西山 和孝

平成25年度宇宙輸送シンポジウム（2014年1月16日-17日. 宇宙航空研究開発機構宇宙科学研究所（JAXA)(ISAS)）, 相模原市, 神奈川県資料番号: SA6000016158レポート番号: STEP-2013-086

The basic properties of an air breathing ion engine, which uses upper atmospheric gases as a propellant, were experimentally investigated. The N 2 environment in a sub-low Earth orbit (altitude of 140-200 km) was simulated by a laser detonation beam source, which has been previously used in studies on atomic oxygen-induced material degradation. The basic properties of the air breathing ion engine were studied using a hyperthermal N2 beam. It is suggested that the hyperthermal N2 molecules thermalized by scattering at the reflector surface in the air breathing ion engine. The efficiency of the collimator was experimentally investigated and the collimator was found to maintain the N2 pressure inside the air breathing ion engine. An ion beam current of 16 mAat an acceleration voltage of 200 V provided a thrust of 0.13 mN for both hyperthermal N2 and atomic oxygen beams. The maximum ion beam current was found to be limited by the space-charge effect. The experimental results strongly indicated the recombination of atomic oxygen into O2 molecules inside the air breathing ion engine.

平成24年度宇宙輸送シンポジウム (2013年1月17日-1月18日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県形態: カラー図版あり形態: PDF資料番号: AA0061856091レポート番号: STEP-2012-008

平成24年度宇宙輸送シンポジウム (2013年1月17日-1月18日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県形態: カラー図版あり形態: PDF資料番号: AA0061856092レポート番号: STEP-2012-009

平成24年度宇宙輸送シンポジウム (2013年1月17日-1月18日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県本研究では、推進剤の投入方法の変更がビーム電流の向上にいかにつながったのか解明するために、光ファイバを活用したプラズマ診断法を確立した。先端にレンズを融着した特殊な光ファイバプローブとレーザ吸収分光法を組み合わせることで、従来の金属プローブでは不可能だったビーム加速状態のマイクロ波放電式イオンエンジンのプラズマ診断を実現している。測定対象は励起中性粒子Xe I 823.16nmとXe I 828.01nmである。前者は準安定準位であり、吸収が大きく1cm刻みの軸方向数密度分布を得た。後者は基底と共鳴遷移線を有するために、吸収が小さく空間分解能は2cmにとどまったが、寿命が充分短いため電子の局所的な情報を反映する。測定結果から、従来の導波管からの推進剤投入では導波管内部で中性粒子を励起させている電子の密度の最大値が存在することが判明した。推進剤の投入位置を導波管から放電室に変更することで、この導波管における電子を抑制し、ビーム電流の向上につながったと考えられる。形態: カラー図版あり形態: PDF資料番号: AA0061856122レポート番号: STEP-2012-039

平成24年度宇宙輸送シンポジウム (2013年1月17日-1月18日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県形態: カラー図版あり形態: PDF資料番号: AA0061856150レポート番号: STEP-2012-067

A 20-cm diameter electron cyclotron resonance xenon ion thruster for space propulsion is under development that generates 500 mA of ion beam current at a microwave discharge power of 100 W. It does not have any moving mechanical parts for microwave impedance matching. Extracted ion currents and reflected microwave powers were experimentally investigated around a nominal frequency of 4.25 GHz for different flow rates. Optimized frequency tuning within 0.6% of the nominal frequency minimized the microwave reflection and maximized the ion current at each flow rate between 0.39 and 1.27 mg/s. However, constant frequency operation at 4.266 GHz is recognized as the best strategy because it provided with fare performance in wide range of flow rate and almost minimum reflection during tentative stop of beam extraction after high voltage breakdowns.

The μ10 cathode-less electron cyclotron resonance ion engines, have propelled the Hayabusa asteroid explorer for seven years since its launch in May 2003. The spacecraft was focused on demonstrating the technology needed for a sample return from an asteroid, using electric propulsion, optical navigation, material sampling in a zero gravity field, and direct re-entry from a heliocentric orbit. The final stage of the return cruise and the subsequent trajectory correction maneuvers have been accomplished by using a special combined operation of neutralizer A and ion source B after the exhaustion of the other neutralizers' lives by the autumn of 2009. The total duration of the powered spaceflight was 25,590 h, which provided a delta-V of approximately 2.2 km/s and a total impulse of 1 MN·s. The degradation trends of the thruster performances have been investigated. It seems that the main cause of the degradation was the decrease in effective microwave power input to the discharge plasma induced by the increase in the transmission loss of the microwave feed system, and not due to the increase in the gas leakage through the accelerator grid apertures enlarged by erosion. Unintentional engine stop events have been summarized and analyzed. Most of them occurred due to the limit check errors of the backward microwave powers. Such errors can be decreased by carefully monitoring the trend change in microwave backward power as a function of xenon flow rate in future missions.

