Sachiko Wakabayashi

Force reflection for ground control of Space robots

Ideas for improving continuous teleoperation and operator performance despite time delays using force-reflecting hand controllers. They have been tested on the Japanese Engineering Test Satellite-7 (ETS-7). Predictive display and predictive simulation are used.

The Right Path: Comprehensive Path Planning for Lunar Exploration Rovers

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 rovers internal and external elements, respectively. In this article, the rovers locomotion mechanism and insolation (i.e., shadow) conditions were considered to be the two elements that ensure the rovers 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 rovers 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 path-planning method.

On-Orbit Construction Experiment by Tele-Operated Robot Arm

On-orbit assembly technology is a key for future large-scale structure construction. For several decades, many concepts of space structures have been proposed and some of them have the idea of robotic construction systems. Authors have developed a concept of a truss joint system for largescale orbital structures and worked for space robotics research. Participating aJapanese space robotics experiment project on Engineering Test Satellite No. 7 scheduled to be launched by NASDA in 1997, the authors will conduct spare truss construction experiments. The experiments have objectives to establish basic technologies of on-orbit assembly work and robotic construction by using NA SDAs manipulator on the satellite. Our experiment system consists of the experiment unit including a truss joint anda deployable truss on the satellite, and our teleoperation facility on the ground The on-board truss unit has been tested in both vibration and thermal vacuum conahtions simulating orbit environment, and the ground teleoperation facility has been developed The actual experiments will start in late 1997.

Motion Behaviors of Landing Gear for Lunar Probes in Atmosphere and Vacuum Tests

In this paper, we investigate and model the motion behaviors in the atmosphere and vacuum of the landing gear of a lunar probe, which contacts the granular material covering the lunar surface. Drop and friction tests were conducted using the footpads of a lander on a lunar regolith simulant. In the drop tests, the footpads were dropped onto the simulant. The impact characteristics of the footpads were then analyzed. In the friction tests, footpads having varying shapes were slid onto the simulant. The sliding characteristics of the footpads were then evaluated. The drop tests showed that the simulant ejected by the footpad impact diminished, and the footpad penetration significantly decreased in the vacuum. The friction tests confirmed that the sinkage caused by the sliding of the footpad generally increased more in the vacuum than in the atmosphere. However, the difference in the sinkages can be negligible depending on the footpad shape. These findings enabled the deriving of fundamental models of landing gear and suggested guidelines for the design and development of landing gear.

Terramechanics evaluation of low-pressure wheel on deformable terrain

In this paper new procedures for the measurement of mobility parameters, such as contact pressure, and an analysis of a low-pressure wheel model on deformable terrain, are presented. Because the lunar surface is covered by regolith which implies an irregular and rough terrain, the rover has difficulty in moving. Therefore a new low-pressure wheel is recommended for high mobility performance and low power consumption with a less complex mechanism. A low-pressure wheel can change its contact shape and pressure distribution to account for terrain. The presented measurement is achieved by a new measurement instrument on the wheel, and we presented analysis model is conducted through analysis of terramechanics mobility dynamics of a low-pressure wheel with normal stress. These procedures are valuable for evaluating the longitudinal velocity of the low-pressure wheel on deformable terrain.

Design and Mobility Evaluation of a Crawler-type Lunar Vehicle

This paper describes a newly designed crawler-type vehicle for the Moon exploration. It aims at achieving higher mobility for bigger and heavier transportations in the future as well as enhancing the mobility of current small or medium sized robotic vehicles, focusing on the slope-climbing capability on pure sand slopes. The designed vehicle has four mesh crawlers to reduce weight and the number of parts. A single crawler test was conducted using a slope traveling test apparatus to obtain the effects of slope inclination on the relationships between slip ratio and vertical load, or between ultimate current and vertical load. The results show that there is an optimal design point for the contact area and that the design point is fairly robust for the weight increase. The power consumption of the single crawler increased linearly along the traveling distance for all the test cases, which means that the slip ratio and current were stable during the test traveling. A single wheel test was conducted for comparison. The wheel’s slip ratio and power consumption were bigger than that of the crawler at a slope of 20 degree and its power consumption increased non-linearly along the traveling distance. The test results obtained so far indicate that a crawler-type vehicle shows higher performance and lower power consumption than a wheel on steep slopes under the experimental

Landing Behavior Analysis of Lunar Probe Based on Drop Tests and RFT in a Vacuum

This letter addresses the influences of footpad shape and ground condition on the motion behavior of a lander in a vacuum. To evaluate the influences, we first developed a drop test apparatus that can conduct repeated drop tests in the vacuum chamber. The footpad drop tests were then conducted with various shaped footpads on different surface conditions. Subsequently, the motion behavior of the footpads in a vacuum was modeled, based on the resistance force theory (RFT) and its penetration characteristics were numerically analyzed. The usefulness of the RFT based model was discussed along with the experimental results. Finally, drop tests were conducted using a four-legged lander to comprehensively analyze its landing behaviors. From the footpad drop tests and numerical analysis based on the RFT, we confirmed the following: 1) the force acting on the footpad is enhanced, and the penetration depth is reduced in a vacuum, 2) the force and kinetic energy conversion rate are smallest for the curved footpad, and 3) an increase in the ground density had a relatively small impact on the penetration depth of the footpads in a vacuum. Furthermore, the drop tests using the lander model confirmed that even if some of the landers footpads land on regolith simulant with different densities, this does not lead to postural imbalance or turnover of the lander in a vacuum.

Borehole geotechnical testing tool for lunar exploration

Soil mechanics study plays a key role in various engineering problems relating to future lunar/planetary surface explorations. In-situ measurement of regolith physical properties is of fundamental importance in developing a framework of lunar/planetary soil mechanics. An in-situ soil investigation package; LSM (lunar soil mechanics investigation system) is being developed as a moon utilization payload for Japans Moon lander SELENE-2, which is planned as a follow-on program of Kaguya program (SELENE). This paper focuses on a soil testing tool, which is one of the subsystems of LSM, and describes a result of laboratory experiments using a prototype model. The equipment developed is a small-diameter tool with a paired-inflatable blade and is used in a pre-frilled borehole for performing two types of soil mechanics test; lateral loading test and direct shear test against the borehole sidewall. In this study, a series of shear tests were demonstrated with a Japanese lunar soil simulant (FJS-1) and the results were compared with results of a triaxial compression test and direct shear box test. The test results showed that the proposed method has a great potential to be a reliable tool that can provide strength parameters on the lunar surface. The characteristics and underlying limitations of the probe were also discussed for future improvements.

A Plan for Lunar Outpost Construction by using Robots

Architecture study for Lunar exploration is carried out by space agencies. JAXA is carrying out research and development of a mobility robot (rover) aimed at the Lunar surface exploration and outpost construction. The target areas for outpost construction and lunar exploration are mainly in mountainous zones, and the moons surface is covered by regolith. Achieving a steady run on such irregular terrain is the big technical problem for rovers. A newly developed lightweight crawler mechanism is good for driving on such irregular terrain because of its low contact force with the ground. This was determined considering the mass and expected payload of the rover. This paper describes composition of the robots designed for construction of lunar outpost, and also gives the scenario for outpost construction. These lunar robot are developed based on space robot technology cultivated by development of the JEMRMS and the ETS-VII robot.

Magnetic Sampler for Regolith Particles on Asteroids

AbstractA magnetic sampler for future sample return missions on asteroids was developed. The sampler had a simple configuration, consisting of a solenoid coil, direct current (DC) power supply, and...