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地球へ向けて帰還中の「はやぶさ(MUSES-C: Asteroid Sample-return Spacecraft)」は現在3台中2台のホイールが故障し、いわばバイアスモーメンタム方式で1軸姿勢制御を行っている。この方式ではシンプルな姿勢安定が実現されるはずだが、2007年3月にニューテーションが発散する傾向を示した。本稿では、この現象がホイール回転軸と探査機慣性主軸の不一致によることを解析と数値シミュレーションによって示し、防止策を提案する。, Since Hayabusa (MUSES-C: Asteroid Sample-return Spacecraft) has lost two of three wheels, its attitude is currently stabilized by one-axis bias-momentum wheel. This method should lead to simple attitude keeping, but the motion showed nutation divergence in March 2007. This paper shows that the cause of the instable motion lies in the difference between the axis of wheel and of inertia, and a way to avoid this instability is proposed., 資料番号: AA0063718021

For the demonstration and verification of solar power satellite's functions, a small demonstration solar power satellite has been examined by USEF and ISAS/JAXA. Structural characteristics and attitude motion in steady operation have already been studied. In this paper, deployment sequence for the stable and fast deployment is investigated. The deployment sequence consists of two-stage truss extension and two-stage panel deployment. At first, attitude motion in the deployment is analyzed through numerical simulations. From the result, it is shown that nonlinear effect can not be negligible when pitch angle exceeds about 0.6 rad. In such a case, because independency of the pitch angle does not hold true for the nonlinearity, pitch motion leads to the large roll and yaw motions. Next, to realize stable and fast deployment, optimization of the deployment is carried out by changing each deployment time, interval and acceleration of the deployment. As an objective function, weighted sum of deployment times, maximum amplitudes of attitude angles and residual amplitudes of attitude angles is used. The optimization is carried out by Powell's method. From the result it is shown that maximum amplitudes of attitude angles are kept within 0.08 rad, and residual amplitudes of attitude angles are kept within 0.01 rad without any active control if about five orbital periods (about eight hours) can be spent for the total deployment., 資料番号: AA0049120010

In the tethered-type solar power satellite, a large panel structure for the power generation and transmission is adopted. A huge number of actuators are required to deploy the large panel in orbit. In our research, a deployment mechanism using coils of shape memory alloy (SMA) has been studied. When the SMA coil is heated by applying an electric current, it works to deploy the folded panels if the coil has a memory for rotation. This mechanism has several advantages as: (1) Simple and light-weight as compared with motor activation, (2) Deployment speed is well controlled to minimize the effect on the attitude of the system during deployment and to suppress the shock when the panel is fully deployed, (3) The shape of the unfolded panels can be controlled using two types of SMA coils (this function can be used to compensate the thermal deformation of the panels), and (4) The oscillation of the panels can be suppressed by heating the SMA coils to the super-elastic state. We have fabricated the hinges containing the SMA coils as shown in this report and integrated them to a test panel composed of 4 x 8 sub-panels. The size of the sub-panel is 12 x 24 cm. The test model is equipped with a latch mechanism using the permanent magnet. In the laboratory test, it is confirmed that the hinge with the SMA coils work well as expected, but it is found that the life of the SMA coils is unexpectedly limited by the metal fatigue. Further study is required to redesign the SMA coils to eliminate the fatigue effect., 資料番号: AA0049120012

A SPS (Solar Power Satellite) which is a part of the Space Solar System (SSPS) project has been studied at the USEF. Quasi-static analysis had been carried out for the practical SPS. The present purpose is to evaluate the attitude stability of the SPS under construction. During construction, it is assumed that the modules of 100 x 95 sq m are arranged in the shape of line. As the result of quasi-static analysis, it is shown that the roll and yaw angular frequencies of attitude motion are twice and once as large as orbital angular velocity in first step of the construction, respectively. Furthermore, as the result of dynamical analysis, amplitudes of the roll and yaw angles tend to divergence in first step. To avoid such a divergence, another model was proposed which is constructed keeping similar configuration. The construction way is called construction with similarity. From the result of simulations, it is shown that divergences in the roll and yaw angles can be avoided in the construction with similarity. However, the stability around the pitch and yaw axes are weak in first step for construction with similarity. In particular, maximum amplitude around the pitch axis is 5 deg. Therefore, both constructions need active attitude control because there are problems in first step of the constructions., 資料番号: AA0047275019