大槻 真嗣

The updated Table 1 with a comment indicating that micrographs #05 and #08 at the bottom of the images should be replaced. However, in the response to author query 4, Micrographs #4 and #8 were changed in Table 1. While processing the suggested changes based on the eProofing comments, the correction team updated the existing table figures and replaced image #05 with the micrograph of image #08 and image #08 with the micrograph of image #04 in the revised table. As a result, the changes got reverted and images were incorrect and duplicated.

Studying the gravity-dependent characteristics of regolith, fine-grained granular media covering extra-terrestrial bodies is essential for the reliable design and analysis of landers and rovers for space exploration. In this study, we propose an experimental approach to examine a granular flow under stable artificial gravity conditions for a long duration generated by a centrifuge at the International Space Station. We also perform a discrete element simulation of the granular flow in both artificial and natural gravity environments. The simulation results verify that the granular flows in artificial and natural gravity are consistent. Further, regression analysis of the experimental results reveals that the mass flow rate of granular flow quantitatively follows a well-known physics-based law with some deviations under low-gravity conditions, implying that the bulk density of the granular media decreases with gravity. This insight also indicates that the bulk density considered in simulation studies of space probes under low-gravity conditions needs to be tuned for their reliable design and analysis.

An accurate target tracking system improves the quality of flyby imaging of the target and consequently aids effective planetary exploration. A vision-based tracking system is one of the more popular systems, utilizing imaging data to achieve the required tracking accuracy. However, recent high-accuracy target tracking requirements cannot be achieved with targeting error feedback only. This paper summarizes the asteroid flyby mission characteristics and requirements, shows how possible error sources in the tracking system, and displays an exemplar control system design. The tracking error source is generally divided into a navigation error, which is a tracking profile generation error, and a control error, which is caused by the control system. A high-quality onboard relative-trajectory determination system is required to improve the navigation accuracy of the control system, because the pre-designed or offline-estimated relative trajectory contains uncertainties that cause the tracking profile generation error. Previous studies focused on this navigation error because of its sensitive effect on control system performance, showing some methods for improvement. This paper discusses how the control system can be improved to achieve greater precision during target tracking by considering the navigation and system characteristics. A realistic case study scenario is defined and analyzed based on an actual target tracking interplanetary probe mission. The characteristics of the designed control system are presented and its performance is analyzed via numerical simulation, using the case study data.

This study aims to establish a general-purpose thermal conductivity measurement method that can take into account the effect of heat loss under atmospheric conditions for measuring the effective thermal conductivity of lattice structures, and to clarify the effective thermal conductivity of lattice structures with different wire diameters. In this paper, calculations by finite element method and measurements using steady state comparative-longitudinal heat flow method and modified temperature profile method were performed to clarify the effective thermal conductivity of the five truncated octahedron unit-cell lattice structures with different wire diameters fabricated by additive manufacturing. The modified temperature profile method is developed to take into account the effect of interfacial thermal resistance in the measurement apparatus. The effective thermal conductivity measured using the steady state comparative-longitudinal heat flow method and calculated with finite element method analysis showed good agreement, confirming that the effective thermal conductivity is strongly dependent on the wire diameter. The effective thermal conductivity obtained by the modified temperature profile (MTP) method was 3 % to 24 % smaller than that obtained by the steady state comparative-longitudinal heat flow method, and the measurement was able to take heat loss into account more concretely. Furthermore, measurements using the MTP method enabled us to obtain reasonable values for the ratio of heat loss in each section, the fin efficiency of the sample, the heat transfer coefficient to the surroundings, and the interfacial thermal resistance between the rods and the sample.

Martian Moons eXploration (MMX) is a mission under development in JAXA in cooperation with NASA, CNES, ESA, DLR to be launched in 2024. This paper introduces the result of its preliminary design and the latest status of the MMX program, putting more weight on the novel part of the mission. The goal of MMX is to reveal the origin of the Martian moons and then to make 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. Additionally, the mission is to survey two Martian moons and return samples from Phobos. Add to those MMX's contribution to the planetary science field, on the growing discussion on the International Space Exploration activities, MMX's contribution to future human Mars exploration is also considered as an essential aspect of the program. Following the system definition study results presented in the previous conference, the following items will be reported in this paper. First, as a result of the comprehensive completion of the Phase-B activities, the preliminary design is completed in coordination with the design of the spacecraft system, mission instruments, and operation plans. This paper describes the proximity and surface operations around Phobos in detail. Second, Phase-C activities have started, incorporating engineering models manufacturing and tests. Those of critical technologies for surface exploration are described in detail. Moreover third, the programmatic aspects, including international cooperation frameworks and the program schedule, are presented.

