森 治

In this paper, the behavior of flexible membranes is investigated via numerical simulations using the multi-particle method (MPM) in which the membrane is replaced by a spring, damper and mass. To verify the model, some experiments on membrane vibration using a vacuum chamber are carried out. These results are compared with the results of numerical simulations using the MPM, and then the membrane structural model based on the MPM is refined to accurately simulate the behavior of membranes in experiments.

Interplanetary Kite-craft Accelerated by Radiation Of the Sun (IKAROS) was launched in May, 2010. IKAROS deployed its membrane in space and generated electricity using its thin-film solar cells on the sail membrane. This paper focused on the fabrication process of the flight model of the thin-film solar cell array. IKAROS had 144 modules of thin-film solar cells with 360 W in total output power. One module was fabricated by stacking 4 layers; protective film, thin-film solar cell, anti-warpage layer and sail membrane. The size of one module is 220 mm x 300 mm x 152.5 μm. They were bonded each other with silicon glue. The connection between module and module or between module and sail membrane were also bonded with silicon glue. The fabricated thin-film solar cell array was examined from the point of possible damages during the fabrication process, resulting in no critical damage to the thin-film solar cell array. Moreover, it successfully generated in the orbit, in comparison to the assumed power generation from the results of the generation test before the launch.

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. © 2012 Elsevier Ltd.

JAXAでは,ソーラー電力セイルをはじめ将来の宇宙膜面構造物の大型化を視野に入れ,支柱等を使用せずにスピンによる遠心力で膜面を展開・展張する方式の検討を進めている.この方式においては,膜面を幾何的に拘束する剛性の高い構造が無いため膜面の運動の自由度は高くなり,これを適切に予測できる技術が重要となる,小型ソーラー電力セイル実証機「IKAROS」の打ち上げ前には様々な状況を想定して数値シミュレーションを用いた展開挙動予測が行われ,安全にセイルを展開できるシーケンスの決定に努めた.そしてIKAROSの打ち上げ後,事前解析情報に基づいてセイル展開を進めた結果,無事セイルの展開に成功した.本稿では,これらの数値シミュレーションによる事前解析の概要について述べるとともに,フライトデータとの比較による数値シミュレーションの有効性の検証,および今後のミッションにおける数値解析による膜面展開挙動の予測法に対する展望についても述べる.

The performance of tank devices, such as porous metals and a metal fiber, on liquid propellant retention was evaluated under microgravity environment. IKAROS carries the gas-liquid equilibrium propulsion system which stores propellant as liquid phase in a storage tank and expels only gaseous propellant from the tank. Surface tension in pores of tank devices holds liquid propellant in them. As a result of microgravity experiments, it was found that the performance on liquid retention is higher than that estimated from results of bubble point experiment, and it strongly depends on the existence of bubbles in liquid propellant. From the results of the experiment, this paper proposes the location of porous metals in the storage tank to prevent bubbles from remaining with propellant consumption.

The Japan Aerospace Exploration Agency (JAXA) makes the world's first solar power sail demonstration of photon propulsion and thin film solar power generation during its interplanetary cruise by IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun). It deployed and spans a membrane of 20 meters in diameter taking the advantage of the spin centrifugal force. It accelerates and controls the orbit using solar radiation pressure successfully. This is the first actual solar sail flying an interplanetary voyage. This paper presents the summary of development and operation of IKAROS and introduces the outline of the extended solar power sail mission toward Jupiter and Trojan asteroids.

Japan Exploration Agency (JAXA) launched a powered solar sail "Interplanetary Kite-craft Accelerated by Radiation Of the Sun (IKAROS)" on May 21, 2010. One of the primal technologies demonstrated at IKAROS is the spin-deployment of the sail whose diameter is 20 m class. After the launch, two-step deployment operation was performed and successful expansion of the sail was confirmed. This paper shows the flight data and observed dynamic motion during the deployment. At the quasi-static first stage deployment, the spin rate of main body shows little oscillation after each step and then damped quickly. The damping ratio of the spin rate after a later step of deployment is estimated by curve-fitting to be 0.0127. At the dynamic second stage deployment, the nutation motion is maintained within ±1.5 deg/s and the spin rate of main body is converged quickly about 60s after the deployment start. These flight result and observed dynamic motion during the deployment are compared with the results of numerical simulations using multi-particle model. These results show that the multi-particle model can simulate the global behavior of membrane sufficiently except the dumping motion of in-plane oscillation between the main body and the expanded membrane.

