橋本 樹明

<p>In an earth observation satellite or a space observatory, micro vibration caused by a mechanical cryocooler is one of the problems that make the performance worse. In this article, we propose an active control method with feedforward signal for a cryocooler. The vibration of a cryocooler appears as a distinct spectrum. This algorithm identifies the transfer function of the control target and calculates the optimal control signal by giving feed-forward signals to this spectrum several times in advance. The effectiveness of the proposed method is confirmed by experiments using a cryocooler, and the effects of fluctuations in the spectrum of vibration and noise are discussed. </p>

<p>This paper describes a separation experiment conducted at extremely high spin rates for OMOTENASHI, being developed as the world's smallest Moon lander. The experiment validated the separation method used in the landing sequence and the tipoff impulse was estimated from the motion of the separated object. The study showed that the tipoff impulse increases superlinearly in the high spin rate region. This information is indispensable in determining the operational spin rate of OMOTENASHI in orbit. The method described in this paper can be applied widely to separation experiments for small spinning satellites and rocket stages.</p>

Currently, several polar explorations of the Moon are planned, because it has been suggested that water ice might be present in the lunar polar region based on remote sensing observation of the lunar surface using a neutron spectrometer and visible to infrared spectrometer. However, the precise amount and state of the water ice are still unknown. At the Japan Aerospace Exploration Agency (JAXA), we are also studying exploration of the lunar surface for resources, especially cold-trapped volatile such as water ice using a rover. Volatile materials are expected to be useful for future human activity on the Moon and there is strong interest in the origin and concentration mechanism of the water ice. Additionally, the polar regions are among the best candidates for long-term activity because of their long sunlight duration. To realize the mission, we are currently developing various technologies peculiar to exploration of lunar polar regions. This paper details the present status of the Japanese Lunar Polar Exploration Mission.

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.

© IMechE 2017. 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.

Recently, several polar explorations of the Moon are planned, because it has been suggested that water ice might be present in the lunar polar region based on remote sensing observation of the lunar surface using a neutron spectrometer and visible to infrared spectrometer. However, the precise amount and state of the water ice are still unknown. At the Japan Aerospace Exploration Agency (JAXA), we are also studying on exploration to the lunar polar regions for resources, especially cold-trapped volatiles such as water ice using a rover. Volatile materials are expected to be useful for future human activity on the Moon and there is strong interest in the origin and concentration mechanism of the water ice. Additionally, the polar regions are among the best candidates for long-term activity because of their long sunlight duration. To realize the mission, we are currently developing various technologies peculiar to exploration of lunar polar regions. This paper details the present status of the Japanese Lunar Polar Exploration Mission.

Minimizing the risk of tipping during landing is critical for achieving successful celestial surface explorations by moon, Mars, and asteroid landers. The footpad is an important part of the mechanism for tip-over prevention of landers because it is the only mechanical part that contacts the terrain surface during landing. The force that acts on the footpad depends on its shape, and so its design is important in preventing overturning of the lander. This study describes the relationship of the attachment angle of the footpad and the force that acts on it based on resistive force theory. This theory describes the relationship between the state of the mechanical part in granular media and the force that acts on its surface. Based on this theory, the footpad's attachment angle is optimized. The relationship between landing performance and the attached angle of the footpad is confirmed through dynamic simulations. The simulation results show that the tilted footpad is effective for safe landings under conditions in which there is a horizontal velocity component during landing.

Copyright © 2018 by the International Astronautical Federation. EQUULEUS is a Lunar L2 orbiter and a 6-Unit CubeSat by JAXA and the University of Tokyo. OMOTENASHI is a 6-Unit CubeSat by JAXA, the world's smallest Lunar lander. EQUULEUS and OMOTENASHI are among the 13 secondary payloads selected by NASA to be launched with Exploration Mission-1 in 2019. Despite their limited size and cost, EQUULEUS and OMOTENASHI are challenging missions, especially in terms of trajectory design and control. EQUULEUS exploits the Earth-Sun-Moon chaotic dynamics and enter a libration point orbit around the L2 of the Earth-Moon system, using a new water propulsion system with low thrust and little propellant. This “Orbit Control Experiment” is one of the main objectives of the mission. OMOTENASHI executes a semi-hard landing that requires breaking the spacecraft to a stop just a few-hundred meters above the Moon's surface. Both missions present new and unique challenges, where the design of the nominal trajectory is mainly driven by the constrains on orbital control capabilities, and operational and robustness considerations. This paper presents the current baselines, and give an overview of the new techniques developed for their design.

