川口 淳一郎

IKAROSとは宇宙航空研究開発機構(JAXA)が開発した小型ソーラー電力セイル実証機であり,2010年5月21日に種子島宇宙センターよりH-IIAロケット17号機によって打ち上げられた.IKAROSは将来の外惑星領域探査ミッションを想定してソーラーセイルおよびソーラー電力セイルを世界で初めて実証した.2011年以降も運用を継続し,数多くの成果をあげている.IKAROSは小規模プロジェクトのため,広報活動に関して,予算をほとんど割くことができない状況であったが,チームメンバーが創意工夫を凝らし,精力的に活動を行った.特にツィッターやブログを通して開発・運用の現場の様子をタイムリーに発信したことで多くのファンを獲得できた.また,TPSにも発信してもらったことでIKAROSの成果が世界中に知れ渡ることとなった.さらに,はやぶさ地球帰還との相乗効果もあり,日本の探査技術が大きく取り上げられる機会となった.本稿では,我々が取り組んできたIKAROSの広報・アウトリーチ活動全般について報告する.

© 2014, Springer Science+Business Media Dordrecht. This work studies periodic solutions applicable, as an extended phase, to the JAXA asteroid rendezvous mission Hayabusa 2 when it is close to target asteroid 1999 JU3. The motion of a spacecraft close to a small asteroid can be approximated with the equations of Hill’s problem modified to account for the strong solar radiation pressure. The identification of families of periodic solutions in such systems is just starting and the field is largely unexplored. We find several periodic orbits using a grid search, then apply numerical continuation and bifurcation theory to a subset of these to explore the changes in the orbit families when the orbital energy is varied. This analysis gives information on their stability and bifurcations. We then compare the various families on the basis of the restrictions and requirements of the specific mission considered, such as the pointing of the solar panels and instruments. We also use information about their resilience against parameter errors and their ground tracks to identify one particularly promising type of solution.

The mineralogy and mineral chemistry of Itokawa dust particles captured during the first and second touchdowns on the MUSES-C Regio were characterized by synchrotron-radiation X-ray diffraction and field-emission electron microprobe analysis. Olivine and low- and high-Ca pyroxene, plagioclase, and merrillite compositions of the first-touchdown particles are similar to those of the second-touchdown particles. The two touchdown sites are separated by approximately 100 meters and therefore the similarity suggests that MUSES-C Regio is covered with dust particles of uniform mineral chemistry of LL chondrites. Quantitative compositional properties of 48 dust particles, including both first- and second-touchdown samples, indicate that dust particles of MUSES-C Regio have experienced prolonged thermal metamorphism, but they are not fully equilibrated in terms of chemical composition. This suggests that MUSES-C particles were heated in a single asteroid at different temperatures. During slow cooling from a peak temperature of approximately 800 degrees C, chemical compositions of plagioclase and K-feldspar seem to have been modified: Ab and Or contents changed during cooling, but An did not. This compositional modification is reproduced by a numerical simulation that modeled the cooling process of a 50 km sized Itokawa parent asteroid. After cooling, some particles have been heavily impacted and heated, which resulted in heterogeneous distributions of Na and K within plagioclase crystals. Impact-induced chemical modification of plagioclase was verified by a comparison to a shock vein in the Kilabo LL6 ordinary chondrite where Na-K distributions of plagioclase have been disturbed.

