Ichiro Nakatani

Continuous plasma outflows from the edge of a solar active region as a possible source of solar wind

The Sun continuously expels a huge amount of ionized material into interplanetary space as the solar wind. Despite its influence on the heliospheric environment, the origin of the solar wind has yet to be well identified. In this paper, we report Hinode X-ray Telescope observations of a solar active region. At the edge of the active region, located adjacent to a coronal hole, a pattern of continuous outflow of soft-x-ray–emitting plasmas was identified emanating along apparently open magnetic field lines and into the upper corona. Estimates of temperature and density for the outflowing plasmas suggest a mass loss rate that amounts to ∼1/4 of the total mass loss rate of the solar wind. These outflows may be indicative of one of the solar wind sources at the Sun.

Micro-hopping robot for asteroid exploration

Abstract Exploration missions for small planetary bodies such as asteroids and comets have received significant attentions in recent years. In upcoming missions, it is very important for planetary science to make science-equipped robots hang around the surface of small bodies. In order to provide an exploration robot on the surface of small bodies whose gravity is very small, the authors have researched the mobility under the micro-gravity and have developed a small robot which is specialized in the micro-gravity environment. This paper describes the mobility and the system design of the developed robot and is accompanied with explanation of the strategy how to explore and navigate along the small body surface.

Small, light-weight rover “Micro5” for lunar exploration

Abstract This paper describes a newly developed rover with small size, lightweight, low power consumption. Unmanned mobile robots for surface exploration of the moon or planets have been extensively studied and developed. A lunar or planetary rover is required to travel safely over a long distance for many days in unfamiliar terrain. This paper presents exploration mission, scientific signification, requirements, and technology of a lunar rover. This paper proposes a new mobility system, which has four wheels and one supported wheel. This novel suspension system is a simple and light mechanism like a four-wheeled rover and provides a high degree of mobility like a six-wheeled rover. Multiple rovers exploration by buddy system is also discussed. The performance of the developed rover is shown by some experiments.

Capture strategy for retrieval of a tumbling satellite by a space robotic manipulator

In autonomous retrieval of a free-flying object, tumbling motion makes it difficult to grapple the objects with an on-board manipulator. This paper presents a new control scheme to capture a tumbling satellite based on a simple dynamical model. The target motion is estimated based on visual information using Kalman filtering technique. The capture planning based on the proposed model becomes simple because the motion of a grapple fixture on a target satellite nearly stops relative to the end-effector of a manipulator. The validity and the usefulness of the proposed method are shown by computer simulations and experiments using a 3-D hardware simulator with 9 degrees of freedom.

New mobility system based on elastic energy under microgravity

This paper proposes a new mobility system for planetary rover using springs and linear actuators. In the microgravity environment, hopping mobility is a possible choice for enhancing a new mobility of the robot. One method to hop is to press ones own to the ground. The proposed robot consists of two masses, and can press ones own to the ground using springs. So the rover can hop from the stationary state by transforming the elastic energy to the kinetic energy using the springs and linear actuators. Furthermore the robot can land without bounding by transforming the kinetic energy to the elastic energy. The simulation studies and the ground experiments shows that the proposed rover could hop and land.

New mobility system for small planetary body exploration

Under the micro gravity environment, such as on the surface of small planetary bodies (asteroids or comets), traditional wheeled rovers are not expected to move effectively due to the low friction and the inevitable detachment from the surface. This paper discusses the friction-based mobility around the surface of small bodies and proposes a new mobility mechanism that drives the rover by hopping. The hop angle and the velocity are analyzed by numerical simulations, which show the effectiveness of the new mobility system.

Study on Mole-Typed Deep Driller Robot for Subsurface Exploration

This paper presents a mobile robotic system designed to perform deep soil sampling for lunar subsurface exploration in the near future. Drilling robots have to carry the excavated regolith backward because of its high density. Therefore a new scheme is proposed, to move forward under the soil by making use of reactive force caused by pushing the discharged regolith. Simple experiments demonstrate the effectiveness of the proposed method.

Microgravity experiment of hopping rover

Under the micro-gravity environment such as on the surface of small planetary bodies (asteroids or comets), traditional wheeled rovers are not expected to move effectively due to the low friction and inevitable detachment from the surface. Therefore, the authors propose a hopping rover suitable for exploration on the surface of small bodies. This paper describes the micro-gravity experiments of a proposed hopping rover which is driven by an internal DC motor torque. The proposed rover could hop under a micro-gravity environment. Experimental results are compared with the computational simulations.

Autonomous retrieval of a tumbling satellite based on predictive trajectory

This paper describes a practical method for autonomous capture of a target satellite in space using an on-board manipulator. In retrieving a satellite, a reference trajectory for control of the manipulator is generated with time delay due to the processing time of the target motion estimator and the manipulator controller. Consequently, the control system shows a poor performance and the end-effector sometimes fails to capture the target satellite. To solve this problem, a control system is proposed, which utilizes predictive trajectory based on the target satellite dynamics. The validity and the usefulness of the proposed control method are shown by computer simulations and experiments using a 3D hardware simulator with 9 degrees of freedom.

Map Matching Scheme for Position Estimation of Planetary Explorer in Natural Terrain

This paper describes a position identification method to precisely estimate the relative movement onboard of an autonomous explorer in such natural terrain as Moon or Mars. This paper proposes a new map matching scheme that registers the visual information of consecutive robot positions and expresses the robot displacement in a common coordinate system. Local elevation maps of the environment are therefore retrieved from the 3D perception of a stereo camera. The proposed scheme consists of three main steps: feature point extraction from map data, matching of features points using triangle configurations and a voting procedure, and direct calculation of the robot displacement in six degrees of freedom using quaternions. The effectiveness of the proposed method is confirmed by computer simulations with synthetic terrain and experiments with stereo perception.