapid (≈ tens of minutes with direct sunlight) and cooling very slow (≈ many hours).There is no absolute temperature threshold; "overheating" depends on the experiment inprocess.This problem is complicated by the fact that the vast majority of Titan flybys approach on thesunlit side and recede on the dark side of Titan. This is due to inbound and outbound flybyshaving been placed at consistent locations in Titan’s orbit. Unfortunately, the ram direction ofINMS and other fields, particles & waves instruments is aligned directly opposite the radiatorsof the cryogenic instruments. Therefore, in order to point the INMS and other fields of view inthe ram direction, the cryogenic instrument radiators must face the sun for many encounters.This problem can be avoided with one of two strategies: pointing the INMS in the anti-ram(instead of ram) direction, or turn the INMS to the ram direction only near closest approach,minimizing the amount of time the radiators are exposed to the sun. Unfortunately, the firststrategy degrades data collection for some of the FPW instruments, and the second may usevaluable reaction wheel or thruster resources that are needed for TMC or atmosphericcompensation.Radiator exposure is still a concern even when the cryogenic instruments are not operating.Since the time constant for cooling is so slow, post-flyby science (even up to a day afterexposure) can still be affected. This means that instrument teams that aren’t concerned withoverheating will still have to constrain themselves in pointing design if cryogenic instrumentteams are planning subsequent observations.2.8.3 DustDuring its travels from the inner solar system to the Saturnian environment, Cassini fliesthrough a large region of space which is known to contain debris at a variety of sizes andabundances. Care must be taken to determine the vulnerabilities of the spacecraft to debrisimpacts, and the likelihood of such impacts causing the loss of mission or a degradation inperformance.For a complete description of Cassini’s vulnerabilities to dust, and the protective strategiesthat have been adopted during the tour, refer to the Cassini Dust Protection Plan D-24251.2.9 Periodic ActivitiesThis section describes activities that are repeated often throughout the mission and are notspecific to one particular subphase (as described in sections 6 and 7).2.9.1 Engineering MaintenanceThere are three activities to be completed in the Periodic Engineering Maintenance (PEM)sequence, which is executed approximately once every three months. The three activities are:

∞ Maintaining the BAIL EEPROM in AACS to protect the data from unrecoverableradiation damage. This activity lasts no more than 6 hours.

∞ Exercising the engine gimbal actuators (both prime and backup) through 25% of fullstroke. This activity lasts one hour.

∞ Exercising all of the reaction wheels (including the backup) by rotating each at least 1/4of a turn to spread the lubricant. This activity lasts for less than one hour. Note that thisactivity imparts a delta-V to the spacecraft and therefore should not be scheduled near aTCM (-3 weeks to +2 weeks).

In addition to the standard PEM activities, there are a number of other required engineeringactivities. SRU calibration must occur once every year. Maneuver related AACS parameterupdates and AACS constraint monitor updates are also common. Also AACS cruise modecheckouts, RWA friction tests, NAC-to-SRU alignment, and HGA(X-band)-to-SRU alignment

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are expected. With the exception of the RWA friction test, all of these activities are planned tooccur only once. The RWA friction test will occur as needed. Finally, SSR characterization isperformed through analysis of the SSR single bit and double bit error information obtainedfrom the internal SSR memory scrub function..2.9.2 Huygens Probe CheckoutsProbe Checkouts are sequences which exercise the Probe systems to maintain their healthduring the long cruise period. Each Probe Checkout is up to a 4 hour test of the Probe missionsequence which records up to 303 Mbits of data (including engineering) to the SSR.The purpose of the cruise checkouts is to verify the capabilities of the Probe system to performits mission at Titan. Therefore, the checkouts have been designed to simulate as closely aspossible the sequence of activities to be performed during the Probe descent to Titan. Someexperiment switch-on and pyro events excepted, the PCDU (Power Control Distribution Unit)and CDMS (Command & Data Management Subsystem) sequences are performed as duringthe normal mission, with simulation by telecommands of the changing DDB (Descent DataBroadcast) which will be transmitted to experiments. During checkout, the Probe/PSE link isconducted with a low power RF signal which essentially tests the whole transmitter except forthe high power amplifiers.Due to the power allocation limits agreed to between JPL and ESA, not all of the Huygensinstrumentation can be operated as it is in the mission descent sequence; therefore, checkoutsequences have been developed to allow payload checkout in different groups, and suchsequences have been used throughout ground testing activities. ESA will conduct ProbeCheckout sequence reviews before each checkout to determine if the specific activities duringany one Checkout need to be changed somewhat.Checkouts must take into account the main constraints agreed to by JPL and ESA, namely:

• Power consumption never to exceed 262 Watts.• ≤ 1 CDS telecommand per second per data chain.• PSA and transmitters in mission mode at switch-on, i.e. the default frequency

includes Doppler shift and the Ultra Stable Oscillators (RUSO/TUSO) are selected.• Orbiter can be in any RTE mode, but Probe data must be recorded.• LGA2 (which is mounted immediately below the probe) cannot be operating during

a Probe Checkout (FR80C5).Several additional constraints exist that must be satisfied during each checkout are:

• For real-time playback, the link must support the Probe Checkout data rate of 24.885kbps. If this is not possible, the link margin must support a data rate of at least 40bps for SSR playback of Probe Checkout data (the lowest mode, 20 bps, isexclusively real-time engineering data with no SSR playback).

• DSN coverage sufficient to return Probe data must be in the Detailed MissionRequest, which documents the antennas requested of the DSN by Cassini, and theMGSO User Loading Profile.

• Telemetry must not interfere with the navigation ranging required. During thoseperiods where either ranging or telemetry is possible (but not both), a compromisemust be reached that allows Probe Checkout data to be returned while still meetingnavigation requirements.

• If Probe telemetry must be played back from the SSR, playback must be completedbefore being overwritten by later data (2.0 Gbit data capacity at the beginning of themission - 303 Mbit of probe and engineering data leaves 1.7 Gbit of volume to record

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engineering at 1650 bps = 11.9 days worth of space). Any nonstandard activitieswhich record additional data on the SSR would shorten this time period.

DSN coverage following each Probe Checkout can be used to observe that the probeequipment temperature is falling back to its normal levels (i.e. that everything has been turnedoff properly). For real-time Probe Checkouts (i.e. those with DSN coverage supporting 24.8kbps or higher rates), the Probe Checkouts have been placed at the beginning of a pass, leavingat least five hours after the Probe Checkout to study the probe temperature profile. For non-real-time Probe Checkouts (checkouts 2 and 3), the Checkouts have been placed to end nearthe beginning of a DSN pass, so that ESA staff may observe the battery temperature over anentire pass (∆8 hours). If SSR playback is possible on this pass, the probe data return isinitiated as well.In either case -- real-time or delayed data return -- it is expected that Probe battery temperaturereadings can be inserted into the Real-Time Engineering (RTE) portion of the telemetry at agranularity acceptable to ESA staff without overly limiting the standard engineering data.2.9.3 Periodic Instrument MaintenancePIMs for pre-Jupiter cruise were done on IM40 telemetry mode and are described in previousmission plans (Rev. L and earlier). In post-Jupiter cruise, the instruments have the opportunityto perform limited maintenance sequences. These limited sequences are contained within thePeriodic Instrument Maintenance (PIM) activity for the first few months after Jupiter. Themain part of the sequence lasts approximately three and one quarter hours and is completedjust prior to DSN coverage. The entire sequence lasts 19 hours and 15 minutes.Data is recorded on the SSR using the RTE 1896 telemetry mode. This mode allows thehousekeeping data from all instruments in the PIM to be recorded to the SSR. It does notsupport the collection of science data. So for the duration of the PIM no science data isrecorded.Maintenance activities for RADAR, ISS, VIMS, and CIRS are completed during the first 3 hoursand 15 minutes of the PIM. ISS has a decontamination activity that extends for 16 hours afterthis time. Total time for the PIM is therefore 19 hours and 15 minutes.Starting in fall of 2001, however, each instrument performs instrument maintenanceindependently.2.10 Contingency PlansThis section contains a summary of the project’s position on major, high-level contingenciesthat have been identified to date. This text documents the bulk of the general discussionamongst the project management, office managers, and key cognizant engineers conceringhow certain contingencies (deemed most likely to occur) are to be handled.2.10.1 When to halt the background sequence (any of the following may apply):1) Halting the background sequence enables the project to measurably reduce a risk to thehealth and safety of the spacecraft, including the Huygens probe and science instruments (e.g.an instrument will otherwise be destroyed by Sun exposure).2) Halting the background sequence enables the project to measurably increase the likelihoodof completing the nominal mission (e.g. an OTM required to remain on the tour has beenmissed; or, the spacecraft is on RCS and the sequence will use excessive hydrazine and renderthe end-of-mission margins negative).3) The project has not understood what is happening with the spacecraft, sequence ortrajectory and enough time has elapsed to convince mission management that either of theabove conditions may be true.

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2.10.2 When to declare a spacecraft emergencyDocument 699-505-3, the system-level procedure titled “Declaring a Cassini SpacecraftEmergency”, states that “a spacecraft emergency should be declared when all resourcesallocated to Cassini for communicating with the spacecraft have been exhausted, and potentialspacecraft health and safety concerns exist.”Furthermore, IOM GFS 98-015:ms (G. Squibb) states that “a spacecraft emergency is defined asany anomaly or on-board condition which requires immediate and unrestricted access to[DSN] resources in order to prevent complete and imminent failure of the mission.”The Cassini Program Manager is the only authority recognized by the DSN for declaring aspacecraft emergency. More specifically an emergency may be declared when:1) The spacecraft is in immediate danger of being lost and added DSN coverage could decreasethe likelihood of losing the mission.2) Project-internal actions, including halting the background sequence, are not sufficient tosafeguard the health and safety of the spacecraft (e.g. the project has asked for additional DSNcoverage and must declare an emergency to attain it).3) The project has not understood what is happening with the spacecraft, sequence ortrajectory and enough time has elapsed to convince mission management that either of theabove conditions may be true.4) When additional passes are needed, and not otherwise available, for TCMs to keep Cassinion the tour and be able to complete the nominal mission. (i.e. if other Projects will not give uppasses voluntarily without a declaration of spacecraft emergency).2.10.3 High-Level Contingency PlansIf one of the following contingencies occurs, the SVT lead executes the anomaly response plan.This text is intended as a supporting resource for the SVT lead and anomaly response team.

Contingency: Lose part or all of a DSN pass in real-time during execution (pass with no specialattributes, e.g. OTM pass).Response: None required. No special effort should be made to manage SSR pointers orotherwise modify playback during that pass.Rationale: There is no time during the pass to determine which data should preferentially beplayed back, and build and uplink associated commands. Determining preferred databeforehand and precise commands required for any potential loss is intractable and is not agood use of project resources.Ramifications: Science teams, navigation team, and spacecraft office must accept possibility oflosing any one pass. Pointers in engineering partitions (P6's) should not be reset wheneverpossible to allow maximum recording time. OPNAV partition sizes should remain fixedwhenever convenient.

Contingency: Lose part or all of a primary OTM pass in real-time during execution.Response: If OTM can be uplinked as scheduled (e.g. only latter portion of pass lost), performmaneuver as planned, even if it executes in the blind. Otherwise, plan to execute the maneuveron the backup pass.Rationale: The purpose of backup OTM passes is to address precisely these kinds ofcontingencies. It is more important that maneuvers execute as planned than execute while thespacecraft is visible.

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Ramifications: SVT leads / ACEs must understand precisely how late OTM sequences can beuplinked and still execute cleanly during the pass. Navigation plan and consumables marginsshould be resilient to loss of any one primary OTM pass. State how much time is needed??Maybe this is part of the OTM package to the ACES?? If the backup OTM pass is used, somescience data normally played back during this pass will be lost.

Contingency: Backup OTM pass must be used to execute a maneuver.Response: Navigation team must identify if orbiter can remain on tour with acceptable ∆Vimpact if maneuver is not executed on backup pass. If not, appropriate staff must be on shiftduring backup pass and be prepared to request additional DSN support, halt the sequence,build emergency OTM commands as needed, and declare a spacecraft emergency (ifnecessary).Rationale: Project must be prepared to respond quickly if maneuver cannot be executed duringbackup window. It is more important to stay on the tour than to preserve any one encounter orequivalent set of science observations.Ramifications: Science sequence may be severely compromised in order to remain on tour andmaintain acceptable propellant margins.

Contingency: Lose part or all of a sequence upload pass in real-time during execution.Response: Use backup passes to complete uplink of sequence.Rationale: The purpose of backup upload passes is to address precisely these kinds ofcontingencies.Ramifications: SSUP uplink process must be resilient to loss of any one pass. Typically this isimplemented as: uplink IEBs (one 9 hour pass); uplink background sequence (one 9 hourpass); margin (one 9 hour pass); last pass of sequence (one pass). The completion of each SSUPprocess is linked to the first uplink pass.

Contingency: Sequence cannot be uplinked in time.Response: If background sequence is on board, but IEBs are not, continue as planned anduplink IEBs as early as feasible. Otherwise, rebuild background sequence for earliest feasiblerestart. Typical turnaround for sequence restart with healthy spacecraft is 1 week.Rationale: Sequence cannot be uplinked late. No instruments have identified health and safetyissues with IEBs that are not consistent with background sequence.Ramifications: Science and engineering teams should be willing to accept loss of data in firstweek of a sequence if uplink is late. If health and safety issues are identified with inconsistentIEBs, instruments should bring this to the attention of the project. Instrument response is TBD.

Contingency: RWA will spend unforeseen, unacceptable amount of time in low RPM region.Response: Execute unplanned RWA bias during downlink pass.Rationale: RWA biasing strategy must be maintained in light of RWA anomalies to date tomaximize likelihood of continued health of wheels.Ramifications: RWA bias can be executed during any downlink pass with little impact tosequence (roll must be stopped; DFPW power margins are sufficient, RSS or DFPW-TCMmargins are TBD). AACS team must remain constantly vigilant for wheel speed departures

2-59

from modeled profiles via TBD procedure, especially after early low Titan flybys on reactionwheels. Science teams must accept possible interruption to downlink roll.

Contingency: Dust model updates identify an unexpected debris crossing.Response: Calculate risk to main engine nozzles and remainder of spacecraft. If crossingconstitutes an unacceptable risk to the spacecraft, halt background sequence and uplinkcommands to assume safe attitude during crossing. If unacceptable risk to nozzles, ensurecover is closed during crossing.Rationale: Maintain health of spacecraft.Ramifications: Science and engineering teams must be prepared to lose observations in orderto maintain spacecraft safety (even with significant uncertainties). Dust model updates mustbe made in a timely manner after arrival via TBD OIA/procedure. Capability to quicklycalculate dust hazards required.

Contingency: ISS haze anomaly recurs.Response: If the haze anomaly returned, depending on the severity, it is likely that additionaldecontamination would be desired/required. ISS decontamination heaters for one camera(NAC or WAC) require 27 W. The decontamination could be required for weeks or months. Asmall amount of degradation would still allow acceptable OPNAVs, although there will befewer stars or opportunities. The Project will decide whether to use decontamination heaters,and whether to modify instrument ON status in OPMODES.Rationale: ISS images are required for OPNAVs which are necessary for navigating the tour.In addition science images of Titan and icy satellites and Saturn are planned. Ensuring thatgood images are available is highly desirable.Ramifications: The 27 W is more than the power margin for many OPMODES. Depending onthe time in tour, some instruments may have to be turned off to permit ISS decontamination,or there may need to be periods of no decontamination to allow OPMODES to continue. Themain ISS OPMODE is ORS RWA and this has 30 W margin at S+3 yrs but only 18W margin atEOM.

Contingency: TCM-20 delays cause increased ∆V and jeopardize the Phoebe Flyby.Response: Calculate a priori the ∆V cost vs time. Pick point where Phoebe targeted flyby mustbe sacrificed in order to preserve reasonable ∆V for tour.Rationale: Do not allow Phoebe delays to significantly impact the overall ∆V available tocomplete the nominal mission.Ramifications: There are many reasons why the pre-Phoebe TCM could be delayed (stationproblems, ME cover problems, safing, etc.). If the TCM is delayed past some point wheresignificantly increased amounts of fuel are needed to flyby Phoebe, the Phoebe flyby should bedropped. This point should be defined prior to the planned TCM.

Contingency: MEA cover does not open for TCMResponse: For SOI, Contingency Plan SOI-CP-Act-01 applies. For Tour, if the cover does notopen completely, additional attempts will be made. Similar to Contingency Plan SOI-CP-Act-01, if both ME cover motors singly, or in parallel, do not open the cover completely, the covermay be ejected. Partial cover opening which allows MEA-A to fire may be acceptable if MEA-

2-60

A is prime. In the case of motor failures or circuit failures, the cover may be ejected. Thiswould be done by firing pyros to release the cover mechanism.Rationale: During Tour, many TCMs are required using the ME. If the ME cover is not open,safe firing of the ME cannot be done. Ejecting the cover will allow either ME to operate. Note:There is no requirement for MEA-B to be capable of firing as long as MEA-A is available.Ramifications: The ME cover is also used as a dust particle shield for the ME. Once the coveris ejected (or otherwise available), the spacecraft must make turns to a safe attitude whenevercrossing dust areas.

Contingency: The spacecraft is on an impacting trajectory.Response: If the Spacecraft is on an impacting trajectory, it must change the trajectory to anon-impacting course in order to continue the mission. This will be done with TCMs either inplanned windows, backup windows, or a newly scheduled window.Rationale: The mission will be over if the spacecraft impacts Saturn or a satellite. Once on animpacting trajectory, the only way to avoid an impact is to change the trajectory by us\ing aTCM.Ramifications: There will be ∆V costs as well as lost science if other than planned windows areused. Science will be considered expendable while efforts to get off an impacting trajectory areon-going.