The mineralogy and mineral chemistry of Itokawa dust particles captured during the first and second touchdowns on the MUSES-C Regio were characterized by synchrotron-radiation X-ray diffraction and field-emission electron microprobe analysis. Olivine and low- and high-Ca pyroxene, plagioclase, and merrillite compositions of the first-touchdown particles are similar to those of the second-touchdown particles. The two touchdown sites are separated by approximately 100 meters and therefore the similarity suggests that MUSES-C Regio is covered with dust particles of uniform mineral chemistry of LL chondrites. Quantitative compositional properties of 48 dust particles, including both first- and second-touchdown samples, indicate that dust particles of MUSES-C Regio have experienced prolonged thermal metamorphism, but they are not fully equilibrated in terms of chemical composition. This suggests that MUSES-C particles were heated in a single asteroid at different temperatures. During slow cooling from a peak temperature of approximately 800 °C, chemical compositions of plagioclase and K-feldspar seem to have been modified: Ab and Or contents changed during cooling, but An did not. This compositional modification is reproduced by a numerical simulation that modeled the cooling process of a 50 km sized Itokawa parent asteroid. After cooling, some particles have been heavily impacted and heated, which resulted in heterogeneous distributions of Na and K within plagioclase crystals. Impact-induced chemical modification of plagioclase was verified by a comparison to a shock vein in the Kilabo LL6 ordinary chondrite where Na-K distributions of plagioclase have been disturbed. © The Meteoritical Society, 2014.

The Planetary Material Sample Curation Facility of JAXA (PMSCF/JAXA) was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants. The performances for the curation of Hayabusa-returned samples had been checked with a series of comprehensive tests and rehearsals. After the Hayabusa spacecraft had accomplished a round-trip flight to asteroid 25143 Itokawa and returned its reentry capsule to the Earth in June 2010, the reentry capsule was brought back to the PMSCF/JAXA and was put to a series of processes to extract recovered samples from Itokawa. The particles recovered from the sample catcher were analyzed by electron microscope, given their ID, grouped into four categories, and preserved in dimples on quartz slide glasses. Some fraction of them has been distributed for initial analyses at NASA, and will be distributed for international announcement of opportunity (AO), but a certain fraction of them will be preserved in vacuum for future analyses. © The Meteoritical Society, 2013.

This study is about evaluating the transient response of large spinning membrane structures in space - especially for spinning solar sails - by two different methods. The flexible sail membrane easily deforms when the spacecraft changes its attitude using thrusters, for example, and the control response including the membrane vibration must be estimated during the actual operation. In order to estimate the motion of the membrane, a numerical method using a multi-particle model is utilized referred to as the continuum analysis in this study. This method is useful for analysis of membrane vibration because it replaces the complex dynamics with simple equations of motion. However, the calculation cost is high and it requires a considerable amount of time. This study introduces the eigenfunction analysis to solve this problem. In this method, the natural vibration modes and the natural frequencies of the whole spacecraft are derived, which reduces the cost dramatically compared to the conventional continuum analysis. In this study, the transient response of a spinning solar sail is analysed using both methods, and advantages and disadvantages are discussed. It is shown that the eigenfunction analysis provides a suitable method to acquire approximate solutions in a very short time.

The attitude motion of the spinning solar sail IKAROS was unique. Its behavior is highly dependent on the sail deformation, which is flexible and easily changed by the attitude motion itself. It is important, therefore, to understand the relation between the sail deformation and the attitude motion in order to obtain better knowledge of sail design and management. In this study, a consideration is made about how the sail deforms with the centrifugal force on it and its physical stiffness, and how it changes the attitude motion. As a result, the effects of each natural vibration mode of the sail on the attitude motion are formularized. The theory is evaluated using the flight-data of IKAROS and estimating its sail deformation.

In a heater control system including a number of elements, the power consumption may exceed the capacity of the power supply when a lot of elements require the power source simultaneously. In such case, the system has some risk of power shortages, while the time-averaged power consumption is enough low for the power supply. If an equipment gathers the information about the temperature of each elements and controls each switches not to turned on simultaneously, the over consumption would be prevented. However, this system needs many cables between center equipment and each elements, and becomes complex and lacks versatility. To solve these problems, authors has proposed a novel multi-agent heater controller that maintains the temperature at each element, while the whole power consumed is kept constant, without any specific server in the system. In this paper, a new developed multi-agent heater controller for spacecraft is introduced and results of experiments to verify the control system are shown. The results are compared with the results of simulations.

