大槻 真嗣

<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>

<p>This paper addresses shock absorption behavior of 3-D additive manufactured truncated octahedron for the landing gear of lunar and planetary explores. The deformation modes of truncated octahedron were predicted by the form finding analyses. The collapse load of each deformation load was calculated by the plastic hinge theory. The predicted load--displacement curve agreed with the experimental results, and thus, the proposed prediction method was verified. </p>

<p>In this paper, we evaluate a mobility system using skids for a small lander. The small lander named Smart Lander for Investigating Moon (SLIM) has been developed by ISAS/JAXA. In the small lander mission such as SLIM, planetary surface exploration after the landing will become difficult due to the restriction of the lander's payload weight for a rover and observation equipment. To solve this problem, we propose the mobility system using skid-sliding to improve exploration capability of the small lander mission. We confirmed the skids' sliding potential of the small lander using numerical simulation. The simulation showed that the small lander can travel to the desired direction using skids and thruster control.</p>

Model Predictive Control (MPC) is one of control methods for the discrete time system. The optimum input is calculated by using Linear Quadratic Regulator (LQR). In MPC, the cross-product term is generally omitted in the evaluation function for LQR. However, the effectiveness of the cross-product term for LQR is confirmed by various researches. Therefore, this paper addresses the expanded form of cross-product term applied to MPC. Simulation of zero momentum spacecraft shows that the cross-product term is effective for consideration of performance to MPC.

<p>This paper studies the feasibility of a hopper for planetary exploration rovers. The proposed hopper is designed based on shape memory alloy(SMA) actuators, because SMA actuators are light in mass compared with traditional electric motors. This paper discusses a design strategy for the proposed hopper to achieve sufficient locomotion capability on planetary surface. Firstly, this paper presents a basic hopper mechanism and its design strategy with SMA physical model. Secondly, semi-optimized design parameters of the hopper are determined based on brute-force searching. Finally, the experimental results show the effectiveness of the proposed hopper for lunar or planetary exploration.</p>

<p> More than 100 spacecrafts have attempted to softly land on the surface of planet such as a moon, Mars, Venus, a comet and an asteroid in the history of space development. Although the landing success rate is approximately 40 percent, there are few failures caused by unexpected environmental influences and large deviations from the supposed environmental conditions. It is considered that this is due to conducting adequate investigation of environment around the exploration area by remote sensing and steadily progressing the mission while obtained Lessons Learned through a series of project. For this article, we first discuss about the space environment in which the planetary explorer works. Then, we outline how we verify and evaluate the specifications of components and system of the spacecraft with the tests partially simulating harsh environments such as heat, radiation and regolith. Furthermore, countermeasures against the harsh environments where the actuator and absolute angle sensor are exposed are also mentioned.</p>

JAXA-RR-16-008

The landing system which is adaptable to different kind of terrain condition is required to achieve touchdown on rough and inclined terrains. However, it is difficult to design a landing system which is applicable to a wide variety of terrains. In the conventional landing gear system, aluminium honeycomb crush and oil damper are used to mitigate landing impact. These classical mechanisms have advantages of simplicity and large shock absorption capability. However, those classical passive landing gears are ill suited for landing to the uneven and inclined areas and for landing with lateral velocity. To prevent from lander tip-over, it is necessary to make landing gear adaptable to wide condition of terrain. In order to solve this problem, we propose a new mechanism for safety landing on an inclination. In general, tipping-over of spacecraft is caused by the torque which is generated by the difference of the force acting on each leg. However, it is difficult to synchronize force acting on the all the landing legs. Here, we focused on the difference of the force acting on each leg. In case of touchdown on the inclination, the force acting on the upper leg is larger than any other legs. In case of touchdown with a lateral velocity, the force acting on the former leg is larger than any other legs. Therefore, if we can convert this force to torque which is acting to the direction against to the rotating of the spacecraft, it becomes possible to prevent tip-over of the spacecraft.

<p>We are planning to explore the caverns through the skylight holes on the Moon and Mars. The holes and their associated subsurface caverns are among the most important future exploration targets. The importance of the lunar and Martian holes and their associated caverns is categorized from two aspects: (1) fresh materials are easily observed and sampled there, and (2) the subsurface caverns provide a safe, quiet environment. The expectation of lunar and Martian hole and cavern exploration is increasing in Japan. We name the project as UZUME (Unprecedented Zipangu (Japan) Underworld of the Moon Exploration) whose name is after a Japanese mythology. The ultimate purpose of the UZUME project is to investigate how to expand human activity and survival in space and on extraterrestrial bodies. </p>

Next-generation lunar/planetary exploration spacecraft need to solve problems of conventional landing methods and mechanisms such as high rebound, impossibility of reuse and high cost. For this purpose, the authors discuss the landing method by means of Base-Extension Separation landing Mechanism (BESM) which uses energy conversion with springs and separable units. In conventional studies, its effectiveness was confirmed for a simple case based on single-axis restriction. However, the investigation of tumble prevention cannot be treated in the simple case. The purpose of this paper is the response analysis with a double-axis case and to discuss the robustness of BESM for more practical landing situations.

The safe and precise landing control method of planetary exploration spacecraft is indispensable to achieve its missions. However, the landing methods used in previous missions have some problems such as high complexity. To improve them, the authors' have focused on the momentum exchange principles and adopted momentum exchange impact dampers (MEIDs) that absorb the controlled object's momentum to extra masses close to the object. This extra mass is called damper mass. Some kinds of MEIDs have been introduced; for example, this paper shows Upper-MEID (U-MEID) that launches the damper mass upward, Lower-MEID (L-MEID) that drops the damper mass downward, and Generalized-MEID (G-MEID) consisting of U-MEID and L-MEID. The authors' previous paper shows the effectiveness of G-MEID. The purpose of this paper is to introduce its improved version called G-MEID-A (G-MEID-Advanced). G-MEID-A can realize downsizing of the damper mass and more effective momentum exchange by tuning of momentum exchange timing. Simulation investigation verifies that the G-MEID-A has some advantages against the rebound reduction of the spacecraft and robustness against some variable conditions.

In future surveys, planetary exploration spacecraft will need to land on rock beds and slopes. Therefore, spacecraft should be equipped with landing methods to facilitate soft landings in these severe regions. However, conventional landing methods have problems such as high rebound, the impossibility of reuse, and excessive resource consumption. To overcome these problems, the authors previously invented several landing methods, but these have practical limitations. Thus, this paper proposes a novel landing mechanism called the base-extension separation mechanism (BESM), which focuses on energy conversion using springs and separable units, and discusses a single-axis falling-type small-scale model of a spacecraft with the BESM. Then, the rebound and acceleration suppression performance is evaluated through simulations. These reveal that the BESM realizes good performance under nominal conditions. The BESM is shown to have good robustness against variations in the ground stiffness, ground damping, spacecraft mass, and installed mass. The study findings reveal that the BESM is a promising method: it overcomes the drawbacks of the conventional methods and our previous inventions. In addition, the BESM generally performs better in soft landings than our previous inventions.

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.