© 2017 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 rocket in 2019. Because of its severe mass and size limitation, soft landing to the surface will be impossible. Hence, semi-hard landing scheme is adopted. That is, OMOTENASHI is decelerated to within around 30 m/s by a small solid rocket motor and shock absorption mechanism is developed for 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 dose meters. This paper shows the latest design and development status of OMOTENASHI.

This paper describes an attitude control method that has been designed to prevent the overturning of lunar and planetary landers, based on a variable-damping shock absorber for the landing gear. 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 new method enables the suppression of any disturbance to the attitude of the lander by adjusting the damping coefficient of each landing leg independently, based on the angular velocity vector and displacement velocity of each leg of the lander. The results of a numerical simulation indicate that the control rule for a three-dimensional system is effective for preventing the overturning of the lander on inclined terrain. The results of the simulation and experiments show that the landing gear with the actively variable damping and the control rule play a major role in preventing the overturning of a lunar or planetary lander.

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. Most of lunar or planetary landers have landing legs to reduce shock at the touchdown. They are usually made by passive elements that use aluminum honeycomb structure. When the spacecraft has horizontal velocity or lands on inclined surface, however, reaction force from legs causes rotational moment and the spacecraft might tumble down. The spacecraft should be designed to have lower center of gravity in order to prevent turnover. To avoid turn over and optimize elasticity and damping parameter of landing legs, we had proposed actively controlled landing legs. Since full-actively controlled legs which use high speed and high torque motors require large mass, large power and complexity, semi-actively controlled landing legs are considered. That is, only damping coefficient is controlled following states of the spacecraft. As a result of our study, damping coefficient should be switched to low or high depending on the sign of angular velocity of the spacecraft and shrinking speed of each landing leg. In the presentation, summary of our study is shown. The control scheme of the landing legs are introduced from theoretical consideration. Effectiveness of the proposed scheme is validated with numerical simulations and scale model experiments.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. The development of highly accurate and safe landing technology is required for the next generation lunar and planetary exploration landers in order to achieve touch down on rough but interesting areas. Especially, the explorations inside craters, highland regions, and the moon holes are demanded to achieve an unprecedented result that is pivotal in investigating the origin of the Earth and the Solar System. These areas, however, are rough terrain. Hence, they are considered to be unsuitable areas for landing. Therefore, for the next generation lunar and planetary landing explorations, the robust touch down technology will become more and more important. For the safe landing to such rough and steep terrain, the landing gear is required to prevent the lander from overturning and reduce the impact of landing in the final phase of landing sequence. In this paper, we propose a new landing gear system that uses a shock absorber with actively-variable damping coefficient and present its advantages for attitude stabilization during touch down.

© 1994-2011 IEEE. This article presents a comprehensive path-planning method for lunar and planetary exploration rovers. In this method, two new elements are introduced as evaluation indices for path planning: 1) determined by the rover design and 2) derived from a target environment. These are defined as the rover's internal and external elements, respectively. In this article, the rover's locomotion mechanism and insolation (i.e., shadow) conditions were considered to be the two elements that ensure the rover's safety and energy, and the influences of these elements on path planning were described. To examine the influence of the locomotion mechanism on path planning, experiments were performed using track and wheel mechanisms, and the motion behaviors were modeled. The planned paths of the tracked and wheeled rovers were then simulated based on their motion behaviors. The influence of the insolation condition was considered through path plan simulations conducted using various lunar latitudes and times. The simulation results showed that the internal element can be used as an evaluation index to plan a safe path that corresponds to the traveling performance of the rover's locomotion mechanism. The path derived for the tracked rover was found to be straighter than that derived for the wheeled rover. The simulation results also showed that path planning using the external element as an additional index enhances the power generated by solar panels under various insolation conditions. This path-planning method was found to have a large impact on the amount of power generated in the morning/evening and at high-latitude regions relative to in the daytime and at low-latitude regions on the moon. These simulation results suggest the effectiveness of the proposed pathplanning method.

