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AKATSUKI’s Second Journey to Venus

7 October 2015 Chikako Hirose

Japan Aerospace Exploration Agency

My STK usage history (2005-2009) • JAXA conjunction assessment system

– JAXA CA system was developed in 2007 and became operational in 2008. – During the transition period, SOCRATES was referred for cross-check. http://www.celestrak.com/SOCRATES/

• Assessment of how to spread space debris after kinetic engagement – By using Two Line Elements of Fengyun 1C, Chinese Anti-satellite Test, how to

spread space debris was assessed.

STK was very useful as an easy-to-use propagator for assessment.

2015 AGI International User's Conference

My STK usage history (2010-) • Trajectory re-design of Japanese Venus explorer, Akatsuki

– Akatsuki was launched in May, 2010. – It reached to Venus in December, 2010, but failed in Venus Orbit Insertion. – During the VOI, the injection by main engine was stopped and Akatsuki was

transferred to Safe Hold Mode.


Period: 96 hours

48 hours

30 hours

PlanResult

Maneuver

STK/Astrogator and Analysis Workbench played active roles in trajectory re-design.

Akatsuki Fact Sheet


Orbit Maneuvering Engine (OME): 500 N

Reaction Control System (RCS): 23 N x 4

RCS: 23 N x 4

Structures 1.04 [m] x 1.45 [m] x 1.40 [m]

Weight (dry) 321 kg (wet) 518 kg (launch) / 362 kg (now)

Instruments 1-micron Camera (IR1) 2-micron Camera (IR2) Ultraviolet Imager (UVI) Longwave Infrared Camera (LIR) Lightning and Airglow Camera (LAC)

Propulsion Orbit Maneuver Engine (OME): 500N Reaction Control System (RCS): 23N x 4 x 2 3N x 4

Telecoms X-band High Gain Antenna – T/R Middle Gain Antenna x 2 Low Gain Antenna x 2

Mission 2 years in Venus orbit

Orbital Events in 2011


Orbital Events

2010 May 20 Launch

Dec 7 Venus Orbit Insertion (VOI) - failed

2011 Sep

7 14

OME Test Maneuver (TM1) (TM2)

Sep 30 Disposal of Oxidizer Test (DOX Test)

Oct 6 12 13

Disposal of Oxidizer (DOX1) (DOX2) (DOX3) – total 65 kg

Nov 1 10 21

Trajectory correction maneuver (DV1) (DV2) (DV3) – total 240 m/s

2015 Winter Venus re-encounter

(c) TM1(d) TM2

(e) DOX Test (f)-(h) DOX1,2,3

(i) DV1

(j) DV2

(k) DV3

(b) VOI (2010)

(c)(d)

(e)(f)

(g), (h)

(i)(j)

(k)

(b)

(c)

(d)

(e)(f)(g), (h)

(i) (j)(k)

Post-DV1,2,3

Pre-DV1,2,3

x 108 km

J2000 Ecliptic coordinate

(a) Launch

(a)

(b)

(a)

Trajectory (Launch – VOI (2010))

Earth

Venus

Akatsuki

• Akatsuki was set to encounter Venus again in 2015 after several trajectory corrections in 2011.

Tough Surroundings


• Since Akatsuki is flying inside of the Venus orbit, the heat input around perihelion is 1000 [W/m2] higher than the one on Venus orbit (approx. 2,600 [W/m2]). Therefore +Z plane (HGA-T/R loaded), which is most tolerant against heat, is always facing toward the Sun.

• The temperature of some equipment is over the design specification. However, they work properly at present. 0

50

100

150

TEM

PERA

TURE

[℃]

HGA-T HGA-R SAP-A SAP-BRCS-THV-AT1 RCS-THV-AT2 RCS-THV-AT3 RCS-THV-AT4RCS-THV-AB1 RCS-THV-AB2 RCS-THV-AB3 RCS-THV-AB4

Solar Paddles

High Gain Antenna

Thruster Valves (AT: +Z plane)

Thruster Valves (AB: -Z plane)

Fig 1.1 Temperature History since Launch

Tough Conditions


(a) Orbital Plane: close to the Venus equator (b) Orbital Direction: Retrograde (c) Umbra: less than 90 minutes (d) Incident Angle: less than 13 degrees to Akatsuki orbital plane

Polar

Propulsion: 330 m/s (RCS) = Ha: 300,000 km

It is difficult to maintain the periapsis because of the solar gravity perturbations.

Observation and System Requirements

Examples


Analysis Cases


1st Approach 2nd Approach 3rd Approach MaintainPeriapsis Altitude

System & ObservationRequirements

(1) VOI(1-1) Retrograde X -(1-2) Posigrade X -(1-3) Polar OK NG (a,b,d)

(2a) Swingby VOI θ: 170 deg (2a-1) Retrograde X - r: 16,000 km (2a-2) Posigrade OK NG (b)

(2a-3) Polar OK NG (a,b,d)

(3a) Swingby VOI(3a-1) Retrograde X -(3a-2) Posigrade OK NG (b)(3a-3) Polar OK NG (a,b,d)

(2b) Swingby VOI θ: 0 deg (2b-1) Retrograde X - r: 150,000 km (2b-2) Posigrade OK NG (b)

(2b-3) Polar OK NG (a,b,d)

(3b) Swingby VOI(3b-1) Retrograde X -(3b-2) Posigrade OK NG (b)(3b-3) Polar OK NG (a,b,d)

Solar Gravity Perturbations!!!