In an interplanetary mission, the influence of solar radiation pressure (SRP) is a dominant disturbance in terms of the attitude control of a spacecraft, and a continuous disturbance due to the SRP shortens their mission life time. On the other hand, practical uses of the SRP are rapidly developed such as in Hayabusa and IKAROS, and their effectiveness is increasingly acknowledged. The objective of this study is to establish attitude control methods of a spacecraft by actively using the SRP. Moreover, we derive general and precise control methods by taking into account that the principal axes of inertia of a spacecraft are usually inclined from its symmetrical axes slightly, and verify the control methods by applying it to a model of Akatsuki.

The attitude motion of the spinning solar sail IKAROS was unique. Its behavior is highly dependent on the sail deformation, which is flexible and easily changed by the attitude motion itself. It is important, therefore, to understand the relation between the sail deformation and the attitude motion in order to obtain better knowledge of sail design and management. In this study, a consideration is made about how the sail deforms with the centrifugal force on it and its physical stiffness, and how it changes the attitude motion. As a result, the effects of each natural vibration mode of the sail on the attitude motion are formularized. The theory is evaluated using the flight-data of IKAROS and estimating its sail deformation.

This paper describes achievements of the IKAROS project, the world's first successful interplanetary solar power sail technology demonstration mission. It was developed by the Japan Aerospace Exploration Agency (JAXA) and was launched from Tanegashima Space Center on May 21, 2010. IKAROS successfully deployed a 20 m-span sail on June 9, 2010. Since then IKAROS has performed interplanetary solar-sailing taking advantage of an Earth-Venus leg of the interplanetary trajectory. We declared the completion of the nominal mission phase in the end of December 2010 when IKAROS successfully passed by Venus with the assist of solar sailing. This paper describes the overview of the IKAROS spacecraft system, how the world's first interplanetary solar sailer has been operated and what were achieved by the end of the nominal mission phase. (c) 2012 Elsevier Ltd. All rights reserved.

Weak stability boundary (WSB) lunar gravity-capture transfers can save much effort (dV) on arrival at the Moon but there is a very narrow window of only a few days in a month to achieve these transfers. This is because WSB transfers require a specific orientation of the orbit with regard to the Sun, the Earth and the Moon to efficiently use the chaotic dynamics of the multi-body problem. In this paper, we propose controlling the orbit through small continuous acceleration. The results show that the window of the WSB transfer can be expanded up to a full month.

This paper proposes a novel strategy for simplified trajectory design in aero-gravity assist missions. In aero-gravity assists, the extent of deceleration and the periapsis altitude are coupled and dependent to each other, which makes it difficult to obtain desired outgoing trajectory. We insert a one-revolution orbit as a trajectory leg just after the aero-gravity assist so that we can utilize degrees of freedom in design for connecting two trajectory before and after the swing-by. After one-revolution interplanetary cruise, the S/C re-encounters the planet and thus has a chance to go to new destination by a usual gravity assist, or to experience aero-gravity assist again, which allows us various interplanetary missions afterward. This paper describes the difficulty in design of aero-gravity assists, outline of our novel approach and its detailed procedures. A case study for Earth aero-gravity assist design is also shown.

In the overall context of a solar sail mission in the vicinity of the Trojan asteroids swarm around the L4 Lagrange point, the purpose of this work is to find an optimal sequence of asteroids rendezvous that accommodates given mission constraints. A currently considered strategy to solve this problem will be presented and design choices will be outlined. A subset of the Trojan asteroids database is first extracted based on orbital elements considerations and a tree containing all the potential sequences is generated. A first set of pruning techniques is applied to the tree in order to quickly reduce the search space by several orders of magnitude. A global optimization method is then used: it combines a branch-and-bound approach and an evolutionary algorithm to find good sequence order, departure date, transfer and coasting durations. In order to enable a fast computation of potential transfer costs, the dynamics are linearized around L4 and the ΔVs are computed analytically. Preliminary results show a drastic reduction of the search space along with a reasonable accuracy on the cost prediction. This method has been used to analyze a tour scenario starting from 588 Achilles and including three rendezvous; the final result provides a list of sequences of potential interest. © 2013 2013 California Institute of Technology.

