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Akatsuki ("Dawn"), originally designated Planet-C, also known as the Venus Climate Orbiter, is a Japanese Space Agency (JAXA) mission designed to study the dynamics of the atmosphere of Venus from orbit, particularly the upper atmosphere super-rotation and the three-dimensional motion in the lower part of the atmosphere, using multi-wavelength imaging. It will also measure atmospheric temperatures and look for evidence of volcanic activity and lightning. The scientific payload consists of the Ultraviolet Imager (UVI), the Longwave Infrared Camera (LIR), the 1-mm Camera (IR1), the 2-mm Camera (IR2), and the Radio Science (RS) experiment.

Spacecraft and Subsystems

The Akatsuki main bus is a 1.6 m x 1.6 m x 1.25 m box with two solar array paddles, each with an area of 1.4 square meters, on opposite (+y and -y) sides and a 1.6 m high gain antenna on the +x side. On the opposite side (-x) from the antenna is a 0.45 m long orbital maneuvering engine. The total launch mass of the spacecraft including propellant was 480 kg, 34 kg of which was scientific instruments.

Propulsion is provided by the 500 N bi-propellant (hydrazine and nitrogen tetroxide) orbital maneuvering engine and 12 mono-propellant (hydrazine) reaction control thrusters, eight with 23 N thrust and four with 3 N. The spacecraft is 3-axis stabilized. Attitude control is achieved using four reaction wheels, two with 20 N-m-s momentum capability and two with 4 N-m-s, which can be unloaded by the reaction control thrusters. Attitude knowledge is obtained using a gyroscopic inertial reference unit, star trackers, sun sensors, and accelerometers.

The solar array panels provide over 1200 W of power in Venus orbit and can rotate about their arms in the y-axis. Power can be used directly or stored in batteries. Communications is via a 20 W X-band (8 GHz) transponder using the 1.6 m slot array high gain dish antenna (for most telemetry data), a pair of medium gain horn antennas mounted on turntables (for housekeeping data downlink when the high gain antenna is not facing Earth), or a pair of low gain antennas (for command uplink). Thermal control is achieved through multilayer insulation, radiators, and heaters designed to keep the inside of the spacecraft below 20 degrees C.

The spacecraft carries a suite of six instruments. The 1-Micron Camera (IR1) will image the deepest levels of the atmosphere at 0.90, 0.97, and 1.01 micron wavelengths. The 2-Micron Camera (IR2) will image the middle and lower atmosphere at 1.73, 2.26, and 2.32 microns. The atmosphere at the height of the cloud tops will be mapped by the Longwave Infrared Camera (LIR) at 10 microns. The Ultraviolet Imager (UVI) will also look at the cloud tops, at 263 and 365 nm. And airglows in the lower thermosphere and lightning in the clouds will be imaged by the Lightning and Airglow Camera (LAC). High precision tracking will be facilitated by the Ultrastable Oscillator (USO).

Mission Profile

Akatsuki launched on an H-IIA rocket on 20 May 2010 at 21:58:22 UTC (21 May, 6:58:22 a.m. JST) from the Tanegashima launch center. The spacecraft separated from the booster 27 minutes after liftoff and went into an Earth phasing orbit and was then put into a Venus transfer orbit. (A small solar power sail demonstration mission, Ikaros, was also launched on the H-IIA rocket.) The spacecraft reached Venus on 07 December 2010 (JST). It began its orbital insertion rocket firing at 8:49 a.m. JST (23:49 UTC, 06 December, 6:49 p.m. EST 06 December) and was scheduled to finish 12 minutes later at 9:01 a.m. JST (00:01 UTC 07 December).

Ignition was confirmed before Akatsuki passed behind Venus for 22 minutes, but communications were not regained on schedule at 00:12 UT. Signals were finally received at 01:28 UT. It was determined that a faulty valve in the fuel pressure system malfunctioned and the engine firing scheduled for 9 minutes, 20 seconds only lasted about 152 seconds, so the spacecraft did not enter Venus orbit but instead flew by the planet. Akatsuki is on course to fly by Venus again and may attempt Venus orbit insertion in November, 2015.

Akatsuki was planned to go into a near equatorial (inclination 172 degrees) 30 hour Venus orbit with an apoapsis of about 79 000 km and a very low periapsis, approximately 300 km above the surface. The mission was to have lasted at least two years, limited primarily by degradation of the on-board batteries.

Spacecraft image for illustrative purposes - not necessarily in the public domain.

Alternate Names

  • Planet-C
  • Venus Climate Orbiter
  • 36576

Facts in Brief

Launch Date: 2010-05-20
Launch Vehicle: H-2A
Launch Site: Tanegashima, Japan
Mass: 320.0 kg
Nominal Power: 1200.0 W

Funding Agency

  • Japan Aerospace Exploration Agency (Japan)


  • Planetary Science

Additional Information

Questions or comments about this spacecraft can be directed to: Dr. David R. Williams.



NameRoleOriginal AffiliationE-mail
Dr. Nobuaki IshiiGeneral ContactInstitute of Space and Aeronautical
Dr. Takeshi ImamuraProject ScientistInstitute of Space and Aeronautical

Selected References

Ishii, N., et al., Current status of the PLANET-C Venus orbiter design, Adv. Space Res., 34, No. 8, 1668-1672, 2004.

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