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「IKAROS」(Interplanetary Kite-craft Accelerated by Radiation Of the Sun)は2010年5月21日に打ち上げられた.IKAROSは日本が提唱するソーラー電力セイル技術の実証機であり,将来に計画されている木星圏探査等での実用を目指し惑星間軌道上で20m級膜面の展開,薄膜太陽電池の発電実証,ソーラーセイルによる光子加速実証,操舵技術実証を目的としている.IKAROSは2012年6月2日より大型ソーラー電力セイルの展開を開始し同年6月9日にセイル展開ミッションを完了,世界で初めての宇宙ヨットとなった.本稿ではIKAROSのセイル展開ミッションの総括として,軌道上で実施したセイル展開ミッションの結果について報告し,またIKAROS用に新規開発したセイル展開機構の紹介,セイルの展張状態の様子を観測するために搭載した2種類のカメラシステムのフライトデータについて報告する.

本稿は,世界初のソーラー電力セイルであるIKAROS(Interplanetary Kite-craft Accelerated by Radiation Of the Sun)のソーラーセイル膜面の構成,その製作法,そして実際の製作の流れについて述べたものである.IKAROSのソーラーセイル膜面は,2種類のポリイミドによるベースフィルム上に,薄膜太陽電池や液晶デバイスをはじめとする各種デバイスを搭載する構造となっている.差し渡し20mの大きさを持つIKAROSのソーラーセイル膜面は,多数の試作モデルの製作を通じて確立した製作法により,ハンドメイドで製作された.その後,IKAROSは2010年5月21日に打ち上げられ,続く2010年6月9日に軌道上でソーラーセイル膜面の展開を完了した.展開後に撮影されたカメラの画像から,ソーラーセイル膜面は亀裂が発生することなく完全に展開できていること,ソーラーセイル膜面を構成する各構成要素が所定の機能を果たしていることなどが確認されている.また,その後の運用により,IKAROSのメインミッションの他に,各種デバイスの経年劣化に関するデータも取得できている.

IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is the world's first solar sail demonstration spacecraft. It was launched in May 2010 and has 14-m-square solar sail. Solar sail is a propulsion system which accelerates the spacecraft with the solar radiation pressure, and its performance is largely affected by its unevenness. In order to recover a shape of the sail in the space, pictures of IKAROS taken in the space with cameras separated from the main body are used because of its structural complexity. There are two types of image analysis method and in this paper shape from shading method, in which the brightness of pixels is focused on, is adopted. Since there are some causes of image degradation and they are difficult to model, some cases are verified to know the detail characteristics. This paper presents the approach for analyzing the pictures to obtain the shape of IKAROS sail, and compares the result with the one of another image analysis method and flight data of the attitude motion.

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.

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.

This paper analyzes the behavior of an interplanetary dust particle on a horseshoe orbit by solving equations of the circular restricted three-body problem (CR3BP) analytically to predict the distribution of dust particles around the Earth's orbit, because in previous research numerical simulation showed that dust particles trapped on a horseshoe orbit contributes a number density of dust particles around the Earth's orbit. An analytical solution is obtained by coordinate transformation and linearization of external forces on the assumption that a horseshoe orbit is an oscillation centered at Lagrange point L3. This paper describes properties of the horseshoe solution and also shows that the analytical solution of the CR3BP is consistent with that of numerical integration.