This paper proposes a strategy for sub-payload spacecraft to extend possibility of interplanetary exploration without interrupting the mission by the main spacecraft. Combination of Earth revolution synchronous orbits and aero-gravity assists at Earth will allow sub-payload spacecraft to control its departure timing, C3 energy and destination independently. A case study of a possible sub-payload bound for Mars is shown and a preliminary mission sequence is presented.

This paper proposes a novel strategy for simplified trajectory design in aero-gravity assist missions. In aero-gravity assists, the extent of deceleration and the periapsis altitude are coupled and dependent to each other, which makes it difficult to obtain desired outgoing trajectory. We insert a one-revolution orbit as a trajectory leg just after the aero-gravity assist so that we can utilize degrees of freedom in design for connecting two trajectory before and after the swing-by. After one-revolution interplanetary cruise, the S/C re-encounters the planet and thus has a chance to go to new destination by a usual gravity assist, or to experience aero-gravity assist again, which allows us various interplanetary missions afterward. This paper describes the difficulty in design of aero-gravity assists, outline of our novel approach and its detailed procedures. A case study for Earth aero-gravity assist design is also shown. © 2013 2013 California Institute of Technology.

This paper proposes a strategy for sub-payload spacecraft to extend possibility of interplanetary exploration without interrupting the mission by the main spacecraft. Combination of Earth revolution synchronous orbits and aero-gravity assists at Earth will allow sub-payload spacecraft to control its departure timing, C3 energy and destination independently. A case study of a possible sub-payload bound for Mars is shown and a preliminary mission sequence is presented.

地球外物質の採取・記載・保管および配布の目的で発足したJAXAキュレーションセンターでは,現在は小惑星イトカワにタッチダウンした探査機「はやぶさ」の試料を取り扱っている.「はやぶさ」から分離して地球帰還した再突入カプセルを受け入れ,その内部の試料コンテナを取り出してクリーンチェンバー内に導入し,開封を行った.試料コンテナ内の残留ガスから地球外起源の希ガスは検出できなかったが,キャッチャー内部からは主にケイ酸塩鉱物から成る微粒子を回収した.初期記載の結果,それらの鉱物比・鉱物組成がLL4-6コンドライト隕石に近いことが分かり,イトカワ試料と確認された.現在までに400個以上の粒子の回収・初期記載を行い,そのうち8割がイトカワ粒子だった.キュレーションセンターではこの試料を初期分析チーム,NASA,国際公募研究に対して配布し,多様な科学成果が挙がっている.

In the overall context of a solar sail mission in the vicinity of the Trojan asteroids swarm around the L4 Lagrange point, the purpose of this work is to find an optimal sequence of asteroids rendezvous that accommodates given mission constraints. A currently considered strategy to solve this problem will be presented and design choices will be outlined. A subset of the Trojan asteroids database is first extracted based on orbital elements considerations and a tree containing all the potential sequences is generated. A first set of pruning techniques is applied to the tree in order to quickly reduce the search space by several orders of magnitude. A global optimization method is then used: it combines a branch-and-bound approach and an evolutionary algorithm to find good sequence order, departure date, transfer and coasting durations. In order to enable a fast computation of potential transfer costs, the dynamics are linearized around L4 and the Delta Vs are computed analytically. Preliminary results show a drastic reduction of the search space along with a reasonable accuracy on the cost prediction. This method has been used to analyze a tour scenario starting from 588 Achilles and including three rendezvous; the final result provides a list of sequences of potential interest.

