Japan Geoscience Union Meeting 2016

Presentation information


Symbol P (Space and Planetary Sciences) » P-CG Complex & General

[P-CG21] Planetary atmosphere, ionosphere and magnetosphere

Wed. May 25, 2016 3:30 PM - 5:00 PM 101A (1F)

Convener:*Takeshi Imamura(Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science), Yukihiro Takahashi(Department of Cosmosciences, Graduate School of Science, Hokkaido University), Yoshiyuki O. Takahashi(Graduate School of Science, Kobe University), Keiichiro Fukazawa(Academic Center for Computing and Media Studies, Kyoto University), Hiromu Nakagawa(Planetary Atmosphere Physics Laboratory, Department of Geophysics, Graduate School of Science, Tohoku University), Chair:Hiromu Nakagawa(Planetary Atmosphere Physics Laboratory, Department of Geophysics, Graduate School of Science, Tohoku University)

3:30 PM - 3:45 PM

[PCG21-01] Akatsuki returns to Venus

*Masato Nakamura1 (1.Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency)

Keywords:Akatsuki, Venus, Exploration

ISAS successfully launched Akatsuki at 06:58:22JST on May 21st 2010, by H-IIA F17. After a half year successful cruise from the earth to Venus, the malfunction happened on the propulsion system during the Venus orbit insertion (VOI) on December 7th, 2010. The engine shut down at 158 sec during the VOI, while we planned 12 min operation. The spacecraft did not enter the Venus orbit but entered an orbit around the Sun with a period of 203 days. The orbital maneuvering engine (OME) was found to be broken and unusable, but most of the fuel still remained. ISAS’s engineers decide to use the reaction control system (RSC) for orbital maneuver and three minor maneuvers in November 2011 were successfully done so that Akatsuki would meet Venus in 2015.
The Akatsuki spacecraft was rotating about the sun with a period of 199 days and was on the trajectory to meet Venus on 22nd of November, 2015 after the orbital maneuvers in November 2011. The date, November 22nd, 2015, was chosen as the shortest encounter timing with consideration of spacecraft's lifetime. Trajectory analysis done later revealed that the orbit around Venus after insertion on 22nd of November, 2015 is unstable. We decided to perform another orbital maneuver in July 2015 to let the spacecraft to meet Venus on 7th of December, 2015 with this date the orbit around Venus would be more stable.
On 7th of December, 2015, the spacecraft approached from outside of Venus orbit and captured by Venus. For the Venus orbit insertion in 2015, termed VOI-R1, four 23 Newton-class thrusters were used as opposed to 500 Newton-class OME used at the 1st VOI in 2010. VOI-R1 burn (1228 seconds) was successfully achieved from 23:51:29 on 6th of December through 00:11:57 on 7th of December (UTC, on-board time).
Akatsuki became the first satellite of a planet in Japan. After VOI-R1, the apoapsis altitude is 0.44 million km with the inclination of 3 degrees. The orbital period is 13 days and 14 hours. The figure shows the VOI-R1 geometry depicted with the Venus center coordinate. For two purposes, to decrease the apoapsis altitude and to avoid long eclipse during the orbiter, we performed a trim maneuver at the first periapsis. The apoapsis altitude is now 0.36 million km with periapsis altitude of 1,000 km - 8,000 km (varying) and the period is 10 days and 12 hours.
Akatsuki will send data over two years to us, and it means that our exploration enters the new era when Japan deliver the continuously changing planet’s data to the whole world.