Contingency: The orbiter “falls off the tour.”Response: Work with Navigation to determine how soon we can get back on the baseline tourand the ∆V cost. (Process is TBD) By definition, falling off the tour means we cannot simplycontinue the tour by modifying existing planned TCMs. There will need to be one or morenew TCMs planned to return Cassini to a Titan synchronous trajectory. The subsequent tourmay or may not have to be redesigned. A tour redesign will take about 4 weeks, followed by ascience redesign activity.Rationale: Once the orbiter falls off the tour, it is imperative that a Titan synchronous orbit bere-achieved in order to salvage as many science goals as possible. Without a Titansynchronous orbit, few if any satellite encounters will occur.Ramifications: If we are off the tour, we will lose science data (except FPW) until the tour isresumed and science observations resume. There will likely be a significant ∆V hit to regainthe tour. Likely many weeks of tour observing will be lost. Major impact on any extendedtour plans.

Contingency: The upcoming trajectory includes a Titan flyby at an altitude exceeding theAACS control authority in the planned attitude.Response: If AACS control authority is exceeded, the spacecraft would go into safing, and theattitude of the spacecraft would be unpredictable. Therefore it would be required that thetrajectory be modified so as to not exceed the AACS control authority. This would require re-planning the prior apoapsis TCM as well as the pre-and post-Titan TCMs, to flyby at a higheraltitude and also allow continuation on the planned tour.Rationale: Having the spacecraft safe is to be avoided since it will lose science data, bothduring the safing incident but also during the recovery period (safing recovery is expected totake at least 1 week).

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Ramifications: Preliminary studies by navigation indicate that Cassini can fly a tour withminimum altitudes somewhat higher than planned (~ 100 km higher) with little to moderate∆V impact. However, science replanning may be significant and some science opportunities(e.g. occultations) may be compromised, perhaps severely.

Contingency: Another RWA is degraded or lost.Response: If a second RWA is degraded or lost, RWA #3 will likely be reinstated to determineif it can function, if even for a short period. If and when RWA#3 as well as another RWA arenot available the choices are a two RWA mission and a thruster-only mission. Two RWAmission is currently under study but would include modifying observations to require onlytwo axis stability.Rationale: Every attempt will be made to extend the useful observation period through EOMRamifications: A two RWA mission will greatly restrict the type of pointing observations thatare available. A thruster-only mission will cause an increase in propellant usage and that willseverely restrict observations that have high fuel usage.

Contingency: The main engine cover has been ejected (or is not available)Response: If the ME cover has been ejected (or not working), there is no cover protection forthe ME. In order to protect the ME from dust particles during ring plane crossings and otherdebris areas (i.e. near Icy satellites), the spacecraft will need to move to a safe attitude duringmany more dust crossings than planned.Rationale: The ME operation is susceptible to dust particle impacts and therefore must beprotected to ensure ME operation through EOM. Turning the spacecraft to put the ME in theanti-RAM direction is the best protection available once the cover is no longer available.Ramifications: Science planning has scheduled science observations for times when the MEcover was considered sufficient protection (i.e. no turn to safe attitude was required). Once theME cover is unavailable, more turns to a safe attitude will be required and some loss of sciencedate will occur.

Contingency: Propellant margins are predicted to be zero or negative by end of nominalmission.Response: Once predictions are made of exceeding propellant margins prior to EOM,observation plans should be modified to stretch the propellant to last until EOM. Examinationof high fuel usage activities will be made (e.g., turns on thrusters, RADAR scans). The state ofRWA will be important. If some turns can be switched to RWA, some savings is available. IfRWA is not available, science activities will need to be curtailed. Analysis of scienceobservations made to date will allow priorities to be set for instruments that have been waitingfor near-EOM geometry. This is not something that can be done in advance because keyparameters are what caused the reduction in the current positive margin, the size of the deficit,and the point in the mission where the negative margins occur. The Project Manager andScience Manager will consider the trade between reducing science or running out of propellantearly (which also reduces science).Rationale: The mission is funded for 4 years and every attempt should be made to havepropellant sufficient to reach EOM.Ramifications: Reducing science observations that are heavy RCS users may have to be made.Raising low Titan flyby altitudes will be considered.

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Contingency: Lose one SSRResponse: Tour science has been planned assuming two SSRs. If nothing is done once oneSSR is lost, science will be lost based on who gets to use the SSR last. Once the SSR is full, laterscience will overwrite data already recorded but not played back. There are several options:

1. Use data policing tables to allow all instruments some percentage of their data (averageuse is 50%)

2. Use data policing tables to prioritize science, allowing higher priority observations ahigher percentage than lower priority observations (note: it is very difficult to prioritizescience observations).

3. Re-plan all science after the SSR loss to reduce data volume by 50%. This is veryworkforce intensive.

Rationale: Doing nothing is probably not acceptable because data played back is somewhatrandom as to who will get their data played back. More likely some reasonable re-planningwill be done whether using data policing tables or re-planning the science observations.Ramifications: 50% of the planned science data will be lost following the loss of one SSR. Amajor effort to decide how to reduce data volume by a factor of 2 will be workforce intensive.

Miss Trajectory Target

Make-up TCM and stay on tour?

Is S/C in Safe Mode?

S/C Recovery(Safing Contingency

Plan)

Return to tour

END

Yes

No

MISSED TCM RISK ASSESSMENT

Yes No

Miss T

CM

TC

M error

Ephereris error

Hum

an errorS

tation down

Nav

ret

urn

to T

itan

proc

ess

Frautnick /Strange

RECOVERY FROM FALLING OFF TOUR

On impacttrajectory?

Yes

Schedule TCM!V Trades

No

Execute TCM to get off impact trajectory

!V Trades

UpcomingRPC with dust concerns?

No

take safety actions

close ME

cover

HG

A to R

AM

Deal with trajectory error

Fall off Tour

Yes

Nav Process to get back onTitan syncronous trajectory.

(Up to 4 week process.Process TBD)

Resume tour withalready planned sequences. (Loss of sequences between event and resumption.)

Possible topick up sametour at laterdate?

Search for occultation opportunities with new tour

Search for Icy Flybys available with new tour.

Define future Titan F/B for rest of mission

END

No

Yes

Science Planning Process to update transition observations. Process TBD.

Science Planning Process to update transition observations. (Parallel Process TBD.)

Whan time permits, studty impact of new tour on extended mission plans/design

Fallen Off Tour

Can a TCMreturn us to Titan ?

NoEND

Plan and implement trajectory to returnto Titan

Start tour re-design process

END

Yes Nav define design for earliest, then latest, part of new tour

SCO evaluation

Science evaluation

Iterate?Yes

No

time constraint(depends on time untill next Titan Flyby)

detailed trajectory design

Plan and implementnew leg(s) of tour

More tourto design?

Yes

Nav

tour

re-

desi

gn p

roce

ss

Nav

ret

urn

to T

itan

proc

ess

Frautnick /Strange

3-1

3.0 OPERATIONAL MODES, GUIDELINES AND CONSTRAINTS, AND CONTROLLED SCENARIO TIMELINES

THIS SECTION IS UNDER PROGRAM CHANGE CONTROL.

This section defines certain elements of the mission and system design for Cassini that are placed under project change control, because they are considered fundamental to the operational strategy for the mission and for constraining operational complexity. These elements include definitions of the operational modes, modules and templates, unique and fixed sequences, transitions, operational guidelines and constraints, and scenario timelines for certain key periods of the mission. 3.1 Operational Mode Definition An operational mode is a resource (power) envelope applied to the spacecraft subsystems and science instruments. The intent of defining operational modes is to maximize the collection of science within a mode (by balancing science and spacecraft power requirements), minimize operational complexity in sequence generation, and allow some flexibility for science instrument states to vary (within the limits of their resource envelopes). The operational mode also uniquely defines the beginning and ending spacecraft state(s) used to transition in and out of the mode. A fixed transition sequence will be defined for each allowed transition between operational modes. The current set of operational modes for the Cassini mission is listed in Table 1.1. Power analysis is one of the mission design primary considerations in verifying the functionality of the operational modes, and this work can be found in the current version of the Cassini Power Report (699-010). Some of the modes listed will only have sufficient power for a portion of the mission (e.g., to SOI+2 years). These modes will cease to be available if and when the power margin drops below the required operating margin. Calibration activities for all instruments, except MAG, are included within their normal operating modes. The MAG calibrations require additional power and separate fixed and/or unique sequences. 3.2 Sequence Constructs Definition A module is a reusable sequence of commands whose relative timing and total duration may be variable. A module cannot extend across operational mode boundaries but may be used in more than one operational mode, provided its activities do not violate that operational mode. A module should define a pointing pattern but can be target and telemetry mode independent (provided its activities do not violate the active telemetry mode). A template is a science planning concept (not a sequence construct like a module) which allows convenient reuse of a sequential series of modules, fixed sequences, gaps, or other templates. Templates are used as a conceptual tool to assemble sets of activities that will typically be used in concert and may cross operational mode boundaries. A unique sequence is a sequence that has a specific purpose, is used once, and does not use modules. (If it did, it would not be a unique sequence, it would be a regular sequence.) Unique sequences can and should take advantage of operational modes in their design if possible, but violation of operational mode constraints is permitted. A fixed sequence is a fixed-duration sequence that is designed and validated once for multiple uses, and does not use operational modes, and admits a fixed list of parameters. Both unique and fixed sequence have no defined global constraints and can include any combination of states. Unique or fixed sequences are checked for constraint violations and must contain required state changes needed to transition into and out of specific predefined operational modes. Should the operational modes preceding and/or following the unique or fixed sequence be different, appropriate transition sequences should be added before or after

3-2

the sequence to ensure that no sequence redesign is required. Each unique or fixed sequence is checked for constraint violations and must contain required state changes needed to transition into and out of a specific predefined operational mode.

Table 3.1 Cassini Operational Modes Operational Mode Mode Type Usage

ORS RWAF Science Optical Remote sensing (ORS) pointing and FPW data acquisition with reaction wheel assembly at full power (RWAF) (includes SCAS power).

ORS RCS Science ORS pointing and FPW data acquisition during rare occasions using reaction control subsystem (RCS) when thruster control and speed are required (includes SCAS)

Downlink/Fields, Particles, and Waves (DFPW)-normal

Science FPW data return with or without S/C rotation during downlink. Also ORS pointing and FPW data acquisition not including SCAS power.

DFPW-TCM Science FPW data return with or without S/C rotation when a TCM (ME or RCS) is to be done.

DFPW-PEM Science FPW data return without S/C rotation during downlink when a engineering activity such as a PEM or RWA friction test is to be done.

RADAR RCS Science RADAR and FPW data acquisition using thrusters

RADAR RWAF Science RADAR and FPW data acquisitions with RWAs

RADAR warmup/radiometry

Science ORS pointing, FPW data acquisition, and RADAR warmup or FPW data acquisition and RADAR radiometry

RSS PIM RWAF Science ORS pointing and FPW data acquisition with Ka-TWTA on in standby mode for Periodic Instrument Maintenance (PIM).

RSS Ka-band RWAF Science Radio science mass or gravity determination or Radio Science engineering activities. Includes ORS and FPW science. X- and Ka-band uplink and downlink.

RSS 3a RWAF Science Radio science Titan atmospheric and Saturn atmospheric and ring occultation measurements, includes ORS and FPW science. S-, X-, and Ka-band downlink. (Valid mode for at least first half of Tour.)

RSS2 RWAF Science Radio science Titan atmospheric and Saturn atmospheric and ring occultation measurements, includes FPW science. S- and X-band downlink.

RSS3 RCS Science Radio Science Titan atmospheric and Saturn atmospheric and ring occultation measurements, includes ORS and FPW science (thruster control). S-, X-, and Ka-band downlink.

VIMS low decontamination (decon) heater – ORS

Science ORS pointing and FPW data acquisition while operating VIMS low decon heater with VIMS in sleep.

VIMS low decon – DFPW

Science FPW data return with or without S/C rotation during downlink while operating VIMS low decon heater with VIMS in sleep.

VIMS high decon – ORS

Science ORS pointing and FPW data acquisition while operating VIMS high decon heater with VIMS in sleep.

VIMS high decon – DFPW

Science FPW data return without S/C rotation during downlink while operating VIMS high decon heater with VIMS in sleep.

Fixed Sequences

3-3

RWA Unload Engineering RWA unload capability during DFPW-normal opmode.

TCM (RCS) Engineering Thruster TCM burn

TCM (Main Engine)

Engineering Ignition transient and steady state main engine TCM burn.

Main Engine Cover actuation

Engineering Main engine cover actuation capability during DFPW-normal opmode.

EGA Exercise Engineering Engine Gimbal Actuation Exercise capability during DFPW-PEM opmode. EGA exercise draws the peak power during the Periodic Engineering Maintenance (PEM).

RWA Friction Test Engineering RWA Friction Test capability during DFPW-PEM opmode.

A transition sequence is a fixed sequence that is used to shift between operational modes. A transition sequence is needed when the end state of a operational mode is not the same as the beginning state of the next mode. Operational modes instrument composition is shown in Table 1.2. Transition sequences are shown in Table 1.5. 3.3 Requirements on the Design of Operational Modes a) Each operational mode shallspecify a maximum power allocation for each instrument and each engineering function specified in the Operational Mode Tables. [Note: Telemetry modes included in Table 1.3 and 1.4 are merely suggestive, for guidance of the user]. The power and thermal envelopes shall be defined so that operations within those envelopes can be conducted safely without requiring power or thermal analysis by the ground. The maximum power allocations for each science instrument and spacecraft subsystem are shown in Table 1.2. The maximum value is the peak power. b) Operational modes shall be designed so as to allow sequencing of system-level activities in the mode through the use of standard sequence components. c) Each operational mode shall have a defined spacecraft state for mode start and mode end. Each of the allowed transitions between end and start states of the different operational modes shall be via transition sequences using standard sequence components. d) Operational modes shall be designed so as to allow sequencing of system-level activities necessary to transition between modes. 3.4 Requirements on the Design of Modules The following rules for module construction and usage shall be followed: a) All modules shall be reusable without validation. As a consequence, the use of module parameters within a module expansion shall be limited to changing either command parameters or the number (greater than or equal to one) of repetitions of actions within the module. b) The module shall include target-relative pointing (but need not be target-specific), telemetry mode, and trigger commands which need to be time synchronized over the execution period of the module. c) Modules shall allow for instrument trigger commands (that are permitted within the operational mode) that are independent of spacecraft pointing, independent of the allowed telemetry mode choices, and that do not need to be synchronized with any other module actions to be executed in parallel with the module.

3-4

d) Modules shall not cross operational mode boundaries. Modules need not assume a specific operational mode, provided their execution will not violate the conditions of the operational mode(s) in which they may be placed. e) Each command contained in a module shall execute at a time relative to a base time. These execution times may be parameters of the module. f) Module design shall not assume any telemetry mode is in effect at the beginning of the module. g) Only one module shall execute at a time and a module shall not initiate another module. h) The Prime Instrument shall define the pointing profile, telemetry mode changes, and module base time for each execution of a module.

Rationale: Defines what is meant by a module and what the constraints are. For a module to save costs, it must be trusted without validation. To make such a validation realizable, the use of parameters is limited to either changing the parameters of commands in the module expansion (e.g. timing), or changing the loop counts of repeated actions (e.g. scans or images or dimensions of a mosaic). This allows validation at the "edge of the envelope" of the possible module expansions. What is not permitted is a module with parameters that turn off some operations and turn on others, since then the amount of validation needed can grow exponentially to adequately cover all possible expansions. When that is needed, separate modules need to be written for different operations.

Modules must allow instrument operations that do not depend on the spacecraft orientation, or on which allowed data mode in that operational mode is active, to be placed anywhere in the time the module occupies. Modules are distinct from transition sequences used to change operational modes, and distinct from each other. While the module cannot cross operational mode boundaries, it must set one of the allowed data modes for that operational mode at the start, to avoid having to interface between modules.

