University of Arizona Student Satellite Project

“UASat”Spring 2000 Formal Review

April 27, 2000

Purpose of Spring 2000 ReviewPurpose of Spring 2000 Review• End of Semester Review of SSPEnd of Semester Review of SSP

• Preparation for UASat Preliminary Design Preparation for UASat Preliminary Design Review (PDR)Review (PDR)– Gathering Team-Level Information Gathering Team-Level Information – Provide System-Level OverviewProvide System-Level Overview– Seek Advice and GuidanceSeek Advice and Guidance

Presentation SchedulePresentation Schedule• 5:00- Project Manager Overview & Introduction5:00- Project Manager Overview & Introduction

• 5:20- Science5:20- Science

• 5:50- Laser Communications5:50- Laser Communications

• 6:10- Guidance, Navigation & Control6:10- Guidance, Navigation & Control

• 6:30- Break6:30- Break

• 6:40- Systems Integration6:40- Systems Integration

• 7:00- Mechanical, Structures & Analysis7:00- Mechanical, Structures & Analysis

• 7:20- Data & Command Handling7:20- Data & Command Handling

• 7:40- Power Generation & Distribution7:40- Power Generation & Distribution

Purpose of SSPPurpose of SSP

1. 1. A hands-on experience through team work on a complex A hands-on experience through team work on a complex system with an objectivesystem with an objective

2. 2. A needed channel for many students to gain self-A needed channel for many students to gain self-confidence & employable skillsconfidence & employable skills

3. 3. An example of intercollegiate, inter-departmental, and An example of intercollegiate, inter-departmental, and interdisciplinary collaborationinterdisciplinary collaboration

4. 4. An avenue to enhance beneficial interactions among An avenue to enhance beneficial interactions among university and communityuniversity and community

5. 5. A test-bed for innovative ideas in a wide variety of areasA test-bed for innovative ideas in a wide variety of areas

UASat MissionUASat Mission• Sprite & Lightning Sprite & Lightning

DetectionDetection• Photometry of Bright Photometry of Bright

StarsStars• Laser Communication Laser Communication

ExperimentExperiment

Purpose of SSPPurpose of SSP

1. 1. A hands-on experience through team work on a complex A hands-on experience through team work on a complex system with an objectivesystem with an objective

2. 2. A needed channel for many students to gain self-A needed channel for many students to gain self-confidence & employable skillsconfidence & employable skills

3. 3. An example of intercollegiate, inter-departmental, and An example of intercollegiate, inter-departmental, and interdisciplinary collaborationinterdisciplinary collaboration

4. 4. An avenue to enhance beneficial interactions among An avenue to enhance beneficial interactions among university and communityuniversity and community

5. 5. A test-bed for innovative ideas in a wide variety of areasA test-bed for innovative ideas in a wide variety of areas

STUDENT DISTRIBUTION CHART as of December 20, 1999

SummaryTotal Percentage

Unspecified Fresh Soph J unior Senior Grad (by major) (of total)

Aerospace Engineering 1.0 2.0 - 2.0 3.0 - 8.0 11.3

Astronomy - 6.5 0.5 1.0 1.0 - 9.0 12.7

Atmospheric Sciences - 2.0 - - - - 2.0 2.8

Biomedical Engineering - - - - - 1.0 1.0 1.4

Chemistry - - - - 1.0 - 1.0 1.4

Computer Engineering - - - 2.0 1.0 - 3.0 4.2

Computer Science - 0.5 - 1.5 2.0 - 4.0 5.6

Electrical Engineering - - 2.0 1.0 2.0 - 5.0 7.0

Engineering Physics - 2.0 1.0 - - - 3.0 4.2

Materials Science and Engineering - - - - 1.0 - 1.0 1.4

Mathematics - - - 0.5 - - 0.5 0.7

Mechanical Engineering - 1.0 - 3.0 1.0 2.0 7.0 9.9

Media Arts - 1.0 - - - - 1.0 1.4

Nondegree - - - - - 1.0 1.0 1.4

Optical Engineering 1.0 - - 1.0 3.0 1.0 6.0 8.5

Physics - 7.0 0.5 1.0 1.0 - 9.5 13.4

Systems and Industrial Engineering - - - - - 1.0 1.0 1.4

Unspecified 5.0 2.0 - - 1.0 8.0 11.3

Total (by class standing) 7.0 24.0 4.0 13.0 17.0 6.0 71.0 studentsPercentage (of total) 9.9 33.8 5.6 18.3 23.9 8.5 active in SSP

