水野 貴秀

We present an overview of the laser altimeter(LIDAR) results for asteroid 25143 Itokawa. The trace of a 7 × 12-m elliptical beam spot made it possible to determine the local surface topography with an accuracy of a few meters in altitude, from a home position roughly 7 km above the surface. Sequential detection of the altitude of the spacecraft during two orbital spans of descent for sampling allowed determination of the asteroid mass as 3.58 × 10 kg ± 5% and 3.54 × 10 kg ± 6%, which are consistent with the most probable mass estimate of 3.51 × 10 kg ± 3% given by Fujiwara et al. [Fujiwara, A., Kawaguchi, J., Yeomans, D.K. et al., 2006. The rubble-pile asteroid Itokawa as observed by Hayabusa. Science 312, 1330-1334]. Together with the total volume of the asteroid deduced from a shape model (i.e., 1.84 × 10 m ± 3%), this estimate by LIDAR suggests that asteroid Itokawa has a low density of 1.9 g/cm ± 9% and a high bulk porosity of about 40%. © 2007 COSPAR. 10 10 10 7 3 3

The ranging instrument aboard the Hayabusa spacecraft measured the surface topography of asteroid 25143 Itokawa and its mass. A typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 Eros, which suggests a surface structure on Itokawa similar to crater ejecta on Eros. The mass of Itokawa was estimated as (3.58 +/- 0.18) x 10(10) kilograms, implying a bulk density of (1.95 +/- 0.14) grams per cubic centimeter for a volume of (1.84 +/- 0.09) x 10(7) cubic meters and a bulk porosity of approximately 40%, which is similar to that of angular sands, when assuming an LL (low iron chondritic) meteorite composition. Combined with surface observations, these data indicate that Itokawa is the first subkilometer-sized small asteroid showing a rubble-pile body rather than a solid monolithic asteroid.

The two-dimensional scanning LIDAR system which used MEMS technology is proposed. The specification of LIDAR under development are measurable range of 50m - 50km, ±5 degrees of scanning angles, 10Hz repetition rate, and ±1m in range finding accuracy. By adopting monolithic YAG laser as a laser source, the tolerance over machine vibration has been improved with volume and weight saving. For a transmitting laser scan, adoption of a magnetic resonance drive type single micro-mirror is considered. In this system, we propose a novel method on the beam scanning mechanism for a receiver telescope with big aperture by using MEMS technology. The scanning optics system of receiver telescope is composed by a telecentric telescope and a micro shutter array. This optical system has achieved a narrow viewing angle corresponding to aperture of the shutter by limiting the view of the telescope that has a wide viewing angle with the shutter. The basic function of the scanning system of receiver optics is already checked experimentally. Copyright © 2006 by ASME.

本論文では小型衛星INDEXの開発を例に従来の開発手法の難点とリスクについて議論し,SRAM型FPGAを搭載品として用いるメリットについて考え,それらを背景に,SRAM型FPGAとソフトコアCPUを用いた信頼性と柔軟性に富む計算機システムを提案する.再構成可能であるという柔軟性をもつ反面,SRAM型FPGAは耐放射線性に不安があり何ら対策を講じずにバスシステムとして用いるのは困難である.そこで本システムは一つのSRAM型FPGAにソフトコアCPUを中心にした3系統の計算モジュールをインプリメントし三重多数決システムを構築した.また,SRAM型FPGAを部分的に再プログラミングする部分再構成機能をエラー解決に用いている.これによりシステム的に信頼性を高めているほか,迅速なエラー解決と不停止システムを実現していることが特徴である.本論文ではこの提案するシステムのテストモデルを構築してその実現性と機能試験を行った結果について述べる.