In this paper, the attitude dynamics of IKAROS, which is spinning solar sail, are presented. The first mode model of out-of-plane sail deformation (FMM) and multi-particle model (MPM) are introduced to analyze the oscillatory motion of the spinning solar sail. Three oscillation modes are derived from the FMM. They are caused by the nutation motion of the main body, as well as the nutation motion and the out-of-plane oscillation of the sail. The precise attitude motion after sail deployment and reorientation using thrusters is calculated using the MPM considering thruster plume. The IKAROS flight data of the nutation angular velocities of the main body after sail deployment or reorientation using thrusters are nearly equal to the analytical data found using the FMM and MPM.

「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.

Microgravity experiments were performed to evaluate liquid propellant retention force of a porous metal. In our gas-liquid equilibrium propulsion system, porous metals are equipped in a storage tank and surface tension in pores of the porous metals holds liquid propellant in them, which ensures expelling of only gaseous propellant from a storage tank. The performance of a porous metal for liquid retention was evaluated by two different microgravity experiments. In the first one, the acrylic tank filled with semilunar porous metals and liquid propellant was rotated by a motor. The performance was evaluated by considering a force balance between liquid retention force and centrifugal force acting on the liquid propellant absorbed in porous metals. In the other one, the internal pressure in the tank was reduced by propellant ejection from a nozzle. The performance was evaluated by exhaustion time. As a result, it was found that liquid retention force was equal to, or higher than analytical value (bubble point pressure), and extractable gas volume of each ejection strongly depends on the existence of bubbles in liquid propellant.

JAXAではIKAROS計画において,ソーラーセイルによる推進と薄膜太陽電池による発電を行うことによって,世界で初めてソーラー電力セイルを実証した.IKAROSはスピンの遠心力を利用して200m^2の大型膜面を展開・展張する技術実証型のミッションであり,膜面に太陽光を受けて惑星間軌道で加速・軌道制御を実現し,世界初のソーラーセイルによる航行を達成した.本稿では,IKAROSのミッションおよびシステムについて紹介し,IKAROSの成果やこれを踏まえた今後の展望について解説する.

While analyzing membrane dynamic characteristics, Multi Particle Method (MPM) has several advantages than Finite Element Method (FEM). This paper presents the influence of spring allocation on the analytical value of flexural vibration using MPM. Two MPM models, one is using parallelogram element and the other is using rectangular element, and FEM model as a reference are used for comparison of the accuracy evaluations. Flexural vibration phenomenon is selected for the comparison of the eigenvalue analysis under applying a shear force upon rectangular membrane. Analytical accuracies of the eigenvalue of the membrane flexural vibration are found to be very much dependent on the shear force value and the spring allocation of the analytical model of MPM.

IKAROS is a small solar power sail demonstration spacecraft developed by JAXA. The spacecraft launched on May 2010 succeeded in deploying a thin solar power sail membrane with 14 meters in width and 7.5 micrometers in thickness. The membrane was folded and wrapped around the spacecraft and unfurled by centrifugal force in two stages. Since the deployment test of the large thin membrane is impossible on the ground, a huge amount of numerical simulations were performed before launch by employing the multi-particle system model (MPM) and the nonlinear elasto-dynamic finite element analysis (NEDA). MPM approximates a thin membrane with a spring-mass-damper system and enables fast numerical simulations. NEDA is based on the energy momentum method which preserves the total energy, the linear momentum and the angular momentum and enables reliable simulations of flexible multi-body systems. In this paper, their numerical results are compared with flight data and the deployment behaviors of the membrane are discussed.

EJSM (Europa Jupiter System Mission) is a planned Jovian system mission with three spacecraft aiming at coordinated observations of the Jovian satellites especially Europa and the magnetosphere, atmosphere and interior of Jupiter. It was formerly called "Laplace" mission. In October 2007, it was selected as one of future ESA scientific missions Cosmic Vision (2015-2025). From the beginning, Japanese group is participating in the discussion process of the mission. JAXA will take a role on the magnetosphere spinner JMO (Jupiter Magnetosphere Orbiter). On the other hand, ESA will take charge of JGO (Jupiter Ganymede Orbiter) and NASA will be responsible for JEO (Jupiter Europa Orbiter). In February 2009, EJSM is prioritized as the first candidate of outer planet flagship mission and mission study continues in the course of Cosmic Vision. The expected launch time of EJSM will be expected in 2020. Currently we are seeking a possibility to combine JMO with a proposed solar sail mission of JAXA for Jupiter and one of Trojan asteroids.