In order to reveal the internal phenomenon theoretically within the electron cyclotron resonance ion thruster μ 10, internal microwave electric field measurement is very important because it is closely related to plasma producing mechanism. We have established a technology of electric field measurement with an optical fiber sensor which uses an Electro-Optic crystal (EO probe). This technology enables electric field measurement in plasma source under beam acceleration without disturbing microwave electric field. In this study, first, validity of electric field measurement using the EO probe in the atmosphere was demonstrated by comparing experimental results with FDTD simulation. Then, we measured axial electric field distribution in the accelerated plasma. This experiments indicated that electric field distribution in the μ10 thruster was related to its beam current. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

In order to reveal the physical processes taking place within the ECR ion thruster "μ 10", internal plasma diagnosis is indispensable. However, the ability of metallic probes to access microwave plasmas biased at a high voltage is limited from the standpoints of the disturbance created in the electric field and electrical isolation. This paper firstly attempts to measure the electronic excitation temperature using an optical fiber with little disturbance. Secondly, coupling with this result, it goes on to successfully measure the axial density profiles of excited neutral xenon under ion beam acceleration by using a novel laser absorption spectroscopy system. The targets of this measurement were metastable Xe I 823.16 nm and non-metastable Xe I 828.16 nm. As a consequence, these two measurements confirmed the existence of electrons at the anti-node of microwaves in the waveguide, which was caused by a propellant injection from the waveguide. Therefore this paper concludes that it is important to avoid the attenuation of microwave propagation to the discharge chamber by the electrons in the waveguide. © 2012 by Ryudo Tsukizaki.

Very low earth orbit satellites enable researchers to find out about aeronomy, accurate gravity and magnetic field mapping, and high-resolution earth surveillance. They orbit the earth at an altitude of lower than 250 km, where the effect of atmospheric drag cannot be discounted. In order to use this orbit, some kind of propulsion for drag make-up is required and propellant mass increase proportionally to the mission time. The Air Breathing Ion Engine (ABIE) is a new type of electric propulsion system which can be used to compensate the drag of a satellite. In the ABIE propulsion system, the low density atmosphere surrounding the satellite is taken in and used as the propellant for the Electron Cyclotron Resonance (ECR) ion engines to reduce the required propellant mass. Therefore ABIE is a promising propulsion system for aerodynamic drag free missions longer than two years. Feasibility and performance of the ABIE depend on the compression ratio and an air intake efficiency. Generally, pressure of a discharge camber is lower than a propellant tank pressure in propulsion system, and the propellant flows to the reaction chambcr from the tank. In the case of ABIE, a static pressure of atmosphere which corresponds to tank pressure is lower than the discharge chamber pressure. The air intake is the most important component to realize the ABIE. The temperature of the atmosphere is from 700K to HOOK at 200km, which is sufficiently low compared with the orbital velocity of 8km/s. Therefore, it can be said it is a uniform and well collimated supersonic flow parallel to the orbital direction. Moreover, the density is thin enough and it is a free molecular flow. The air intake consists of a collimator section and a reflector section. The collimator section will be composed of gaps between concentric cylinders. This part does not intercept the entering neutral particles, and they impact the reflection part on the downstream side directly. However, the backflow from the discharge chamber to the upstream side through the collimator section cannot easily leak out, because it is thermalized to the same level of temperature as the chamber walls and it has a velocity in a random direction. We simulate the relation between the ABIE and the rarefied atmosphere on such a super low earth orbit in a vacuum chamber. We verified the pressure rise inside the air intake. Copyright © (2012) by the International Astronautical Federation.

In order to reveal the physical processes taking place within the "μ10" microwave discharge ion thruster, internal plasma diagnosis is indispensable. However, the ability of metallic probes to access microwave plasmas biased at a high voltage is limited from the standpoints of the disturbance created in the electric field and electrical isolation. In this study, the axial density profiles of excited neutral xenon were successfully measured under ion beam acceleration by using a novel laser absorption spectroscopy system. The target of the measurement was metastable Xe I 5p 5( 2P 03/2)6s[ 32] 02 which absorbed a wavelength of 823.16 nm. Signals from laser absorption spectroscopy that swept a single-mode optical fiber probe along the line of sight were differentiated and converted into axial number densities of the metastable neutral particles in the plasma source. These measurements revealed a 10 18 m -3 order of metastable neutral particles situated in the waveguide, which caused two different modes during the operation of the μ10 thruster. This paper reports a novel spectroscopic measurement system with axial resolution for microwave plasma sources utilizing optical fiber probes. © 2011 American Institute of Physics.

