森 治

In this paper, the attitude motion and attitude control strategy of spinning solar sail are discussed. As the spinning type solar sail does not have any rigid structure to support its membrane, the impulsive torque by the RCS can introduce oscillatory motion of the membrane. Thus, an "oscillation free" attitude controller is needed, which takes into account the flexibility of the membrane and avoid unnecessary oscillatory motion. First, the dynamics model and numerical model were introduced, and the validity of these models and dominant out-of-plane membrane vibration mode is examined by membrane vibration experiment and comparison between both models. Then, based on the analysis of the dynamics of torque-free motion, it was shown that a spinning solar sail has three oscillation modes of nutation, one of which is equal to the spinning rate of the spacecraft. The dominancy of each nutation mode was analytically and numerically discussed. Then, we discussed the spin axis maneuver control using conventional RCS. It was analytically shown that continual impulsive torque synchronizing the spin rate can excite nutation velocity and that a controller is needed to damp the nutation while controlling the spin axis at the same time. The authors proposed new controller named Flex-RLC and improved one. Their effectiveness was verified by numerical simulations using precise multi-particle numerical model which can express higher order oscillatory motion of the flexible membrane, and it was found that the proposed method can control the attitude of spinning solar sail while drastically reduces the nutation velocity compared with conventional control logic. So, it can be said that the proposed method is promising fast and stable controller for spinning solar sail. © 2009 by ASME.

The present study develops a new three-dimensional Timoshenko beam finite element (FE) whose length can be varied during transient dynamic analyses. The variable-length element enables the dynamic deployment analysis of exible appendages with non-negligible bending stiffness. In addition, the developed scheme employs an implicit time integration whereby energy and momentum in the system is properly conserved, and no artificial numerical damping is introduced. As a result, the scheme makes it possible to evaluate the impact of structural damping on the system's dynamics. The developed beam element is then used in an FE model of a solar sailcraft currently developed in Japan, and its deployment dynamics is analyzed allowing for the bending stiffness of the bundled membranes, as well as the effect of some realistic design imperfections. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

New thruster system using less toxic fuel, which vapor pressure is relatively low, has been developed for small or micro size spacecraft, which has less space or weight budget, etc. In this system, the tank store the fuel in liquid state, the thruster system ejects the fuel in gas state using vapor pressure to obtain thrust. This means high energy efficiency and the constant thrust level maintained right before fuel exhausted, compared to the widely used cold gas thruster. To achieve that the thruster system separate the fuel into gas phase from liquid phase, the tank has porous metal inside itself. The porous metal absorbs the liquid state fuel and only gas state fuel can pass through the porous metal. And having the porous metal inside the tank, the thruster system can reduce the effect of sloshing, and the heater control can be achieved easily because of the enhancement of the thermal conductivity. Furthermore, the surface area is drastically increased, so vaporization occurs everywhere in ejecting the fuel, which keeps the constant thrust level. This paper presents the experimental result of this gas-liquid equilibrium thruster. And it is shown that this tank system has the effectiveness mentioned above.

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.

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. However, the attitude control system of the solar sail, which controls the direction of the sail and thus the propulsive force, has not been much studied, although this constitutes the essential part of the orbital control using solar sail. This paper discusses the attitude dynamics and the control method of a spinning type solar sail spacecraft. The spinning type solar sail 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 vibration 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 and the effect of solar radiation pressure, which can deform the membrane of solar sail, on the controller were verified by numerical simulations using more precise multi-particle numerical model.

The Japan Aerospace Exploration Agency (JAXA) will make the world's first solar power sail craft demonstrate for both its photon propulsion and thin film solar power generation during its interplanetary cruise. The spacecraft deploys and spans its membrane of 20 meters in diameter taking the advantage of the spin centrifugal force. The spacecraft weighs approximately 300kg, launched together with the agency's Venus Climate Orbiter, PLANET-C in June of 2010. This will be the first actual solar sail flying an interplanetary voyage.

This paper describes the navigation and the guidance strategy of the small spacecraft for flyby using the images of the target. We derived navigation and guidance accuracies of this mission analytically, and confirmed them by numerical simulation. 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 in image. This uncertainty affects the guidance accuracy from the target. In this paper, a method to calculate the target center from the tangent points of the sun is proposed. The validity of the method is examined in the experiment.

