AKATSUKI s Second Journey to Venus. 7 October 2015 Chikako Hirose Japan Aerospace Exploration Agency

Transcription

1 AKATSUKI s Second Journey to Venus 7 October 2015 Chikako Hirose Japan Aerospace Exploration Agency

2 My STK usage history ( ) JAXA conjunction assessment system JAXA CA system was developed in 2007 and became operational in During the transition period, SOCRATES was referred for cross-check. 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.

3 My STK usage history (2010-) Trajectory re-design of Japanese Venus explorer, Akatsuki Akatsuki was launched in May, 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. Result Plan 48 hours Period: 96 hours 30 hours Maneuver STK/Astrogator and Analysis Workbench played active roles in trajectory re-design.

4 Akatsuki Fact Sheet Reaction Control System (RCS): 23 N x 4 RCS: 23 N x 4 Orbit Maneuvering Engine (OME): 500 N Structures Weight Instruments Propulsion Telecoms Mission 1.04 [m] x 1.45 [m] x 1.40 [m] (dry) 321 kg (wet) 518 kg (launch) / 362 kg (now) 1-micron Camera (IR1) 2-micron Camera (IR2) Ultraviolet Imager (UVI) Longwave Infrared Camera (LIR) Lightning and Airglow Camera (LAC) Orbit Maneuver Engine (OME): 500N Reaction Control System (RCS): 23N x 4 x 2 3N x 4 X-band High Gain Antenna T/R Middle Gain Antenna x 2 Low Gain Antenna x 2 2 years in Venus orbit

5 Orbital Events in 2011 J2000 Ecliptic coordinate Earth Pre-DV1,2,3 (a) (b) VOI (2010) (b) Post-DV1,2,3 (b) Akatsuki (k) (j) (i) (c) (d) (k) DV3 (c) TM1 (d) TM2 (j) DV2 (e) (e) DOX (i) DV1 (f) Test (f)-(h) DOX1,2,3 Venus (g), (h) (a) (i) (j) (k) (a) Launch (g), (h) (f) (e) (d) (c) Trajectory (Launch VOI (2010)) x 10 8 km 2010 May 20 Launch Dec Sep 7 14 Orbital Events Venus Orbit Insertion (VOI) - failed OME Test Maneuver (TM1) (TM2) Sep 30 Disposal of Oxidizer Test (DOX Test) Oct Nov Disposal of Oxidizer (DOX1) (DOX2) (DOX3) total 65 kg Trajectory correction maneuver (DV1) (DV2) (DV3) total 240 m/s 2015 Winter Venus re-encounter Akatsuki was set to encounter Venus again in 2015 after several trajectory corrections in 2011.

6 Tough Surroundings TEMPERATURE[ ] HGA-T HGA-R SAP-A SAP-B RCS-THV-AT1 RCS-THV-AT2 RCS-THV-AT3 RCS-THV-AT4 RCS-THV-AB1 RCS-THV-AB2 RCS-THV-AB3 RCS-THV-AB4 High Gain Antenna Solar Paddles Since Akatsuki is flying inside of the Venus orbit, the heat input around perihelion is 1000 [W/m 2 ] higher than the one on Venus orbit (approx. 2,600 [W/m 2 ]). Therefore +Z plane (HGA-T/R loaded), which is most tolerant against heat, is always facing toward the Sun Thruster Valves (AT: +Z plane) Thruster Valves (AB: -Z plane) The temperature of some equipment is over the design specification. However, they work properly at present. Fig 1.1 Temperature History since Launch

7 Tough Conditions 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 Polar (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

8 Examples

9 Analysis Cases 1st Approach 2nd Approach 3rd Approach Maintain Periapsis Altitude System & Observation Requirements (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!!!

10 Solar Gravity Perturbation Solar Gravity Perturbation (SGP) θ 3 3 d d d = Gm, R = Gm 1+ 3cos 3 d1 d d R 1 8 II (Sun-Venus Fixed Rotating Frame) I 8 II (Sun-Venus Fixed Rotating Frame) I d 1 d 2 2 Sun m d θ Venus 0-2 Venus III IV III IV (a) Insertion to Posigrade Orbit (b) Insertion to Retrograde Orbit Fig. 1. and areas caused by the SGP

11 Geometry of Analysis Cases 4 (Sun-Venus Fixed Rotating Frame) x 10 5 [km] 4 (Sun-Venus Fixed Rotating Frame) x 10 5 [km] OK SWB1 0deg +2 nd Approach (2b) (1) 1 st Approach NA (2a) SWB1 170deg +2 nd Approach OK (1) 1 st Approach NA (2b) NA NA SWB1 170deg + 2 nd Approach (2a) -2-2 SWB1 0deg +2 nd Approach (a) Insertion to Posigrade Orbit (b) Insertion to Retrograde Orbit Fig. 2. Geometry of Analysis Cases

12 Retrograde Orbit Insertion I 600,000 Effect by the Solar Gravity Approach in December Effect by the Solar Gravity 400, ,000 Sun 0 Approach in November Venus Change of approach direction -200, ,000 Effect Effect -600, , , , , , ,000 (Sun-Venus Fixed Rotation Frame) Fig 3. Change of approach angle

13 Retrograde Orbit Insertion II Retrograde Posigrade 2. posigrade 3. retrograde VOI (Nov. 22) Venus Sun Dec. 31 Nov. 22 Venus (Venus centered Inertial Frame) Hill radius Fig. 4 GBM Trajectory in Inertial frame Fig. 5 GBM Trajectory in Sun-Venus fixed rotating frame Make the most of the solar gravity perturbations. (Gravity Brake)

14 Candidate Cases of Re-VOI (1a) (1b) (1c) 1st approach 2nd approach 3rd approach Venus Circular Orbit maintaining altitude Ha [km] x 1000 VOI (approach from inside of Venus's orbit) Retrograde NA - Direct NA - Polar OK 300 VOI (Hohmann Transfer Method) Retrograde C OK 330 Direct NA - Polar OK - VOI (Gravity Break Method) Direct -> Retrograde OK 300 (2a) Swingby VOI θ 170 Retrograde NA - r 16,000km Direct B OK 300 Polar OK 410 (2b) Swingby Summary VOI Retrograde NA - Direct OK - Polar OK 410 (3a) Swingby VOI θ 0 Retrograde NA - r 150,000km Direct OK 410 Polar OK 410 (3b) Swingby 2015 AGI VOI International User's Conference Retrograde NA - A D VOI Ha (x1000) [km] A. Polar November 22, B. Posigrade July 1, C. Retrograde (Hohmann Transfer) December 5-13, D. Retrograde (Gravity Brake) November 22,

15 Orbital Events in July Aug 29 Dec 7 Orbital Events Trajectory correction maneuver (DV4-1) (DV4-2) (DV4-3) 9 th & Last Perihelion Venus Orbit Insertion (VOI-R1) VOI-R Phase Control (PC1, 2,...) VOI-R1 VOI-R2 PC2 PC1 Fig Altitude History (Apoapsis)

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17 Akatsuki Official Report Covers Spacecraft Specification (- 2009) Operation Result (2010) Operation Result & Trajectory Design ( )