大槻 真嗣

<p>This study aims at improving the actuator which has hold-down and releases mechanism using Shape Memory Alloy (SMA). The SMA actuator, which is discussed in this study, consists of an SMA tube, a restraint, and a heater. These kinds of actuators can achieve high power density; however, their force generation trajectories are affected by the environmental temperature variation because of their huge heat capacity. This paper discusses the method to track the required force trajectories for drive timing improvement. First, previous studies are introduced. Then, this paper points out the problems in previous research and describes the details of the modeling to improve simulation accuracy. The hysteresis model of SMA is introduced and the system identification method used in this study is shown. Finally, the experiment is performed to identify the hysteresis characteristics of SMA. The result was consistent with the trend of the detailed model. Moreover, the constraints for the system identification were derived from the experiment results. </p>

<p>Spacecraft landing gear employed in space missions is required to achieve secure touchdown on rough and inclined terrains. Generally, when a spacecraft performs a free fall from a certain altitude, its landing gear needs to absorb the impact of touchdown. Conventional landing gear, such as the honeycomb crush absorber, absorbs the impact of landing through plastic deformation of its structure. However, such landing gear cannot effectively prevent the spacecraft from tipping over, and the non-reusability of such landing gear often leads to an increase in experimental costs. To address these issues, this paper proposes a novel landing gear mechanism that comprises a contraction lock mechanism with multiple springs for enhancing reusability. The proposed mechanism varies the spring constant by operating the contraction lock mechanism according to the touchdown response, and thus potentially prevents the spacecraft from tipping over. The effectiveness of the proposed mechanism in the case of inclined terrains is verified through conducted simulations. Furthermore, the performance of the proposed mechanism is compared with that of the conventional plastic deformation shock absorber in terms of adaptability to variations in the spacecraft's initial velocity and initial attitude angle. The obtained results show that the proposed mechanism can be effective in executing secure landings on inclined terrains.</p>