原始太陽系円盤を構成していた初期物質を探るためには,惑星形成時の熱変成の影響を免れた小惑星・彗星・惑星間塵といった小天体の研究が不可欠である.なかでも木星のラグランジュ点付近に存在するトロヤ群小惑星は,小惑星と彗星の間をつなぐ天体であり,原始太陽系円盤の物質分布や微惑星の成長・移動プロセスを調べる上で重要なターゲットである.本稿では,日本が世界に先駆けて実証したソーラー電力セイル技術を用いたトロヤ群小惑星探査ミッションを提案する.この探査は(1)トロヤ群小惑星の詳細な物質組成や熱史・衝突史を調べることで,その起源と進化を明らかにする, (2)惑星間塵の空間分布を測定することで,彗星・小惑星からの生成率や軌道進化に関する理解を深め,その結果を他の惑星系に応用する, (3)惑星間塵の影響の少ない小惑星帯以遠からの宇宙赤外線背景放射観測によって,宇宙初期に形成された第一世代の星を調べる,という科学目標をあわせ持つ,惑星科学・天文学・宇宙工学の融合ミッションである.

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.

This study investigates the trajectory analysis of small solar sail demonstration spacecraft IKAROS considering the uncertainty of solar radiation pressure. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop on the ground. In this paper, a practical analysis of estimating the solar sail force model from Doppler and range observable is investigated. This is demonstrated by orbit determination including parameter estimation of solar sail model. Some examples are described to investigate better parameters to estimate the solar sail force model.

The present study develops a new three-dimensional Timoshenko beam finite element whose length can be varied during transient dynamic analysis. The variable-length element enables the dynamic deployment analysis of flexible appendages with nonnegligible bending stiffness. In addition, the developed scheme employs an implicit time integration whereby energy and momentum in the system are properly conserved, and no artificial numerical dissipation is introduced. The developed beam element is then used in an finite element model of a solar sailcraft, and its deployment dynamics are analyzed allowing for the nonzero bending stiffness of the bundled membranes, as well as the effect of some realistic design imperfections.

The Japan Aerospace Exploration Agency (JAXA) will make the world's first solar power sail craft demonstration of photon propulsion and thin film solar power generation during its interplanetary cruise by IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun). The spacecraft deploys and spans a membrane of 20 meters in diameter taking the advantage of the spin centrifugal force. The spacecraft weighs approximately 310kg, launched together with the agency's Venus Climate Orbiter, AKATSUKI in May 2010. This will be the first actual solar sail flying an interplanetary voyage.

JAXA launched the world's first deep space solar sail demonstration spacecraft "IKAROS" on May 21, 2010. IKAROS was injected to an Earth-Venus trajectory to demonstrate several key technologies for solar sail utilizing the deep space flight environment. IKAROS succeeded in deploying a 20 m-span solar sail on June 9, and is now flying towards the Venus with the assist of solar photon acceleration. This paper describes the mission design, system design, solar sail deployment operation and current flight status of IKAROS. © 2011 Elsevier Ltd. All rights reserved.

The tether sampling method is a new minor-body sampling method proposed by the authors. It consists of three phases; 1) shooting a corer to penetrate the surface of a minor-body, 2) pulling up the corer with tether using a reel mechanism, 3) recovering the corer into a storage box. In this paper, the recovery phase is focused on, and its feasibility under micro-gravity is examined using parabolic flights. The experimental setup and parameters are described in this paper, and the experimental results indicate that the retrieval phase in tethered sampling method is feasible to work under micro-gravity.

The solar sailing spacecraft is one of the promising propulsion systems for the future deep space exploration mission. Japan Aerospace Exploration Agency (JAXA) has been studying the spin solar sail spacecraft which has a squared-shape type solar sail. One of the most significant objective to control the satellite orbit of the spacecraft is to estimate the thrust force induced by the photon, namely to establish the acceleration model before the launch. In a view point to use this model in orbit, the calibration of the acceleration model and evaluation of the dynamics on orbit are also important issue. This paper presents the way to construct the acceleration model of the Solar Radiation Pressure (SRP) on ground, and the calibration and evaluation strategy for this model by using the on-orbit data.