The Japan Aerospace Exploration Agency (JAXA) makes the world's first solar power sail craft IKAROS demonstration of photon propulsion and thin film solar power generation during its interplanetary cruise. The spacecraft deploys and spans a membrane of 20 meters in diameter using the spin centrifugal force. It also deploys thin film solar cells on the membrane, in order to evaluate its thermal control property and anti-radiation performance in the real operational field. The spacecraft weighs approximately 310kg, launched together with the agency's Venus Climate Orbiter, AKATSUKI on May 21, 2010. This paper presents the summary of development and operation of IKAROS.

A study on the post-HINODE Solar Observation Mission has been started by members in the solar physics community. One candidate of the mission targets on the observation of the solar polar region from the orbit largely inclined with the ecliptic plane. In order to achieve this severe mission target, possible trajectory sequences are investigated considering the application of various trajectory manipulation techniques. Three major trajectory options are listed up to achieve the mission objective. The first option, "SEP option", is characterized by the usage of solar electric propulsion (SEP) combined with the earth gravity assists. The other options are characterized by the usage of planetary gravity assists, and SEP is not used in these options. They are named "Jupiter option" and "Venus option" respectively. The comparison among the trajectory options is discussed in the paper, not only from the aspect of the orbital mechanics, but also from the aspects of the spacecraft design and operation.

Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 μm, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-μm-sized craters but also a large number of sub-μm- to several-μm-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-μm-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

Hayabusa was a JAXA sample-return mission to Itokawa navigated, in part, by JPL personnel. The spacecraft survived several near mission-ending failures at Itokawa yet returned to Earth with an asteroid regolith sample on June 13, 2010. This paper describes NASA/JPL's participation in the Hayabusa mission during the last 100 days of its mission, wherein JPL provided tracking data and orbit determination, plus verification of maneuver design and entry, descent and landing. © Copyright 2011 California Institute of Technology. Government sponsorship acknowledged.

Microparticles recovered from the Asteroid 25143 Itokawa surface by the Hayabusa mission have been examined for the occurrence of soluble organic compounds. After five individual particles (∼50 to 100 μm in diameter) were rinsed with organic solvents on a diamond plate, two extracts were hydrolyzed with hydrochloric acid for amino acid analysis (AAA), and three extracts were combined for time of flight-secondary ion mass spectrometry (ToF-SIMS) to look for other organic compounds, including polycyclic aromatic hydrocarbons. The organic compounds detected by both methods have the same concentrations as those in blank levels, indicating that indigenous organic compounds are not found in this study. Based on the sensitivities of AAA and ToF-SIMS with the reference sample analyses, the concentrations of indigenous organics in the samples are below part-per-million (ppm), if present. Copyright © 2012 by The Geochemical Society of Japan.

Solar power sail is a deep space probe to be powered by hybrid propulsion of solar photon acceleration and ion engines to explore outer planetary region of the Solar System without relying on nuclear technology. The Japan Aerospace Exploration Agency (JAXA) launched the world's first deep space solar sail demonstration spacecraft "IKAROS" (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) on May 21, 2010. IKAROS succeeded in deploying a 20m-span solar sail on June 9 and demonstrated several key technologies for solar sail utilizing the deep space flight environment. JAXA is currently studying an outer solar system exploration mission using the demonstrated solar power sail technology. The mission plans to fly for Jupiter, where the spacecraft drops a tiny Jovian probe and performs a swing-by for a Trojan asteroid. Current scenario consists of the rendezvous with one of the Trojan asteroids that are at the Lagrange points L4/L5 associated with Sun-Jupiter system. About as large as 50m sail should be deployed for this mission according to preliminary mission analysis and related research is intensively being carried out in JAXA. JAXA plans to initiate the project in a few years and looks at the launch around 2020. © 2012 by JAXA.

