The result of Venus Orbit Insertion of Akatsuki on December 7th, 2015

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Masato Nakamura1, Ko-ichiro Sugiyama2, Takeshi Imamura3, Nobuaki Ishii2, Takumi Abe2, Yasuhiro Kawakatsu2, Chikako Hirose2, Takehiko Satoh4, Makoto Suzuki2, Munetaka Ueno5, Atsushi Yamazaki6, Naomoto Iwagami7, Shigeto Watanabe8, Makoto Taguchi9, Tetsuya Fukuhara10, Yukihiro Takahashi8, Manabu Yamada11, Masataka Imai12, Shoko Ohtsuki13, Kazunori Uemizu6, George L Hashimoto14, Masahiro Takagi15, Yoshihisa Matsuda16, Kazunori Ogohara17, Naoki Sato16, Yasumasa Kasaba18, Toru Kouyama19, Naru Hirata20, Ryosuke Nakamura21, Yukio Yamamoto22, Takeshi Horinouchi8, Masaru Yamamoto23, Yoshi-Yuki Hayashi24, Junichi Nakatsuka6, Hiroki Kashimura25, Takeshi Sakanoi18, Hiroki Ando26, Shin-ya Murakami6, Takao Sato6, Seiko Takagi27, Kensuke Nakajima23, Javier Peralta6 and Yeon Joo Lee28, (1)Inst Space & Astron Science, Kanagawa, Japan, (2)Inst Space & Astron Science, JAXA, Kanagawa, Japan, (3)JAXA, Kanagawa, Japan, (4)ISAS/JAXA, Sagamihara-Shi, Japan, (5)ISAS/JAXA, Kanagawa, Japan, (6)ISAS/JAXA, Sagamihara, Kanagawa, Japan, (7)The University of Tokyo, Bunkyo-ku, Tokyo, Japan, (8)Hokkaido University, Sapporo, Japan, (9)Rikkyo University, Tokyo, Japan, (10)Hokkaido Univ., Sapporo, Japan, (11)Chiba Institute of Technology, Planetary Exploration Research Center, Narashino, Japan, (12)Graduate School of Hokkaido University, Sapporo, Japan, (13)Senshu University, Kanagawa, Japan, (14)Okayama University, Okayama, Japan, (15)Universiy of Miyazaki, Miyazaki-Gun, Japan, (16)Tokyo Gakugei University, Koganei, Tokyo, Japan, (17)University of Shifa Prefecture, Hikone, Shiga, Japan, (18)Tohoku University, Sendai, Japan, (19)AIST - National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan, (20)University of Aizu, Aizu-Wakamatsu, Japan, (21)National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan, (22)ISAS Institute of Space and Astronautical Science, Kanagawa, Japan, (23)Kyushu University, Fukuoka, Japan, (24)Kobe University, Kobe, Japan, (25)JAMSTEC, Yokosuka, Kanagawa, Japan, (26)ISAS/JAXA, 3-1-1 Yoshinodai/Sag, Japan, (27)Tokai University, Tokyo, Japan, (28)JAXA Japan Aerospace Exploration Agency, Sagamihara, Japan
Japan launched Venus Climate Orbiter ‘Akatsuki’ (JAXA’s mission code name: PLANET-C) to observe the dynamics of the Venus atmosphere globally and clarify the mechanism of the atmospheric circulation. The launch was on May 21st , 2010 from the Tanegashima Space Center. The cruise to Venus was smooth, however, the first Venus Orbit Insertion (VOI) trial on December 7th, 2010 tuned out to be a failure. Later Akatsuki has been orbiting the sun. Fortunately we keep the spacecraft in a healthy condition and surprisingly we have found another chance to let this spacecraft to meet Venus in 2015. Next VOI trial will be done on December 7th, 2015 and we report the result of this operation at this AGU meeting.

This mission is planed to answer the question described below. The radius of the Earth and Venus are almost the same. In addition the radiation from the sun is also almost the same. The climates of these planets, however, are much different. For example, the strong zonal wind is observed on Venus with the period of 4 days, where Venus rotates westward with the period of 243 days. The wind speed is about 100 m s-1. This is called super rotation. We will investigate from data from Akatsuki what attributes to the difference of the climates between Earth and Venus. AKATSUKI was designed for remote sensing from an equatorial, elliptical orbit to tract the atmospheric motion at different altitudes using 5 cameras (3xIR, UV, Visible) and by the radio occultation technique.

The first VOI has failed due to a malfunction of 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 a result the main engine (orbital maneuvering engine, OME) became oxidizer-rich and fuel-poor condition, which led to an abnormal combustion in the engine with high temperature, and finally the engine was broken. We decide to use RCS thrusters for Trajectory Control Maneuvers’ (TCMs) and finally insert Akatsuki into the orbit. Total thrust force of 4 RCS thrusters is 20 % of that of the main thruster and the orbit after VOI-R becomes a larger ellipse (apoapsis altitude will be finally 3.2x106km ) than the original plan in 2010. We have already done major 6 TCMs before July 31st, 2015 to let the spacecraft to meet Venus in December.