3-5

Table 1.2 Operational Mode Composition ORS (RWA) ORS (RCS) Downlink

FP-normalDownlink FP-

TCM

Downlink FP-

PEM

RADAR wu/Rad

Margin

Power 652.4 563.8 668.3 669.0 647.0 669.4

Violations

ORS

CIRS on 46.0 on 46.0 on 46.0 on_ss 34.0 on 46.0 on_ss 34.0

ISS on 45.6 on 45.6 on 45.6 sleep 38.7 sleep 38.7 on 45.6

UVIS on 13.0 on 13.0 on 13.0 on 13.0 on 13.0 on 13.0

VIMS on 27.3 on 27.3 on 27.3 sleep 12.9 sleep 12.9 on 27.3

MAPS

CAPS on 21.0 on 21.0 on 21.0 on 21.0 on 21.0 on 21.0

CDA on 25.0 on 25.0 on 25.0 on 25.0 on 25.0 on 25.0

INMS on 26.6 on 26.6 on 26.6 on 26.6 on 26.6 on 26.6

MAG on 13.4 on 13.4 on 13.4 on 13.4 on 13.4 on 13.4

MIMI on 25.9 on 25.9 on 25.9 on 25.9 on 25.9 on 25.9

RPWS on 16.9 on 16.9 on 16.9 on 16.9 on 16.9 on 16.9

SCAS on 24.0 on 24.0 off 0.0 off 0.0 off 0.0 off 0.0

R F

RADAR off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 wuRad 53.0

RSS/KAT kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9

RSS/KEX off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/KaTWTA off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/SBT off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

Instruments Total 293.6 Total 293.6 Total 269.6 Total 236.3 Total 248.3 Total 310.6

AACS Base

AFC (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6

SRU 4.9 4.9 4.9 4.9 4.9 4.9

SRU Supp Htr 0.9 0.9 0.9 0.9 0.9 0.9

SRU Repl Htr 1.8 1.8 1.8 1.8 1.8 1.8

Sun Sensor 1.9 1.9 1.9 1.9 1.9 1.9

IRU 26.7 26.7 26.7 26.7 26.7 26.7

RWA full 90.4 off 0.0 full 90.4 full 90.4 full 90.4 full 90.4

RCS

VDECU on 2.1 on 2.1 on 2.1 on 2.1 on 2.1 on 2.1

MPD on 1.7 on 1.7 on 1.7 on 1.7 on 1.7 on 1.7

Thrusters off 0.0 4 17.0 off 0.0 off 0.0 off 0.0 off 0.0

Catbed Htrs 8 18.4 4 9.2 8 18.4 8 18.4 8 18.4 8 18.4

Main Engine

Accelerometer off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA heaters off 0.0 off 0.0 off 0.0 on 34.0 off 0.0 off 0.0

REA valve off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA OX htr (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4

EGA off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

AACS Subtotal 172.8 Subtotal 90.2 Subtotal 172.8 Subtotal 206.8 Subtotal 172.8 Subtotal 172.8

PMS

Press. Xdcrs (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8

PCA Line Htr 1.3 1.3 1.3 1.3 1.3 1.3

Temp Control

RSP R/Htr htr off 0.0 htr off 0.0 htr off 0.0 htr off 0.0 htr off 0.0 htr off 0.0

ATCs 9.4 9.4 9.4 9.4 9.4 9.4

RFS

X-TWTA sleep 10.7 sleep 10.7 on 50.6 on 50.6 on 50.6 sleep 10.7

DST 9.8 9.8 9.8 9.8 9.8 9.8

TCU 6.0 6.0 6.0 6.0 6.0 6.0

USO 2.7 2.7 2.7 2.7 2.7 2.7

CDS

CDS (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0

CDS EU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

PMS REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

RSP REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

REU delta 7.5 7.5 7.5 7.5 7.5 7.5

SSR (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5

PPS

Pwr Control 7.4 7.4 7.4 7.4 7.4 7.4

Pwr Distrib. 12.4 12.4 12.4 12.4 12.4 12.4

PPS REU (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4

SSPS Losses 2.5 2.5 2.5 2.5 2.5 2.5

Cable Losses 15.0 15.0 15.0 15.0 15.0 15.0

Rad. & Age 2.0 2.0 2.0 2.0 2.0 2.0

Thermal Flux RWA on 6.0 RWA off 0.0 RWA on 6.0 RWA on 6.0 RWA on 6.0 RWA on 6.0

FP Margin 20.0 20.0 20.0 20.0 20.0 20.0

Engineering Total 358.8 Total 270.2 Total 398.7 Total 432.7 Total 398.7 Total 358.8

RTG@SOI 729.0 729.0 729.0 729.0 729.0 729.0

margin 76.6 165.2 60.7 60.0 82.0 59.6

RTG@EOM 692.0 692.0 692.0 692.0 692.0 692.0

margin 39.6 128.2 23.7 23.0 45.0 22.6

3-6

RADAR

(RWA)

RADAR (RCS)

RSSP (RWAF)

RSSK (RWAF)

RSS3a (RWAF)

RSS2 (RWAF)

Margin

Power 680.4 625.1 679.9 695.0 714.5 676.7

Violations >EOM by 3 >EOM by 22.5

ORS

CIRS on_ss 34.0 on 46.0 on 46.0 on_ss 34.0 on_ss 34.0 on_ss 34.0

ISS sleep 38.7 on 45.6 on 45.6 on 45.6 on 45.6 sleep 38.7


VIMS sleep 12.9 on 27.3 on 27.3 on 27.3 on 27.3 sleep 12.9

MAPS


CDA on 25.0 on 25.0 on 25.0 on 25.0 noart 11.7 on 25.0

INMS on 26.6 on 26.6 on 26.6 on 26.6 on 26.6 on 26.6




SCAS off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

R F

RADAR on 85.3 on 85.3 off 0.0 off 0.0 off 0.0 off 0.0

RSS/KAT kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9 off 0.0 kat_on 8.9

RSS/KEX off 0.0 off 0.0 kex_on 3.6 kex_on 3.6 kex_on 3.6 off 0.0

RSS/KaTWTA off 0.0 off 0.0 standby 8.0 katwta_opr 35.1 katwta_opr 35.1 off 0.0

RSS/SBT off 0.0 off 0.0 off 0.0 sbt_on 41.7 sbt_on 41.7


AACS Base

AFC (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6

SRU 4.9 4.9 4.9 4.9 4.9 4.9

SRU Supp Htr 0.9 0.9 0.9 0.9 0.9 0.9

SRU Repl Htr 1.8 1.8 1.8 1.8 1.8 1.8

Sun Sensor 1.9 1.9 1.9 1.9 1.9 1.9

IRU 26.7 26.7 26.7 26.7 26.7 26.7

RWA full 90.4 off 0.0 full 90.4 full 90.4 full 90.4 full 90.4

RCS



Thrusters off 0.0 4 17.0 off 0.0 off 0.0 off 0.0 off 0.0

Catbed Htrs 8 18.4 4 9.2 8 18.4 8 18.4 8 18.4 8 18.4

Main Engine

Accelerometer off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA heaters off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA valve off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA OX htr (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4

EGA off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0


PMS

Press. Xdcrs (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8

PCA Line Htr 1.3 1.3 1.3 1.3 1.3 1.3

Temp Control


ATCs 9.4 9.4 9.4 9.4 9.4 9.4

RFS

X-TWTA sleep 10.7 sleep 10.7 on 50.6 on 50.6 on 50.6 on 50.6

DST 9.8 9.8 9.8 9.8 9.8 9.8

TCU 6.0 6.0 6.0 6.0 6.0 6.0

USO 2.7 2.7 2.7 2.7 2.7 2.7

CDS

CDS (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0

CDS EU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

PMS REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

RSP REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

REU delta 7.5 7.5 7.5 7.5 7.5 7.5

SSR (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5

PPS

Pwr Control 7.4 7.4 7.4 7.4 7.4 7.4

Pwr Distrib. 12.4 12.4 12.4 12.4 12.4 12.4

PPS REU (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4

SSPS Losses 2.5 2.5 2.5 2.5 2.5 2.5

Cable Losses 15.0 15.0 15.0 15.0 15.0 15.0

Rad. & Age 2.0 2.0 2.0 2.0 2.0 2.0

Thermal Flux RWA on 6.0 RWA off 0.0 RWA on 6.0 RWA on 6.0 RWA on 6.0 RWA on 6.0

FP Margin 20.0 20.0 20.0 20.0 20.0 20.0


RTG@SOI 729.0 729.0 729.0 729.0 729.0 729.0

margin 48.6 103.9 49.1 34.0 14.5 52.3

RTG@EOM 692.0 692.0 692.0 692.0 692.0 692.0

margin 11.6 66.9 12.1 -3.0 -22.5 15.3

3-7

RSS3 (RCS) RWA Unload (DFPW)

TCM RCS

TCM ME ME Cover EGA Exercise (PEM)

Margin delta from DFPW delta from DFPW_normal

Power 660.1 676.1 659.3 661.5 671.3 687.3

Violations

ORS

CIRS on 46.0 on 46.0 on 46.0 on_ss 34.0 on_ss 34.0 on 46.0

ISS on 45.6 on 45.6 sleep 38.7 sleep 38.7 on 45.6 on 45.6


VIMS on 27.3 on 27.3 sleep 12.9 sleep 12.9 on 27.3 on 27.3

MAPS


CDA on 25.0 on 25.0 on 25.0 noart 11.7 on 25.0 on 25.0

INMS on 26.6 on 26.6 on 26.6 sleep 16.6 on 26.6 on 26.6




SCAS off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

R F

RADAR off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/KAT kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9

RSS/KEX kex_on 3.6 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/KaTWTA katwta_opr 35.1 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/SBT sbt_on 41.7 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0


AACS Base

AFC (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6

SRU 4.9 4.9 4.9 4.9 4.9 4.9

SRU Supp Htr 0.9 0.9 0.9 0.9 0.9 0.9

SRU Repl Htr 1.8 1.8 1.8 1.8 1.8 1.8

Sun Sensor 1.9 1.9 1.9 1.9 1.9 1.9

IRU 26.7 26.7 26.7 26.7 26.7 26.7

RWA off 0.0 full 90.4 full 90.4 off 0.0 full 90.4 limited 60.4

RCS



Thrusters 4 17.0 4 17.0 6 26.1 2 8.7 off 0.0 off 0.0

Catbed Htrs 4 9.2 4 9.2 2 4.6 6 13.8 8 18.4 8 18.4

Main Engine cover motor 15.0

Accelerometer off 0.0 off 0.0 off 0.0 on 3.1 off 0.0 off 0.0

REA heaters off 0.0 off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA valve off 0.0 off 0.0 off 0.0 trans 90.0 off 0.0 off 0.0

REA OX htr (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4

EGA off 0.0 off 0.0 off 0.0 on 49.0 off 0.0 on 49.0


PMS

Press. Xdcrs (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8

PCA Line Htr 1.3 1.3 1.3 1.3 1.3 1.3

Temp Control


ATCs 9.4 9.4 9.4 9.4 9.4 9.4

RFS

X-TWTA on 50.6 on 50.6 on 50.6 on 50.6 on 50.6 on 50.6

DST 9.8 9.8 9.8 9.8 9.8 9.8

TCU 6.0 6.0 6.0 6.0 6.0 6.0

USO 2.7 2.7 2.7 2.7 2.7 2.7

CDS

CDS (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0

CDS EU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

PMS REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

RSP REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

REU delta 7.5 7.5 7.5 7.5 7.5 7.5

SSR (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5

PPS

Pwr Control 7.4 7.4 7.4 7.4 7.4 7.4

Pwr Distrib. 12.4 12.4 12.4 12.4 12.4 12.4

PPS REU (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4 (2) 5.4

SSPS Losses 2.5 2.5 2.5 2.5 2.5 2.5

Cable Losses 15.0 15.0 15.0 15.0 15.0 15.0

Rad. & Age 2.0 2.0 2.0 2.0 2.0 2.0

Thermal Flux RWA off 0.0 RWA on 6.0 RWA on 6.0 RWA off 0.0 RWA on 6.0 RWA on 6.0

FP Margin 20.0 20.0 20.0 20.0 20.0 20.0


RTG@SOI 729.0 729.0 729.0 729.0 729.0 729.0

margin 68.9 52.9 69.7 67.5 57.7 41.7

RTG@EOM 692.0 692.0 692.0 692.0 692.0 692.0

margin 31.9 15.9 32.7 30.5 20.7 4.7

3-8

RWA Friction Test

VIMS Decon Low-ORS

VIMS Decon Low-DFPW

VIMS Decon High-ORS

VIMS Decon High-DFPW

Margin delta from DFPW_PEM

Power 672.8 654.2 680.9 690.0 691.0

Violations

ORS

CIRS on_ss 34.0 on 46.0 on_ss 34.0 on_ss 34.0 on_ss 34.0

ISS sleep 38.7 on 45.6 on 45.6 on 45.6 on 45.6

UVIS on 13.0 on 13.0 on 13.0 on 13.0 on 13.0

VIMS sleep 12.9 sleep/D-low 51.9 sleep/D-low 51.9 sleep/D-high 100.9 sleep/D-high 100.9

MAPS

CAPS on 21.0 on 21.0 on 21.0 on 21.0 on 21.0

CDA on 25.0 on 25.0 on 25.0 on 25.0 on 25.0

INMS on 26.6 on 26.6 on 26.6 on 26.6 on 26.6

MAG on 13.4 on 13.4 on 13.4 on 13.4 on 13.4

MIMI on 25.9 on 25.9 on 25.9 on 25.9 on 25.9

RPWS on 16.9 on 16.9 on 16.9 on 16.9 on 16.9

SCAS off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

R F

RADAR off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/KAT kat_on 8.9 kat_on 8.9 kat_on 8.9 kat_on 8.9 off 0.0

RSS/KEX off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/KaTWTA off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

RSS/SBT off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

Instruments Total 236.3 Total 294.2 Total 282.2 Total 331.2 Total 322.3

AACS Base

AFC (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6 (2) 19.6

SRU 4.9 4.9 4.9 4.9 4.9

SRU Supp Htr 0.9 0.9 0.9 0.9 0.9

SRU Repl Htr 1.8 1.8 1.8 1.8 1.8

Sun Sensor 1.9 1.9 1.9 1.9 1.9

IRU 26.7 26.7 26.7 26.7 26.7

RWA 4 wheels 120.4 full 90.4 full 90.4 full 90.4 limited 60.4

RCS

VDECU on 2.1 on 2.1 on 2.1 on 2.1 on 2.1

MPD on 1.7 on 1.7 on 1.7 on 1.7 on 1.7

Thrusters 4 17.0 off 0.0 off 0.0 off 0.0 off 0.0

Catbed Htrs 4 9.2 8 18.4 8 18.4 8 18.4 8 18.4

Main Engine

Accelerometer off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA heaters off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA valve off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

REA OX htr (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4 (2) 4.4

EGA off 0.0 off 0.0 off 0.0 off 0.0 off 0.0

AACS Subtotal 210.6 Subtotal 172.8 Subtotal 172.8 Subtotal 172.8 Subtotal 142.8

PMS

Press. Xdcrs (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8 (18) 5.8

PCA Line Htr 1.3 1.3 1.3 1.3 1.3

Temp Control

RSP R/Htr htr off 0.0 htr off 0.0 htr off 0.0 htr off 0.0 htr off 0.0

ATCs 9.4 9.4 9.4 9.4 9.4

RFS

X-TWTA on 50.6 sleep 10.7 on 50.6 sleep 10.7 on 50.6

DST 9.8 9.8 9.8 9.8 9.8

TCU 6.0 6.0 6.0 6.0 6.0

USO 2.7 2.7 2.7 2.7 2.7

CDS

CDS (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0 (2) 24.0

CDS EU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

PMS REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

RSP REU (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2 (2) 6.2

REU delta 7.5 7.5 7.5 7.5 7.5

SSR (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5 (2) 19.5

PPS

Pwr Control 7.4 7.4 7.4 7.4 7.4

Pwr Distrib. 12.4 12.4 12.4 12.4 12.4

PPS REU (2) 5.4 (2) 6.6 (2) 5.4 (2) 5.4 (2) 5.4

SSPS Losses 2.5 2.5 2.5 2.5 2.5

Cable Losses 15.0 15.0 15.0 15.0 15.0

Rad. & Age 2.0 2.0 2.0 2.0 2.0

Thermal Flux RWA on 6.0 RWA on 6.0 RWA on 6.0 RWA on 6.0 RWA on 6.0

FP Margin 20.0 20.0 20.0 20.0 20.0

Engineering Total 436.5 Total 360.0 Total 398.7 Total 358.8 Total 368.7

RTG@SOI 729.0 729.0 729.0 729.0 729.0

margin 56.2 74.8 48.1 39.0 38.0

RTG@EOM 692.0 692.0 692.0 692.0 692.0

margin 19.2 37.8 11.1 2.0 1.0

3-10

Table 3.3 Cassini Peak Data Rate Guidelines by Operational Mode Preferred Op Mode vs. Telemetry Mode Usage S&ER-1 S&ER-2 S&ER-3 S&ER-4 S&ER-5 S&ER-5a S&ER-6 S&ER-7 S&ER-8 RTE & SPB

OP MODE TYPES

ORS x x x x x x x

DL FPW or RWA Unload

x

RADAR wu x

RADAR rad x x

RADAR full x

RSS wu x x x x x x x x

RSS/RCS x x x x x x x x x

RSS/RWA x x

TCM x x

3-11

Notes: RADAR warmup is in S&ER-5A

RADAR radiometry is in S&ER-5A or S&ER-8 RADAR full power is in S&ER-8

Table 3.4 Telemetry Mode Pickup rates S&ER-1 S&ER-2 S&ER-3 S&ER-4 S&ER-5 S&ER-5a S&ER-6 S&ER-7 S&ER-8 RTE & SPB

Stellar occultations

Titan Saturn Saturn Icy Satellites &

OpNav

Icy Satellites

Icy Satellites

FPW & INMS

RADAR/ INMS

DL FPW

ORS CIRS 4 4 4 4 4 4 4 0 0 4

ISS 121.856 60.928 182.784 0 365.568 304.64 243.712 0 0 0

UVIS 32.096 32.096 32.096 5.032 5.032 5.032 5.032 0 0 5.032

VIMS 182.784 94.208 94.208 18.432 18.432 18.432 94.208 0 0 0

MAPS CAPS 16 16 16 16 4 4 8 16 16 16

CDA 0.524 4.192 4.192 4.192 0.524 0.524 4.192 0.524 0.524 0.524

INMS 1.498 1.498 1.498 1.498 1.498 1.498 1.498 1.498 1.498 1.498

MAG 1.976 1.976 1.976 1.976 1.976 1.976 1.976 1.976 1.976 1.976

MIMI 8 8 8 8 4 4 8 8 8 8

RPWS 60.928 182.784 60.928 365.568 30.464 60.928 60.928 365.568 30.464 365.568

RADAR 0 0 0 0 0 7.6 0 0 364.8 0

3-12

Table 1.5 Mode to Mode Transitions Table 1.5 Mode to Mode Transitions

TO 1 2 3 4 5 6 7 8 9 10 11 12 13

FR

OM ORS

(RWAF)ORS (RCS)

DFPW-normal

DFPW-TCM DFPW-PEMRADAR Wu/Rad

RADAR (RWA)

RADAR (RCS)

RSSP (RWAF)

RSSK (RWAF)

RSS3a RWAFRSS2

(RWAF)RSS3 (RCS)

