川口 淳一郎

火星複合探査WGは数多くの議論を通じて,MELOS計画の根幹である科学目標とそれに答えるための科学要求をまとめてきた.火星はなぜ赤いのか?この単純でしかし奥深い問題に答えるには,大気圏・表層・固体圏を一つの惑星システムとして捉える複合探査が必要である.MELOSは,まさにそれを目指そうとしている.

By Hayabusa spacecraft, for the first time, we saw the real appearance of a very small solar system body, asteroid Itokawa, which is an S-type asteroid only about 500 m in length. We had a lot of scientific results form the observation of Hayabusa. Hayabusa is now on the way to the earth and it will come back in June 2010. While working for Hayabusa, we have been considering post-Hayabusa missions, Hayabusa-2 and Hayabusa-Mk2. Hayabusa-2 is a kind of replica of Hayabusa and it will explore a C-type asteroid. Hayabusa-Mk2 is newly developed spacecraft and its target is much more primitive objects such as P or D-type asteroids or dormant comets. In this way, we are considering programmatic missions for the exploration of primitive bodies. Since there are many small bodies in the solar system, we should have such strategic approach. From 2006, Hayabusa-Mk2 is considered with the European reserchers for small bodies of the solar system. And it was proposed to Cosmic Vision of ESA with the name of 'Marco Polo.' It has passed the first selection so now we are in the assessment phase. We hope that both Hayabusa-2 and Marco Polo will be realized in the future. We also hope that we will get the clues to solve the mysteries of the birth and evolution of the solar system and the life.

'HAYABUSA' is a Japanese inter-planetary spacecraft built for the exploration of an asteroid named 'ITOKAWA.' The spacecraft is powered by a 13.2 Ah lithium-ion secondary battery. To realize maximum performance of the battery for long flight operation, the state-of-charge (SOC) of the battery was maintained at ca. 65% during storage, in case it is required for a loss of attitude control. The capacity of the battery was measured during flight operations. Along with the operation in orbit, a ground-test battery was discharged, and both results showed a good agreement. This result confirmed that the performance of the lithium-ion secondary battery stored under micro-gravity conditions is predictable using a ground-test battery. (C) 2008 Published by Elsevier B.V.

This paper describes the attitude dynamics of spacecraft with large flexible structure, such as huge antenna or membrane of solar sail. The coupled motion of the rigid spacecrafts with the flexible structure is complicated, and it is important to predict the motion for the design of configuration or operation planning. It requires a lot of time to calculate the motion of the flexible structure by numerical simulation, and the analysis using simple model is important for exhaustive validation. In this study, a simplified model of the attitude dynamics considering the first vibration mode of flexible structure is introduced. Using this model, the vibration mode of the attitude motion of spacecraft is analyzed. The result of the analysis is confirmed with numerical simulation and compared with the result obtained by use of proven model.

The Japanese spacecraft, HAYABUSA, was launched on May 9, 2003 and spent more than 2.5 years approaching the asteroid ITOKAWA. This spacecraft used 13.2 Ah lithium-ion secondary cells. After HAYABUSA touched down on ITOKAWA in December 2005, it could not communicate for seven weeks due to a malfunction of the attitude control. During this period, four of 11 lithium-ion secondary cells were over-discharged, and solar power was unavailable due to the spacecraft's tumbling motion. However, the battery power was still indispensable for sealing the container with the asteroid sample. The seven remaining healthy cells were slowly recharged using minimum current. During this time, ground simulation tests using similarly-built and intentionally short-circuited cells were carried out to evaluate the battery's operational safety. After its safety was confirmed, the lithium-ion secondary battery was used to transfer, latch, and successfully seal the sample container into the reentry capsule. The necessary power for these actions was supplied by the battery.

'HAYABUSA' is a Japanese interplanetary spacecraft for the exploration of an asteroid named 'ITOKAWA.' The spacecraft is powered by a 13.2 Ah lithium-ion secondary battery. To realize maximum performance of the battery for long flight operation, the state-of-charge (SOC) of the battery was maintained at ca. 65% during storage in case it is required for contingency operations. To maintain this SOC condition, the battery is charged once a week. We further charge the battery up to 4.1 V/cell using bypass circuits to balance the cells every four months. The capacity of the battery was measured during the flight operation, which revealed the appropriate capacity for the expected mission.

「はやぶさ」は2003年5月9日に内之浦からM-V5号機によって打ち上げられた、世界初の小惑星サンプルリターンミッションを有する探査機である。2005年9月12日に目的の小惑星Itokawaに到着し、数多くの科学的、工学的な成果を挙げた。「はやぶさ」は、その主たる推進機関として電気推進(Ion Engine System; IES)を採用している。軌道決定の観点からは、電気推進による微小推力の加速度モデル誤差が、軌道決定および軌道予報の精度に大きな影響を及ぼすため、この推力を如何にモデル化するかということと、必要に応じて推力推定を行うことが、重要な課題となる。資料番号: AA0063223019レポート番号: JAXA-SP-06-015

Hayabusa spacecraft performed the final descents and touchdowns twice in November 2005. In final descent phase, terrain alignment maneuvers were accomplished to control both altitude and attitude with respect to the surface by using four beams Laser Range Finder onboard. Then Hayabusa spacecraft made dynamic touchdowns the surface of the asteroid by the sampler system to collect samples automatically. This paper presents the terrain alignment maneuver and touchdown scheme. This paper also describes the novel sample horn system and touchdown dynamics. Touchdown tests on the ground are presented. Then the flight results on touchdown dynamics are shown and discussed. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Hayabusa spacecraft performed the final descents and touchdowns twice in November 2005. In final descent phase, terrain alignment maneuvers were accomplished to control both altitude and attitude with respect to the surface by using four beams Laser Range Finder onboard. Then Hayabusa spacecraft made dynamic touchdowns the surface of the asteroid by the sampler system to collect samples automatically. This paper presents the terrain alignment maneuver and touchdown scheme. This paper also describes the novel sample horn system and touchdown dynamics. Touchdown tests on the ground are presented. Then the flight results on descent and touchdown dynamics are shown and discussed.

The locations of the pole and rotation axis of asteroid 25143 Itokawa were derived from Asteroid Multiband Imaging Camera data on the Hayabusa spacecraft. The retrograde pole orientation had a right ascension of 90.53° and a declination of -66.30° (52000 equinox) or equivalently 128.5° and -89.66° in ecliptic coordinates with a 3.9° margin of error. The surface area is 0.393 square kilometers, the volume is 0.018378 cubic kilometers with a 5% margin of error, and the three axis lengths are 535 meters by 294 meters by 209 meters. The global Itokawa revealed a boomerang-shaped appearance composed of two distinct parts with partly faceted regions and a constricted ring structure.

第20号科学衛星「はやぶさ」は,世界初の惑星圏天体からの試料採取とその帰還をめざした,我が国独自の惑星探査機である.「はやぶさ」は,2003年に打ち上げられてからイオンエンジンで航行し,昨年9月に小惑星イトカワに到着し,近傍に滞在した3ヶ月間の間に,近傍での詳細な科学観測を行うとともに,11月にはイトカワ表面に降下・着陸させその試料の採取を2回にわたって試みた.着陸域は非常に狭い範囲に限定されていたにも関わらず,「はやぶさ」は,プロジェクトチームの創意工夫によって,2回にわたる着陸に成功した.本報告は,「はやぶさ」探査機によって行われた飛行と観測,そして着陸にいたる記録である.