Purpose of SSPPurpose of SSP

1. 1. A hands-on experience through team work on a complex A hands-on experience through team work on a complex system with an objectivesystem with an objective

2. 2. A needed channel for many students to gain self-A needed channel for many students to gain self-confidence & employable skillsconfidence & employable skills

3. 3. An example of intercollegiate, inter-departmental, and An example of intercollegiate, inter-departmental, and interdisciplinary collaborationinterdisciplinary collaboration

4. 4. An avenue to enhance beneficial interactions among An avenue to enhance beneficial interactions among university and communityuniversity and community

5. 5. A test-bed for innovative ideas in a wide variety of areasA test-bed for innovative ideas in a wide variety of areas

UA

NASA NSF

Local Community

Industry

SSP

SSP needs the support from the four vertices: UA, Local Community, Industry, & Gov’t

KCH21.VI.1998

Human resourcesSpace & facilities Operational SupportSpaceGrant

HES launch

Curriculum development

Scholarships, Mentorships, Donations

Internship.Components Sub-systemsTechnical expertiseTesting facilities

Criteria for SuccessCriteria for Success

• Minimum CriteriaMinimum Criteria– Continuous flow of graduates with experience.Continuous flow of graduates with experience.

• Ultimate accomplishmentUltimate accomplishment– Delivery of UASat for NASA launch and Delivery of UASat for NASA launch and

successful operation in flight, followed by successful operation in flight, followed by scientific and technological return.scientific and technological return.

ManagementManagement• Project Manager- Jon Alberding, BMEProject Manager- Jon Alberding, BME

• Recruiting, Fundraising, Resources, Administration, Recruiting, Fundraising, Resources, Administration, Systems Integration & Intra-Team CommunicationSystems Integration & Intra-Team Communication

• Project Assistant- Ether Adnan, MISProject Assistant- Ether Adnan, MIS• Project Communication, Administration, Account Project Communication, Administration, Account

ManagementManagement

• System Engineer- Christiano Adabi, SIESystem Engineer- Christiano Adabi, SIE• System DocumentationSystem Documentation

• InterfacesInterfaces

• BudgetsBudgets

• Design DatabaseDesign Database

Management (Cont.)Management (Cont.)• Project MentorsProject Mentors

– Dr. K. C. Hsieh, PhysicsDr. K. C. Hsieh, Physics– Dr. Hal Tharp, ECE (sabbatical)Dr. Hal Tharp, ECE (sabbatical)

• SI MentorSI Mentor– Dr. Terry Bahill, SIEDr. Terry Bahill, SIE

• Administrative MentorAdministrative Mentor– Susan Brew, SpaceGrantSusan Brew, SpaceGrant

SSP org chart as of 26 April 2000

LeaderW. Null

LeaderB. Shucker

LeaderK. Chugh

Project ManagerJ. Alberd ing

Evaluation & Selection PanelR. Lorenz & members

Admin. AssistantEther Adnan

Project MentorK. C. Hsieh

Admin. MentorS. Brew

Systems Engr.C. Abadi

Systems MentorT. Bahill

Mission Advisory PoolL.Broadfoot & members

LeaderA. Valenzuela

LeaderD. Sing

LeaderM. Hay

MSATeam

PGDTeam

TTCTeam

GNCTeam

DCHTeam

LCSTeam

SC2Team

SC1Team

LeaderD. Klea.

LeaderW. Chee

MentorU. Fink

MentorW. Wing

MentorJ. D.