This paper describes an analysis for the membrane dynamics and deformation of solar power sail demonstrator "IKAROS". After the successful deployment of membrane, some images of the whole sail membrane of IKAROS were taken by separation cameras. From these data, it has estimated that the membrane of IKAROS had a deformation different from the prediction considering the solar radiation pressure. In this paper, these observed deformations of membrane are reported and compared with the results of numerical simulation using multi-particle model. A membrane's deformation over time observed in the images taken by side monitor cameras is also reported and the cause of the changing is discussed. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

This paper describes an analysis for the membrane dynamics and deformation of solar power sail demonstrator "IKAROS". After the successful deployment of membrane, some images of the whole sail membrane of IKAROS were taken by separation cameras. From these data, it has estimated that the membrane of IKAROS had a deformation different from the prediction considering the solar radiation pressure. In this paper, these observed deformations of membrane are reported and compared with the results of numerical simulation using multi-particle model. A membrane's deformation over time observed in the images taken by side monitor cameras is also reported and the cause of the changing is discussed. ©2012 AIAA.

Solar power sail is a deep space probe to be powered by hybrid propulsion of solar photon acceleration and ion engines to explore outer planetary region of the Solar System without relying on nuclear technology. The Japan Aerospace Exploration Agency (JAXA) launched the world's first deep space solar sail demonstration spacecraft "IKAROS" (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) on May 21, 2010. IKAROS succeeded in deploying a 20m-span solar sail on June 9 and demonstrated several key technologies for solar sail utilizing the deep space flight environment. JAXA is currently studying an outer solar system exploration mission using the demonstrated solar power sail technology. The mission plans to fly for Jupiter, where the spacecraft drops a tiny Jovian probe and performs a swing-by for a Trojan asteroid. Current scenario consists of the rendezvous with one of the Trojan asteroids that are at the Lagrange points L4/L5 associated with Sun-Jupiter system. About as large as 50m sail should be deployed for this mission according to preliminary mission analysis and related research is intensively being carried out in JAXA. JAXA plans to initiate the project in a few years and looks at the launch around 2020. ©2012 AIAA.

It is well known that the thrust force of the solar sail due to the solar radiation pressure is changed by the orientation of the sail with respect to the Sun direction. Therefore, the orbit of the solar sail can be controlled by changing the attitude of the spacecraft. In this study, we consider the spinning solar power sail IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun), which succeeded to become the world's first flight solar sail in orbit. The IKAROS attitude, i.e. the spin-axis direction is nominally controlled by the rhumb-line control method. By utilizing the solar radiation pressure (SRP) torque, however, we are able to change the direction of the spin-axis only by controlling its spin rate. This is because the spin axis direction relates to the balance between the angular momentum of spinning and the SRP torque. Thus, we can control the solar sail's orbit by controlling the spin rate. The main objective in this study is to construct the orbit control strategy of the spinning solar sail via the spin rate control.

A fuel-free attitude control system for a spinning solar sail which utilizes solar radiation pressure was developed. This system consists of thin-film devices attached to the sail that electrically control their optical parameters such as reflectivity, and the attitude control torque is generated by switching their optical parameters synchronizing with spin motion. Attitude control torque model for a sail of arbitrary shape and deformation was derived. The control system was implemented for Japanese interplanetary solar sail demonstration spacecraft IKAROS and the on-orbit attitude control performance was evaluated.

The power supply management system was originally developed at JAXA to manage the risk of electric power scarce due to excess access from each device. The main idea is to decrease the peak amount of limited power in a spacecraft by changing in switching time based on demand-response from each device. For realization, the system features "decentralized system" and "priority setting" on each device. The decentralized system, in which each device has its own controller and changes information each other, contributes to the robustness of the system since a defect of the controller does not affect other parts of the system while the limited power is allocated based on the priority level of each device. Experiments were taken for heater control equipment to demonstrate the practical performance of the novel power system. In the experiments, six devices were prepared with heater controllers which received duty signals, and set the target temperature for each of the devices. The experiments were initiated by providing sufficient power and checked if all the devices were fully working, and then decreased the power supply to observe the behavior of the temperatures under limited resource. As a result, all of the devices met the temperature requirements even under short energy supply. To quantitatively evaluate the benefits of the new system when applied to public infrastructure systems, multiple small electrical trains (HO gauge) whose electrical power provision system is basically the same as the real one have been arranged. The experiments also give the deeper understanding of behavior of first-order motor-driven system in view point of energy consumption. Presently, the priority setting system is being implemented to the small train system, to show whether similar results as the heater control case are also achieved. In conclusion, this paper will present the newly constructed power system and elaborate its ramifications together with the experimental and simulation results. Copyright © (2012) by the International Astronautical Federation.