This study proposes a descent control system for a space lander with a large amount of fuel, to protect the lander from overturning when landing on microgravity objects. As sloshing is a major problem during descent, it is desirable to construct a control system that considers the sloshing dynamics. We derive a model of the lander considering fuel dynamics, determine the fuel-optimal trajectory for guidance, design a fuel state estimator for navigation, and design a tracking controller. The effectiveness of the proposed method is evaluated using a physical simulator. The proposed method achieves simultaneous stabilization of the lander and fuel, and is shown to be effective in preventing overturning.

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 ratio of force output to mass allows for the SMA actuator to achieve a high energy 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-energy-density SMA actuators. In addition, a suitable model is established for the force trajectory control method based on the thermomechanical coupling response characteristics. A thermal balance model is constructed under a vacuum environment. Furthermore, a hysteresis characteristic model of the phase transformation is introduced, and it reduces the heating profile limitation. The SMA’s generation 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.

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. [Figure not available: see fulltext.].

Landing on celestial bodies typically includes a free fall to the body surface and requires energy dissipation. Landing sites can exhibit many uncertainties, especially in surface parameters. Therefore, robustness is required irrespective of variations in landing conditions. Conventional mechanisms, such as shock absorbers or airbags, have repeatedly achieved safe landings; however, they are not reusable in the ground-verification phase and cause complexity. This study proposes a robust, lightweight, and simple rebound suppression mechanism with reusability in the ground verification phase by simultaneously considering the characteristics of mechanical energy and momentum exchange aspects. The design characteristics are clarified mainly through numerical discussions, and the effectiveness of the proposed mechanism is demonstrated in comparison to existing momentum exchange mechanisms. The results show a promising rebound suppression capability compared with those of the previously suggested mechanisms and an improvement in robustness against uncertainties. A case study is also shown to verify the proposed mechanism’s effectiveness. Numerical simulation results for a fictional landing mission created from real microgravity landers show that the proposed mechanism achieves the energy dissipation requirement, combined with the plastic deformation mechanism of the shock-absorbing material.

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.

This study analyzes the surface sliding behavior of space probes in simulated extraterrestrial environments. When a space probe lands on an extraterrestrial body, its landing gear (footpad, landing legs) contacts and slides along the ground surface. The influence of various parameters (i.e., footpad size, velocity, ground condition, atmospheric pressure, and gravity) on the friction behavior of footpads was experimentally evaluated herein. First, we developed an experimental system that can perform footpad sliding tests repeatedly. Subsequently, the system was used to perform tests under various conditions: 1) on ground under normal atmospheric conditions, 2) in a vacuum, and 3) in reduced gravity. The tests performed in a vacuum and in reduced gravity indicated that the friction behavior of the footpad is largely unaffected by atmospheric pressure and gravity. The findings obtained herein offer useful design and control guidelines for space probes landing on extraterrestrial bodies.

In Martian Moons eXploration (MMX), JAXA plans to land a space probe on the surface of Phobos. For such future satellite and planetary explorations, it is important to understand the dynamic interaction between the soft ground and the mechanical system under low gravity. So far, to investigate the dynamic interaction, experiments under the artificial low gravity using a drop tower facility are utilized. However, to correctly interpret and effectively utilize the results of the drop tower experiment, it is necessary to clarify the difference from the natural low gravity environment, such as the effect of gravity transition due to the fall. In this study, we performed the discrete elements method (DEM) analysis of the pad collision to the granular media, mimicking the drop tower experiment. First, we examined a lifting of granular surface owing to gravitational transition. It was revealed that the lifting of ground surface is caused by release of elastic energy of particles. Next, we performed a pad collision analysis, and compared reaction force, sinkage, and particle movement with those obtained from the experiment. We confirmed that the DEM analytical results show good agreement with experimental results. Then, we examined the effect of packing condition of granular media and the difference between the artificial low-gravity and the natural low gravity conditions.

This paper presents a novel approach to sampling subsurface asteroidal regolith under severe time constraints. Sampling operations that must be completed within a few hours require techniques that can manage subsurface obstructions that may be encountered. The large uncertainties due to our lack of knowledge of regolith properties also make sampling difficult. To aid in managing these challenges, machine learning-based detection methods using tactile feedback can detect the presence of rocks deeper than the length of the probe, ensuring reliable sampling in unobstructed areas. In addition, given the variability of soil hardness and the short time available, a corer shooting mechanism has been developed that uses a special shape-memory alloy to collect regolith in about a minute. Experiments on subsurface obstacle detection and shooting-corer ejection tests were conducted to demonstrate the functionality of this approach.

<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>

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.

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.

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.