Carothers

MentorE. Fasse

MentorL. Schooley

MentorA. Witulski

MentorW. Chen

MentorC.Weidman

Current UASat ScheduleCurrent UASat Schedule• Requirements Review (Completed 8/18/98)Requirements Review (Completed 8/18/98)

• Preliminary Design Review (Late ‘00, Preliminary Design Review (Late ‘00, Early ‘01)Early ‘01)

• Critical Design Review (Spring ‘02)Critical Design Review (Spring ‘02)

• Mission Readiness Review (Fall ‘03)Mission Readiness Review (Fall ‘03)

• Delivery to NASA (Spring ‘04)Delivery to NASA (Spring ‘04)

UASat PDR PreparationUASat PDR Preparation• Program Management Program Management

group works with Teamsgroup works with Teams

• Program Management Program Management group forms Preliminary group forms Preliminary Gantt chartGantt chart

• Negotiate Final Schedule Negotiate Final Schedule (TL, Mentor, PM, SE)(TL, Mentor, PM, SE)

• Teams review IMAGE Teams review IMAGE PDRPDR

• Teams review PDR Teams review PDR outlined by System outlined by System Engineer/Project ManagerEngineer/Project Manager

• Negotiate Final Schedule Negotiate Final Schedule (TL, Mentor, PM, SE)(TL, Mentor, PM, SE)

Management-Level PDR Management-Level PDR RequirementsRequirements

• Risk ManagementRisk Management– Schedule ControlSchedule Control

• No real means of controlNo real means of control– Need for Risk Mitigation StrategyNeed for Risk Mitigation Strategy

• Technical Oversight Group Technical Oversight Group • Better Communication about Schedule Slip Better Communication about Schedule Slip • Quantitative Evaluation of Schedule Quantitative Evaluation of Schedule

Performance Performance • What To Do If Slippage Occurs?What To Do If Slippage Occurs?

Management-Level PDR Requirements Management-Level PDR Requirements • Cost ControlCost Control

– Inherent ControlsInherent Controls

• Student ProjectStudent Project• Students Build Some Components/SubsystemsStudents Build Some Components/Subsystems

– Knowledge of Actual Costs for Bought ItemsKnowledge of Actual Costs for Bought Items

– Cost Tracking Strategy & Plan for When Reserves UtilizedCost Tracking Strategy & Plan for When Reserves Utilized

• DescopingDescoping– Decision Tree, Options & ConsequencesDecision Tree, Options & Consequences

• Performance Assurance Implementation Plan (PAIP) Performance Assurance Implementation Plan (PAIP)

Questions on ManagementQuestions on Management• How to retain Lower-Division Students?How to retain Lower-Division Students?

• How to have a Risk Mitigation Strategy How to have a Risk Mitigation Strategy with limited resources & maintaining with limited resources & maintaining Educational Requirements?Educational Requirements?

• How to acquire needed resources?How to acquire needed resources?

• How to formulate a plan to cost-effectively How to formulate a plan to cost-effectively acquire needed components?acquire needed components?

• How to implement a PAIP?How to implement a PAIP?

How to Contact SSPHow to Contact SSP

• SSP HQSSP HQ– Physics and Atmospheric Sciences, Room 569Physics and Atmospheric Sciences, Room 569

• PhonePhone– (520) 621-2574(520) 621-2574

• Email:Email:– ssp-admin@uasat.arizona.edussp-admin@uasat.arizona.edu

• World Wide WebWorld Wide Web– http://uasat.arizona.eduhttp://uasat.arizona.edu

“The Student Satellite Project at the University of Arizona is the best evidence I have discovered anywhere of the creative initiative of Americans committed to the Space Program, which has been an important part of my life for forty years.

When I joined JPL as a young engineer in 1958, soon after the launch of America's first satellite, the adventure of space exploration had captured the imagination of young people all over America, and there was no bureaucracy to slow us down. The new NASA in 1998 recognizes the importance of youthful energy and innovative capacity, and welcomes such initiatives as the SSP. This is a very exciting development, heralding as new day for both NASA and our students. They have done their part, with the encouragement of the University of Arizona. Now it is time for the community to step up to the challenge of demonstrating that all of Arizona stands behind this incredible initiative of the young men and women of the SSP who are reaching beyond the skies.”

Peter Likins, June 17, 1998.

