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AKATSUKI’s Second Journey to Venus
7 October 2015 Chikako Hirose
Japan Aerospace Exploration Agency
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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
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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.
2015 AGI International User's Conference
Period: 96 hours
48 hours
30 hours
PlanResult
Maneuver
STK/Astrogator and Analysis Workbench played active roles in trajectory re-design.
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Akatsuki Fact Sheet
2015 AGI International User's Conference
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
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Orbital Events in 2011
2015 AGI International User's Conference
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.
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Tough Surroundings
2015 AGI International User's Conference
• 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
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Tough Conditions
2015 AGI International User's Conference
(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
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Examples
2015 AGI International User's Conference
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Analysis Cases
2015 AGI International User's Conference
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!!!
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Solar Gravity Perturbation
2015 AGI International User's Conference
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)
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Geometry of Analysis Cases
2015 AGI International User's Conference
(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
SWB1170deg+2nd Approach
SWB10deg+2nd Approach
(Sun-Venus Fixed Rotating Frame) x 105 [km]
Acceleration Deceleration
Deceleration Acceleration
NA
OK
OK
(2a)(2b)
(1)
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Retrograde Orbit Insertion I
2015 AGI International User's Conference
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
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Retrograde Orbit Insertion II
2015 AGI International User's Conference
Fig. 4 GBM Trajectory in Inertial frame
(Venus centered Inertial Frame)
PosigradeRetrograde
Earth @ Nov. 22Earth @ Dec. 31
Sun @ VOI(Nov. 22)
Venus
Acceleration
Acceleration Deceleration
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)
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Candidate Cases of Re-VOI
2015 AGI International User's Conference
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
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Orbital Events in 2015
2015 AGI International User's Conference
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
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2015 AGI International User's Conference
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Akatsuki Official Report Covers
2015 AGI International User's Conference
Spacecraft Specification (- 2009)
Operation Result (2010)
Operation Result & Trajectory Design
(2011-2012)