The Japan Aerospace Exploration Agency (JAXA) is studying the feasibility of using the solar power sail as a new propulsion engine for deep space exploration missions. In this paper, the sail shape and equipment layout for missions utilizing small-sized solar power sails are proposed. The two-stage deployment method of the sail is also proposed. The sail need to be deployed statically at the first stage, and two types of deployment mechanisms are introduced. On the other hand the second stage of the deployment can be performed dynamically, and the oscillating motion of the membrane is converged by tethers connecting the membrane to the main body. The deployment motions are analyzed by numerical simulations using multi-particle models in order to verify the deployment. They are compared with the results calculated by finite element method models. The numerical simulation results are discussed from the technological viewpoint of the sail deployment dynamics and mechanisms.

Solar sail is one of the promising propulsion systems for future deep space exploration missions as it does not require any fuel to acquire propulsive force. Although folding method and deployment mechanism of the sail have been intensively developed, attitude control of the solar sail, which is necessary for the orbital control by the solar sail, has not been much studied. This paper discusses the attitude dynamics and the control method of a spinning type solar sail spacecraft. The spinning type solar sail, where the sail equipped around the spacecraft hub is to be deployed and extended by centrifugal force, has no rigid structure supporting its membrane. This type of mechanism has the advantage in its simple and lightweight structure, however, the attitude control is difficult due to the flexibility of the membrane. In this paper, we introduced a mathematical dynamics model including first oscillation mode of the membrane which can handle coupled motion of a rigid spacecraft and a flexible membrane, and analytically developed a controller that can avoid unnecessary oscillatory motion. The performance of the controller was verified by numerical simulations using more precise multi-particle numerical model.

Miniaturization and high performance are always required for space equipments. But, it can be said that miniaturization and high performance are generally contradictory requirements. In this research, a fluid loop insulation and cooling system was built as a means of realizing both miniaturization and high voltage. For the working fluid of the system, fluorinated inactive liquids were used which can provide high electrical insulation and thermal conductivity. In this paper, to begin with, the electrical insulation property of the fluorinated inactive liquids was verified by an experiment. Then the dynamics model of the constructed insulation and cooling system was derived by a system identification experiment. Finally, a control law for temperature control was constructed using the estimated model and cooling performance of the system was examined by both numerical simulations and experiments.

The instruments and actuators in the attitude control system of small spacecraft are restricted in weight and space, and need to be reduced in weight and size. The rhumb line control strategy is one of the most popular schemes in reorientation of spin-stabilized spacecraft, since it requires only a spin sun sensor and a single axis reaction control system. By being combined with active nutation control, rhumb line control can reorient the spin axis of the spacecraft to any direction. To verify the control strategy, we manufactured an attitude controller and demonstration experiments were conducted using a motion table at ISAS/JAXA. This paper reviews the configuration of the controller and the outlines of the experiments, and evaluates the control performance. The same type of controller was installed in the Solar Sail Subpayload Satellite (SSSAT) launched in September 2006. An attitude control experiment in orbit was not conducted because of trouble with the satellite, but new control logic for the SSSAT was implemented for the attitude controller. This paper also reviews the control logic of the SSSAT.

In the proposed gas-liquid equilibrium thruster, fuel is mainly stored in the liquid phase in the tank and is ejected in the gas phase, powered by the vapor pressure of the fuel. As compared to conventional thrusters, the thrust level of this thruster is low. However, the system configuration of this thruster is simple because components such as combustors or high-pressure reservoirs are not required. Further, this thruster is lighter than other thrusters. Fuels with low toxicity and that are easily available can be selected in this thruster from many kinds of fuel candidates. As a result, this thruster can be easily handled. This thruster can be used as an actuator for controlling the attitude and maneuvering the orbit of small satellites.

