大槻 真嗣

<title>Abstract</title> The Martian Moons eXploration (MMX) mission will study the Martian moons Phobos and Deimos, Mars, and their environments. The mission scenario includes both landing on the surface of Phobos to collect samples and deploying a small rover for in-situ observations. Engineering safeties and scientific planning for these operations require appropriate evaluations of the surface environment of Phobos. Thus, the mission team organized the Landing Operation Working Team (LOWT) and Surface Science and Geology Sub-Science Team (SSG-SST), whose view of the Phobos environment is summarized in this paper. While orbital and large-scale characteristics of Phobos are relatively well known, characteristics of the surface regolith, including the particle size-distributions, the packing density, and the mechanical properties, are difficult to constrain. Therefore, we developed several types of simulated soil materials (simulant), such as UTPS-TB (University of Tokyo Phobos Simulant, Tagish-lake based), UTPS-IB (Impact-hypothesis based), and UTPS-S (Simpler version) for engineering and scientific evaluation experiments.

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Shape memory alloys (SMAs), well-known as the force source in space-use nonexplosive actuators, generate force through temperature-based phase transitions. The force amount is related to the volume and mass of the SMA. This study presents a method to improve the force-generation profile of the SMA actuator, which consists of an SMA tube, a mechanical restraint, and a heater. The high SMA mass ratio of the actuator allows it to achieve high power density; however, its force trajectories are affected by the environmental temperature variance because of its huge heat capacity. The uncertainties of the force trajectories limit the applications of the actuator. This paper proposes a method to achieve the required force trajectories under temperature variance to enlarge the application of the high power density SMA actuators. In addition, a suitable model is established for the force-trajectory control method based on the thermo-mechanical coupling response characteristics. A thermal balance model is constructed under vacuum environment. Furthermore, a hysteresis characteristic model of the phase transformation is introduced, and it reduces the heating profile limitation. The force trajectory is designed based on the model predictive control method. The designed trajectory is realized using a simple temperature-measurement feedback control method based on the proportional-integral-derivative method. To illustrate the system design, the holding– release mechanism application is selected. The effectiveness of the proposed methods is verified through specific test piece system identification and control simulations, which are performed both numerically and experimentally under temperature variance.

Copyright © 2020 by the International Astronautical Federation (IAF). All rights reserved. Transformable spacecraft under development is an innovative system that consists of several structural components, such as panels, connected together by internal force actuators. The spacecraft can change its structure drastically by driving installed actuators and achieve the following four features simultaneously. The first feature is "attitude change by internal force using non-holonomic characteristic of the system". It is possible to orient the spacecraft to an arbitrary direction by repeating the deployment of the panel in an appropriate order by the internal force actuator. The second feature is that "change of the structure enables the multiple functions by switching modes". Two telescopes will be installed for scientific missions utilizing the features of the transformable spacecraft and used to realize two different observation modes. One is a mode in which each telescope is oriented to different directions to perform wide-field observation (single telescope mode). The other is a mode in which two telescopes are pointed in the same direction. This mode enables the spacecraft to work as an interferometer (interferometer mode). The third feature is "orbit control and orbit keeping by controlling the solar radiation pressure on the spacecraft with the use of change of spacecraft structure". Since the spacecraft can change its structure by the internal force actuator, the orbit control and orbit keeping are achieved without fuel consumption. By utilizing this feature, the spacecraft will be injected into an artificial halo orbit around Sun-Earth Lagrangian point L2, and the technology demonstration of the transformable spacecraft and the observation mission will be performed in the orbit. The fourth feature is "passive cooling of observation equipment by use of panels as sunlight shield". In the observation mode, observation in the infrared region is performed and sufficient cooling is required. Appropriate arrangement of panels enables shielding of sunlight, and then the passive cooling of the observation equipment is realized. As a result, disturbance due to refrigerator is eliminated, which contributes to precise observation in addition to the contribution by non-holonomic attitude control without disturbance. This paper shows the analysis and experimental results for feasibility studies and conceptual designs of above four features. Furthermore, development status of the system and each subsystem to realize the spacecraft are introduced.

Copyright © 2020 by the International Astronautical Federation (IAF). All rights reserved. A 6U CubeSat “OMOTENASHI” will be the world's smallest moon lander which is launched by NASA SLS Artemis-1. Because of its severe mass and size limitation, it will adopt semi-hard landing scheme. That is, OMOTENASHI is decelerated from orbital velocity to less than 50 m/s by a small solid rocket motor and shock absorption mechanism has been developed to withstand the high-speed impact. Ultra small communication system (X-band and P-band) is also developed. It observes radiation environment of Earth and moon region with portable dosimeters. This paper shows the mission outline, the design, and the development results of OMOTENASHI.

Copyright © 2020 by the International Astronautical Federation (IAF). All rights reserved. Martian Moons eXploration (MMX) is a mission to Martian moons under development in JAXA with international partners to be launched in 2024. This paper introduces the system definition and the latest status of MMX program. “How was water delivered to rocky planets and enabled the habitability of the solar system?” This is the key question to which MMX is going to answer in the context of our minor body exploration strategy preceded by Hayabusa and Hayabusa2. Solar system formation theories suggest that small bodies as comets and asteroids were delivery capsules of water, volatiles, organic compounds etc. from outside of the snow line to entitle the rocky planet region to be habitable. Mars was at the gateway position to witness the process, which naturally leads us to explore two Martian moons, Phobos and Deimos, to answer to the key question. The goal of MMX is to reveal the origin of the Martian moons, and then to make a progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer-part of the early solar system. The mission is to survey two Martian moons, and return samples from one of them, Phobos. In view of the launch in 2024, the phase-A study was completed in February, 2020. The mission definition, mission scenario, system definition, critical technologies and programmatic framework are introduced int this paper.

第29回アストロダイナミクスシンポジウム (2019年7月22-23日. 宇宙航空研究開発機構宇宙科学研究所), 相模原市, 神奈川県資料番号: SA6000153031レポート番号: B-5

This paper describes an attitude control method to prevent the overturning of lunar and planetary landers. The proposed control method that is based on a variable-damping shock absorber for the landing gear is experimentally validated. Conventionally, the landing gear of lunar and planetary landers has a fixed shock attenuation parameter that is not used proactively for attitude control of the lander during the touchdown sequence. The proposed method suppresses any disturbance to the attitude of the lander by adjusting the damping coefficient of each landing leg independently, based on the angular velocity and displacement velocity of each landing leg. First, the control method for the variable damper is presented. Second, the result of a landing experiment conducted in a two-dimensional plane is shown. These results indicate that the proposed semi-active landing gear system is effective for preventing the overturning of the lander on inclined terrain.