國中 均

Four units of the microwave discharge ion engine "μ10", which generates 8mN thrust and 3,200sec specific impulse with 350W electric power, are devoted to the main propulsion on the "HAYABUSA" asteroid explorer. The spacecraft was input in the deep space by M-V rocket on May 9, 2003. After vacuum exposure and several runs of baking for reduction of residual gas the ion engine system established the continuous acceleration of the spacecraft. In the first year the spacecraft changed its eccentricity of the orbit by the maneuver of the on engines m a one-year Earth-synchronous orbit. On May 19, 2004 just one year later after the launch, the spacecraft steered its course by means of the Earth swing-by and got on the transfer orbit toward the target asteroid, even on which the ion engines accelerated continuously. The spacecraft passed by the aphelion 1.7 astronautical unit on February 18, 2005 so that the microwave discharge ion engine μ10s became the electric propulsion to arrive at the furthest space from Sun. On the beginning of May 2005, the ion engine system reaches the total number of space operational time 23,000hour during two years, and the spacecraft approaches the asteroid at 400,000km remaining distance. The HAYABUSA spacecraft is about to rendezvous with the asteroid "Itokawa" on September 2005. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

The performance of the MagnetoPlasmaDynamic (MPD) thruster is strongly affected its electrode configurations. We started systematic approach to understand the relation between the thrust performance and electrode geometry. They are consisted of three main elements detail observation of internal flow field using Two-Dimensional MPD (2-D MPD) device, direct trial and error experiment and precise numerical simulation. In this paper, we mention the characteristics of 2D MPD device and the comparison between three Converging-Diverging anodes with different throat diameters. Our final goal is to optimize the electrode configuration under a fixed operational condition.

The MUSES-C spacecraft was launched on May 9, 2003 and has been propelled by microwave discharge ion engines. The mission duration is four years in total and most of it is the cruising phase driven by ion propulsion. After one-year acceleration it succeeded the Earth swing-by on May 19, 2004 and still on the way to the asteroid "ITOKAWA". Active thrust vector control contributes to keep the reaction wheels within an appropriate rotation rate. The hydrazine thruster firing tunes off the ion engines before it and restart them again after it. Depending on the operation of ion engines the heater power is adjusted. These operations are autonomously controlled on the spacecraft without supervisions from Earth. A ground operation system that integrates all the process required for ion engine operations such as orbit synthesis, orbit determination, operation scheduling, command generation and telemetry data analysis has been developed. Automation of on-board and ground operations saves the operation cost and time, and makes the operation stable and reliable.

The microwave discharge ion engine generates plasmas of both the main ion source and the neutralizer using 4GHz microwave without discharge electrodes and hollow cathodes, so that long life and durability against oxygen and air are expected. The MUSES-C "HAYABUSA" asteroid explorer installing four microwave discharge ion engines "μ10"s was input in the deep space by M-V rocket No.5 on May 9, 2003. After vacuum exposure and several runs of baking for reduction of residual gas the ion engine system established the continuous acceleration of the spacecraft toward the asteroid "ITOKAWA". The Doppler shift measurement of the communication microwave revealed the performance of ion engines, which is 8mN thrust force for a single unit with 3,200sec specific impulse at 23mN/kW thrust power ratio. At the end of March 2004 the ion engine system accumulated the operational time 10,600 hour & unit and consumed 12kg Propellant, and then input the spacecraft on the orbit to encounter Earth. HAYABUSA will execute the Earth swing-by on May 19 and arrive at the asteroid in 2005 and return to Earth again in 2007. © 2004 by the American Institute of Aeronautics and Astronautics, Inc.

The MUSES-C was launched on May 9(th) of this year and was named 'Hayabusa'. It takes an aim at the world's first sample and return from a near Earth asteroid, 1998SF36 now renamed "Itokawa". The spacecraft is a kind of technology demonstrator with four key technologies. The paper presents a quick report on the initial operation of the ion engines aboard and will show how the attitude control has been performed incorporating the closed loop de-saturation function onboard. The paper also presents how much delta-V has been applied to the spacecraft as well as how the orbit determination under the low-thrust acceleration has been performed.

Strategy of formation flying for the X-ray Evolving Universe Spectroscopy mission (XUES) is discussed. in which an X-ray telescope of 10 in diameter and 50 in focal length will be constructed in orbit by formation flying the X-ray mirror and the focal plane X-ray detectors on two separate spacecrafts. We first studied the thrust, force required to keep the detector spacecraft (DSC) in the non-Keplerian orbit. We find the, direction of the thrust vector rotates twice per a single spacecraft orbital evolution along a circle parallel to the orbital plane. The absolute value of thrust needs to be varied by a factor of two or less. The maximum thrust force required is 0.47 N assuming a 600 km altitude and a 4000 kg DSC mass. The present baseline design requires no moving mechanism. instead requires a large amount of propellant because of relatively, low thruster efficiency. The spacecraft is estimated to weigh about 6000 kg. We studied an alternative design in which the thruster efficiency is optimized and showed that the spacecraft mass can be reduced to 4000 kg. This. however. requires a rotation mechanism and additional constraints on the spacecraft operation.

If a dense plasma were exhausted near the center of a magneetic sail, the magnetic field could be expanded far away from the spacecraft, thus the energy of the solar wind can be captured by this huge magnetic field in spite of very low-density solar wind. Then the magnetic sail can propel a spacecraft by the solar wind in the inerplanetary space. Such a magnetoplasma sail was analytically studied, and large thrust to power ratio as much as 250mN/kW was explained. When applied to short-term deep space missions, the magnetoplasma sail has great advantage against other electric propulsion systems because of its ability to achieve larger thrust to power ratio. © 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

As one of malfunctions on the ion thruster the lack of neutralization is investigated by means of the ground experiment using a 2cm microwave discharge ion thruster and a miniature model similar to the MUSES-C spacecraft. Electron leak form the plasma beam to the high voltage solar array caused a slight charging. No electron emission resulted in the full charging and pulled back the extracted ions to the thruster again, when the so-called virtual anode was formed in front of the decel grid. Based on the experimental simulation a design philosophy on the ion thruster and the spacecraft is described. © 2001 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

MUSES-C space mission requires the ion engine system (IBS) 16,000 hours in the operational time. The ion thruster is driven by 4.2GHz microwave in the result that the hollow cathodes are completely eliminated. The life critical parts are screened to the electro-static grid system and the microwave feeder of the neutralizer. The engineering model of the microwave discharge ion thruster was evaluated for the lifetime by several methods: the numerical simulation, accelerated wear tests and the real time endurance test. Combining these techniques MUSESC/ IES is concluded to have a good capability to endure the required life. © 2000 The American Institute of Aeronautics and Astronautics Inc. All rights reserved.

MUSES-C space mission requires the ion engine system (IBS) 16,000 hours in the operational time. The ion thruster is driven by 4.2GHz microwave in the result that the hollow cathodes are completely eliminated. The life critical parts are screened to the electro-static grid system and the microwave feeder of the neutralizer. The engineering model of the microwave discharge ion thruster was evaluated for the lifetime by several methods: the numerical simulation, accelerated wear tests and the real time endurance test. Combining these techniques MUSESC/ IES is concluded to have a good capability to endure the required life. © 2000 The American Institute of Aeronautics and Astronautics Inc. All rights reserved.