This paper describes the navigation and the guidance strategy of the small spacecraft for flyby using the images of the target small body. We derived navigation and guidance accuracies of this mission analytically, and confirmed them by numerical simulations. For high accurate flyby, the center of the target needs to be measured accurately. However the shade area on the target surface makes it difficult to know the target center position from the information of the center of brightness on image. This uncertainty caused the guidance error. To resolve this problem, this paper proposes a method to calculate the target center from the tangent points of the sun light. The validity of the method is examined in the experiment.

Institute of Space and Astronautical Science (ISAS) of Japan Aerospace Exploration Agency (JAXA) is currently planning the missions that the small probe 'interceptor' flybys near Earth objects. Interceptor is very small probe. An interceptor observes spectrum, takes close images, and determines mass of an NEO (near earth object) during a flyby. The weight of interceptor is less than 10 kg. This paper shows three types of missions. In general, it is impossible to determine the relative orbit during flyby only with optical information. Thus, the optical navigation needs to be combined with the radio navigation that should provide the relative velocity vector information. In this paper, the integrated guidance and navigation strategy of interceptor is proposed. The interceptor needs the thruster for the attitude and orbit control. This paper introduces the development of the gas-thrust equilibrium thruster for small satellites. © 2007 Elsevier Ltd. All rights reserved.

A tethered satellite cluster system, which consists of a cluster of satellites connected by tethers and which can maintain and change formation via active control of tether tension and length to save thruster fuel and improve control accuracy is proposed. The concept can be applied to tethered multisatellites for in-orbit servicing, which can perform various missions, including inspection, casting, capture, recovery, moorage, and deorbiting of an uncontrolled satellite. The rotational motion of such a system that the satellites in formation flying are required to rotate about the center of mass of the system on the same desired plane is considered. The equilibrium conditions that the tether tension imposes on the rotational motion are given, and a coordinated control method for the thrusters, the reaction wheels, and the tether tension/torque is proposed. Numerical simulations and ground experiments show that the control of the tether tension and torque not only saves thruster fuel, but also improves the position and attitude accuracy of formation flying. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Japan Aerospace Exploration Agency (JAXA) is currently studying "Solar Sail" populsion for future deep space explorations. One of the key technologies to realize a solar sail is how light and how compact we can make the photon acceptance surface. JAXA has conducted extensive studies on utlizing centrifugal force to deploy the photon acceptance surface. The final objective is to realize a 7.5μm-thickness and 50m diameter polyimide membrane, combined with a thin flexible solar cells, as the photon acceptance surface that will be needed around the Jupiter orbit. In August 9, 2004, JAXA launched the S-310 sounding rocket, which tested two different shapes of membranes during the zero-gravity flight. The first type of membrane looked like a "clover-leaf", and another is like a "fan". These two membranes, both of them having 10m diameter, were unfolded sequentially during the zero-gravity flight under the free spin condition, and their behavior was observed by onboard cameras. This paper focuses on the "clover-leaf" solar sail, which was fully deployed successfully, and introduces the S-310-34 experiments, and then shows the flight results and postflight evaluations. © 2006 Lister Science. All rights reserved.

We have proposed a self-reconfigurable parallel robot, which can be configured to 4R and 5R closed kinematic chains. By mounting it on a crawler mechanism, this paper proposes a parallel mechanism mobile robot. The combined mobile robot can gain some useful functionalities from the advantage of its parallel mechanism other than just locomotion, such as carrying an object by making use of its shape and getting over a bump by control of its center of gravity or zmp. In general, for a crawler robot to get over a vertical bump, friction is necessary in the vertical direction of the bump. The proposed sequence of getting over a bump does not rely on friction. Furthermore, cooperation of two or more such robots gains functionalities such as forming three-dimensional structures. Using two robots, we verify that the 4R robot can elevate the 5R robot, which enables the latter to reach a certain height in which it cannot alone. We analyze the statics of this motion to evaluate the necessary joint torque of the 4R robot.