Presentation SchedulePresentation Schedule• 5:00- Project Manager Overview & Introduction5:00- Project Manager Overview & Introduction

• 5:20- Science5:20- Science

• 5:50- Laser Communications5:50- Laser Communications

• 6:10- Guidance, Navigation & Control6:10- Guidance, Navigation & Control

• 6:30- Break6:30- Break

• 6:40- Systems Integration6:40- Systems Integration

• 7:00- Mechanical, Structures & Analysis7:00- Mechanical, Structures & Analysis

• 7:20- Data & Command Handling7:20- Data & Command Handling

• 7:40- Power Generation & Distribution7:40- Power Generation & Distribution

UASat: Guidance, Navigation, UASat: Guidance, Navigation, and Controlsand Controls

Presented by Brian Shucker and Martin LeblPresented by Brian Shucker and Martin Lebl

http://uasat.arizona.edu/gnchttp://uasat.arizona.edu/gnc

GNC Team MembersGNC Team MembersTeam MembersTeam Members::• Greg Chatel (AME)Greg Chatel (AME)• Barry Goeree (AME)Barry Goeree (AME)• Andreas Ioannides (Phys)Andreas Ioannides (Phys)• Gregg Radtke (ME)Gregg Radtke (ME)

Team MentorTeam Mentor::• Dr. Fasse (AME)Dr. Fasse (AME)

• Marissa Herron (AME)Marissa Herron (AME)• Martin Lebl (CSc)Martin Lebl (CSc)• Brian Shucker (CSc/Math)Brian Shucker (CSc/Math)• Roberto Furfaro (AME)Roberto Furfaro (AME)

GNC Subsystem RequirementsGNC Subsystem Requirements• Science and Technical ObjectivesScience and Technical Objectives

– Lightning and Sprite observationLightning and Sprite observation• requires attitude knowledge with respect to Earthrequires attitude knowledge with respect to Earth• requires horizon pointingrequires horizon pointing

– Stellar PhotometryStellar Photometry• requires attitude knowledge with respect to the starsrequires attitude knowledge with respect to the stars• requires inertial pointingrequires inertial pointing

– Laser Communication SystemLaser Communication System• requires attitude knowledge with respect to Earthrequires attitude knowledge with respect to Earth• requires ability to perform groundstation tracking slew maneuverrequires ability to perform groundstation tracking slew maneuver

– Power GenerationPower Generation• requires attitude knowledge with respect to Sunrequires attitude knowledge with respect to Sun• requires inertial pointingrequires inertial pointing

• Three axis control requiredThree axis control required

SensorsSensors• Sensors UsedSensors Used

– Attitude Sensors: Attitude Sensors: Magnetometer, Coarse Sun Magnetometer, Coarse Sun SensorSensor

– Spatial Sensor: GPSSpatial Sensor: GPS– Rate Sensor: Integrating Rate Rate Sensor: Integrating Rate

GyrosGyros

• Sensor Measurement RatesSensor Measurement Rates– Power vs. Accuracy Trade-OffPower vs. Accuracy Trade-Off– Optimization Technique TBD Optimization Technique TBD

i.c.

kt

ut

t

k

i.c.

GainUpdate

StateUpdate

CovarianceUpdate

StateModel

ut

CovarianceModel

P

x kx

kP

kP ( )

kx ( )

kKkx ( )

kx ( )

kx ( )

kP ( )

kP ( )

z

kP ( )

kx ( )

Extended Kalman Filter Block Diagram-- Discrete Measurement Updates-- Continuous Dynamic Propagation Models

In from instruments

Out to controller

The Kalman FilterThe Kalman Filter

• State Variable: State Variable: • Measurement UpdatesMeasurement Updates

– Gain Matrix:Gain Matrix:

– State Update:State Update:

– Covariance Update:Covariance Update:

• Dynamic Propagation Between MeasurementsDynamic Propagation Between Measurements– Data from rate gyros will be numerically integratedData from rate gyros will be numerically integrated

– Equations of motion are excluded to simplify the analysisEquations of motion are excluded to simplify the analysis

