Tetsuo YOSHIMITSU

In lunar or Martian exploration, compact and ultra-light rover is required or Smart Lander for Investigating Moon (SLIM) as the optional rover from the viewpoint of cost reduction and short-term development. Inflatable structure technology is most appropriate way for such ultra-light rover. However, there are not enough researches on rovers with shock absorbing inflatable wheel. Basic architecture of the ultra-light rover wheel with shock absorbing using inflatable structure technology is clarified.

The planetary surfaces are covered with soft soil, so the wheel of planetary rover easily slips and loses the traction. This paper presents a terramechanics-based wheel dynamics model to improve the rover mobility via considering the dynamic wheel sinkage. Terramechanics is a study of soil properties and an interaction between the wheel and soft soil. Since terramechanics-based wheel model considers only the static state of wheel sinkage, the wheel model is not applicable to the dynamic condition. Understanding the traction mechanics in the dynamic wheel sinkage is important in order to predict the wheel motion in the static state. We propose the dynamic normal force model to treat the dynamic wheel sinkage via considering the state variation of soil condition. Besides we present the wheel driving model in the dynamic wheel sinkage by considering the shear deformation modulus. We evaluate the proposed models by simulations.

Planetary surface is covered by soft soil. Thus wheel slips and gets stuck easily. Wheel slippage causes wheel stuck, navigation error, and difficulty in climbing slopes. Purpose of this research is to develop wheel control system for efficient travelling on soft soil. The efficient travelling is that a rover is able to travel on high speed and small wheel slippage on soft soil. Considering strong control system for disturbance, it is important to incorporate terramechanics theory. In this paper, wheel dynamics model based on terramechanics is proposed, and the dynamics model is verified it is appropriate for dynamic motion by simulation analysis.

Many space missions are being undertaken to improve our understanding of the solar system and how to use space resources. Nowadays, since MER's success, exploration of planetary surfaces is being focused on. Rovers have the capability of reaching important scientific areas on planetary surfaces. Rovers traverse unknown environments in limited missions. Therefore, rovers are expected to have the ability to explore as widely as possible and to navigate themselves efficiently. The conventional navigation systems based on stereo vision or laser range finder are not wide enough to obtain distant area environment information. Since understanding wide environment makes rover navigation more efficient, detailed terrain maps are not necessarily required. This paper proposes an efficient image- based navigation by a single camera.

Investigations into small planetary bodies are becoming more attractive, and some missions to small bodies have already been sent. As such bodies have numerous geographical features, the next requirement is direct surface investigations by rovers. Localization of rovers is required to navigate them to specific points. However, conventional methods of localization are not adequate on small bodies because of the small body's irregular shape and small mass. We proposed an efficient method of localizing rovers on small bodies. It uses two-way range measurements between the rover and mother spacecraft. The measurements are conducted repeatedly. This method can be used over the whole surface of the investigating body, and it only needs one spacecraft. Numerical simulations demonstrated the effectiveness of the proposed method assuming an Itokawa-sized-asteroid, whose maximum diameter is 600[m]. In this paper, the sensitivity direction is analyzed, which indicates the preferable orbit of spacecraft and the sufficient number of measurement.

Direct investigations are required for future missions to small planetary bodies, in addition to obtain terrain maps and collecting samples from the surface. Rovers, mobile robots on surface of a planetary body, are effective in investigating into several specific points. We proposed a method of localization for navigating rovers to specific features. The proposed method measures two-way range between the rover and the mother spacecraft orbiting around the investigating planetary body using radio waves. The proposed method can be applied with reasonable accuracy on large and small planetary bodies and it can particularly be used with sub-hundred-meter-sized bodies, which conventional methods cannot be applied to. Sensitivity analysis of the proposed method is summarized in this paper, according with estimation errors in rotation parameters of the planetary body. A method of estimation is described here, which takes into account errors of rotational parameters.

Lunar or planetary exploration robots (rovers) move to long-distance destination under the limited conditions such as unknown environment and time delay. Rovers are required to move autonomously and efficiently. Rovers need the ability to recognize the environment widely and to plan route and sensing depending on the situation. This paper proposes a behavior planning scheme for rovers based on environment understanding. The proposed method includes route planning and sensing planning.

The MUSES-C mission is the world's first sample and return attempt to/from the near Earth asteroid. In deep space, it is hard to navigate, guide, and control a spacecraft on a real-time basis remotely from the earth mainly due to the communication delay. So autonomy is required for final approach and landing on an unknown body. It is important to navigate and guide a spacecraft to the landing point without hitting rocks or big stones. In the final descent phase, cancellation of the horizontal speed relative to the surface of the landing site is essential. This paper describes various kinds of robotics technologies applied for MUSES-C mission. A global mapping method, an autonomous descent scheme, and a novel sample-collection method, and asteroid exploration robot are proposed and presented in detail. This paper also presents the flight data and results.