1 ORS (RWAF) RWA_2_RCSSCAS_off X_operate

SCAS_off ORS_sleep X_operate ME_htr_on

SCAS_off ORS_sleep X_operate

SCAS_off RADAR_low_on

1>7>8 Rad_wuSCAS_off

RWA_2_RCS RADAR_on

SCAS_off RCS_off

X_operate RSS_P_on

N

SCAS_off KaT_off RCS_off

X_operate RSS_sKa_on

SCAS_off ORS_sleep

RCS_off X_operate RSS_S_on

1>2>14 ORS_RCS

2 ORS (RCS) RCS_2_RWASCAS_off

RCS_2_RWA X_operate

SCAS_off ORS_sleep

RCS_2_RWA X_operate ME_htr_on

SCAS_off ORS_sleep

RCS_2_RWA X_operate

SCAS_off RCS_2_RWA

RADAR_low_on2>7>8 Rad_wu

SCAS_off RADAR_on

SCAS_off RCS_2_RWA

RCS_off X_operate RSS_P_on

N

SCAS_off KaT_off

RCS_2_RWA RCS_off


SCAS_off ORS_sleep

RCS_2_RWA RCS_off

X_operate RSS_S_on

SCAS_off X_operate

RSS_sKa_on

3 DFPW-normal X_standbyX_standby

RWA_2_RCSORS_sleep ME_htr_on

ORS_sleepX_standby


X_standby RWA_2_RCS RADAR_on

RCS_off RSS_P_on

RCS_off RSS_P_on RSS_K_on

KaT_off RCS_off RSS_sKa_on

ORS_sleep RCS_off

RSS_S_on

3>2>14 ORS_RCS

4 DFPW-TCMME_htr_off X_standby ORS_wake

ME_htr_off X_standby ORS_wake

RWA_2_RCS

ME_htr_off ORS_wake

N


RADAR_low_on

4>7>8 Rad_wu


RWA_2_RCS RADAR_on

ME_htr_off RCS_off

ORS_wake RSS_P_on

N

ME_htr_off KaT_off

ORS_wake RCS_off

RSS_sKa_on

ME_htr_off RCS_off

RSS_S_on

4>2>14 ORS_RCS

5 DFPW-PEMX_standby ORS_wake

X_standby ORS_wake

RWA_2_RCSORS_wake N

X_standby ORS_wake


X_standby ORS_wake

RWA_2_RCS RADAR_on

RCS_off ORS_wake RSS_P_on

NKaT_off RCS_off

ORS_wake RSS_sKa_on

RCS_off RSS_S_on

3>2>10 ORS_RCS

6 RADAR Wu/Rad RADAR_low_offRADAR_low_off RWA_2_RCS

RADAR_low_off X_operate

RADAR_low_off ORS_sleep X_operate ME_htr_on

RADAR_low_off ORS_sleep X_operate

ORS_sleep RADAR_high_on

RWA_2_RCS RADAR_high_o

n

RADAR_low_off RCS_off

X_operate RSS_P_on

N

KaT_off RADAR_low_off

RCS_off X_operate

RSS_sKa_on

RADAR_low_off ORS_sleep

RCS_off X_operate RSS_S_on

7>2>14 ORS_RCS

7 RADAR (RWA)RADAR_off ORS_wake

RADAR_off ORS_wake

RWA_2_RCS

RADAR_off ORS_wake X_operate

RADAR_off X_operate ME_htr_on

RADAR_off X_operate

RADAR_high_off ORS_wake

RWA_2_RCS ORS_wake

RADAR_off ORS_wake


N

KaT_off RADAR_off ORS_wake

RCS_off X_operate

RSS_sKa_on

RADAR_off RCS_off

X_operate RSS_S_on

8>2>14 ORS_RCS

8 RADAR (RCS)RADAR_off

RCS_2_RWARADAR_off

RADAR_off RCS_2_RWA

X_operate

RADAR_off ORS_sleep

RCS_2_RWA X_operate ME_htr_on

RADAR_off ORS_sleep

RCS_2_RWA X_operate

RADAR_high_off RCS_2_RWA

ORS_sleep RCS_2_RWA

RADAR_off RCS_2_RWA


N

KaT_off RADAR_off

RCS_2_RWA RCS_off


RADAR_off ORS_sleep

RCS_2_RWA RCS_off

X_operate RSS_S_on

RADAR_off X_operate

RSS_sKa_on

9 RSSP (RWAF) N N N N N N N N RSS_K_On N N N

10 RSSK (RWAF)RSS_off

X_standby RCS_on

via ORS RWA for at least 32

minutesRSS_off RCS_on

RSS_off ORS_sleep

RCS_on ME_htr_on

RSS_off ORS_sleep

RCS_on

RSS_off X_standby RCS_on

RADAR_low_on

11>7>8 Rad_wuvia RadWu for at least 32 minutes

N N N N

11 RSS3a RWAFRSS_off

X_standby RCS_on


minutesRSS_off RCS_on

RSS_off ORS_sleep

RCS_on ME_htr_on

RSS_off ORS_sleep

RCS_on

RSS_off X_standby RCS_on

RADAR_low_on


N N N N

12 RSS2 (RWAF)

RSS_off X_standby ORS_wake

RCS_on


minutes

RSS_off ORS_wake

RCS_on

RSS_off RCS_on

ME_htr_on

RSS_off RCS_on

RSS_off X_standby ORS_wake

RCS_on RADAR_low_on


N N N N

13 RSS3 (RCS)RSS_off

X_standby RCS_2_RWA

RSS_off X_standby

RSS_off RCS_2_RWA

RSS_off ORS_sleep

RCS_2_RWA ME_htr_on

RSS_off ORS_sleep

RCS_2_RWA

RSS_off X_standby

RCS_2_RWA RADAR_low_on

14>7>8 Rad_wuRSS_off

X_standby RADAR_on

N N N N

Grey N = not allowed

Green = can be done via warmup

trans Limited Power

Table 1.5 Mode to Mode Transitions

3-13

3.5 Mission Design Guidelines & Constraints The purpose of this subsection and Subsections 1.3 and 1.4 is to establish mission design guidelines and constraints that govern how the various Program systems and subsystems will be used to achieve science return, while providing assurance that the scenarios can be reliably developed with the available Program resources. These guidelines and constraints are intended to establish an envelope within which the mission scenarios are designed, developed, implemented, and executed. This minimizes unnecessary optimization and management turbulence. In general, these items are of a medium to long-range planning nature. Their purpose is to define and balance the interfaces between the Spacecraft Office, the Mission Support and Services Office, and the Science and Uplink Operations Office. The distinction between a guideline and a constraint is as follows. Each constraint is binding, necessitating formal waiver approval if it is to be violated. Guidelines have a solid level of support within the Program and should therefore be honored if they do not lead to appreciable science loss or increase in mission risk and cost. Guidelines & constraints have been organized by topic and labeled with NNNNN - G# for guidelines and NNNNN - C# for constraints. The 3-5 letter abbreviations NNNNN stand for the category of the guideline or constraint: OPS for Operational Modes and Sequence Constructs, SEQ for Sequence Development, POINT for Spacecraft Pointing, TEL for Telecommunications Strategies for Uplink & Downlink, DATA for Management of On-Board Data, PRESAT for Pre-Saturn Science Activities, ESB for Earth Swingby, MEO for main engine operations, and MISC for Miscellaneous. Numbering is done by category and restarted each new subsection. During the post-launch scenario development, the Mission Design Team has three principal areas of responsibility:

a) Perform long-term studies to show feasibility of scenarios within consumable constraints and Program operating constraints; b) Develop and update appropriate mission design guidelines and constraints; Coordinate scenario design with the science and uplink teams to ensure consistency with the guidelines and constraints.

3.5.1 Operational Modes and Sequence Constructs Constraint OPS-C1 Operational Mode Usage Each operational mode shall be defined in Subsection 1.1 and adhere to the design constraints in Subsection 1.1.3 and 1.1.4.

Rationale: See discussion in Subsection 1.1.1

Constraint OPS-C5 Transitions from Operational Mode to Unique Sequence The state transitions required from (to) any operational mode into (out of) a unique sequence shall be built into the unique sequence.

Rationale: Consolidates the unique sequence design activity into one effort.

Constraint OPS-C6 Allowed Instrument Commanding Instrument state changes within an operational mode shall not require any CDS controlled heater commands.

Rationale: This and the power allocations in Table 1.2 will ensure that remotely generated state change commands by the instruments do not require special integration into the spacecraft sequence.

Constraint OPS-C7 Operational Mode Transitions All spacecraft activities required to change from one mode to another mode shall be defined in a transition sequence. Standard transition sequences shall be used for the mode switches

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indicated in Table 1.5 The scenario design shall allow windows long enough and sufficient power margins for all transition activities. Science is permitted during a transition if an instrument is on in both the preceding and following mode. During the transition, however, the instrument has no flexibility for state changes other than those required during the transition.

Rationale: Defines transition rules, prevents arbitrary science interruptions.

3.5.2 Sequence Development

Constraint SEQ-C3 Scenario Development Activity Priority Windows shall be inserted during scenario development for the following activities, in the following priority:

a) Propulsive Maneuvers and Supporting Activities Rationale: Windows shall be set aside for spacecraft propulsive maneuvers and their corresponding turn times. OPNAV opportunity windows to support maneuver design shall be inserted. (Note that science activities are permitted if they do not conflict with the maneuver or supporting activities.)

b) Reaction Wheel Unloads Rationale: Reaction wheel unloads shall be scheduled periodically from SOI-6 months to EOM, when the predicted accumulated angular momentum reaches a SCO defined limit.

c) Science Activities Rationale: Windows shall be inserted for science activities and their related engineering support activities, including OPNAV images scheduled to enhance pointing performance, if necessary.

d) Other Engineering Activities Rationale: Windows shall be provided for engineering activities including performance tests and calibrations.

Constraint SEQ-C5 OP NAV Sequencing Spacecraft Operations (Navigation) personnel shall act as the Prime Instrument Team for the purpose of sequencing optical navigation images.

Rationale: Avoids an additional unique interface.

Constraint SEQ-C6 Late Update No more than one late update (change to sequence prior to uplink) per sequence during the Saturn tour shall be allowed to incorporate sequence changes due to navigation and spacecraft clock drift updates.

Rationale: Late updates allowed to meet accuracy requirements, primarily for targeted satellite flybys during the tour. Limit of one late update minimizes the Sequence Virtual Team workload. Late updates will only be changes to target vectors and module start times, and will be inserted into the sequence process as determined by the SVT. Should there be more than one tour targeted flyby in a sequence, pointing requirements may not be able to be met on all flybys unless multiple late updates to update pointing are approved by the Program.

Constraint SEQ-C7 Live Update No more than one sequence "live update" (change to sequence pointing and timing after it has been uplinked) per week shall be allowed. The live update capability shall be supported beginning with the Approach Science subphase, approximately SOI - 6 months.

Rationale: "Live updates" are needed to meet accuracy requirements. Limit of one "live update" per week limits the Sequence Virtual Team workload. "Live updates" will only be changes to IVP and movable block start times.

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Constraint SEQ-C8 DSN Support for Real-time Commands Real-time commands shall not require additional DSN passes over those regularly scheduled, except to support spacecraft emergencies or critical events.

Rationale: DSN passes are a critical resource, and except for emergencies or critical events, it is prudent to limit real-time commanding to regularly scheduled passes. (Real-time commands may be sent during any pass scheduled for other purposes.)

Constraint SEQ-C9 On-board Distributed Sequence Timing Changes Once a distributed sequence has been loaded on-board, all timing changes (such as ephemeris changes, clock drifts, or movable blocks) that affect system-level commands and activities shall be implemented by changing CDS command execution times.

Rationale: Changes to internal instrument sequence timing could result in unexpected interactions. For example, no instrument commands that independently change the timing of microphonics are allowed.

Constraint SEQ-C10 Triggered Instrument Execution Time Definition Instrument execution time in a trigger command shall be a relative time (as opposed to an absolute time) and is defined to be relative to the receipt of the trigger command by the instrument.

Rationale: Distributed sequencing does not mean independent sequencing--all instrument activities must be directly tied to the CDS sequence, and can be shifted or canceled by changing only the CDS sequence.

Constraint SEQ-C12 Huygens Probe Checkout Sequencing Constraint No other spacecraft activities shall be sequenced during a Probe Checkout.

Rationale: MPVT/SPVT /SVT cannot verify that CDS command bandwidth would not be exceeded in the presence of other activities, since Probe telecommand frequency cannot be checked explicitly.

Constraint SEQ-C13 OPNAV Image Return (was a guideline, SEQ-G3) Optical navigation images shall be returned at the next available downlink opportunity following exposure. All OPNAV images shall be compressed using lossless compression to reduce the total volume of OPNAV data downlinked.

Rationale: Time-critical navigation products require that OPNAVs be returned as soon as possible. Op Nav data volume shall be compressed to increase science data allocation.

Constraint SEQ-C15 Superior Conjunction Downlink Data Rate Downlink data rate shall be reduced to 1896 bps (RTE or S&ER) when the SEP angle falls to 2.0° or lower.

Rationale: X-band capability begins to be degraded when the SEP angle is low and degrades more as the angle decreases. 1896 bps is the minimum data rate which can record science data and provides higher reliability during down link than higher rates. The constraint does not forbid the recording of science data during the SEP<2° period.

Constraint SEQ-C16 SSR Library Allocation Restriction No team shall write to nor read from any portion of the Library Region of the SSR that is beyond their allocated space. The library region will always be flown as non-equivalent, except during the Probe Relay mission, when the Library Region will be flown equivalent since it contains the vectors for the relay.

Rationale: Writing information beyond the assigned allocation will likely result in overwriting another team’s commands. Reading from areas outside the assigned space will have unexpected in-flight results.

Library Region Allocation

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Default Partions 0 & 1 Non-default Partions 2 & 3 Subsystem Starting

Record # # ALFs % Total Max #

IEB Starting Record #

# ALFs % Total Max # IEB

CDS 0 768 8.2 NA 0 768 8.2 NA OPNAV 768 256 2.7 32 768 256 2.7 32 Probe/Seq. 16000 128 1.4 NA 16000 128 1.4 NA SVT modules 16128 1024 10.9 NA CAPS 17152 1920 20.5 240 CIRS 16128 768 8.2 96 CDA 16896 768 8.2 96 INMS 17664 4096 43.7 512 ISS 19072 4608 49.2 576 MAG 21760 128 1.4 16 MIMI 21888 512 5.5 64 RADAR 23680 640 6.8 80 RPWS 22400 640 6.8 80 UVIS 23040 128 1.4 16 VIMS 23168 1152 12.3 144 reserve 24320 23 0.2 N/A 24320 23 0.2 NA Total 9367 9367

Constraint SEQ-C17 Validation of Instrument Commands For all orbiter instruments, all instrument commands are to be validated on that instrument’s engineering model prior to first time transmittal to and execution on the spacecraft.

Rationale: First time use of instrument commands are more likely to cause unforeseen events. Note: Validation of all instrument sequences on engineering models is encouraged as resources permit, but is not required, once all commands in a sequence have been previously validated and subsequently executed in flight.

Constraint SEQ-C18 Downlink Pass Block There shall be only one downlink pass block in the background seuence for each primary and backup TCM/OTM pass. For “split passes”, the downlink pass block shall execute at the beginning of the pass.

Rationale: Downlink pass blocks produce numerous 6ASSIGN commands as part of the block expansion. If a downlink pass block executes after the beginning of a pass, there is a possibility these commands might ovelap with the OTM block execution. If 6ASSIGNs execute during OTM execution, this may disrupt the OTM block’s telemetry strategy and cause loss of science and engineering data during the OTM.

Guideline SEQ-G2 OPNAV Image Scheduling Optical navigation images should be scheduled at a rate of no more than 8 per day during the tour. OPNAVs should only be scheduled when such data (including reasonable margin) significantly improve TCM design, near target pointing, satellite ephemerides, or trajectory reconstruction.

Rationale: Defines the maximum needed.

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Guideline SEQ-G6 Superior Conjunctions Spacecraft activities should be limited when the SEP angle is ≤ 3°.Spacecraft pointing changes should not be requested inside 3° (however, rolls about the Z-axis, with –Z to Earth, are allowed) Planned activities should not require successful commanding inside 3°, or successful playback inside 2°. Downlinks should not be requested inside 1°, except for cruise Radio Science Conjunction experiments.

Rationale: X-band capability begins to be degraded when the SEP angle is low and degrades more as the angle decreases. The minimum angle for communication depends on solar noise conditions. Limiting spacecraft activities during known periods of uncertain communication is prudent. Downlinks inside 1° SEP are unlikely to be successful.

Guideline SEQ-G7 Timing Control

Ring or Saturn observations which need timing control better than 13 seconds (1 σ) should be scheduled on orbits with no Titan inbound encounter.

Rationale: Titan perturbs the orbit and tight timing control may not be available at Saturn. Preliminary analysis indicates timing uncertainties following a Titan encounter range from about 2to 60 seconds (1 sigma), depending on the altitude of the flyby (the larger uncertainties from closer flybys).

Guideline SEQ-G8 Quiet Periods Development and Operations activities should allow for vacations and/or reduced workload during weekends and JPL observed holidays.

Rationale: Allows for time off to prevent staff overload. During these periods every attempt should be made to manage activities that require special preparation, analysis or monitoring.

Guideline SEQ-G10 First Time Event Scheduling First Time cruise events should not be scheduled in the same sequence time period as a key spacecraft event (e.g., probe activities, unique activities with a geometric constraint such as encounters or opposition experiments) in order to allow adequate time to recover from possible safing between the first time event and the key event.

Rationale: First time activities are unproven in flight and are more likely to induce safing than an activity that has been run before. Allowing sufficient time between first time activities and time critical events is prudent. Events such as PIM and PEM, which are repeated many times and are not geometry dependent are not considered key events since they can be rescheduled with minimal impact. Two to six weeks is a reasonable time before most events to recover from safing, perform fault analysis, and redesign and uplink the canceled sequence.