This paper proposes a novel strategy for a space probe to descent and land on the asteroid surface with high accuracy of a few meters by utilizing several artificial markers deployed from the probe. Results of a numerical experiment indicated that the proposed method showed higher performance than conventional one. It will allow us to guide the probe with high mobility to the desired points such as small craters, which will be of great significance for understanding local geology and geography of the asteroid, or avoiding boulders and too rough regions.

This paper proposes a novel strategy for a space probe to descent and land on the asteroid surface with high accuracy of a few meters by utilizing several artificial markers deployed from the probe. Results of a numerical experiment indicated that the proposed method showed higher performance than conventional one. It will allow us to guide the probe with high mobility to the desired points such as small craters, which will be of great significance for understanding local geology and geography of the asteroid, or avoiding boulders and too rough regions.

This paper presents IKAROS extended missions. IKAROS entered its extended operation phase at the beginning of 2011. In the extended operation, the spin rate was decreased to observe the deformation of the sail under low centrifugal force environment. On Oct. 18, 2011, IKAROS transferred to the reverse spin to enhance the knowledge about the effect of stiffness of membrane against the solar radiation pressure. We investigated the change of the attitude motion by the reverse spin mission. At the end of 2011, IKAROS moved to hibernation mode because the Sun angle was increased. We searched for IKAROS considering the attitude and orbital motion during hibernation. On Sep. 6, 2012, we succeedcd in tracking IKAROS which came out of hibernation. A solar power sail can be a hybrid propulsion system with a solar sail by activating the ultra-high specific impulse ion engines with the power generated by thin film solar cells. This paper also introduces an advanced solar power sail mission toward Jupiter and Trojan asteroids via hybrid electric photon propulsion.©2012 by the International Astronautical Federation.

「ソーラーセイル」は,太陽光の圧力をセイルに受けて宇宙空間を航行する宇宙帆船であり,燃料なしで推進力を得ることができる.一方,「ソーラー電力セイル」は,薄膜太陽電池をセイルの一部に貼り付けて,発電も同時に行う.ソーラー電力セイルはソーラーセイルにより燃料を節約できるだけでなく,大面積の薄膜太陽電池を利用して,太陽から遠く離れた場所でも必要電力を確保できる.この電力を用いてイオンエンジンを駆動すれば,光子加速と合わせたハイブリッド推進が可能となる.JAXAではこれを踏まえてソーラー電力セイル探査機による木星圏探査計画を提案している.この計画のリスク軽減のフロントローディングとして開発されたのが,小型ソーラー電力セイル実証機「IKAROS」であり,世界で初めてソーラー電力セイルを実証することに成功した.本稿では,IKAROSのミッションおよびシステムの概要を説明し,開発・運用について紹介する.

本稿では,小型ソーラー電力セイル実証機IKAROSのセイル展開方式として採用した,遠心力展開方式について, JAXAにて著者らが行ってきた研究開発を概説する. IKAROSは世界に先駆けてJAXAが実施したソーラー電力セイル技術の宇宙技術実証であり,宇宙機全体のスピンによる遠心力を利用してセイルの展開・展張をするという独特な方式を採用している.著者らは,軽量かつスケーラブルなセイル展開システムとして遠心力展開方式を採用し,研究開発を行ってきた.本活動は, 2002年にJAXA内に発足したソーラーセイルワーキンググループが中心となり,全国の多数の大学研究機関とともに行ってきたものである.最終的な目標はφ50m級のソーラー電力セイルを実現することにあり,φ20m級のセイルを搭載したIKAROSはその最終段階の宇宙技術実証試験と位置付けられたものである.ここでは,本研究開発活動の主要な柱である遠心力展開技術について紹介し, IKAROSプロジェクト発足以前に著者らが行ってきた主要な試験プロセスと数値シミュレーション技術について概説する.