The purpose of this study is to develop a simple but useful robot with passive joints. As an example of such a robot, this paper presents dynamic rolling of a 5R closed kinematic chain, only two of whose joints are actuated.When it rolls, it has one DOF for its absolute orientation besides two DOFs for its shape. The absolute orientation is independent of the constraint for forming the closed kinematic chain. If its unactuated joints were actuated, the closed form would be over-actuated but the absolute orientation could not be driven directly. We show that the absolute orientation is subject to an acceleration constraint, not a velocity constraint. Therefore, the formulation of the dynamics of the rolling motion makes it possible to control the absolute orientation. The shape and orientation of the robot cannot be controlled simultaneously. This paper proposes a control strategy switching the shape and orientation controllers. The orientation controller reduces a negative acceleration caused by gravity which acts on the robot. We verify the control strategy by computer simulations and experiments.

This paper proposes a self-reconfigurable planar parallel robot which is capable of reconfiguring itself to various types of planar parallel robots in the horizontal plane. The robot can change its workspaces by coupling and decoupling of a platform and two or more 2R open kinematic chains with second joints unactuated (limb). The platform should be light and therefore no additional actuators are used for reconfigurations. We have already shown that uncertainty singular configurations are appropriate for coupling of two limbs. This paper describes positive and negative aspects of the uncertainty singularity for coupling and decoupling. In addtion, decoupling needs to be carried out with more care than coupling. It must be considered to assure the safety of a decoupled limb and to prevent unexpected decoupling of other limbs. We propose feasible coupling and decoupling configurations for the proposed self-reconfigurable planar parallel robot. We also introduce our real robot and show its coupling mechanism, which is designed to be easy to couple and hard to decouple. Experiments are carried out to verify reconfigurations to change workspaces.

This paper discusses dynamic and stable reconfigurations of self-reconfigurable planar parallel robots that can be done by coupling and decoupling of two underactuated robots on a horizontal plane. The limbs of the parallel robots are 2R open kinematic chains with their second joints unactuated. Two types of self-reconfigurable parallel robots are considered. One is formed by two limbs, and the other is by a limb and an underactuated robot consisting of two limbs and a platform. Uncertainty singularities enable them to self-reconfigure without additional actuators at their coupling mechanism. In this paper, we propose dynamic contact motion control to move them from an initial contact configuration to an uncertainty singular configuration while maintaining their contact. This paper also considers dynamic stability at their uncertainty singularities as equilibrium and shows that there exist geometrically stable configurations without feedback control, which are useful for decoupling. Experiments with real robots are carried out to verify the effectiveness of the dynamic contact motion control and stability analysis.

We propose the concept of Tethered Satellite Cluster Systems. The system consists of the satellites connected by tethers, and keeps and changes the formation with active tension/length control of the tether. The purpose of the system is the saving of the thruster fuel required for the coordinated mission and the improvement of the control precision, using tether tension. The system is applied to tethered service satellites, which perform the missions, for example an autonomic inspection, casting, capture, moorage and deorbit of an uncontrolled satellite. In this paper, we treat the rotating motion; satellites rotate on the center of the mass of the system with the formation in same plane. We establish the coordinated control method using tension and thrust. This control method can decrease the fuel consumption of the thruster, for utilizing the tether tension/torque equilibriums. It can also improve the control precision. Moreover, we establish the formation control method without thrust for the transition to the objective formation.

In this paper, the dynamics of tether winding target is analyzed. This problem is not peculiar to capture of an uncontrolled satellite with tether. It contains the common technology to casting the tether in order to moor the floating object in space, or to operating tether in the ground. This paper presents three-dimensional model of a tether and a target. The tether is divided into concentrated masses in order to consider the tether motion. The target is regarded as a prism. In formulation of the system, the friction and the normal reaction between the target and the concentrated mass is defined as contact force. And the impulse equations applied to the case that more than two concentrated masses collide with the target in the same time, is derived. In numerical simulations, the verification of this model is presented by the comparison with fundamental two-dimensional model of a tether and a target, and three-dimensional winding motions, the sideslip and the gyro effect, are shown.