Guideline SEQ-G11 Sequence Memory IEB No IEBs in tour should be placed in sequence memory, with the exception of RADAR in normal sequence development

Rationale: There is not enough sequencing memory in the CDS non-privileged sequence machine to sequence all of the instrument IEBs in Tour. Since RADAR will be off during S/C uplink periods, RADAR IEBs may be stored in CDS non-privileged memory. Exceptions that would allow other teams to store IEBs in sequence memory may be made on a case-by-case basis at the discretion of the SVTL.

Guideline SEQ-G12 Data Volume Margins The following margins should be maintained during sequence planning. Design Product Data Volume Margin Up to end of SOP Implementation 2% Final uplink 1%

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The Data Volume Margin is the total additional data volume that can be absorbed and played back within 1 week, expressed as a percentage of the playback capacity within that week.

Rationale: The Data Volume Margin as expressed here is precisely that quantity that the Cassini SSR Management Tool computes in version 10.2 and later. These margins are set aside to allow for small changes in telecom performance, downlink pass configuration, DSN scheduling, and sequence planning. They are intended to prevent significant replanning should small changes arise. Larger data volume margins to protect against more significant changes cannot be accommodated since they would result in unacceptable reductions in science observations and increases in DSN requests.

3.5.3 Spacecraft Pointing Constraint POINT-C1 Spacecraft Articulation Margin Policy TBD. (This constraint will contain the Project’s margin policy for turn rates and accelerations on reaction wheels and thrusters. Combined with AACS deliveries of the available raw articulation resources, this will provide all the necessary information for planners to design turns.) Constraint POINT-C4 Prime Instrument One science instrument shall be designated "prime" during science observing time in which the spacecraft pointing is not already determined. An instrument team will specify the spacecraft pointing for the interval in which it is prime.

Rationale: The purpose of this constraint is to avoid extra interfaces by defining that there shall be a single instrument that controls pointing during each observation period. The burden of any coupled pointing design rests solely on the instrument teams themselves.

Constraint POINT-C5 Prime Instrument Specified Attitude Prime instruments shall leave the spacecraft axes at: Science Planning-specified attitude at the end of their time as a prime instrument.

Rationale: The Science Planning Team is responsible for managing and defining the waypoint strategy used for Tour. A waypoint strategy will be adopted that minimizes any unnecessary spacecraft slewing.

Constraint POINT-C6 Turns to Targets The SPVT shall be responsible for spacecraft turns when both the target body and prime instrument change.

Rationale: Defines who has control of turns.

3.5.4 Telecommunications Constraint TEL-C1 Cruise DSN Coverage Cruise DSN coverage shall be requested consistent with that specified in the Project Service Level Agreement (PSLA)

Rationale: The PSLA is the controlling document for DSN coverage requests. DSN coverage is required for downlink spacecraft telemetry and uplink commands, and to provide navigation data for maneuvers, planetary encounters, conjunctions, instrument checkouts, cruise science, etc.

Constraint TEL-C2 Tour DSN Coverage (was a guideline, TEL-G3) An average of one downlink period per day (exclusive of Radio Science passes) shall be scheduled during the tour.

Rationale: Consistent with the 15 hour science recording/9 hour downlink operations concept. Provides flexibility in scheduling DSN resources while also constraining their average load. Occultation periods and gravity field flybys generally require two DSN stations for complete coverage of the event. Radio Science geometric experiments which require consecutive DSN passes shall be accommodated on an occasional basis (estimated at ~ one additional pass per month, averaged over the four years of the tour).

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Constraint TEL-C9 High Activity Downlink High activity data return shall be calculated assuming one of the following DSN and spacecraft configurations: 1) northern hemisphere 70 meter DSN pass, ranging off, 90% confidence; 2) northern hemisphere 70/34 meter arrayed pass, ranging off, 90% confidence. High Activity passes shall be requested up to 35% of the time. Actual data return shall be accomplished with equivalent performance DSN configurations.

Rationale: Specifies the expected data return configuration adequately for planning purposes. Northern hemisphere stations may have different performances (e.g. the Goldstone low noise feed upgrade); “equivalent performance” implies performance equivalent to whichever station is requested. High Activity days are capable of returning 4 Gbit per day.

Constraint TEL-C10 Low Activity Downlink Low activity data return shall be calculated assuming a northern hemisphere 34 meter DSN pass, ranging on, 90% confidence. Actual data return shall be accomplished with equivalent performance DSN configurations.

Rationale: Specifies the expected data return configuration adequately for planning purposes. Low Activity days are capable of returning 1 Gbit per day.

Constraint TEL-C12 Telemetry Link Confidence Level The Spacecraft Operations Office and the Science Planning Team shall design sequences such that the telemetry link provides the following probabilities of telemetry being successfully received by the ground during the following mission phases or activities: Mission Phase or Activity Probability Level Saturn tour ≥ 90 % * Cruise ≥ 85 % *Dual playbacks shall be used for critical data and other data as specified in DATA-C4.

Rationale: 004 requirement.

Constraint TEL-C14 Data Rate Switches and DSN Lockup Data transmitted during initial DSN lockup, data rate switches, and unexpected outages (e.g., bad weather or station problems) shall be assumed to be lost.

Rationale: Operations staffs from Cassini and from other missions have indicated that strategies to recover data transmitted during DSN lockup (i.e. at frame sync) and data rate switches are expensive and complicated. DSN lockup is estimated to be ~ ten seconds at kilobit and higher data rates, and data rate switches are expected to take even less time. Due to the low amount of data lost, these strategies are not needed.

Constraint TEL-C15 Radio Science Occultation Pass Strategy During Radio Science Occultation experiments, telemetry modulation shall be turned off.

Rationale: Telemetry modulation is turned off to increase the signal-to-noise ratio during Radio Science occultation experiments.

Constraint TEL-C16 Command Uplink Background sequence design shall not require more than two command uploads per sequence. For each upload, time shall be set aside during the pass for two uplink attempts and one verification period during one pass.

Rationale: Breaking up detailed sequences into multiple pieces involves significant ground complications and coordination and should be minimized. Whenever possible, sequences should only require one command upload.

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Guideline TEL-G2 Real-time Commands The use of real-time commands should be constrained to those activities which cannot be accomplished via the stored sequence.

Rationale: Real-time commands increase cost and risk.

Guideline TEL-G5 Length of Downlink Period Downlink periods should be 9 hours in length, unless a longer pass is required to return 4 Gbit on a high activity day or 1 Gbit on a low activity day.

Rationale: Restricts planners from overly burdening the DSN by regularly scheduling long passes.

3.5.5 Management of On-Board Data Constraint DATA-C5 Probe Data Protection Probe relay data shall be dual recorded (the same data recorded on each SSR) and kept stored on-board the orbiter until ground command is received by the orbiter authorizing deletion of the probe relay data. The ground command shall be issued after it has been verified that the correct data has been received at JPL (for data in non-protected partitions in SSR A and B) and at ESOC (for data in protected partitions in SSR A and B). Uplink window opportunities shall be provided after the transmission of probe data to allow data deletion or overwriting from the SSR. The windows shall be scheduled following a TBD (24) hour period on the ground during which data quality is verified.

Rationale: Prompt uplink windows following ground receipt of probe data can free up SSR space for post-flyby science collection by releasing the write protection flag.

Constraint DATA-C6 Engineering Data Engineering data shall be continuously recorded in all flight sequences.

Rationale: Allows the spacecraft health to be tracked and attitude to be reconstructed. Under normal conditions, it is not necessary that all engineering data be downlinked.

Constraint DATA-C7 SSR Partition During tour operations, each SSR shall be capable of storing telemetry in at least three partitions. The partition layout of these shall be the same on both SSRs.

Rationale: Typically partitions will be needed for engineering (except AACS), science (plus AACS), and OPNAVs and/or high-value science. Identical layouts minimize the chance of problems caused by an unexpected SSR swap. The partition sizes may vary between SSRs but the same partitions must exist. The minimum size for a partition is one frame, or 8800 bits.

Constraint DATA-C9 SSR Instrument Data Recording An instrument's data recording shall be monitored by CDS and stopped once the data volume equals the data volume allocation for that instrument.

Rationale: Data volumes must be policed to protect all engineering and instrument data allocations. CDS has been identified as the authority best suited to data volume policing. CDS performs data policing via data volume allocations uploaded from the ground with each sequence upload.

Constraint DATA-C10 Navigation SSR allocation The navigation data volume allocation for OPNAVs shall be maintained separately from the ISS data volume.

Rationale: Navigation data volume allocations will typically supplement the ISS data volume allocation just before the OPNAV is taken.

Constraint DATA-C11 SSR Priority Playback Only OPNAVs and probe mission data shall be allowed priority in the playback sequence during the tour, except for post-anomaly diagnostic data retrieval.

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Rationale: Prioritized playback of specific instrument data is very difficult as all data are mixed within the science and engineering partition. Neither science nor engineering managers have requested prioritized playback of any specific data, unless a spacecraft fault has occurred.

Constraint DATA-C12 High-Value Data High-Value data as specified by a science team or SCO, shall be written into a separate partition on-onboard the spacecraft (but not write-protected).

Rationale: Provides additional protection, and permits a science team or SCO to use part of its data volume allocation to protect important data.

Constraint DATA-C13 High-Value Data Playback Data selected as high-value shall be played back over two separate DSN passes as executed by the on-board sequence. Thereafter, the data shall be released without the necessity of ground verification of receipt of the data. High value data playback shall be counted within the downlink data allocation of the relevant team for both playbacks.

Rationale: Provides additional protection of High-Value Science (or Engineering) Data from accidental loss of DSN coverage on one of two days, loss of all or part of relay from DSN to JPL, inclement weather, etc.

Constraint DATA-C14 SSR Playback During Cruise and Tour, all data recorded on the solid state recorders in partitions 4 and 5 shall be played back by the end of the last pass in each sequence.

Rationale: Carryover of recorded data is not allowed between sequences to simplify SSR management. (There is no requirement to playback engineering data on partition 6 unless there is an anomaly.)

3.5.6 Pre-Saturn Science Activities Constraint PRESAT-C11 Quiet Spacecraft for Radio Science During Cruise During certain Radio Science cruise activities (Gravitational Wave Experiments, GWE Systems Tests, Solar Conjunction Experiments, HGA calibrations, and RSS ICO tests), a "quiet spacecraft" is required and shall be defined as follows: 1) S/C attitude controlled by RWAs and no firings of RCS thrusters or the main engine; 2) No motion imparted to spacecraft by any other instrument (i.e., no articulation, moving filter wheels, etc.); 3) No state changes (includes power changes or transients greater than 28 Watts) and with other disturbances (such as activating and deactivating heaters, transmitters, etc. minimized.

Rationale: Radio Science investigations are sensitive to all small forces imparting motion to the spacecraft, including other instruments' motions and state changes. From PRESAT-C6: Reduction of the reaction wheels momentum buildup can be accomplished without thruster use, for instance through 180 degree slow rolls about the Earth line every 10 days. This motion takes care of the momentum buildups for the X- and Y- axes. Calculations show that the Z momentum buildup is slow enough that it does not require unloading within the 40 days of the GWE. From PRESAT-C8: If 28 W of collimated (worst case) thermal radiation changes direction, it can result in a differential translational acceleration over the time scales of interest equal to the goal of 699-004 requirement 4213-1.

3.5.7 Saturn Tour & SOI Constraint TOUR-C1 Activities prior to SOI The following conditions shall apply while the SOI critical sequence is active: a) attitude shall be X-band to Earth, until the start of the turn for the ascending ring plane

crossing preceding the SOI burn. The secondary axis shall be between +X to Saturn North Pole and +X to Saturn North Pole -40 degrees (roll about spacecraft Z with +X toward Saturn)

b) no spacecraft attitude changes except to support ring plane crossing and the SOI burn.

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c) Instruments are quiescent(Quiescent means no power state changes, no s/w modifications)

-instrument internal sequences, initiated prior to SOI critical sequence activation, may be executing.

- instruments may lower their high voltage states prior to the SOI burn from an instrument internal sequence already executing

d) no AACS control mode changes e) no real-time commands f) no sequenced bus commands except for engineering commands issued from the critical

sequence. Exception: S/C telemetry mode changes (including corresponding subcarrier and mod-index changes) between any RTE&SPB telemetry mode and S&ER-10 are allowed to execute from the background sequence until 12 hours before the first critical activity executes [about 29 hrs before the SOI burn])

g) during the critical sequence, only one SSR is available, due to the SSR ping-pong bit being disabled

Rationale: Defines a Quiet Period before SOI where safing is unlikely due to lack of activity, and allows time to recover from safing if needed.

Constraint TOUR-C2 Titan Atmospheric Model Update The Science and Uplink Office shall investigate on the first Titan flyby the Titan atmospheric density and provide a Titan atmospheric model using that data by one month after the first Titan flyby.

Rationale: Allows adjustment of Titan flyby altitudes. It is expected that AACS will also conduct an analysis of the controlled response of the first Titan flyby in support of minimum Titan flyby altitude decision.

Constraint TOUR-C3 Probe Release at Late Dates Probe release shall not be attempted less than 9 days before Titan encounter.

Rationale: Provides sufficient time for emergency maneuvers on failure of Orbital Deflection Maneuver.

Guideline TOUR-G1 Post-Separation Imaging of the Probe Images of the Huygens probe should be acquired by both the NAC and the WAC during the time periods from probe separation to probe separation + 1 day and again from ODM to ODM + 3 days. Preferred observation times are probe separation + 1 day and ODM + 3 days.

Rationale: Images of the probe after separation can be used to estimate the probe trajectory and adjust the HGA pointing direction for the data relay. They can also be used to determine the probe’s approximate orientation for anomaly diagnosis. Images taken shortly after separation can also be used for public outreach.

3.5.8 Miscellaneous Constraint MISC-C1 (formerly C-44) Checkout of Redundant Hardware Operating subsystems shall not be switched to standby redundant units for status or calibration unless: a) critical sequences require immediate unit switching in response to a failure in the primary operating unit, or b) the spacecraft has experienced a stressful environment (particle hits, etc.) and knowledge of the redundant unit status could substantially affect future plans, or c) one of the following allowed activities:

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1) SRU “Backup” unit, which may undergo yearly performance characterizations. The unit shall not be set to “Prime” during the maintenance.

• switching the AACS bus during the BAIL maintenance activity

• switching the Probe Support Avionics (PSA) unit during Probe operational activities

• switching to backup UVIS CPU2 during Instrument Checkout as done during ATLO tests

• operating the backup EGA during periodic maintenance

• operating the backup RWA during periodic maintenance

• switching to backup MAG processor/power supply during Instrument Checkout as done during ATLO tests

Rationale: Checking redundant units does not save costs or increase mission reliability. Exceptions reflect activities where designed activities are an allowed in-flight repeat of ATLO tests during ICO, activities where SCO has adopted the prelaunch development design which reflects periodic use of the backup unit, and where the activity (BAIL maintenance) requires the use of a separate unit.

Constraint MISC-C2 In-Flight Use of Redundant Units Prior to SOI plus 2 years, mission and sequence design shall be based upon the assumption that redundant spacecraft units are not available for the enhancement of mission return, with the exception noted below. The exception is: redundant data storage devices shall be used to capture critical science data and engineering diagnostic data redundantly, and may be used to enhance mission return beginning with sequence C40, 20 October 2003.

Rationale: Controls use of redundant units to a reasonable level.

3.6 Controlled Scenario Timelines The following scenario timelines are under change control: SOI and Probe Mission. The timelines are repeated on the following pages from the appropriate sections in this document. These timelines are not completely up to date, but are intended only to reflect the last scenario design that was reviewed across the project and subsequently approved via ECR.

