Toward Venus orbit insertion ofAkatsuki	
Takeshi Imamura (JAXA, Japan)

Lightning andAirglow Camera	

Mid-IR Camera	UV Imager	Ultra-Stable Oscillator	

1µm Camera	
2µm Camera	Development and launch	••••Objective: Understanding the atmospheric
dynamics and cloud physics of Venus
Spacecraft– Designed for remote sensing from anequatorial, elliptical orbit– Mass: 500 kg (incl. fuel) Payload: 35 kg– Three-axis attitude control
Science instruments– 1µm Camera (IR1)	
– 2µm Camera (IR2)	
– Longwave IR Camera (LIR)– Ultraviolet Imager (UVI)– Lightning and Airglow Camera (LAC)– Ultra-stable oscillator (USO)
Launched in May 2010

3-D observation of the atmospherefrom Venus’s orbit	

Integration at ISAS	
Launch by H2Ain May, 2010	

Failure of Venus orbit insertion	
••The Venus orbit insertion (VOI) has failed on Dec 7, 2010 due to a malfunctionof the propulsion system.
The check valve between the helium tank and the fuel tank was blocked by an
unexpected salt formation during the cruising from the Earth to Venus. As aresult the orbital maneuvering engine (OME) became oxidizer-rich and fuelpoor condition, which led to an abnormal combustion in the engine with hightemperature, and finally the engine was broken.
VOI trial on Dec. 7, 2010	

propulsionsystem	Toward the next VOI trial	•

Since the main engine (OME) was destroyed, we decided to use theattitude control thrusters (or reaction control system, RCS) for furtherorbit maneuvers. RCS does not require oxidizer, and we disposed theoxidizer of 65 kg in Oct 2011 to reduce the weight.
• An orbit control maneuver was conducted using RCS in Nov 2011. This
operation enabled a Venus encounter in 2015.

Thermal condition	
Solar flux (W/m2)	

Akatsuki perihelion(0.6AU) 3655W/m2

Launch(May 21,2010)	

Perihelion(April 17)	VOI(Dec 7)	

Venus orbit (0.7AU)
2649W/m2
Earth orbit 1400W/m2	

Date	Today	 VOI
(Dec 7,2015)	

5

Venus orbit insertion
Dec 7, 2015
ΔV = 196 m/s	Akatsuki	Sun	Orbital maneuver	
Late July 2015
ΔV = 87 m/s	

Last (9th)perihelion passage
Aug 29, 2015	

Venus	

Event	

Date	

ΔV	

DV4	

late July, 2015	

87 m/s	Apoapsis	

Period	VOI-R1	 Dec 7, 2015	

196 m/s	

4.9 x 105 km	

16.2 days	

VOI-R2	 Dec 7, 2015	

3 m/s	

4.7 x 105 km	

15.3 days	

PC1	

Mar 25, 2016	

32 m/s	

3.2 x 105 km	

8.7 days	PC2	

Jun 14, 2017	

2 m/s	

3.1 x 105 km	

8.4 days	RCS	 thruster	 (23N)	 

Thrust	  force	

Broken	 main	 thruster	 (500N)	 

The	  total	  power	  of	  4	  RCS	  thrusters	  is	  approximately	  20%	  of	  the	  main	  thruster.	  Observation plan in the new orbit	
Successive global images ofatmosphere and ground surface(~9 days)

Limb images

Orbital period ~ 9 days
Ground station	
Temperature / H2SO4vapor / Ionosphereby radio occultation- Close-up images- Stereo viewing- Lightning- Airglow

Venus to be seen from Akatsuki’s apoapsis(an equivalent 2x2 binned VMC image)	

190 pixels	

V0470_0048	

3D observations	Akatsuki

Temperature and H2SO4
vapor profiles (RS)
Airglow （LAC）	
Sulfur dioxide（UVI）	

90 km

Cloud temperature（LIR）	
Lower clouds（IR1, IR2）	

65 km

Wind vectors

50 km

Carbon monooxide（IR2）	
Lightning （LAC）	
Water vapor（IR1）	

35-50 km

StratosphereClouds

Troposphere

Surface
Active volcanoes / Minerals（IR1）Latitudes to be observed (UDSC+IDSN32)	

Dec	  7,	  2015	  (VOI)	  to	  Dec	  31,	  2015	  Ini@al	  checkout	

Jan	  1,	  2016	  to	  Mar	  31,	  2016	  	  Ini@al	  C/O	  à	  Regular	  obs	Orbital	  mo@on	  Orbital	  mo@on	  Earth	Earth	

Trajectory of Akatsuki in a frame fixed to Venus and Sun(Center: Venus)	

Summary and additional information	
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We have developed a detailed VOI plan, in which the attitude control
thrusters are used instead of the main thruster. The date of VOI isDecember 7, 2015.
The spacecraft has passed through the perihelion 8 times, and the final
perihelion passage is scheduled for August 29. We are carefully
monitoring the change of the temperature of the spacecraft.
NASA DSN support for orbital determination ongoing
The new orbit around Venus is a long elliptical one with the orbital periodof 8-16 days. The spatial resolution to be achieved around the apoapsis
becomes worth as compared to the original orbit whose period is 30
hours, although we can get high-resolution images in close proximity ofVenus.
We are going to install an onboard software which extracts a portion of
the image area containing Venus for observations from far distances. This
enables increase of the number of images to be obtained.
All of the science instruments have been switched off for more than three
years due to thermal constraints. Some of them will be turned on before
VOI.