This paper presents what the Hayabusa spacecraft experienced when it restarted the three axis stabilization. Due to the loss of two wheels aboard and also due to the loss of fuel, the primary axis of inertia of the spacecraft was tilted offset to the geometrical axis. The instability was observed unexpectedly since there was little thought about the instability associated with the single wheel system. The results can be applied for other spacecraft. The flight results are shown as well.

This paper describes the attitude dynamics and the control method of a spinning solar sail spacecraft. The solar sail considered here has no structure supporting membrane, therefore estimation of the effect of membrane flexibility is one of the problems to solve for the future validation flight. In this study, we established a dynamic model including membrane vibration to handle a coupled motion of a rigid spacecraft and a flexible membrane, and focus on the consideration of attitude control method. The result is confirmed with numerical simulation by use of Multi Particle Model(MPM).

The paper presents the attitude reorientation taking the advantage of solar radiation pressure without use of any fuel aboard. The strategy had been adopted to make Hayabusa spacecraft keep pointed toward the Sun for several months, while spinning. The paper adds the above mentioned results reported in Sedona this February showing another challenge of combining ion engines propulsion tactically balanced with the solar radiation torque with no spin motion. The operation has been performed since this March for a half year successfully. The flight results are presented with the estimated solar array panel diffusion coefficient and the ion engine's swirl torque.

宇宙探査の中でも天体への着陸ミッションは目標地点への高精度な航法・誘導が非常に重要である。本研究では2005年に探査機はやぶさが小惑星イトカワに着陸した際に用いられた航法アルゴリズムを基に、事前観測で得られた対象天体モデルを利用し、探査機が撮像した画像を入力として自律的に自己位置を推定するアルゴリズムを考案し、シミュレーションにより精度、ロバスト性等の検証を行った。

The proposed balloon experiment for deploying large-sized membrane, which is intended to be shown in this paper, is postponed to September, 2008. We are now designing a new structure and mechanism of a spacecraft which is to be validated at the balloon experiment. We proposed "Multi-step deployment" of membrane in this paper, which reduces the risk of complexity of the deploying system compared to conventional system. In addition, we analyzed the feasibility of attitude control required for orbital maneuver with conventional chemical thruster and positively solved. The amount of propellant is also calculated and found to be feasible. The system we discussed in this paper is to be equipped with a newly designed spacecraft planned in 2010s. Copyright IAF/IAA. All rights reserved.

The proposed balloon experiment for deploying large-sized membrane, which is intended to be shown in this paper, is postponed to September, 2008. We are now designing a new structure and mechanism of a spacecraft which is to be validated at the balloon experiment. We proposed "Multi-step deployment" of membrane in this paper, which reduces the risk of complexity of the deploying system compared to conventional system. In addition, we analyzed the feasibility of attitude control required for orbital maneuver with conventional chemical thruster and positively solved. The amount of propellant is also calculated and found to be feasible. The system we discussed in this paper is to be equipped with a newly designed spacecraft planned in 2010s. Copyright IAF/IAA. All rights reserved.

This paper discusses dynamics of large membrane for achieving spinning solar sail-craft proposed by the Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). For comprehending the dynamics, firstly, two types of grand-scale experiments were conducted. One was an ice rink experiment. The other was a balloon experiment. In the both experiments, we succeeded in deploying 10m and 20m diameter membrane and observing the motion. Secondly, we constructed a numerical model using a multi-particle method, and numerical simulations were conducted. We drew a comparison between results of experiments and numerical simulations. The effectively of the multi-particle model was then indicated in this paper. Copyright © 2007 by ASME.

ISAS/JAXA is studying a deployment method using centrifugal force for solar sail mission. The larger sail is required to be deployed statically as for actual spacecraft. We scheduled to deploy the square sail of diameter 20m using a high altitude balloon. In this paper, the mechanisms for static first and second stage deployments are proposed and developed experiment system is introduced. And the operation and results are shown in detail.

