Planet C (VCO, Akatsuki)

Spacecraft nº:

Japanese spacecraft nº: 163

Launch data: Designation  36576 / 10020D Launch date  20 May 2010 - 21:58:22 UTC  21 May 2010 - 06:58 JST Launch site  Tanegashima, YLP-1 Launch vehicle  H-2A-202 (flight F17) Mission  Venus Orbiter Elliptical orbit around Venus: Perigee / Apogee  300 x 80000 km Eccentricity  0.992 Inclination  172 deg Period  30 hrs Solar orbit:

Spacecraft data: Prime contractor   Platform   Operator  JAXA Mass at launch  640 kg including 320 kg of propellants and 34 kg of scientific instruments. Dry Mass   kg Basic shape  box Dimension (m)  1.6 x 1.6m x 1.25m Solar array  2 solar arrays, each with an area of 1.4 m2 Stabilization   DC power  1200 W Design lifetime

Credit: ISAS / JAXA

Description:

• 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 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 will be 480 kg, 34 kg of this will be 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 4 reaction wheels, two with 20 Nms momentum capability and two with 4 Nms, 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 scientific payload consists of six instruments including:
  • 1. 1-µm camera (IR1)
  • 2. 2-µm camera (IR2)
  • 3. Longwave IR camera (LIR)
  • 4. Ultraviolet imager (UVI)
  • 5. Lightning and airglow camera (LAC)
  • 6. Ultra-stable oscillator (USO/Radio Science)
  
  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. The LAC will look for lightning in the visible wavelengths of 552 to 777 nanometers.
• Communications is via a 8 GHZ X-band 20 W transponder using the 1.6 m slot array high gain dish antenna used for most telemetry data. Akatsuki also has a pair of medium gain horn antennas mounted on turntables and two low gain antennas for command uplink. The medium gain horn antennas will be used for housekeeping data downlink when the high gain antenna is not facing Earth.

Objectives:

Mission details:

• Akatsuki left the Sagamihara Campus on 17 March 2010, and arrived at the Tanegashima Space Center's Spacecraft Test and Assembly Building 2 on 19 March, 2010. On 4 May, Akatsuki was encapsulated inside the large payload fairing of the H-IIA rocket that launched the spacecraft, along with the IKAROS solar sail, on a 6-month journey to Venus. On 9 May, the payload fairing was transported to the Tanegashima Space Center's Vehicle Assembly Building, where the fairing was mated to the H-IIA launch vehicle itself.
• Launch delayed because of weather from its initial 18 May scheduled target.
• Japan's PLANET-C (puranetto-c) Venus probe, Akatsuki, was launched from Tanegashima on May 20, 2010 at 2158 UTC. Akatsuki is Japanese for 'Dawn' or 'Daybreak' - just like the Russian 'Rassvet', a popular spacecraft name this week.
• Launch was by H-IIA 202 rocket, flight F17. F17 reached a 292 x 306 km x 30.0 deg low Earth orbit at 2210 UTC and deployed three cubesats: KSAT for Kagoshima University, Negai* ("Negai-star" but always written with a star symbol) for Soka University in Tokyo, and Waseda-Sat 2 for Waseda University in Tokyo. KSAT carries an experiment to study atmospheric water vapor.
• F17's second stage restarted at 2220 UTC to accelerate to escape velocity. It cutoff at 2224 UTC, and then deployed three spacecraft into a 0.72 x 1.07 AU x 2.0 deg solar orbit: Akatsuki, Unitec-1 and Ikaros. Unitec-1 will space-qualify university-built spacecraft computers; Ikaros will test a solar sail; and Akatsuki will become a Venus-orbiting weather satellite with visible, infrared and ultraviolet cameras. The PAF900M adapter separating Akatsuki and Ikaros was jettisoned into solar orbit.
• Akatsuki was planned to initiate orbit insertion operations by igniting the orbital maneuvering engine at 23:49:00 on 6 Dec 2010. The burn was supposed to continue for 12 minutes, to an initial orbit of 180,000 - 200,000 km apoapsis / 550 km periapsis / 4 days orbital period around Venus.
• The orbit insertion maneuver was confirmed to have started on time. But after the expected blackout due to occultation by Venus, the communication with the probe did not recover as planned. The probe was found to be in safe-hold mode, spin-stabilized state with 10 minutes per rotation. Due to the low communication speed through low-gain antenna, it took a while to determine the state of probe. JAXA stated on December 8, that the probe's orbital insertion maneuver has failed. At a press conference on 10 December, officials reported that Akatsuki's engines fired for less than 3 minutes far short of what was required to enter into Venus orbit.
• The probe remains in solar orbit.
• JAXA is developing plans to attempt another orbital insertion burn when the probe returns to Venus in 6 years. This requires placing the probe into a hibernation state to prolong its life beyond the original 4.5 year design. JAXA expressed some confidence in keeping the probe operational, pointing to reduced battery wear, since the probe is orbiting the Sun instead of its intended Venusian orbit
• The Akatsuki spacecraft (Venus Climate Orbiter, Planet-C) was launched on 2010 May 20 into a 0.72 x 1.07 AU x 2.0 deg heliocentric orbit which took it to a Venus encounter on 2010 Dec 6. However the probe's main bipropellant engine failed to complete the orbit insertion burn, and Akatsuki flew on past Venus.
  During 2011 Oct the engine's oxidizer supply was dumped to reduce mass, and the smaller monopropellant hydrazine reaction control thrusters were used to tweak the probe's post-flyby solar orbit to set up a late 2015 re-encounter with Venus. The probe is now (Dec 2014) in a 0.611 x 0.722 AU x 3.5 deg orbit around the Sun compared to Venus' 0.72 x 0.73 AU x 3.4 deg (the inclination is reported relative to the ecliptic plane of the Earth's orbit). It is therefore the innermost of any of humanity's currently active artificial planets; only the Messenger probe in orbit around Mercury is closer to the Sun. Mariner 10 and Helios 1 and 2, in the 1970s, also ventured into sub-Cytherean space. Akatsuki will reach perhelion on Feb 11, 2015 and again on Aug 28 before beginning the approach to Venus. The ISAS team have not yet finalized the new orbit insertion plan, trying to slow down enough to be captured by Venus while using only the RCS thrusters will be an impressive trick, and I wish them the best of luck in trying to pull it off. Akatsuki's unexpected stay in solar orbit has let it focus on non-Venusian science for the time being, scientists have used its radio signals to Earth to probe the solar wind, revealing acoustic waves in the outer solar corona up to 20 solar radii (Miyamoto et al. 2014, Astrophysical J. 797, 51).