This paper discusses coupling of two 2R open kinematic chains with their second joints unactuated in the horizontal plane. When they are not coupled, they can operate as independent underactutaed manipulators and when they are coupled, they can operate as a single 5R parallel manipulator which has the same number of actuators as its degrees of freedom. In the horizontal plane, they cannot make use of gravity for motion generation. In parallel mechanisms, uncertainty and stationary-uncertainty singularities exist in general. If the two open kinematic chains form such a singular configuration when they touch with each other, they can exert force with each other and therefore can be coupled easily. In addition, at a stationary-uncertainty singular configuration, they can escape from it after they are coupled simply by controlling their joint velocities. We propose a coupling mechanism without actuation, which can be a smooth free joint when coupling is achieved. The two open kinematic chains can reach an uncertainty singular configuration if they touch with each other at certain initial configurations. This paper analyzes this motion and show such initial configurations. We experimentally verify the proposed coupling.

This paper proposes a novel manipulation method with a quadruped robot using its whole body. The quadruped robot we have developed can take various postures. Two of its legs can support its body by standing on the knees and the other two can serve as arms. The robot can hold a relatively big and heavy object with its two arms and can manipulate the object by moving its body. The two legs standing on the knees form a closed link system. Its desired configurations during the manipulation are at an increased mobility singularity if all knees and tips of the two legs are in contact with the floor. The problem with the singularity is that the mobility of the robot changes significantly around it. This paper shows a contact condition for the legs free from such a singularity. We conduct experiments to verify that our quadruped robot can perform the manipulation. A possible application of the manipulation is loading/unloading an object onto/from the body of a quadruped robot.

Serial link robots with unactuated (passive) joints are attracting research interest. If two of such robots can couple with each other, they can reconfigure to a parallel robot, which can make the number of actuators equal to the number of degrees of freedom. If they can couple with each other at different portions of them, they can constitute a reconfigurable parallel robot. This paper proposes this concept of a robot, presenting that two two-link robots, the first joints of which are unactuated, can reconfigure to a 5-link planar parallel configuration and a 4-link planar parallel configuration plus one actuated link. This reconfigurable parallel robot has only two actuators but can have multiple functions by reconfigurations. Due to the unactuated joints, whether or not the two-link robots can couple with each other is a non-trivial problem. We propose coupling sequences for forming the 4-link and 5-link configurations and verify those experimentally.

We have participated in the ARLISS (A Rocket Launch International Student Satellite) project since 1999 to design, manufacture and operate small satellites. These satellites called CanSat are the size of soft drink can (350ml). We launched five CanSats on the Black Rock desert in Nevada, U.S, to 12,000ft using amateur rocket, and dropped them with parachutes in July 2000. During their dropping, we operated these CanSats and tested their functions. Furthermore, we conducted additional experiments in Taiki town, Hokkaido, Japan using a balloon to check functions that didn't work well in ARLISS experiment. In this paper, we describe the mission, subsystem design and results of. the experiments on each CanSat, and report the results of the additional balloon experiments.

This paper treats control strategy for tether-based method of damping angular momentum of failed satellites. A simple two-dimensional model of a tether, a controller and a circular/elliptic target is used for numerical simulations in order to gain clear understanding of the tether control. Several tether control methods are proposed using tension, length of the tether and the distance between the target and the controller. Numerical simulations yield the following results : 1)the tether tension can transfer from the angular momentum of the target to that of the controller ; 2)if the target is circular, the angular momentum of the target is reduced linearly using by constant tension control ; and 3)relationships between the target angular momentum change and model parameters are obtained.

Our previous report discussed a two-dimensional formulation of tethered dynamics with friction and impact : the dynamics between a captured target and a tether with load masses at the end of the tether. This paper conducts the numerical simulation on the dynamics, and clearly shows the following results : 1) the impacts cause motion state transitions, and the stick-slip motion of tether causes friction state transitions, 2) the tether tension can transfer from the angular momentum of target to that of wheel and weight, 3) relationships between the target angular momentum and the model parameters and conditions for winding the target are shown in terms of the initial conditions, and 4) the motion after winding is described in detail. These results shed light on the complicated motion of the tethered multibody.