A fuel-free attitude control system for a spinning solar sail which utilizes solar radiation pressure was developed. This system consists of thin-film devices attached to the sail that electrically control their optical parameters such as reflectivity, and the attitude control torque is generated by switching their optical parameters synchronizing with spin motion. Attitude control torque model for a sail of arbitrary shape and deformation was derived. The control system was implemented for Japanese interplanetary solar sail demonstration spacecraft IKAROS and the on-orbit attitude control performance was evaluated.

It is well known that the thrust force of the solar sail due to the solar radiation pressure is changed by the orientation of the sail with respect to the Sun direction. Therefore, the orbit of the solar sail can be controlled by changing the attitude of the spacecraft. In this study, we consider the spinning solar power sail IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun), which succeeded to become the world's first flight solar sail in orbit. The IKAROS attitude, i.e. the spin-axis direction is nominally controlled by the rhumb-line control method. By utilizing the solar radiation pressure (SRP) torque, however, we are able to change the direction of the spin-axis only by controlling its spin rate. This is because the spin axis direction relates to the balance between the angular momentum of spinning and the SRP torque. Thus, we can control the solar sail's orbit by controlling the spin rate. The main objective in this study is to construct the orbit control strategy of the spinning solar sail via the spin rate control.

The orbit of a solar sail can be controlled by changing the attitude of the spacecraft. In this study, we consider the spinning solar power sail IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun), which is managed by Japan Aerospace Exploration Agency (JAXA). The IKAROS attitude, i.e.; the direction of its spin-axis, is nominally controlled by the rhumb-line control method. By utilizing the solar radiation torque, however, we are able to change the direction of the spin-axis by only controlling its spin rate. With this spin rate control, we can also control indirectly the solar sail's trajectory. The main objective of this study is to construct the orbit control strategy of the solar sail via the spin-rate control method. We evaluate this strategy in terms of its propellant consumption compared to the rhumb-line control method. Finally, we present the actual flight attitude data of IKAROS and the change of its trajectory. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

This paper introduces a new attitude control system for a solar sail, which leverages solar radiation pressure. This novel system achieves completely fuel-free and oscillation-free attitude control of a flexible spinning solar sail. This system consists of thin-film-type devices that electrically control their optical parameters such as reflectivity to generate an imbalance in the solar radiation pressure applied to the edge of the sail. By using these devices, minute and continuous control torque can be applied to the sail to realize very stable and fuel-free attitude control of the large and flexible membrane. The control system was implemented as an optional attitude control system for small solar power sail demonstrator named IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun). In-orbit attitude control experiments were conducted, and the performance of the controller was successfully verified in comparison with the ground-based analytical performance estimation. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in (16)O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.

Regolith particles on the asteroid Itokawa were recovered by the Hayabusa mission. Their three-dimensional (3D) structure and other properties, revealed by x-ray microtomography, provide information on regolith formation. Modal abundances of minerals, bulk density (3.4 grams per cubic centimeter), and the 3D textures indicate that the particles represent a mixture of equilibrated and less-equilibrated LL chondrite materials. Evidence for melting was not seen on any of the particles. Some particles have rounded edges. Overall, the particles' size and shape are different from those seen in particles from the lunar regolith. These features suggest that meteoroid impacts on the asteroid surface primarily form much of the regolith particle, and that seismic-induced grain motion in the smooth terrain abrades them over time.