))](ˆ([)(ˆ)(ˆ kkkkk xhzKxx

)(][)( kkkk PHKIP

])([)( kTkkk

Tkkk RHPHHPK

MagnetometerMagnetometer• Advantages:Advantages:

– Can be used throughout orbit (sunside and Can be used throughout orbit (sunside and darkside)darkside)

– Low powerLow power– Relatively affordable sensorRelatively affordable sensor

• Disadvantages:Disadvantages:– Cannot be used with the magneto torquers onCannot be used with the magneto torquers on– Only so much precision can be achieved using Only so much precision can be achieved using

itit

GPS board – Space RatedGPS board – Space Rated• Space rated boardSpace rated board

– Advantages: Advantages: • Proven Heritage DesignProven Heritage Design• Radiation HardenedRadiation Hardened

– Disadvantages: Disadvantages: • ExpensiveExpensive

GPS board -- TerrestialGPS board -- Terrestial• Terrestial boardTerrestial board

– Advantages: Advantages: • Relatively InexpensiveRelatively Inexpensive

– Disadvantages: Disadvantages: • Needs modification to the firmware by Needs modification to the firmware by

manufacturermanufacturer• May need Radiation shielding depending on May need Radiation shielding depending on

where it is mountedwhere it is mounted• Obviously still non-heritage design (only Obviously still non-heritage design (only

flew on ASUSAT, but never been turned on flew on ASUSAT, but never been turned on before ASUSAT expired.)before ASUSAT expired.)

Coarse Sun SensorCoarse Sun Sensor• Sensor implemented using the solar panels, Sensor implemented using the solar panels,

and additional photo diodes to give and additional photo diodes to give complete coverage.complete coverage.

• Only a course sensor for the power Only a course sensor for the power generation modegeneration mode

Coarse Sun SensorCoarse Sun Sensor• Advantages:Advantages:

– Inexpensive designInexpensive design– Very low powerVery low power

• Disadvantages:Disadvantages:– Only works on the sun sideOnly works on the sun side– Only useful for determining the sun vector for Only useful for determining the sun vector for

power generationpower generation

Current StatusCurrent Status

• TheoryTheory– Kalman Filtering is understoodKalman Filtering is understood

– Main reference: Lefferts, Markley and Shuster (1982) Main reference: Lefferts, Markley and Shuster (1982)

• Sensor models are not completeSensor models are not complete• Matlab CodeMatlab Code

– Most equations are codedMost equations are coded

– Integration with other modulesIntegration with other modules

• DocumentationDocumentation– Tech. NoteTech. Note

Current EndeavorsCurrent Endeavors• Finish sensor modeling (h(), H)Finish sensor modeling (h(), H)• Further develop & test Matlab codeFurther develop & test Matlab code

– Get it running and integrated with other systemsGet it running and integrated with other systems– Refine estimates to get more realistic numbersRefine estimates to get more realistic numbers– Generate plots and graphs to obtain pointing Generate plots and graphs to obtain pointing

accuracyaccuracy

• Look into what would deployable solar Look into what would deployable solar panels allow us to do in terms of additional panels allow us to do in terms of additional sensors, and what changes to the current sensors, and what changes to the current design would it necessitate. design would it necessitate.

Open Issues & ConcernsOpen Issues & Concerns

• Can we meet the accuracy requirements?Can we meet the accuracy requirements?– We won’t know until the simulation is complete.We won’t know until the simulation is complete.– Possibilities for improving accuracyPossibilities for improving accuracy

• Add sensors: GPS attitude estimation system Add sensors: GPS attitude estimation system (GPS Compound Eye), low power Star tracker(GPS Compound Eye), low power Star tracker

• Adjust sensor ratesAdjust sensor rates• Change the dynamic model to include Change the dynamic model to include

equations of motionequations of motion

What if we go to deployable solar What if we go to deployable solar panels ?panels ?

