橋本 樹明

We obtained color images of near-Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8-3.7 m/pixel. Whole-disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88-inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk-resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite-like materials have been exposed through weathered layers by excavation. By also examining close-up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels. © The Meteoritical Society, 2007.

Hayabusa spacecraft performed the final descents and touchdowns twice in November 2005. In final descent phase, terrain alignment maneuvers were accomplished to control both altitude and attitude with respect to the surface by using four beams Laser Range Finder onboard. Then Hayabusa spacecraft made dynamic touchdowns the surface of the asteroid by the sampler system to collect samples automatically. This paper presents the terrain alignment maneuver and touchdown scheme. This paper also describes the novel sample horn system and touchdown dynamics. Touchdown tests on the ground are presented. Then the flight results on touchdown dynamics are shown and discussed. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Hayabusa spacecraft performed the final descents and touchdowns twice in November 2005. In final descent phase, terrain alignment maneuvers were accomplished to control both altitude and attitude with respect to the surface by using four beams Laser Range Finder onboard. Then Hayabusa spacecraft made dynamic touchdowns the surface of the asteroid by the sampler system to collect samples automatically. This paper presents the terrain alignment maneuver and touchdown scheme. This paper also describes the novel sample horn system and touchdown dynamics. Touchdown tests on the ground are presented. Then the flight results on descent and touchdown dynamics are shown and discussed.

Balloon-based Operation Vehicle (BOV) is currently developed at JAXA for the realization of microgravity environment. As for this research, second experiment of 2006 and third experiment of 2007 are already planned. As a member of the control and electric system group, we estimate a method to detect the relative position of an integumentary covering as an inner shell of an experimental device with laser sensors. In this paper is explained a summary of a microgravity experimental device and shown it about an experiment performed in May, 2006.

This paper discusses on control law of the micro-gravity experimental vehicle with a balloon. To attain the micro-gravity environment, it is necessary that the experiment sphere in the experiment module does not collide with inner shell of the vehicle. This is achieved by designing the control law with 16 gas-jet thrusters. The velocity during free fall is accelerated to a supersonic region by the end of experiment. The design of control law corresponding to the remarkable increase of dynamic pressure is required. The performances of actual thrusters have high non-linearity. This paper proposes a new control law of thruster to control the vehicle with high accuracy.

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.

The spacecraft Hayabusa performed the descent flights to the target asteroid ltokawa in November of 2005. The surface of ltokawa has a lot of boulders and there are few flat areas where the spacecraft can touch down safely. With the reaction wheels lost prior to the touchdown events, it was very difficult to control translational motion accurately, since the guidance accuracy of several millimeters per second was requested. To accurately determine the spacecraft position, a landmark tracking scheme with the help of the ground operation was introduced and developed in the Hayabusa mission. The Hayahusa project team developed new tools that combined human assist with the computer aided terminal display. The proposed landmark tracking scheme did contribute to the successful precise navigation to the specified area on the surface. This paper presents a descent navigation method with the landmark tracking used for the Hayahusa mission, including the developed ground operation tools.

A Magnetic Bearing Wheel (MBW) with inclined magnetic poles is under development, which enables the 5-DOF magnetic bearing to be composed of six electromagnets. This paper deals with the low disturbance control method of the MBW. This method feeds back force/moment disturbance of the MBW, and generates rotor position command to reduce the disturbance, which can decrease the disturbance induced by all disturbance factors such as rotor static/dynamic imbalance, sensor detection surface distortion, magnetic pole surface distortion, and resonance of the MBW and the MBW foundation.

This paper discusses on control law for Balloon Based Micro-Gravity Experimental Vehicle. The vehicle is carried up to an altitude of 40km by a balloon and released. During the free fall, micro-gravity environment is provided in a spherical laboratory floating in the vehicle. Gas-jet thrusters control the vehicle to keep the clearance between the laboratory and the inner wall of vehicle. The disturbances acting on the vehicle is related to the dynamic pressure of vehicle, thus the proposed control law uses a compensatory factor that is given as a function of the dynamic pressure. The numerical results show that the controller has robustness against the initial position error.

2003年5月に打ち上げられた工学実験探査機「はやぶさ」は2005年夏に小惑星ITOKAWAに到着後、表面のサンプルを採取して2007年に地球に持ち帰る計画である。サンプル採取の前に、高度約10kmの地点から2ヶ月程度、可視光カメラ、近赤外線センサ、X線センサを用いて小惑星の観測を行い、科学観測とともに、着陸地点の選定に役立てることとしている。本稿では、「はやぶさ」の観測センサと観測計画の概要を述べる。

Lunar Imaging Camera (LIC) is a small, compact and lightweight monochromatic imager designed and developed for LUNAR-A, Japanese lunar mission. The scientific objectives of the camera address impact cratering, tectonic processes, volcanic features, and optical properties of the regolith surface.The image sensor is a linear CCD and is aligned with the spin axis of the spacecraft, which orbits the Moon at altitudes of 200-300 km. The two-dimensional image is taken using the spin motion of the spacecraft. The total field of view (FOV) of the camera is 360°(around the spin axis)×14.6°(along the CCD-array). LIC obtains an image in one spin. The angular resolution of the camera is about 20 arcsec/pixel at a spin rate of 3 rpm. The spatial resolution is about 25 m/pixels at the surface when the altitude is 250 km. The spin axis of the LUNAR-A approximately points toward the Sun, therefore, LIC can take images of the lunar surface with highly oblique illumination conditions near the terminator. A series of pre-flight tests of LIC was performed. In those tests, the hardware performance and the functions of LIC were verified and the data for radiometric and geometric corrections were obtained. This paper outlines the scientific objective, characteristics of LIC, the procedure and the results of the pre-flight tests and the operation plan of LIC.

MUSES-C engineering spacecraft for asteroid sample and return technologies was successfully launched on May 9th, in 2003 and was renamed as Hayabusa in orbit. The spacecraft is now in the cruising phase toward the asteroid 1998SF36. This report presents the outline of Hayabusa spacecraft. This report also describes AOCS(Attitude and Orbit Control System), which is focused on the cruising phase functions, autonomous star identification, Ion engine gimbal control, back-up attitude control mode, etc. The performance evaluated in orbit is also shown in this report.