宇宙科学研究所が科学衛星打ち上げロケット及び観測ロケットの追跡用レーダとして開発した「新精測レーダ」について述べている．従来から長年にわたって使用してきた「精測レーダ」の老朽化を考慮し，かつレーダの機能・性能の大幅な向上を目指して開発・製作したもので，１９９５年度に鹿児島宇宙空間観測所に設置された．アンテナの口径を７ｍと大型化し，また中間周波数（IF）以降の信号処理を全てディジタル化することによってＳＮ比の向上を図り，二次レーダの回線マージンを従来の精測レーダに比べて，約１０dB改善することができた．また一次レーダモードでは，圧縮比１０００というパルス圧縮を実現して，最大探知距離を大幅に拡大した．新精測レーダはこれまでＭ－Ｖ型ロケット３機と数々の観測ロケットの追跡運用に使用され，予定した機能を果たしてきている．付録：ロケット追跡レーダの歴史‐東京大学時代から宇宙科学研究所まで‐資料番号: SA0200051000

This paper describes outline of the piggy-back satellite "INDEX" for demonstration of advanced satellite technologies as well as for observation of fine structure of aurora. Aurora observation will be carried out by three cameras(MAC) with a monochromatic UV filter. Electron and ion spectrum analyzer (ESA/ISA) will measure the particle phenomena together with the aurora hanging. INDEX satellite will be launched in 2002 by Japanese H2-A. The satellite is mainly controlled by the high-speed, fault-tolerant on-board RICS processor (three-voting system of SH-3). The attitude control is a compact system of three-axis stabilization. Although the size of INDEX is small (50Kg class), several newly-developed technologies are applied to the satellite system, including silicon-on-insulator devices, variable emittance radiator, solar-concentrated paddles, lithium-ion battery, and GPS receiver with all-sky antenna-coverage. © 2001 International Astronautical Federation. Published by Elsevier Science Lt d.

A single mode oscillation on the circular free electron laser has been studied. The operation mode was TM81 (11.77 GHz) whose frequency width was 0.3% (= Δf f) and the total radiation power was about 600 kW using a rotating hollow electron beam (442 kV). The observed permissible detuning between the oscillation frequency and the beam mode was 3% at TM81 oscillation. © 1995.

Coherent microwave and millimeter wave emission from a rotating electron beam in a circular wiggler magnetic field (circular free electron laser) has been studied. The circular wiggler, which consists of a coaxial waveguide and an azimuthally periodic magnetic field, is compact as compared with a conventional linear FEL. Tunable radiation frequency (TM coaxial waveguide mode) was observed to be typically 11-38 GHz using a mildly relativistic electron beam of energy less than 500 kV, about 150 A current and about 8 mus pulse width. The total radiation power was about 840 kW at 11.5 GHz of TM6.1.

Generation of microwave radiation from a rotating electron beam in a circular wiggler magnetic field (circular free-electron laser) has been studied. The electron beam is emitted by a velvet-covered cathode; its energy is typically 300–500 keV and its beam current is 160 A. Measured frequency, power and pulse width of the radiated microwave are 12.7 GHz, 11 kW and 500 ns, respectively. Measured frequency agrees with the theoretical prediction. The interaction between the beam mode and the traveling magnetic waveguide mode is discussed based upon the dispersion relation.

Generation of microwave radiation from a relativistic rotating electron beam in a circular wiggler magnetic field (circular free electron laser) has been studied. The beam energy was 280-420 keV, typically, and the axial component of the rotating current was 80 A. Tunable radiation frequency was observed with the grating spectrometer to be typically 11-14 GHz and 36 GHz. This device produced total radiation powers of 115 kW at 12 GHz and 6 kW at 36 GHz. © 1992.

Formation of a rotating, relativistic electron beam with properties suitable for a circular free electron laser has been studied. The rotating, relativistic electron beam is generated by the method of injecting a straight-moving, hollow, relativistic electron beam (typical energy 500 keV) into a magnetic cusp. By decreasing the axial transition width of the cusp, the beam off-centering motion is suppressed and the beam current is increased by a factor of 4 (from 50 A to 200 A).