• Need the Coarse Sun Sensor to be Need the Coarse Sun Sensor to be implemented solely by photo diodesimplemented solely by photo diodes

• Have enough power for additional sensors:Have enough power for additional sensors:– GPS compound eye:GPS compound eye:

• Works both sunside and darksideWorks both sunside and darkside– Low Cost Start TrackerLow Cost Start Tracker

• Greatly increases our pointing accuracyGreatly increases our pointing accuracy

KinematicsKinematics

Direction of Perigee

Vernal equinox

Line of Nodes

Satellite

x

y

zh

Inclination 51.6ºAltitude 407 kmRight ascending node TBDArgument of perigee 0Eccentricity e 0Orbit period 92.7 minutes

frame origin z-axis x-axisEarth-Centered Inertial (ECI) center of Earth celestial pole mean equinoxEarth-Fixed Frame (ECF) center of Earth celestial pole prime meridianOrbit Frame (ORB) center of Earth orbit normal ascending nodeSpacecraft Frame (SCF) c.m. of satellite telescope axis first side panelDesired Frame (D) c.m. of satellite

• Set of 4 miniature reaction Set of 4 miniature reaction wheels used for primary wheels used for primary controlcontrol

Attitude Control: Reaction WheelsAttitude Control: Reaction Wheels

y

z

x

e1,rw

e2,rw

e3,rw

e4,rw

RW1 RW2 RW3 RW4Rotor inertia 0.6387 0.6710 0.6194 0.6581 10-3kg m2

Max speed 8000 8000 8000 8000 RpmMax torque 7.4 7.4 7.4 7.4 10-3 NmElectr. losses 1.7708 1.7708 1.7708 1.7708 WViscous friction 0.3305 0.3827 0.3653 0.3131 10-6Nms/radCoulomb friction 0.3045 0.2896 0.2747 0.3195 10-3 NmMotor efficiency 0.9 0.9 0.9 0.9Torque gain 0.95 1.08 0.91 1.09

Controller Block DiagramController Block Diagram

Dynamics and State Estimation

Wheel SpeedManagement

Model-basedCompensation

Viscous Term

PseudoInverse

Elastic Term + + +

ecidAeciscA

scfsc

scfd

scfel

scfvisc

scfsc

scfmdl

rwfsc rw

wsm

scfsc

rw

drw,

scfd

eciscA

rw

Magnetic TorquersMagnetic Torquers• Student designed and builtStudent designed and built

• Used for momentum dumping and detumblingUsed for momentum dumping and detumbling

• Free-air coil design selectedFree-air coil design selected– Simplest, least costly designSimplest, least costly design– Linear response to input current simplifies control Linear response to input current simplifies control

requirements.requirements.– Possible issues with stray magnetic fieldsPossible issues with stray magnetic fields

• Three requiredThree required

Coil Design FormulaeCoil Design Formulae

0a

NR

0aNM

222

AM

mRiP

Aa

mV

0

AM

ami

0

0Naa

432

• Moment equation:Moment equation:

• Power, current, voltage and resistance:Power, current, voltage and resistance:

• Mass and wire size:Mass and wire size:

mas

s [k

g]m

ass

[kg]

Power [watts]Power [watts]

Design OptimizationDesign OptimizationTotal Mass vs. Power Total Mass vs. Power

ConsumptionConsumption• SpecificationsSpecifications

– Dipole moment of Dipole moment of 5 Am5 Am22

– Power consumption Power consumption of 0.3 Wof 0.3 W

• 16 mA at 20 V16 mA at 20 V

– Uses 32 gauge square Uses 32 gauge square magnet wire magnet wire

– Total mass of 3 kgTotal mass of 3 kg

Mounting PossibilitiesMounting Possibilities

• Two ideasTwo ideas– Designed to fit within Designed to fit within

side beamside beam

– Wrapped into groove Wrapped into groove on exterior of satelliteon exterior of satellite

• Three coils form Three coils form mutually perpendicular mutually perpendicular axesaxes

Momentum Dumping Control Momentum Dumping Control AlgorithmAlgorithm

• The approach is to consider both the need The approach is to consider both the need and efficiency of dumping at a particular and efficiency of dumping at a particular time.time.

• Use change in angular momentum to Use change in angular momentum to estimate direction of the earth’s magnetic estimate direction of the earth’s magnetic field in the absence of magnetometer field in the absence of magnetometer reading.reading.