SSOOII EEvveennttss TTiimmeell iinnee

145 150 155 160 165 170 175 180 185 190 195 200

Solar Conjunction

PhoebeTargeting TCMbi-prop pressurizationSOI-35

SOI Final Clean-upSOI+15 d

SaturnPeriapsis

SOI initial Clean-upSOI+2 d

Start Quiet PeriodSOI-8 d

Activate Critical Sequence

CriticalSequenceExecution

PhoebeFlybySOI-19 d Phoebe

Clean-up TCMSOI-15 d

}

sequence S1 sequence S2

ApproachClean-up (if neededSOI-10 d)

Quiet Period CSpre-Quiet Period post-Burn Period

Passesperday 0

123

Day of Year(DOY)

Earth,Sun Probe at Entry

Cassini/Huygens Probe Relay Timeline

HGA to probeHGA to Earth HGA to Earth

0-2h 6m-4.0h

Time from TCA

ProbeEntry

ProbeTouchdown

Probe Link(~4.5 hr)

Surface Science:S/C will continue totrack probe for ~60 minutes(Probe battery life ~ 5 hrs)

Probe Events

CoastPhase

Orbiter Probe

Support

Orbiter Science

Receive & Record Probe Data

All instruments OFF

Probe DataPlayback

Turn HGAto Probe

Orbiter ClosestApproach

(TCA)

Turn HGAto Earth

Change to

Science resumes (at most) 2 days after playback

(7.86 hrs req'd for both SSRs)

(Probe may request additional playbacks)

Quiet period* begins TCA-8 days

*Quiet period restrictions:

SSRs write-protected

Spacecraft turns and rolls (S/C in RCS mode)Power state changesEngineering configuration changesAACS Mode Changes

No quiet period restrictions on: SSR data playbackMAPS data collection

All instrument data cleared from SSRs

Cassini-Titan range: 74689 km Cassini-Titan range @ TCA 60000 km

(interface altitude 1270 km)

PRLY tlm mode,PSAs ON

(~12 min)

OPERATIONAL MODES DATA MANAGEMENTOPS-C1 ACTIVE DATA-C1 deleted by ECR 100413OPS-C2 deleted by ECR 100413 DATA-C2 deleted by ECR 100413OPS-C3 Changed to guideline G3 by ECR 100413 DATA-C3 deleted by ECR 100413OPS-C4 deleted by ECR 100413 DATA-C4 deleted by ECR 100413OPS-C5 ACTIVE DATA-C5 ACTIVEOPS-C6 ACTIVE DATA-C6 ACTIVEOPS-C7 ACTIVE DATA-C7 ACTIVEOPS-C8 deleted by ECR 100413 DATA-C8 deleted by ECR 100413OPS-C9 deleted by ECR 100413 DATA-C9 ACTIVEOPS-C10 deleted by ECR 100413 DATA-C10 ACTIVEOPS-G1 deleted by ECR 100413 DATA-C11 ACTIVEOPS-G2 deleted by ECR 100413 DATA-C12 ACTIVEOPS-G3 deleted by ECR 100930 DATA-C13 ACTIVESEQUENCING DATA-C14 ACTIVESEQ-C1 deleted by ECR 100413 DATA-G1 deleted by ECR 100413SEQ-C2 deleted by ECR 103363, see SEQ-G12 DATA-G2 deleted by ECR 100413SEQ-C3 ACTIVE DATA-G3 deleted by ECR 102776SEQ-C4 deleted by ECR 100413 PRE-SATURNSEQ-C5 ACTIVE PRESAT-C1 deleted by ECR 100413SEQ-C6 ACTIVE PRESAT-C2 deleted by ECR 100413SEQ-C7 ACTIVE PRESAT-C3 deleted by ECR 100413SEQ-C8 ACTIVE PRESAT-C4 deleted by ECR 100413SEQ-C9 ACTIVE PRESAT-C5 deleted by ECR 100413SEQ-C10 ACTIVE PRESAT-C6 deleted by ECR 82324SEQ-C11 deleted by ECR 100413 PRESAT-C7 deleted by ECR 100413SEQ-C12 ACTIVE PRESAT-C8 deleted by ECR 82324SEQ-C13 ACTIVE, was SEQ-G3 PRESAT-C9 deleted by ECR 100413SEQ-C14 deleted by ECR 100930 PRESAT-C10 deleted by ECR 100413SEQ-C15 ACTIVE PRESAT-C11 ACTIVESEQ-C16 ACTIVE PRESAT-G1 deleted by ECR 100413SEQ-C17 ACTIVE PRESAT-G2 deleted by ECR 100413SEQ-C18 ACTIVE PRESAT-G3 deleted by ECR 100413SEQ-G1 deleted by ECR 100413 EARTH SWINGBYSEQ-G2 ACTIVE ESB-C1 deleted by ECR 100413SEQ-G3 changed to constraint by ECR 100413 ESB-C2 deleted by ECR 100413SEQ-G4 deleted by ECR 100413 ESB-C3 deleted by ECR 100413SEQ-G5 deleted by ECR 100413 ESB-C4 deleted by ECR 100413SEQ-G6 ACTIVE ESB-C5 deleted by ECR 100413SEQ-G7 ACTIVE ESB-C6 deleted by ECR 100413SEQ-G8 ACTIVE ESB-C7 deleted by ECR 100413SEQ-G9 changed to constraint by ECR 100413 ESB-C9 deleted by ECR 100413SEQ-G10 ACTIVE ESB-C10 deleted by ECR 100413SEQ-G11 ACTIVE ESB-C11 deleted by ECR 100413SEQ-G12 ACTIVE ESB-C12 deleted by ECR 100413POINTING ESB-C13 deleted by ECR 100413POINT-C1 ACTIVE ESB-C14 deleted by ECR 100413POINT-C2 deleted by ECR 81904 ESB-C15 deleted by ECR 100413POINT-C3 deleted by ECR 100413 ESB-C16 deleted by ECR 100413POINT-C4 ACTIVE ESB-C17 deleted by ECR 100413POINT-C5 ACTIVE ESB-C18 deleted by ECR 100413POINT-C6 ACTIVE ESB-C19 deleted by ECR 100413TELECOMMUNICATIONS TOURTEL-C1 ACTIVE TOUR-C1 ACTIVETEL-C2 ACTIVE TOUR-C2 ACTIVETEL-C3 deleted by ECR 100413 TOUR-C3 ACTIVETEL-C4 deleted by ECR 100413 TOUR-G1 ACTIVETEL-C5 deleted by ECR 100413 TOUR-G2 deleted by ECR 101102TEL-C6 deleted by ECR 100413 MAIN ENGINE OPERATIONTEL-C7 deleted by ECR 100413 MEO-C1 deleted by ECR 100413TEL-C8 deleted by ECR 100413 MEO-C2 deleted by ECR 100413TEL-C9 ACTIVE MEO-C3 superceded by MEO-C5, ECR 82287TEL-C10 ACTIVE MEO-C4 deleted by ECR 100413TEL-C11 deleted by ECR 100413 MEO-C5 deleted by ECR 82287TEL-C12 ACTIVE MEO-C6 deleted by ECR 100413TEL-C13 deleted by ECR 100413 MEO-G1 deleted by ECR 100413TEL-C14 ACTIVE MEO-G2 deleted by ECR 100413TEL-C15 ACTIVE MISCELLANEOUSTEL-C16 ACTIVE, was guideline TEL-G1 MISC-C1 ACTIVETEL-G1 changed to constraint by ECR 100413 MISC-C2 ACTIVETEL-G2 ACTIVE MISC-C3 superceded by MEO-C6 per ECR 81999TEL-G3 deleted by ECR 100413 MISC-G1 deleted by ECR 82227TEL-G4 deleted by ECR 102776 MISC-G2 superceded by MEO-C6 per ECR 81999TEL-G5 ACTIVE

Mission Plan Guidelines & Constraints History

1 8/10/05

Mission Plan Compliance with the Project Policies & Requirements Document Reqt. No. Requirement Title Achieved? DiscussionSec 2 Project Policies and Constraints

22-1D Project Goal YesThe complete Mission Plan addresses this goal by demonstrating a mission design that balances mission success with complexity that could drive cost. A high probability of proper operation is addressed by such aspects of the mission design as (continues) maintaining margins in other consumable budgets, such as gyro and reaction wheel usage; slowly lowering the Titan flyby altitude during the tour; reducing ring plane crossing risk until later in the tour, etc.

22-2D Project Priorities YesThe complete Mission Plan addresses these priorities. While there are no major compromises in the design, examples of these considerations in the scenario development are: minimum payload activity in first year after launch, cautious (continues)

approach for the Earth flyby scenario, probe deployment on the first Saturn orbit with a backup opportunity on the second orbit, carefully constrained payload operation near SOI, and so forth.

22-3B Mission Set: primary, backup, and secondary launch opportunities Yes The complete Mission Plan addresses the primary mission. Backup and secondary missions have

been defined [2.2].22-4 Titan IV/Centaur Launch Vehicle Yes Baseline vehicle is Titan IV/Centaur [3.1, 4.3].22-5 Launch Readiness Date Yes Primary mission baseline has earliest launch date on October 6, 1997 [4.3].

22-6 Cassini End of Mission and End of Project Yes Mission design complies [2.1, 7.1.10]

23-1 Inertial Reference Frame Yes Mission design and navigation software uses J2000 as the primary reference frame.Sec 3 Science Investigation Objectives

31-1C Pre-Saturn Yes Scenarios for payload operations in the interplanetary mission and the Saturn approach phase support these objectives [5, 6].

31-2 Saturnian System Yes Scenarios for Saturn system observations from pre-SOI through the tour support these objectives [6,7].

32-1B Orbiter Science Investigations Yes Scenarios for Saturn system observations from pre-SOI through the tour support these investigations [6,7].

32-2 Probe Science Investigations Yes Probe scenario supports these investigations [6.3].

321-1 En Route Gravitational Wave Experiment Yes Opportunities and plans for gravity wave experiments have been identified [5.5, 6.1].

321-2D En Route Solar Conjunction Experiment Yes Shown in Cruise timeline (Figure 2.1) and Mission Events Table (Table 2.1); DSN coverage may

need to be added in DMR

322-1B Titan Objectives YesPlans for Saturn tour will provide many observational opportunities for these objectives [6.3, 7]. Conflicting instrument requirements, such as pointing, power, and data rate will require allocation of observations to certain Titan flybys.

323-1B Saturn Objectives Yes Plans for Saturn tour will provide observational opportunities for these objectives [6.1, 6.3, 7].324-1B Ring Objectives Yes Plans for Saturn tour will provide observational opportunities for these objectives [6.2, 6.3, 7].325-1B Icy Satellite Objectives Yes Plans for Saturn tour will provide observational opportunities for these objectives [6.1, 6.3, 7].326-1B Magnetosphere Objectives Yes Plans for Saturn tour will provide observational opportunities for these objectives [6, 7].

331-1A Reference Operational Modes Yes Reference operational modes have been defined [8] and future scenario work will define the detailed implementation.

Mission Plan Compliance with the Project Policies & Requirements Document Reqt. No. Requirement Title Achieved? Discussion

331-2B Jupiter Science (not precluded) Yes Mission design can accommodate limited Jupiter science for the distant flyby, but no firm decision is made, pending better understanding of ground system capability [5.5.3].

Sec 4 Project Derived Requirements411-1 Launch Vehicle Resiliency Yes Baseline vehicle is Titan IV/Centaur [3.1,4.3] with fallback mission for SRM [2.2,4.3].

411-2 Launch Vehicle/Spacecraft Separation Yes Launch sequence shows no unnecessary delay in separation after the injection burn. Separation

is planned 10 minutes after MECO-2 [4.4].411-3 Contingency Launch Period Yes Eleven contingency launch dates have been defined for the primary mission [4.2, 4.3].

411-4 Launch Period Duration YesBaseline launch period for the primary mission is 30 days in duration. Launch periods for the secondary mission (35 days) and the backup mission (18 days) have also been defined. [2.2, 4.2, 4.3]

411-5B Probability of Impact Yes - Prelim Requirement on the Centaur collision/contamination avoidance maneuver to avoid impact with other planetary bodies will be defined in the Target Specification [4.4].

411-6C Sufficiently High Parking Orbit YesParking orbit altitudes are defined to achieve minimum 10-day lifetime, and a preliminary SHO contingency strategy has been defined to simply the commanding of maneuvers to raise the orbit altitude [4.4].

412-1 Gravity Assist Yes Trajectory design complies [5.1].

413-1 Near-SOI Science Yes SOI scenario provides near-SOI science observations with relatively small increase in sequence complexity [6.2].

414-1 Probe Delivery Orbit Yes Trajectory design provides for probe delivery on the first Saturn orbit, and a backup opportunity on the second orbit [6.3].

414-2B Probe Data Acquisition Yes Probe relay scenario complies [6.3].414-3 Probe Approach Velocity Yes Trajectory design complies; baseline value is 5.75 km/sec [6.3].414-4D Probe Delivery Tracking Yes Probe entry is planned far away from Solar conjunctions [6.3].414-5D Probe Delivery Orbit Yes Probe entry is on an inbound Titan flyby [6.3].415-1 Tour Duration Yes Trajectory design complies [7.1].

415-2 Tour Geometry Requirements No (but mostly)The current reference tour exceeds or complies with most, but not all, of these criteria. Specific trade-offs between the achieve-able geometry and science objectives for the tour will be made in close consultation with the Project Science Group.

415-3B Titan Flyby Frequency Yes Titan flybys as close as 16 days, but no closer, are planned according to agreed-upon ground system constraints and the TCM spacing is provided [7.1, 7.4].

415-4B Satellite Flyby Minimum Altitudes Yes Minimum planned Titan flyby altitude is 950 km. Studies of Titan atmospheric models are continuing. Minimum planned icy satellite flyby is 500 km [7.1, 7.2].

415-5B Attitude Control Monopropellant Allocation Yes Current hydrazine budget for attitude control activities is 22.1 kg with 3-sigma AACS statistics

and conservative mission assumptions [3.2.3].

416-1 Mission Scenarios Yes - PrelimResource operating margins for spacecraft consumables have been allocated [3.2.3], payload operating constraints within the operating modes are preliminary [8.1], ground system margins are not yet worked in detail.

416-2 D Mission Contingency Yes The mission contingency mass is creatable from several potential mission trade-offs including Saturn arrival date, SOI burn delay, initial orbit period, average Titan flyby altitude, etc.

416-3 Ring Hazards Prior to Probe Delivery Yes - Prelim The ring crossings before and after SOI through the F-G gap satisfy this probability based on the risk constraint equation documented in the MRRD [6.2, 7.2].

Mission Plan Compliance with the Project Policies & Requirements Document Reqt. No. Requirement Title Achieved? Discussion

416-4 Environmental Hazards After Probe Delivery Yes The tour design meets this requirement via gradual reduction of the Titan flyby altitude and the

ring plane crossing strategy.

416-5B Uplink Windows Yes - Prelim The Mission Plan is not yet at this level of detail. A mission constraint for uplink windows is defined [8.3].

416-6 Adequate Tracking and Communications Yes No important events planned within 5-deg SEP. The tour design specifically avoided targeted

satellite encounters within 5-deg SEP [7.2].

416-7B Operability of Operational Modes Yes - PrelimA preliminary definition and operating strategy for the operational modes have been made, particularly to minimize power and thermal analysis, but only preliminary assessments of the overall operability of the mission have been made [8.1].

416-8B Interface Simplicity Yes This guideline has been included in the mission design approach.

416-9B Operational Power Margins Yes The power analysis used for definition of the operational modes includes 20-Watt operating margin in all power modes with additional margin [8.3].

417-1 Personnel Holidays Yes SOI and probe mission trajectory design complies [6.2, 6.3].

418-1D Earth Swingby Requirements on Mission Design Yes Earth swingby requirements have been included in Section 8.

441-1 Space-to-Ground Telemetry Link BER Yes Telecom data used for mission design for all mission phases assumes BER no greater than 1.0E-6.

441-2D Space-to-Ground Telemetry Link Confidence Level Yes

95% link confidence level used in telecom analysis for all cruise and emergency link calculations. 90% link confidence used for Saturn tour data return predictions. Greater than 95% confi-dence for critical science activities at Saturn will be achieved

441-4 Ground-to-Space Command Link Error Rate Yes Uplink error rate of 1.0E-9 is achieved by 1.0E-5 telecom error rate and CDS error detection.

441-6C Maximum Allowable Communications Outage Period Yes Minimum tracking coverage frequency is once per week in cruise [5].

441-7 Ground-to-Space Command Link Confidence Level Yes Telecom data used for mission design for all mission phases based on 99% uplink link confidence

level.4421-4 Redundancy Policy Yes - Prelim No current plans to use redundant units for mission enhance-ments, other than the SSR.4422-1B Critical Events Yes - Prelim Work on the critical sequences and fault protection is very preliminary.

4423-2B Earth Swingby Yes Mission design studies to support this requirement are documented in the Earth Swingby Plan (699-70-3).

Sec 5 Verification

5412-3D Sequence Validation Yes Mission design will provide supporting scenarios for flight sequence testing and for definition of early cruise sequences.

542-1 Operational Scenario Capabilities Yes - Prelim This verification will be the continuing role of the Scenarios Working Group, where representatives from science, flight system, and ground system review proposed scenarios.