はやぶさに続く始原天体ミッションとして、C型小惑星の表面および地下物質に適した試料採取機構・運用方法を検討している。従来のはやぶさの技術と運用をベースラインにしつつも、有機物や含水鉱物を採取する観点からの改良点として、収量の増加と層序情報の維持が挙げられる。そこで「コアラー撃ち込み＆テザーによる引き抜き法」と「自由面発破による人工クレーター形成の可能性」の基礎開発を実施してきた。それらの成果を報告する。

小惑星探査機「はやぶさ」による小惑星イトカワの観測で、500m程度の小さなＳ型小惑星についての理解が深まったが、我々は、さらに次の小天体探査ミッションについての検討を行っている。次のミッションとしては、Ｓ型と同様に小惑星帯で主要なタイプとなっているＣ型小惑星の探査を行いたい。このタイプでは、有機物や水をより多く含んでいると思われており、生命前駆物質の科学としても重要である。ここでは、これまでのミッション検討結果をまとめて報告する。また、是非、多くの研究者に小天体探査に参加してもらうことを呼びかけたい。

The small satellite, demonstrating the power generation by film solar cell of solar sail, has developed. In this mission, the thruster system is required, because of the spin up to deploy the sail using the inertial force, the active nutaion control and the orbital maneuver to raise the perigee altitude. In the small satellite, the thruster system has to be simple and light weight. In this paper, the gas-liquid equilibrium thruster is developed. This system uses LPG (Liquefied Petroleum Gas) as fuel, so it is easy to handle the system. And this thruster can bring the fuel as liquid in the tank and eject the fuel as gas using the gas liquid equilibrium pressure to produces the thrust, so the fuel tank only needs to resist the vapor pressure of the fuel and the system can be simplified. We show the fundamental performance and the feasibility of this gas-liquid equilibrium thruster. The gas-liquid equilibrium thrusters have the good possibility of the small satellites' thruster system. And if this system would prove its performance in the actual small solar sail mission, this thruster system could be hopeful thruster widely used for the small satellites.

At the Institute of Space and Astronautical Science(ISAS),Japan Aerospace Exploration Agency(JAXA), Spinning Solar Sail-craft is proposed and examined the possibility. In August 2006, a membrane of 20[m] in diameter was deployed statically by using a flying balloon. The size of membrane is the largest in the world, furthermore, to deploy statically is the first achievement in the world. This paper shows the experiment apparatus and the results. Additionally, numerical simulation is used to analyze the behavior of the membrane. The deployment of membrane is divided first stage and second stage. At first stage deployment, the membrane deploys dynamically because the accident occurs. However, the deployment is successful. At second stage deployment, the membrane deploys statically and finally forms square-shape. The numerical simulation accords with the behavior of membrane. The membrane has the inclination by gravity, so the experiment can examine the out-of-motion of the membrane. And the membrane is affected by air drag, the contortion of the membrane is also examined. As a conclusion, to deploy a membrane of 20[m] in diameter statically is the first achievement in the world, and to analyze the behavior of the membrane is meaningful for the realization of Solar Sail-craft.

A large scale system including multi-elements that turn on and off their electric circuits such as heaters has some high risk of running short of the resource, that is power in this case, and may sometimes go down. The power consumed may exceed the capacity of the power supply, when a lot of the elemental heaters are switched on at the same instance. On average, even in that case, the power consumed may be enough low for the power to be supplied with adequate margin. If a very sophisticated server is built and concentrates allocating resource to the elements keeping the peak power consumed in the whole system lowered by gathering information from them, this shutdown may be circumvented. However, such specific server, even though built, is very much tuned to a specific system structure and not flexible, while the system had better be easily reconfigured and be robust for small mull functions that could occur. The paper here presents 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, dynamics behavior of tether retrieval with a reel mechanism in a tethered sampling method in deep space is discussed. The tethered sampling method proposed by authors is investigated as a candidate for soil sample collection method of minorbodies For the next minorbody exploration mission. The method consists of three phases: 1) shooting a corer together with a tether, 2) inserting the corer into a surface and collecting soil in the corer, 3) pulling back and retrieving the corer with the tether. This paper mainly deals with dynamics of the tether and corer in the recovery phase, and numerical simulations and fundamental experiments of the tether dynamics are conducted using a tether control mechanism. A tether tension control is proposed and tether and corer coupled dynamics are made clear by the numerical simulation. Moreover, experimental investigations are conducted by using a sampler horn and a reel mechanism which can control the tether tension and measure the tether length and velocity. The results of the experiments are compared with the results of the numerical simulation to show the feasibility of the proposed method.