• Dipole moment calculationsDipole moment calculations

TheoryTheory

• Need and efficiency calculationsNeed and efficiency calculations

Start

Stop

Need

Efficiency

BStop

HMax

H0

HStop

BMax

Detumbling

Conditions for Torquer ActivationConditions for Torquer Activation

• Start ConditionsStart Conditions

• Stop ConditionStop Condition

• Velocity RestrictionVelocity Restriction

Current StatusCurrent Status• Have opted for a torque coil designHave opted for a torque coil design

• Remaining hardware work is in mounting Remaining hardware work is in mounting details.details.

• Need to purchase or build amplifiersNeed to purchase or build amplifiers

• Some fine tuning of momentum dumping Some fine tuning of momentum dumping control constants may be necessary.control constants may be necessary.

Attitude Control SimulationsAttitude Control Simulations• Attitude dynamics and orbital kinematics are simulated.Attitude dynamics and orbital kinematics are simulated.

• Magnetic field is modeledMagnetic field is modeled

• The control laws are sampled at 4Hz.The control laws are sampled at 4Hz.

• The aerodynamic drag torques are modeled. Solar The aerodynamic drag torques are modeled. Solar pressure, gravity gradient and residual magnetic moment pressure, gravity gradient and residual magnetic moment are not modeled.are not modeled.

• The reaction wheels models include: Coulomb and viscous The reaction wheels models include: Coulomb and viscous friction, limited torque capability (7.4·10friction, limited torque capability (7.4·10-3-3 Nm), Nm), misalignment (4misalignment (4oo), uncertainty in gain (10%) and ), uncertainty in gain (10%) and uncertainty in inertia (4%).uncertainty in inertia (4%).

• The satellite core model includes: uncertainty in the The satellite core model includes: uncertainty in the moments of inertia (5%) and principal axes of inertia (4moments of inertia (5%) and principal axes of inertia (4oo).).

Ground tracking maneuverGround tracking maneuver

Telescope axis pointing errorTelescope axis pointing error

0 200 400 600 800 1000 12000

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5x 10

-3

Time (s)

Poi

ntin

g er

ror

(deg

rees

)

-3

10 200 400 600 800 1000 1200

-1

0

1x 10

0 200 400 600 800 1000 1200-1

0

0 200 400 600 800 1000 1200-1

0

1

0 200 400 600 800 1000 1200-1

0

1

Time (s)

Rea

ctio

n W

heel

Tor

ques

(N

m)

Reaction wheel torquesReaction wheel torques

Reaction wheel speedsReaction wheel speeds

0 200 400 600 800 1000 12000

100

200

300

400

500

600

700

800

900

1000

Time (s)

Rea

ctio

n W

heel

Spe

eds

(rpm

)

Detumbling/Momentum DumpingDetumbling/Momentum DumpingDetumbling Algorithm:

• Want K.E. to decrease, which happens when

• This condition is satisfied with

• Since change in B is due to spacecraft rotation,

Magnetic MomentMagnetic Moment

Time(s)

120006000 8000 1000040002000-5

0

5

-5

0

5

-5

0

5

X

Y

Z

Reaction Wheel MomentumReaction Wheel Momentum

Time(s)

120006000 8000 1000040002000

HRWA

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Spacecraft Body MomentumSpacecraft Body Momentum

Time(s)

120006000 8000 1000040002000

Hbody

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Total MomentumTotal Momentum

Time(s)

120006000 8000 1000040002000

Htotal

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Questions? Comments?Questions? Comments?

Presentation SchedulePresentation Schedule• 5:00- Project Manager Overview & Introduction5:00- Project Manager Overview & Introduction

• 5:20- Science5:20- Science

• 5:50- Laser Communications5:50- Laser Communications

• 6:10- Guidance, Navigation & Control6:10- Guidance, Navigation & Control

• 6:30- Break6:30- Break

• 6:40- Systems Integration6:40- Systems Integration

• 7:00- Mechanical, Structures & Analysis7:00- Mechanical, Structures & Analysis

• 7:20- Data & Command Handling7:20- Data & Command Handling

• 7:40- Power Generation & Distribution7:40- Power Generation & Distribution