Shape memory alloy (SMA) actuators can generate force via the phase transition of the SMA, related to its temperature variations. The amount of force and the response duration length are approximately proportional to the SMA's volume and mass. The higher-power actuator, which consists of a single SMA tube, has mechanical simplicity and high reliability; however, it has a relatively long driving duration, and actuation timing uncertainties caused by the environmental temperature variations. Because of its huge heat capacity, the environment temperature variations affect the actuator's temperature, the phase transformation uncertainties, and force generation profiles, resulting in differences in the actuation timing that are tens of seconds. This paper proposes a suitable feedback control system consisting of two methods. One is the construction of a physical model for SMA tube thermomechanical coupling response that has suitable complexity for the real-time control system design by the limited application condition. The other is a reference trajectory generation and tracking method by using the model predictive control method with a constructed physical model, resulting in a possible drive timing uncertainty reduction. The effectiveness of the proposed methods was verified by specific test piece system identification and control simulations performed both numerically and experimentally. In addition, the effectiveness of the online control system itself was confirmed by comparing the results of a traditional control system using the proportional integral derivative method. The result indicates the potential of the possible application system for SMA actuators.

This letter presents the hopping performance evaluation on three types of terrains and novel foot pad designs for efficient traverse of hopping rovers. Hopping rovers, called Hopper, are expected to explore scientific richness areas where wheeled vehicles are hard to traverse. In order to succeed in the robotic planetary exploration, optimization and efficient designs of rovers are essential. Almost all planetary surfaces are covered with sand, called regolith, which makes hopping efficiency bad. In this letter, we discover the hopping performance on three kinds of terrains. Moreover, we also propose the method of increasing hopping performance on soft soil. Inspired by the conventional wheeled vehicle design, treads, called grouser, are installed on the bottom of the foot pad. While grousers are effective on hard ground and soft soil, they are ineffective on bilayer terrain. Bilayer means that hard ground is covered with thin regolith. And the other novel grouser shape is designed based on the soil interaction model using a multi-objective evolutionary algorithm. The proposed design improves the hopping performance on soft soil in comparison with the straight grouser.

© 1986-2012 IEEE. The 6U CubeSat OMOTENASHI, which is due to be launched in 2020 by NASA's Space Launch System, will be the world's smallest moon lander. Its main mission is to present the possibility of nanomoon landers to enable distributed multipoint lunar exploration and participation by the commercial sector. The severe mass and size limitations of OMOTENASHI make a soft landing on the surface impossible, so instead a semihard landing scheme has been adopted. That is, a small solid rocket motor will decelerate the spacecraft to around 50 m/s, followed by the use of shock absorption mechanisms for high-speed impact. An ultrasmall telecommunication system (X-band and P-band) has also been developed. The spacecraft will also observe the radiation environment between the Earth and the Moon using commercial portable dosimeters for future manned exploration. This paper describes the mission objectives, the mission sequence, the spacecraft configuration, and the technologies developed for OMOTENASHI.

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.

This paper presents the current development status of the optional payload named Lunar Excursion Vehicle (LEV) for the Japanese future Lunar landing mission SLIM. The deployable exploration system LEV is released from the lander at the few meters above the Lunar surface after the lander's terminal deceleration is finished. LEV consists of two probes that will move and observe around the landing site autonomously. They also help acquire the evidence of SLIM landing by taking pictures of the final status of the lander.

<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 the control methods for discrete time systems. The optimal input is calculated by using Linear Quadratic Regulator (LQR). The weight matrices in the evaluation function for LQR are determined by a designer with professional experience and a trial & error approach. Therefore, even if the same system is targeted, the performance can differ depending on the designer. This paper proposes a new weight selection algorithm using Simultaneous Perturbation Stochastic Approximation (SPSA) for MPC. A new evaluation function is proposed for the selection algorithm. Numerical values of the overshoot and the settling time are directly applied as the user's requirements in this evaluation function. The optimal weight matrices numerically satisfying those requirements can be selected by the proposed algorithm. Simulation study of a zero momentum spacecraft shows that the proposed method is effective for the weight selection with consideration of performance.

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.

<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>

© 2018 Trans Tech Publications, Switzerland. Generally, commercial motors are produced as the lineup of series of outer diameter. The output power is changed with their length. However, the production number of space motor or power assist leg motor is small, while the power ratio versus motor weight is very important factor. The geometric study is proposed in this paper; especially, such problems of outer rotor versus inner rotor motor, outer diameter versus length. The motor characteristics are assumed with the FEM simulation. These constants depend on the motor pole number and driving amplifiers. Hence the exact geometrical dimensions should be determined with the careful simulation. Before simulation rough geometrical size can be determined, then the exact simulation will be carried out to determine the motor dimension and estimate the produced motor characteristics. The results are planned to compare with some of the experimental results.

Various planetary terrains or asteroids, which are hard to traverse with wheeled platforms, are expected to be explored. Bekker's model cannot be applied to estimate the motions of rovers without wheels, such as the hopping rover (hopper). In this paper, the resistive force theory (RFT) approach is introduced. This approach is not based on Bekker's model, and is expected to apply to any platform. However, this RFT approach only applies to static or quasi-static motion, such as in the case of slow motions. To apply the RFT approach to dynamic motions, such as hopping, the effect of velocity as a dynamic variable is also studied. Through the hopping experiments, the effectiveness of RFT with the velocity-term approach is investigated and compared to the RFT approach.