In this paper, direction control of balloon gondola with only untwisting motor is proposed. Typically a reaction wheel and another actuator for unloading the reaction wheel are in use to control the attitude (or direction) of the gondola. Although this method can get high accuracy control performance, two actuators spend many resources of the gondola. The proposed method uses only untwisting motor installed above the gondola to rotate. This method can not realize such high accuracy control performance but realize direction control with the most simple configuration. The proposed method is applied to prototype GAPS (General Anti-Particle Spectrometer) balloon experiment in 2012. This paper shows control design for this experiment and the results of the proposed method.

© 2014 IAA. The Japan Aerospace Exploration Agency (JAXA) views the lunar lander SELENE-2 as the successor to the SELENE mission. In this presentation, the mission objectives of SELENE-2 are shown together with the present design status of the spacecraft. JAXA launched the Kaguya (SELENE) lunar orbiter in September 2007, and the spacecraft observed the Moon and a couple of small satellites using 15 instruments. As the next step in lunar exploration, the lunar lander SELENE-2 is being considered. SELENE-2 will land on the lunar surface and perform in-situ scientific observations, environmental investigations, and research for future lunar utilization including human activity. At the same time, it will demonstrate key technologies for lunar and planetary exploration such as precise and safe landing, surface mobility, and overnight survival. The lander will carry laser altimeters, image sensors, and landing radars for precise and safe landing. Landing legs and a precisely controlled propulsion system will also be developed. A rover is being designed to be able to travel over a wide area and observe featured terrain using scientific instruments. Since some of the instruments require long-term observation on the lunar surface, technology for night survival over more than 2 weeks needs to be considered. The SELENE-2 technologies are expected to be one of the stepping stones towards future Japanese human activities on the moon and to expand the possibilities for deep space science.

Lunar or planetary exploration is scientifically meaningful because they can give us the hint to throw a light on the origin and evolution of the solar system or the earth, the inner structure of planets, etc. In lunar or planetary exploration missions, it is important to save the weight of spacecraft. Light weight spacecraft leads to low cost and getting more chance to go to the space. Conventionally a lander carries a rover to the surface of the celestial body and the rover traverses the rough terrain to explore in wide region. If the lander and the rover are united, however, the total weight of the spacecraft could be reduced. The authors have already proposed a novel pulley suspension mechanism, which is called Load Equalization Pulley Suspension mechanism: LEPS mechanism, for rovers. The performance of the proposed mechanism as a suspension mechanism of rovers has been evaluated. In this paper, the application of LEPS mechanism to the landing gears of the lander is discussed. By applying the proposed mechanism to the landing gears, the lander can move around the wide region of the surface after landing. The landing dynamics model of the proposed "Movable lander" with LEPS mechanism is introduced. The landing performance is evaluated by 2-dimensional model. The simulation results show that LEPS mechanism has an advantage over normal landing gears.

This paper presents an actively controlled landing gear system and its experimental validations. Active landing gear uses an variable coefficient damper as an shock absorber. We executed landing experiment with the two dimension lander model which introduced an magnetorheological damper as an shock absorber. Damping coefficient is controlled to reduce attitude disturbance during touchdown based on lander attitude and displacement of landing leg. The result of model experiment indicates that the active landing gear can reduce attitude disturbance which causes the lander overturning.

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This paper describes the attitude control method for overturning prevention for a lunar planetary lander which uses a semi-active damper on the landing leg. In order to achieve safe landing on uneven terrain especially a sloped ground, a novel landing gear system is required. The landing leg with variable damping is one of the solutions for touchdown without overturning. Conventional landing gear for lunar and planetary lander has a fixed shock attenuation parameter and it is not used proactively for attitude control of the lander in the touchdown sequence. By controlling the damping coefficient of the each landing leg, it becomes possible to suppress the disturbance on the attitude of the lander, and it prevents overturning. First, the strategies for the overturn prevention for the lander by changing damping coefficient of landing legs are shown and the control rules based on the lander and landing leg state values are proposed. In the second place, the mathematical model of lander based on the differential algebraic equation in vertical two-dimensional plane is presented. Besides footpad-ground contact model is also described. Finally, touchdown simulations on a sloped terrain with the proposed landing gear control method are shown. Numerical simulations show that the proposed landing gear system works well during the touchdown on a sloped terrain.