Solar Gravity Perturbation


Deceleration

Deceleration

(Sun-Venus Fixed Rotating Frame)

III

III IV-8

-6

-4

-2

0

2

4

6

8

-8 -6 -4 -2 0 2 4 6 8

Venus

Acceleration

Acceleration-8

-6

-4

-2

0

2

4

6

8

-8 -6 -4 -2 0 2 4 6 8

(Sun-Venus Fixed Rotating Frame)

IV

1mSun

1d

d

Deceleration

Deceleration

III

III

Acceleration

Acceleration

2d

θ

Venus

(a) Insertion to Posigrade Orbit (b) Insertion to Retrograde Orbit

Fig. 1. Acceleration and Deceleration areas caused by the SGP

θ232

1331

1 cos31, +=

−−=

ddGm

ddGm RddR 1Solar Gravity Perturbation (SGP)

Geometry of Analysis Cases


(a) Insertion to Posigrade Orbit (b) Insertion to Retrograde Orbit

Fig. 2. Geometry of Analysis Cases

-4

-3

-2

-1

0

1

2

3

4

-4 -3 -2 -1 0 1 2 3 4

Deceleration Acceleration

1st ApproachSWB1170deg+ 2nd Approach

SWB10deg+2nd Approach

(Sun-Venus Fixed Rotating Frame) x 105 [km]

Acceleration Deceleration

NA

NA

NA

(1)

(2b)

(2a)

-4

-3

-2

-1

0

1

2

3

4

-4 -3 -2 -1 0 1 2 3 4

1st Approach



(Sun-Venus Fixed Rotating Frame) x 105 [km]


Deceleration Acceleration

NA

OK

OK

(2a)(2b)

(1)

Retrograde Orbit Insertion I


Change of approach direction

-600,000

-400,000

-200,000

0

200,000

400,000

600,000

-600,000 -400,000 -200,000 0 200,000 400,000 600,000

Approach in November

Approach in December

Deceleration Effect by the Solar Gravity

Acceleration Effect by the Solar Gravity

Acceleration Effect

Deceleration Effect

Sun Venus

(Sun-Venus Fixed Rotation Frame) Fig 3. Change of approach angle

Retrograde Orbit Insertion II


Fig. 4 GBM Trajectory in Inertial frame

(Venus centered Inertial Frame)

PosigradeRetrograde

Earth @ Nov. 22Earth @ Dec. 31

Sun @ VOI(Nov. 22)

Venus

Acceleration


Deceleration

3. retrograde2. posigrade

1. 4.

5.

6.

Sun

Venus

Fig. 5 GBM Trajectory in Sun-Venus fixed rotating frame

Hill radius

Make the most of the solar gravity perturbations. (Gravity Brake)

Candidate Cases of Re-VOI


maintainingaltitude

Ha [km]x 1000

(1a) VOI (approach from inside of Venus's orbit)Retrograde NA －

Direct NA －

Polar OK 300

(1b) VOI (Hohmann Transfer Method)Retrograde OK 330Direct NA －

Polar OK －

(1c) VOI (Gravity Break Method)Direct -> Retrograde OK 300

(2a) Swingby VOIθ 170° Retrograde NA －

r 16,000km Direct OK 300Polar OK 410

(2b) Swingby VOIRetrograde NA －

Direct OK －

Polar OK 410

(3a) Swingby VOIθ 0° Retrograde NA －r 150,000km Direct OK 410

Polar OK 410

(3b) Swingby VOIRetrograde NA －

3rd approach2nd approach1st approach

Venus Circular Orbit

C

A

D

Summary VOI Ha (x1000) [km]

A. Polar November 22, 2015 300

B. Posigrade July 1, 2016 300

C. Retrograde (Hohmann Transfer) December 5-13, 2015 330

D. Retrograde (Gravity Brake) November 22, 2015 300

B

Orbital Events in 2015


Orbital Events

2015 July 17 24 31

Trajectory correction maneuver (DV4-1) (DV4-2) (DV4-3)

Aug 29 9th & Last Perihelion

Dec 7 Venus Orbit Insertion (VOI-R1)

VOI-R2

2016 Phase Control (PC1, 2, ...)

Fig 2.2.1 Altitude History (Apoapsis)

VOI-R1 VOI-R2

PC1

PC2

Akatsuki Official Report Covers


Spacecraft Specification (- 2009)

Operation Result (2010)

Operation Result & Trajectory Design

(2011-2012)

akatsuki’s second journey to venus - agidownloads.agi.com/u/images/gallery/events/iuc/...the venus...

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