544-1 Qualitative Risk Assessment TBDA qualitative risk assessment has not yet been performed for the mission design but, in general, the elements of mission risk are similar to Galileo: long cruise phase with multiple close planetary flybys, probe deploy/relay, orbit insertion maneuver, etc

PMISSION PLAN ECR CHANGE LOG

ECR SUBJECT APPROVED SECTIONS IMPLEMENTED 103565r1 OpMOde Transition Block Changes 13 April 05 3 Table 1.2,1.5 August 2005 Rev 0 chg 1 103536 OpMode Transition block changes 13 Dec 04 8 Table 1,5 August 2005 Rev 0 chg 1 103719 CDA OpMode Transition block changes 12 Dec 04 3 Table 1,5 August 2005 Rev 0 chg 1 103565 Op Mode Transition Updates for RSS 30 Sept 04 3 Table 1,5 August 2005 Rev 0 chg 1 103363 MP-Data Volume Margin 15 Mar 04 3 August 2005 Rev 0 chg 1 102816 MP-Downlink Pass Block Restriction durng

OTM passes 26 Sept 03 3 October 2003 - Rev O

103052 MP-Allow dual SSR use in Cruise 24 Sept 03 3 October 2003- Rev O 103030 OPMODE transition Block Update 23 Sept 03 3 (Table 8.5) October 2003- Rev O 102776 MP-Delete Obsolete Guidelines; Add Data

Constraint for SSR Playback 2 July 03

3 October 2003- Rev O

102770 OPMODE Definition Update 9 May 03 3 October 2003- Rev O 102626 MP-1st time use of Instrument Commands 6 Mar 03 3 October 2003- Rev O 100386 PMS Flight Rules Clean-up 24 Feb 03 2 (5.5.2) October 2003- Rev O 101027 MP-Sequence Memory IEB 13 Jan 03 3 October 2003–Rev O 102348 MP-SSR Lobrary Region Update 9 Dec 02 3 October 2003–Rev O 102317 Opmode Transition Block Mods 16 Sept 02 3 October 2003–Rev O 102321 MSS D9.0 New IVP and Movable Block

Sequence Regions 5 Sept 02 2 October 2003–Rev O

100868 MP-SSR CD Library Allocation Restriction 19 Dec 01 3 October 2003–Rev O 101102 SOI Constraints 13 May 02 8 May 2002 – Rev N 100867 OpMode Changes 27 Mar 02 8 May 2002 – Rev N 100930 Mission Plan Constraints 9 Jan 02 8 May 2002 – Rev N 100947 Conjunction Restrictions 9 Jan 02 8 May 2002 – Rev N 100857 Dual SSRs 31 Oct 01 8 May 2002 – Rev N 100655 Mission Plan Timeline Update 14 May 01 8 June 2001-Rev M 100413 Updates to MP Guidelines and Constraints 9 May 01 8 June 2001-Rev M 82356 Tour Data Rate Selection 31 October 00 8 June 2001-Rev M 82324 Quiet S/C for Radio Science during Cruise 23 August 00 8 June 2001-Rev M 82394 Change to Definition of Critical Data 2 August 00 8 June 2001-Rev M 82354 Reusuable Sequence Constructs 18 July 00 8 June 2001-Rev M 100133 PSLA Update 25 June 00 Table J.2 10 July 2000-Rev L 100127 VIMS Stellar Calibration 26 May 00 5 (add to text) 10 July 2000-Rev L 82355 Tour Downlink Strategy 16 May 00 8 10 July 2000-Rev L 82357 Tour Downlink Durations 16 May 00 8 10 July 2000-Rev L 82358 Tour Arrayed Passes 16 May 00 8 10 July 2000-Rev L 82359 DSN PSLA update 8 Feb 00 Table J.2 26 Jan 2000-Rev K 82392 Deletion of Table 8.2 25 Jan 00 Table 8.2 26 Jan 2000-Rev K 82338 Change Timing of GWE Test 19 Jan 00 Section 5 26 Jan 2000-Rev K 82210 Operational Mode Definitions 5 Aug 99 Table 8.5 26 Jan 2000-Rev K 82211 Telemetry Mode Changes 14 July 99 Table 8.6 26 Jan 2000-Rev K

4-1

4.0 SELECTED REFERENCE PROJECT POLICY REQUIREMENTS (FROM 004) The following is a list of requirements from the Project Policies and Requirements document that are still active, relevant and may need to be checked by Mission Planning. Design requirements and pre-launch requirements have been removed. 413-1 Near-SOI Science. The Mission Design shall be capable of acquiring science data at Saturn closest approach in a manner that does not compromise reliably achieving Saturn orbit. 414-2B Probe Data Acquisition. The Mission Design shall provide for probe data acquisition for 180 minutes from entry into Titan's atmosphere. 414-4D Probe Delivery Tracking. The Mission Design should place Probe entry at least 45 days after and at least 10 days before solar conjunction. 415-2 Tour Geometry Requirements. The Saturnian orbital tour shall include the following:

a) ≥ 10 orbits with a Saturn periapsis ≤ 250,000 km. b) ≥ 1 Saturn magnetotail excursion, apoapsis ≥ 40 Rs and within 3 Rs of the Sun-Saturn line, night side. c) ≥ 4 close (≤ 10,000 km) targeted flybys of icy satellites including Enceladus and the dark side of Iapetus, with a goal of ≥ 4 additional non-targeted icy satellite flybys to ≤ 30,000 km. d) Saturn inclinations ≥ 50˚ for ring observations and ≥ 2 occasions with large differences in solar incidence angles. e) Saturn and Titan phase angle range from 0.1 to 175˚. f) Saturn and Titan latitude and Saturn inclinations well distributed from approximately 0˚ to 85˚. g) A minimum of 21 Titan passes. h) A minimum of 25% of the Titan passes suitable for RSS occultation measurements at a range of latitudes (range ≤ 50,000 km). i) ≥ 6 Titan low altitude passes (≤ 1,000 km or as dictated by safety) j) Solar, Earth and stellar occultations of Saturn, Titan, and rings distributed in latitude, longitude, ring opening angle, and dayside/nightside coverage.

415-3B Titan Flyby Frequency. The Mission Design shall not schedule spacecraft flybys of Titan closer than 16 days, or TCM executions closer than -3 days and +2 days of every Titan encounter. 415-4B Satellite Flyby Minimum Altitudes. The Mission Design shall not include Titan flyby altitudes lower than 950 km (or as compatible with revised Titan atmosphere models and the risk limits of 416-4), or icy satellite flyby altitudes lower than 500 km. 415-5B Attitude-Control Mono-Propellant Allocation. Mission Design shall design the overall mission profile and scenario level of attitude-control activities (including reaction wheel unloading) to not require more than 40 kg of hydrazine at the 95% probability level. 416-3 Ring Hazards Prior to Probe Delivery. Given that the Spacecraft is functioning properly at 1 day before SOI, the probability of delivering the Probe to its prescribed relay link envelope shall be ≥ 99.7%, insofar as ring particle hazards are concerned. 416-4 Environmental Hazards After Probe Delivery. For a minimum of one year following Probe Mission Completion (PMC), both Orbiter risk and the probability of mission redesign shall be controlled. For non-catastrophic environmental hazard events (those associated with the ring environment and the Titan atmosphere leading to temporary performance degradation), each of the above two risk factors shall be ≤ 5%. For catastrophic environmental hazard events (those leading to permanent loss of function), the risk factors shall each be ≤ 1%. 43213-2B Control of Activities Associated with a Geometric Event. The COS shall be able to time commands to control activities associated with closest approach for Saturn, Titan, and targeted icy satellite flybys with the following accuracies.

4-2

Target Timing Accuracy Titan and targeted icy satellites 3 sec (1 sigma) Saturn (for Titan inbound orbits) TBD sec (1 sigma) Saturn (all other orbits) 2 sec (1 sigma) 43214-4 Instrument Resource Allocation Violations. The COS shall not correct instrument resource allocation violations, except to allow replacement, if schedule permits, or to delete the violating observations from the sequence. 43214-5B Sequence Design Throughput Time. The COS shall require no longer than 10 weeks (goal 5 weeks) to design and implement four-week-duration sequence loads. 43224-1B Sufficient Navigation ∆V. The COS Navigation function shall ensure a probability of ≥0.95 of being able to correct for navigation flight path errors (stochastic plus bias-related for Earth swingby) through EOM. This requirement shall be met for a ∆V allocation that does not exceed 500 m/s (less 10 m/s for each Titan encounter fewer than 35 total encounters) for the bipropellant system, and that does not exceed 50 kg for the monopropellant system. 43224-2 Target-relative Pointing Prediction. The COS shall be capable of providing the following ephemeris-related 99% radial pointing prediction accuracies:

a) 2.2 mrad of the apparent direction of the Earth for RSS Ka-band occultation experiments. b) 2.4 mrad relative to Titan, icy satellites, up to 10 orbiting "rocks", and features in Titan's and Saturn's atmospheres for CIRS at > 30,000 km c) 3.1 mrad relative to Titan, icy satellites, up to 10 orbiting "rocks", and features in Titan's and Saturn's atmospheres for ISS, VIMS, UVIS at > 20,000 km.

43224-4 Target-Relative Pointing Reconstruction. The COS shall be able to reconstruct target-relative pointing at ranges ≥ 10,000 km to ≤ 2.0 mrad, 95% radial, in cases where support imaging ("C-smithing") is not utilized. 43224-6D Radar Target-Relative Pointing Control. The COS shall provide a total pointing control of the Ku-Band electrical boresight, relative to the target's center of mass, 95% radial, with spacecraft inertial pointing accuracy capability as specified in 4213-9D, as follows:

a) In the scanning radiometry mode: 17 mrad. This requirements refers to Titan, Saturn and the other satellites. b) In the scanning altimetry mode (low resolution) at Titan at altitudes from ~ 25,000 km to ~ 10,000 km: 17 mrad. c) In the nadir pointing altimetry mode (high resolution) at Titan: 8 mrad at 10,000 km and 17 mrad at 4,000 km. d) In the imaging modes (low resolution and high resolution) at Titan at altitudes < ~4,000 km: 50 mrad. e) During radiometric calibrations: 3.5 mrad. f) During spotlight mode: no requirement

43225-1 Inertial Pointing Reconstruction. The COS shall reconstruct the history of the pointing of the instruments relative to inertial space to an accuracy of ≤ 1.1 mrad, 95% radial, for the narrow angle camera. 43225-2D Radar Target-Relative Pointing Reconstruction. The COS shall provide a total pointing reconstruction accuracy of the Ku-Band electrical boresight relative to the target's center of mass, 95% radial, of ≤ 1.7 mrad with spacecraft inertial pointing reconstruction accuracy capability as specified in 43228-1B Reconstruction of Time of a Geometric Event. The COS shall reconstruct the time of closest approach to Saturn, Titan, and targeted icy satellites with an accuracy of 300 msec (1 sigma). 4362-1 Anomaly Priority. Except for critical events (see 4422-1), the resolution of any major spacecraft-related anomaly shall take precedence over other activities.

5-1

5.0 MISSION PLANNING PROCEDURES 5.1 CONSTRAINT CHECK FOR SEQUENCE _____ PHASE ____________ON DATE_________ This procedure performs a end-to-end check of the mission-level activities and requirements, including DSN passes, navigation tracking and maneuver strategy to ensure that the basic sequence structure can safely support maneuvers and encounters. This procedure should be exercised at two stages: at SOP Implementation and SOP Update. The full textual procedure should be conducted near the beginning of each phase, and the Excel checklist should be filled out at the end. 5.2 How to Obtain Sequence Information and Reports You should be able to find the ap_downlink “text”, “nav”, “check”, SMT report and SPASS on the SP home page for the sequence. The SPASS is also available in CIMS. Be prepared to refer to the other, following documents available as follows. The MP home page: the Mission Plan and the CIRS/VIMS consumables page, and the latest tour events list; the “Procedures” folder: this document, the RSS DSN plan, the DSN weekly maintenance plan, and the Excel MP checklist template; at http://rapweb/Downtime.html: the DSN major downtimes schedule. Write down the sequence start and end time of the sequence from the Mission Plan. Also write down who the SP and SVT leads are for your sequence. 5.2.1 Navigation Review N1) Identify all maneuvers from the navigation events in CIMS (not the

DOWNLINK_PASS events with “OTP”). Refer to the DSN report or CIMS and ensure that for each maneuver, there is a primary and backup downlink pass that have consistent times, are at least 9 hours long, and are no more than a day apart. Verify that only one downlink pass is present for each maneuver (even for split-complex passes; SEQ-C18).

N2) Check that the primary contains the string “OTP” in the downlink pass name and the backup contains “OTB”. Check that the gap time, which is the first parameter of the downlink pass, is 01:22 for the primary pass only.

N3) Determine if there are any nontargeted flybys of any “rocks” less than 20,000 km (refer to John’s latest tour events timeline). With the latest trajectory, determine the actual flyby distance (e.g. with digit). Contact the navigation team to determine if there is any chance of hitting this body. N4) Examine the ap_downlink nav report for skipped days, i.e. days with no navigation tracking, or days with insufficient nav tracking (“NO”s). If two parts of a handover pass combine to 5:50, and each segment is 2 hours or longer, this is acceptable. N5) Inspect the balance of Madrid / Goldstone coverage. There should be on average 1 Madrid pass every 9 days. Also, there should be at least 4 passes between targeted encounters (for short orbits, fewer than 4 may be acceptable). N6) Check the OPNAV events or data volume to ensure that no more than 8 OPNAVs have been scheduled on any one day (SEQ-G2), and that the data volume is no greater than 8.7 Mbit per OPNAV (SEQ-C13).

5-2

N7) Identify all RSS events in the sequence and ensure that none impact nav tracking in a way that the ap_downlink nav report cannot illustrate (e.g. USO PIM). N8) Provide the nav team with a copy of the nav report whether or not there are any problems, and review any issues identified above. 5.2.2 Dust Crossing Review H1) Identify all dust hazards within the sequence from the tour events table or Dust Protection Plan (not from the sequence). These are NOT ring plane crossings. H2) For all hazards which require HGA to RAM pointing, ensure there is an MP event present that ends in _PRIME in CIMS. The event should start no later than 5 minutes before dust ingress and end no earlier than 5 minutes after egress (5 minutes is margin). H3) Refer to the SPASS and check that the orbiter is on HGA to RAM point for the entire duration of the crossing. (CDA may have negotiated slight offsets from this attitude for data collection with John Smith on a case by case basis.) H4) For all crossings (including HGA to RAM crossings), refer to the sequence to check that the main engine cover is closed before and opened after the crossing. Check that the cover is open during all primary or backup maneuver passes. 5.2.3 DSN Review D1) Examine the DSN pass lengths. If a significant number of passes are longer than 9 hours, find out why. In general, it is less burdensome to the DSN to schedule a 9 hour 70m pass than a 11 hour 34m pass (i.e. if we need the data volume, we should upgrade, not lengthen; TEL-C2, TEL-G5). D2) Study the messages in the “ap_downlink report check” report to discern where passes conflict with DSN weekly maintenance by more than 1-2 hours. Conflicts with 34m stations can be solved by hopping to another 34. Conflicts with 70m stations may be resolved by carrying over into the next segment, using a 70m on another day, moving the pass to use the 70 at another complex, using a 34m array, or using a 70 or 70/34 array outside of the maintenance period, but keeping a 34 from the main complex up the entire time (for tracking). Work with the SP lead or the TWT that owns the pass to determine a solution. D3) Look for handover passes. Consider changing these to one-complex passes if

possible (i.e. if they do not conflict with weekly maintenance). D4) Refer to the RAP home page (http://rapweb/Downtime.html) for major downtimes that have been approved. If any downtimes fall within your sequence, check to see if station requests conflict with the major downtimes, If so, work whatever data volume or other issues arise from that station being unavailable. D5) Net data margin should be 2% or greater at all times by the end of SOP, and 1% or greater by final uplink (SEQ-C2, DATA-C14). If the margins are too low, upgrade coverage as necessary to raise the margins to an acceptable level. D6) If there are any special playbacks planned during the sequence (e.g. for high-value data, as with SOI, Probe Relay, Ta), check that CDS has thoroughly reviewed the playback strategy and commanding and it has been or will be tested in ITL (DATA-C12, C13). D7) Check the Mission Plan for conjunctions during your sequence. Check the SPASS to ensure that the spacecraft is at Earth-point when SEP ≤ 3° (SEQ-G6). Check that there are no downlink passes when SEP ≤ 2° (SEQ-C15). However, there should still be daily DSN passes during the entire conjunction period.

5-3

D8) Check the SPASS or CIMS for prime radio science activities (i.e. occultations, gravity or mass events). Compare the DSN resources requested against those listed in the Radio Science DSN request document to ensure they are consistent. Ensure that telemetry will be off for occultations (i.e. no downlink pass; TEL-C15). Work any potential mismatches with an RSS representative. D9) Inspect the balance of 34m / 70m coverage. Over a sequence no more than 35%

of the passes should require a 70m station (RSS passes do not count). If the ratio is significantly more than 35%, understand why and determine if the ratio can be reduced easily while maintaining acceptable margins (TEL-C9).

D10) Check that the last four downlink passes in a sequence are marked “SEQ” (unless the last pass has a maneuver, in which case it is superceded by “OTP”). All but the last pass must be at least 9 hours long and be free of maneuvers. Look at the nav report to verify that uplink begins 10 minutes after the start of pass in each case. If not, there may be a transmit limit that reduces the uplink time – contact the SVT lead for your sequence to determine what impact that may have. D11) Check to ensure that no DSN passes are only for real-time commands (SEQ-C8). D12) Identify the first uplink pass and write down the epoch of the start of the pass. Contact the SVT lead for the sequence and/or Vickie Barlow. Check that the SSUP process is scheduled consistently with the uplink time. D13) Understand and work other errors identified by “ap_downlink report check” (TEL-C9, C10). 5.2.4 Wrap-up (end of phase) W1) Fill in the Excel MP and Nav checklists (Jim may do the Nav checklist for each sequence) and document any issues you have identified in the comment areas and in the SPLAT table. Send the worksheet electronically to the SP lead(s) for your sequence and review with them issues you have identified. W2) Find out what CIRS/VIMS consumables are used during the sequence, and ensure the CIRS/VIMS home page is up to date. Let Kim know if you make any changes in case she has to request a reassessment of the whole-tour usage.

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5.2 DSN PLAN FOR SEQUENCE _____ PHASE ____________ON DATE_________ This procedure reviews the DSN schedule for a sequence, updates it, and prepares the report to be sent to the DSN schedulers for final mid-range scheduling of the sequence. The output product is an electronic file containing all DSN requests, along with a spreadsheet of additional notes for the sequence. The schedule should be fully mature, and changes after this delivery should be discouraged. This procedure should be executed after SOP implementation, some weeks before Aftermarket begins, about 33 weeks before start of execution. The MP lead should work closely with the SP lead to ensure that the schedule is as accurate as possible. Be prepared to refer to the following documents available as follows. The SP sequence page: the SMT and DSN reports, and SPLAT; the MP home page: the Mission Plan; the “Procedures” folder: this document, the RSS DSN plan and the DSN weekly maintenance plan; at http://rapweb/Downtime.html: the DSN major downtimes schedule. Scheduling S1) At least two weeks before your DSN plan due date, contact the DSN scheduler and verify the actual due date for the DSN schedule. Depending on their schedule, and where the sequence lies, you may have more time than you think. Also, perhaps only the first few days of the sequence are required at first. S2) Contact the SP lead and make him/her aware of the DSN schedule date and that all DSN coverage issues need to be resolved. S3) Contact the RSS rep (Aseel) to make him/her aware when their inputs are due. 5.2.1 DSN Review D1) Review the SPLAT with the SP lead for any items that are related to DSN coverage. Decide on a course of action and implement these changes, either in CIMS, or in a temporary sequence file used to generate DSN requests. D2) Net data margin should be 2% or greater at all times by the end of SOP implementation, and 1% or greater by final uplink. If the margins are too low, upgrade coverage as necessary to raise the margins to an acceptable level. If margins seem unnecessarily high, consider – only if resources are ample – downgrading passes. Look especially for 70/34 arrays that could be downgraded to single-antenna passes to reduce risk. D3) Inspect the latest downtimes on http://rapweb/Downtime.html against your

notes from the previous sequence; check to ensure that no major downtimes have changed.