JAXA is planning moon exploration missions following Kaguya (SELENE). The first Japanese moon lander is SELENE-2 whose missions include technology demonstrations, scientific observations, investigations for future moon utilization, and social or political purposes. Its phase-A study started in the summer of 2007. SELENE-2 will land on the near side of moon and perform in-situ geological and geophysical observations to improve the knowledge on the origin and the evolution of the moon. Investigations of surface environment are important for future lunar exploration including human activity. It also demonstrates precise landing, hazard avoidance, surface mobility, and night survival technologies. In this paper, recent progress of technology development for SELENE-2 is presented.

For touchdown mission on rough but interesting terrain where no space probe has gone before, like "crater central hill" and edge of lunar lava tube hole, an actively controllable landing system is required. This paper proposes an of actively controlled landing leg system by using a variable coefficient damper. Further, to show the effectiveness of the actively controlled landing leg system, we simulate touchdown based on mathematical models. Further, show the effectiveness of the actively controlled landing leg system based on the proposed controller. Simulation model is virtually-fixed in two-dimensional plane, and investigates robustness of lander to touchdown to slope terrain and the case where the lander has initial horizontal velocity and initial attitude angle error.

JAXA is planning moon exploration missions following Kaguya (SELENE). The first Japanese moon lander is SELENE-2 whose missions include technology demonstrations, scientific observations, investigations for future moon utilization, and social or political purposes. Its phase-A study started in the summer of 2007. SELENE-2 will land on the near side of moon and perform in-situ geological and geophysical observations to improve the knowledge on the origin and the evolution of the moon. Investigations of surface environment are important for future lunar exploration including human activity. It also demonstrates precise landing, hazard avoidance, surface mobility, and night survival technologies. In this paper, recent progress of technology development for SELENE-2 is presented.

For touchdown mission on rough but interesting terrain where no space probe has gone before, like 'crater central hill' and edge of lunar lava tube hole, an actively controllable landing system is required. This paper proposes an of actively controlled landing leg system by using a variable coefficient damper. Further, to show the effectiveness of the actively controlled landing leg system, we simulate touchdown based on mathematical models. Further, show the effectiveness of the actively controlled landing leg system based on the proposed controller. Simulation model is virtually-fixed in two-dimensional plane, and investigates robustness of lander to touchdown to slope terrain and the case where the lander has initial horizontal velocity and initial attitude angle error. © 2013 IEEE.

When a spacecraft lands, a large shock load can lead to undesirable responses such as rebound and tripping. The authors previously discussed the problem of controlling these shock responses using momentum exchange impact dampers (MEIDs). An active/passive- Hybrid-MEID (HMEID), which included an active actuator, was proposed, and stiffness control was applied. The stiffness control method controls spring coefficient between the damper mass and the body mass. The MEIDs' performances are evaluated by the maximum rebound height, which is proportional to mechanical energy of the spacecraft. However, the time responses of the energies have not been explained. In addition, the effectiveness of MEIDs was evaluated only in a one-dimensional motion simulation. This paper includes theoretical analyses, simulation studies, and experiments. The time responses of the energies of MEIDs are discussed. This paper proposes a robust landing gear system for spacecrafts using HMEID and evaluates its robustness against ground stiffness variation. In this paper, MEIDs are applied to a mass-damper-spring-model, which takes ground viscosity into account. Effectiveness of the proposed model is verified by simulations and some experimental results. © 2012 by Yohei Kushida, Susumu Hara, Masatsugu Otsuki, Yoji Yamada, Tatsuaki Hashimoto, and Takashi Kubota.

JAXA is planning moon exploration missions following Kaguya (SELENE), whose missions include technology demonstrations, scientific observations, investigations for future moon utilization, and social or political purposes. SELENE-2 is the first Japanese moon lander. Its phase-A study started in the summer of 2007. It will demonstrate precision landing, hazard avoidance, surface mobility, and night survival technologies. In-situ geological and geophysical observations will contribute to improve the knowledge on the origin and the evolution of the moon. Investigations of surface environment and possible in-situ resource will be useful for future human exploration. In this paper, recent progress of research and development for SELENE-2 is presented. Key Words: Lunar exploration. Precision landing. Rover, Night survival. Copyright © (2012) by the International Astronautical Federation.