矢野 創

Marco Polo is being studied in the ESA Cosmic Vision programme as a sample return mission to a near-Earth asteroid (NEO) with participation by JAXA, with launch planned in the 2018-19 timeframe. In reponse to ESA's Declaration of Interest call in 2008, the Institute of Space Systems of the German Aerospace Center (DLR) led a proposal for a separate lander 'MASCOT' (Marco Polo Surface Scout) to be carried on the mission. The proposal was recommended by ESA for a feasibility study which was subsequently carried out from late 2008 to September 2009. In parallel to the Marco Polo flight opportunity, MASCOT was studied for the Hayabusa-2 mission currently studied by JAXA as the immediate successor to the currently flying Hayabusa mission. Launch would be earlier, taking place in 2014. The MASCOT study started with a preliminary assessment of lander type, landing mode, mobility options and their impact on minimum achievable mass and volume. Differentiation was made between legged landers ('landing in a defined orientation'), landing packages ('landing with uncontrolled orientation') and the number of achievable landing sites (single vs. multiple) and thus the degree of mobility. The analysis showed that a legged lander in the mass range of 70 kg-100 kg - with full mobility - , a weeks-long lifetime and ≃14 kg P/L is feasible, given the weak gravity of potential target NEOs. Reducing size and capability, a legged lander of 30-40 kg was then conceived by giving up mobility, reducing lifetime and by cutting the P/L to ≃10 kg. Finally, a mobile package version with an uprighting mechanism ('MASCOT-XS') and 3 kg of P/L was found feasible for a total mass of 10-15 kg. The constraints imposed by both the Marco Polo and Hayabusa-2 missions mandate MASCOT-XS to be the baseline for the MASCOT design.

Dust particles which are observed as zodiacal light exist around the Earth's orbit and can create a characteristic distribution by the Earth's gravity. This paper investigates the distribution by numerical simulation on the assumption that dust particles trapped in horseshoe orbits contribute the distribution, because the orbit has the following characteristics. The velocity of a trapped dust varies by its location on the horseshoe orbit and the dust will transit with time to wider horseshoe orbit. And this paper also considers the possibility that these particles are trapped or not and reveals that the possibility depends on the dust diameter.

In the Hayabusa-2 pre-project, science case and onboard instruments are studied to conduct in situ observation at the surface of NEO 1999JU3, with a candidate 10kg class small lander. Science requirements, strawman payloads, and operation scenario will be briefly described at the meeting.

ベピコロンボ日欧共同水星探査計画における水星磁気圏探査機に搭載予定の圧電素子型宇宙塵計測器(MDM）では、探査期間において-140～170℃程度の間で温度が変動する。その温度変動がPZTセンサーのレスポンスにどのように影響するかを評価する必要があり、そのためのバンデグラフを用いた微粒子加速による温度特性評価実験を中心に報告する。

地球には様々な物質が降り注いでおり、その中でもμmサイズの宇宙塵では衝突時の衝撃は無視でき、ほとんど分解を受けずに地上に有機物が届けられたはずである。宇宙塵は地球上での汚染の影響を考えると宇宙空間での直接捕獲が望まれる。我々は宇宙ステーション上での捕獲、暴露実験を計画しているが、本研究ではその準備として宇宙空間での暴露実験を想定した各種放射線に対するアミノ酸の安定性の評価、そしてダスト捕集材であるAGに含まれるアミノ酸ブランク分析を行い、ダスト中のアミノ酸分析の可能性の検討を行った。遊離アミノ酸への照射実験ではフェニルアラニンなどの複雑な構造のアミノ酸ほど回収率が減少する傾向が見られた。今後は宇宙塵マトリックスを模擬した鉱物を混ぜる事で回収率の変化を議論する予定である。捕獲ダスト中のアミノ酸分析に関してはα-アミノイソ酪酸、イソバリンをターゲットとし、共にfmolオーダーでの検出法を検討していく予定である。

たんぽぽ計画では、ISS（国際宇宙ステーション）上での微生物と生命の材料になりうる有機化合物の天体間の移動の可能性の検証と、微小隕石の検出および解析実験を行うことを提案する。低軌道上で超低密度エアロゲルを一定期間曝露することで宇宙空間での微小隕石やその他の微粒子を捕集することを計画している。エアロゲルを回収後地上にて、エアロゲル表面と衝突トラックの顕微鏡観察の後、様々な解析を行う。エアロゲル中に残存した粒子に関して、鉱物学的、有機化学的、および微生物学的な検討を行う。一方、宇宙環境下での微生物の生存可能について検証するため、微生物の宇宙曝露実験も行う。我々は、エアロゲルで捕集された微粒子からの微生物の検出手法について現在検討している。また微生物の宇宙曝露実験について、宇宙の極限環境を模擬した条件下での微生物の生存率等の検討をしている。

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.

The asteroid exploration spacecraft "HAYABUSA" took high resolution pictures of asteroid "ITOKAWA". ITOKAWA is a rubble-pile asteroid, whose shape and regolith size distribution are unique. These features are caused by composition of the Brazil-Nut effect and centrifugal force by spin. The Brazil-Nut effect is generally known as the phenomenon that causes larger particles to rise to the top of the shaken granular mixtures. In this study, the behaviors of various size particles on the ground or in the space are analyzed by numerical simulation using Multi-Particle model, which is model of a rubble-pile asteroid. At first, the behaviors of particles on the ground are simulated, and it is confirmed that Brazil-Nut effect occurs. Next, the behaviors of particles in the space are simulated. From this simulation results, the internal distribution of particles' upward trend is obtained. It is compared with the known information of ITOKAWA, and the inferred internal structure of rubble-pile asteroid is discussed.

東京大学重照射研究設備は、1ミクロン程度の微粒子を数km/sを超える速度まで加速できる世界でも数少ない静電加速器施設である。これを用いて開発中の宇宙塵検出器の現状について報告する。

資料番号: AA0063706013