D4) Look for any passes in your sequence, or in the next sequence, that have a configuration that has not been used for a long time (3 months or more; e.g. Canberra, array). Consider adding one or more shadow passes in the weeks before the event to ensure DSN proficiency. D5) Work any other DSN-related warnings or errors produced by ap_downlink. 5.2.2 RADIO SCIENCE REQUESTS R1) One week before the DSN plan is due, obtain the RSS requests. Make sure they

are in seg format. Run “ap_downlink report check” on the requests to make sure they are formatted correctly and there are no glaring errors.

R2) Review the requests and ensure they are consistent with the RSS DSN scheduling guidelines (at end of procedures). Understand what each request is for.

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R3) If any RSS activities are changed and affect navigation tracking, contact the Nav team to ensure that the change is acceptable.

R4) Add the passes to the sequence via “ap_downlink ingest paste”. Produce Output Report and Publish O1) Run “ap_downlink report faster” on the sequence to generate the raw data file. O2) Inspect the configuration codes in the report. Look for zeros that need fixing;

review RSS passes with an RSS team member to ensure the codes are correct. Make sure RSS ORT passes are listed as “best efforts only” and only the primary passes are requested (no “_b” passes).

O3) Create a notes worksheet in excel from the DSN PLAN template. Use the SMT report to add notes appropriate to data volume margins. Determine which 70m passes are crucial for science return vs. those that could fall a day earlier or later.

O4) Review the DSN passes with the navigation team and determine which maneuvers are especially large, time-critical, or compromised. Make notes in the spreadsheet as appropriate. Determine if any passes are especially critical for tracking and also make notes as appropriate.

O5) Finish off the notes for each pass and review the spreadsheet with the SP lead. O6) Publish the raw data file and spreadsheet to the DSN scheduler, SPVT lead, and the RSS team member if radio activities are present. Review the products to ensure they understand their meaning. Send a full seg file to the SPVT lead so they may bring CIMS up to date.

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5.3 DSN INGESTION FOR SEQUENCE _____ PHASE ____________ON DATE_________ This procedure obtains the official, fully negotiated DSN schedule for a sequence, and determines the impacts of any changes on the sequence. This procedure should be executed about one week before the start of SOP Update. The MP lead should work closely with the SP lead to understand any impacts to the sequence. 5.3.1 DSN Ingestion D1) Check the DOM to see if a DSN file has been posted by the schedulers; if not, contact the schedulers and request one for the sequence. D2) Review the delivered passes versus the requested schedule and note all deviations. D3) If deviations could cause reductions in data playback, ask the SP lead to ingest

the new schedule via “ap_downlink ingest update”, hand-edit the downlink passes as needed, recomputed the data rates via “ap_downlink recomputed downlink”, and rerun SMT to determine the impact. You can perform this instead depending on the relative workload and personalities of you and the SP lead.

D4) If the new schedule will cause data loss, and the SP lead agrees that the schedule should be upgraded, contact the DSN scheduler to try to renegotiate the pass(es) in question.

D5) Contact an RSS team representative if any of their passes have changed.

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5.3.2 RSS DSN Scheduling guidelines

• Definitions: RSS science passes = occultations and gravity passes (including Nicole’s new Ka-band gravity requests)

- non-science includes ORTs, engineering passes, boresight cals, etc. everything else

• RSS will submit complete sets of requests per sequence to MP by one week before MP's submission to the schedulers

- any activities that affect data playback should have been fully worked with SP

- assumes MP provides accurate submission schedule, and accurate playback schedule is available from CIMS

• RSS science passes are to be scheduled to the fullest ability of MP/DSN

- changes shall be submitted and worked whenever they are discovered

- changes after submission to schedulers are discouraged, but will be accepted

• Non-science passes are to be scheduled on a best-efforts basis by MP/DSN

- no changes will be entertained after submission to the schedulers (except reductions, deletions and configuration details which do not affect playback, nav tracking or start/stop times)

- shall not overlap DSN weekly maintenance (up to 1 hour conflicts are OK)

- no risk to boresight cals and USO tests as they lie in existing playback passes

• One or two ORTs, per RSS science activity are to be requested

- if the DSN is performing well after the first few months of RSS science, future ORTs should be reduced/released

• One or two of new Ka gravity supports per sequence, on average, are to be requested

• DSN requests are submitted to the schedulers only by Mission Planning up to the end of SOP Update

- configuration details which do not affect playback, nav tracking or start/stop times can be worked directly with the schedulers

• RSS reported ~ 100+ ORT passes and ~ 40 new Ka gravity support for the tour. If these numbers should be exceeded, these guidelines will be reevaluated.

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CIMS activity decoder ring (refer to CIMS activity types for true reference) OBSERVATION_PERIOD

SP_RRRNA_DDDOBSNNN###_NA where RRR = rev number of start epoch, DDD = complex and antenna of following downlink pass (e.g. G34), NNN = notes field

DOWNLINK_PASS SP_RRREA_DDDDDDNNN###_PRIME where RRR = rev number of start epoch, DDDDDD = antenna and complex (e.g. G34BWG, M70MET, G70ARR, C34HEF), NNN = notes field (NON for no notes, or SEQ for sequence boundary pass, OTP for primary OTM pass, OTB for backup OTM pass, CLS for MEA cover closes, OPN for MEA cover opens, RSS for radio science pass, etc.), ### = DOY of start epoch. parameters: gap time in hh:mm:ss (time off-Earth for OTMs), DSN lockup time at start of pass in seconds where SSR playback pauses, data rate change time in mid-pass in seconds where SSR playback pauses, then 6 parameters which determine the SSR playback partition order, then up to 5 pairs of modes and epochs which define the telemetry rates during the pass. default: 00:00:00, 300, 60, SSRAP5, SSRBP5, SSRAP4, SSRBP4, SSRNULL, SSRNULL, [modes & epochs] default for OTM primary: 00:00:00, 300, 60, SSRAP5, SSRBP5, SSRAP4, SSRBP4, SSRNULL, SSRNULL, [modes & epochs]

DSN_PASS SP_RRRNA_DDDDDDNNN###_NA parameters: DSS ID code, precal time, postcal time, DSN label, DSN config code, ignore, ignore, ignore, ignore, ignore, ignore, ignore. default: [DSS ID}, 3600, 900, “TKG PASS”, “N00X”, “”, “”, “”, “”, “”, “”, 0

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6.0 SATURN SYSTEM MYTHOLOGY Until the middle of the nineteenth century, the satellites of Saturn bore numerical designations only. In 1847, John Herschel proposed that the satellites be named after Saturn’s ‘brothers and sisters, the Titans and Titanesses.’ Titans and Titanesses were brothers and sisters not of Saturn, but of Kronos, Saturn’s Greek counterpart. Hesiod, Homer’s younger contemporary, gives us the family history of the tribe of the Titans. Using some of Hesiod’s own words, here is an outline of the story. In the beginning, there was Chaos, and after him came Gaia (the Earth). Gaia’s first-born was Ouranos (the Sky), the ‘one who matched her every dimension.’ Gaia ‘lay with Ouranos, and bore him Okeanos, Koios, Krios, Hyperion, Iapetus, Theia, Rhea, Themis, Mnemosyne, Phoebe, and Tethys.’ Her youngest-born was the ‘devious-devising Kronos, most terrible of her children.’ Hesiod assigned the name Titans to the enumerated twelve children. Kronos, upon urging from Gaia, attacked his father Ouranos with the sickle she provided. Following the attack, Kronos became the supreme ruler of the world. Kronos took Rhea as his wife. She bore him five children. Remembering the fate of his father, Kronos swallowed each child right after it was born. Zeus was the sixth-born. To save the baby, Rhea tricked her husband into swallowing a stone instead. At some later point, Kronos was made to regurgitate the stone and the five children he swallowed. (Hesiod does not say when and how.) With his siblings’ help, Zeus initiated a rebellion against Kronos and the Titans. The Titans suffered a defeat in a terrible battle during which ‘all earth was boiling.’ Zeus imprisoned the defeated gods in Tartaros, ‘a moldy place, at the uttermost edges of the monstrous earth’ and, along with his Olympian allies, assumed the lordship over the world. Although Kronos’ rule passed, it was long remembered as the Golden Age of mankind, when people ‘lived as if they were gods, their hearts free from all sorrow, without hard work or pain.’ Saturn, a Latin deity perhaps associated with farming, received some of the attributes of Kronos. The Romans adopted also the legend of the golden age. In their version, Saturn was the king of Italy in the long forgotten days when, as in the age of Kronos, life was all play and no work. John Herschel gave the name Titan to the moon of Saturn which was discovered first and which happened to be the largest. The other four moons discovered in the seventeenth century he named Iapetus, Rhea, Dione, and Tethys. The minute inner satellites first observed by his father, John Herschel chose to name Enceladus and Mimas. Two satellites found in the nineteenth century received the names of Hyperion and Phoebe. The remaining satellites known at present were discovered in the twentieth century. They include Janus, Pan, Atlas, Prometheus, Pandora, Epimetheus, Telesto, Kalypso, and Helene. Of the eighteen named satellites, only Iapetus, Rhea, Tethys, Hyperion, and Phoebe bear the names of Saturn’s ‘brothers and sisters, the Titans and Titanesses.’ A brief description of the meaning of the satellites’ names is given below. The satellites are listed in the order of the increasing distance from Saturn. Pan (pan) Half-goat, half-human, the Arcadian Pan was worshipped as the patron of shepherds and as the personification of nature. Atlas (AT-less) Son of Iapetus. After the defeat of the Titans, Zeus ordered Atlas, ‘at earth’s uttermost places, near the sweet-singing Hesperides’ to uphold the vault of the sky. Hesiod refers probably to the Pillars of Hercules, the edge of the world known to the ancient Greeks Prometheus (pro-MEE-thee-us)

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Hesiod presents Prometheus, son of Iapetus, as an immortal who sided with the mortals and as a prankster who liked to annoy his cousin Zeus. The ultimate annoyance was stealing ‘the far-seen glory of weariless fire’ and giving it to mankind. For this, Zeus fastened Prometheus to a mountain in the Caucasus, and he let loose on hin ‘the wing-spread eagle, and it was feeding on Prometheus’ imperishable liver, which by night would grow back to size from which the spread-winged bird had eaten in the daytime.’ Pandora (pan-DOR-ah) The world’s first woman. Creating Pandora was the punishment Zeus meted out to mankind for the Prometheus’ brazen acts of disobedience. Pandora arrived equipped with a jar that contained all the misfortunes, curses and plagues. Once the lid was lifted, the evil asserted itself in the world. ‘Hope was the only spirit that stayed there, in the unbreakable closure of the jar, this was the will of the cloud-gathering Zeus.’ Epimetheus (epp-ee-MEE-thee-us) Son of Iapetus, brother of Prometheus, husband of Pandora. Pictured as weak-minded, he is the one who lifted the lid on the Pandora’d jar. Janus (JANE-us) An exalted Roman god, a figure of great antiquity and obscure origin. Always represented as having two faces, one looking forwards, the other backwards, Janus presided over the past, present, and future, over gates, doorways, entrances, and beginnings in general, and over war and peace. At every sacrifice, in every prayer, he was the first god invoked, taking precedence before Jupiter. When war was declared, the portals to the sanctuary of Janus on the Forum were opened. They were shut again on the declaration of peace. During the entire history of Rome, this happened on a handful of occasions only. As the most ancient of kings, Janus is supposed to have given the exiled Kronos a warm welcome in Italy, and to have offered him a share of the royal duties. Mimas (MY-muss) One of the Giants, children of Gaia born of the blood of Ouranos. Methone (me-thoe'-nee) Another one of the Alkyonides, a daughter of Alkyoneus. Pallene (pa-lee'-nee) One of the Alkyonides, the seven beautiful daughters of the Giant Alkyoneus. When their father was slain by Heracles, they threw themselves into the sea, and were transformed into halcyons (kingfishers) by Amphitrite. Enceladus (n-SELL-uh-duss) One of the Giants, children of Gaia born of the blood of Ouranos. Giants, the last race of Hesiod’s monsters, were beings of enormous size and invincible strength. Later depictions show them as having hideous faces, bristling beards, hanging hair, skins of wild animals for garments, tree trunks for weapons, and twin serpents for legs. Tethys (TEE-thiss) The youngest of Titanesses, Tethys married her brother Okeanos, and bore him three thousand Okeanides, the ‘light-stepping’ sea-nymphs, and ‘as many Rivers, the murmurously running sons.’ Telesto (tell-ESS-toe) A daughter of Tethys and Okeanos, an Okeanide.

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Calypso (kal-IP-so) A daughter of Tethys and Okeanos, an Okeanide. For Homer and other authors, she is a daughter of Atlas. In the course of the Odysseus’ tortuous return to Ithaca, his ship ran aground on the fabled island of Ogygia, the home of the lonely Kalypso. Odysseus kept her company for seven years, after which he departed ‘on a jointed raft.’ Dione (die-OH-nee) Dione presents a problem in the genealogy of the Greek gods. To Hesiod, she is a daughter of Tethys and Okeanos, and thus an Okeanide. She is mentioned in a number of other incarnations; for instance as a daughter of Ouranos and Gaia (this would make her a Titaness), or as a daughter of Kronos, or of Atlas. In some localities she was also worshipped as the wife of Zeus (instead of Hera). Helene (heh-LEEN) The divinely beautiful wife of Menelaos, the king of Sparta, Helen (Helene) was abducted by Paris, the son of Priam, the king of Troy. Over Helen the Greeks fought the all-destructive Trojan War. Polydeuces (pol'-i-dew'-seez) Another name for Pollux, one of the twin sons of Leda who was impregnated by Zeus disguised as a swan. He and his brother Castor are known as the Gemini, Latin for twins. Polydeuces was known as a boxer and won many Olympic events. He was also one of Jason's Argonauts on Jason's quest for the golden fleece. During the quest, Polydueces proved himself by killing an evil king and allowing the quest to continue Rhea (ree-uh) A Titaness, married to her brother Kronos. Titan (TIE-tan) Not a single deity, but a generic name for the children of Ouranos and Gaia. Hyperion (high-PEER-ee-on) The fourth-born Titan, Hyperion took for a wife his sister Theia. ‘Theia brought forth great Helios and shining Selene, the Sun and Moon, and Eos the Dawn who lights all earthly creatures and the immortal gods who hold the white heaven.’ Solar and lunar deities, dominant in the affairs of other ancient civilizations, played a minor part in the religious life of ancient Greels. Iapetus (eye-AP-eh-tuss) Iapetus, a Titan, took Klymene, his niece, the ‘light-stepping daughter of Okeanos, to be his wife.’ Their sons were Atlas, Prometheus, and Epimetheus. Phoebe (FEE-bee) Phoebe, a Titanness, bore to her brother Koios the goddess Leto, ‘the gentlest of all who are on Olympus. Leto, who had lain in the arms of Zeus, bore Apollo and Artemis, children more delightful than all the other Olympians.’ In later antiquity, Phoebe was honored as the goddess of the Moon. L. Roth, 8 Aug 96

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CASSINI AND HUYGENS, THE SCIENTISTS The seventeenth century appears to us as an epoch of gallant manners, lavish costumes, comical wigs, and incomprehensible wars -- all without much relevance to the present. Yet the seventeenth century, despite its remoteness and extravagance, was a time of towering significance. Modern science was born in the seventeenth century and it was in the seventeenth century that mankind's view of the cosmos underwent the most drastic change since the beginning of recorded history. Giovanni Domenico Cassini (1625-1712) and Christiaan Huygens (1629-1695) were two of the learned men of that tumultuous period who, by showing to the incredulous public the new wonders of the sky, helped to usher in the age of science and alter our perception of the world.

Giovanni Domenico Cassini Christiaan Huygens .

Both Cassini and Huygens came from well-to-do families -- one in Italy, the other in Holland, both received the best education available, both were extraordinarily industrious, and both did most of their lives' work in Paris, as members of the Royal Academy of Sciences established in 1666 by Louis XIV, the fabled Sun King. Huygens earned the invitation to join the Academy and the associated Royal Observatory as a result of having discovered Titan (the first of a number of moons of Saturn to be discovered subsequently) and the rings of Saturn. Before joining the Academy, Huygens also invented the pendulum clock, the first accurate timekeeping device. While still in Italy, Cassini gained fame by having measured the rotation periods of Jupiter and Mars, and by virtue of his extensive observations of the motions of the moons of Jupiter. (The moons of Jupiter were discovered by Galileo some fifty years earlier.) At Paris, Cassini extended his meticulously precise observations to Saturn, discovering four more moons -- Iapetus, Rhea, Dione, and Tethys, and also discovering a gap in the rings of Saturn, later named the Cassini Division. Towards the end of his life, Huygens returned to Holland where he continued to do pioneering work in mechanics and optics. Cassini stayed at

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the Paris Observatory where, in addition to conducting regular astronomical observations, he led the development of the new arts of geodesy and map-making.

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CASSINI PROJECT DOCUMENT CHANGE NOTICE

TITLE: Changes to the Cassini Mission Plan DOCUMENT TITLE: Cassini Mission Plan, PD 699-100, Rev. O, change 1 JPL D-NUMBER: JPL D-5564, Rev. O, chg 1

DOCUMENT CHANGE ID: Revision O, Chg1 PAGE 1 OF 1 DATE: 2005 August 8

DESCRIPTION OF CHANGE: This revision documents changes since revision O. All changes based on the latest knowledge of mission activities and spacecraft capabilities have been documented. Approved ECRs since the previous release have been incorporated (although approved ECRs are effective as soon as they are approved). In addition, the MP procedures in Section 5 have been updated as well as the Mythology section to include three new moons: Pallene, Methone, and Polydeuces.

DISTRIBUTION Document Distribution List:

list maintained by Mission Planning

APPROVED BY:

2005 August 8 . David Seal, Mission Planning Lead Date Custodian: Jim Frautnick

cassini mission plan (pdf) - caps

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