The objectives of the DECi-hertz Interferometer Gravitational Wave Observatory (DECIGO) are to open a new window of observation for gravitational wave astronomy and to obtain insight into significant areas of science, such as verifying and characterizing inflation, determining the thermal history of the universe, characterizing dark energy, describing the formation mechanism of supermassive black holes in the center of galaxies, testing alternative theories of gravity, seeking black hole dark matter, understanding the physics of neutron stars and searching for planets around double neutron stars. DECIGO consists of four clusters of spacecraft in heliocentric orbits; each cluster employs three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by three pairs of differential Fabry-Perot Michelson interferometers. Two milestone missions, DECIGO pathfinder and Pre-DECIGO, will be launched to demonstrate required technologies and possibly to detect gravitational waves. © 2011 IOP Publishing Ltd.

The erosion of accelerator grid aperture due to impingement of charge-exchange ions limits the normal operation of the microwave discharge ion engine, in which long life and high reliability are inherent because of electrode-less plasma generations. A commercially available image scanner and image-analysis software enabled to statistically analze the diameters of the huge number of apertures in the fl at C/C grids. This measurement method was applied to the accelerator grids of μ10 ion engine after the 20,000 hour endurance test and μ20 ion engine under ion machining in 30 hours. As a result, it was revealed that the erosion distribution of the μ10 grid had the azimuthal dependence. Moreover, we obtained the design guide for the next μ20 accelerator grid, to make the apertures with tapered shape on the side of upstream.

Based on the success of the Japanese asteroid explorer Hayabusa, the ECR ion thruster μ10 will be installed in Hayabusa's successor, Hayabusa-2, and is scheduled to be commercialized for use in geostationary satellites within the next three years. To increase the thrust force of the μ10 as much as possible without major design changes, luminescence measurements were conducted using an optical fiber probe. The probe gave an internal view of the μ10, and it was discovered that there was plasma in the waveguide. As the plasma, the density of which is higher than the cut-off density, interferes with the transmittance of microwaves, the propellant injection location was changed. In addition to the change in propellant injection location, the grid system was also refined. These improvements increased the thrust force from 8.0 mN to 10.1 mN with a decrease in specific impulse by 40 sec from 3200 sec to 3160 sec.

The study on the post- HINODE Solar Observation Mission has been started by members in the Solar physics community. One candidate of the mission targets is the observation of the high latitude region of the Sun, which requires the injection of the space observatory (spacecraft) into the orbit largely inclined with the ecliptic plane. Reported in this paper is the trajectory design result for this orbit transfer by way of the Solar electric propulsion and the Venus/Earth gravity assists. The sequence is divided into two phases, the Venus Earth Gravity Assist (VEGA) phase and the sequential Electric Propulsion Delta-V Earth Gravity Assist (EDVEGA) phase. The designed trajectory through the sequence is provided, and it is compared with the trajectory solely using the sequential EDVEGA strategy.

A study on the post-HINODE Solar Observation Mission has been started in the Solar physics community. One candidate of the mission targets on the observation of the Solar polar region from the orbit largely inclined with the ecliptic plane. Following the paper presented in the previous meeting, this paper focuses on the mission design option which uses the Solar electric propulsion. The design is refined and optimized based on the further analyses on the sensitivity to parameters and the additional consideration of practical constraints. The newly obtained mission baseline and its features are discussed as well.

A space gravitational-wave antenna, DECIGO (DECI-hertz interferometer Gravitational wave Observatory), will provide fruitful insights into the universe, particularly on the formation mechanism of supermassive black holes, dark energy and the inflation of the universe. In the current pre-conceptual design, DECIGO will be comprising four interferometer units; each interferometer unit will be formed by three drag-free spacecraft with 1000 km separation. Since DECIGO will be an extremely challenging mission with high-precision formation flight with long baseline, it is important to increase the technical feasibility before its planned launch in 2027. Thus, we are planning to launch two milestone missions. DECIGO pathfinder (DPF) is the first milestone mission, and key components for DPF are being tested on ground and in orbit. In this paper, we review the conceptual design and current status of DECIGO and DPF. © 2010 IOP Publishing Ltd.

The cathode-less electron cyclotron resonance ion engines, μ10, propelled the Hayabusa asteroid explorer, launched in May 2003, which is focused on demonstrating the technology needed for a sample return from an asteroid, using electric propulsion, optical navigation, material sampling in a zero gravity field, and direct re-entry from a heliocentric orbit. It rendezvoused with the asteroid Itokawa after a two year deep space flight with a delta-V of 1.4 km/s, 22 kg of xenon propellant consumption and 25800 hours of total accumulated operational time of all the four ion engines added up. Though it succeeded in landing on the asteroid on November 2005, the spacecraft was seriously damaged. This delayed the Earth return in 2010 from the original plan in 2007. Reconstruction on the operational scheme using remaining functions and newly uploaded control logic made Hayabusa leave for Earth in April 2007. After a coasting period of 2008, the ion propulsion was reignited in February 2009. Although most of the neutralizers were degraded and unable to be used by fall of 2009, a combination of an ion source and its neighboring neutralizer has been successfully operated for the last 3230 hours including a series of final trajectory correction maneuvers. Before reentry, the total accumulated operational time reached 39637 hours consuming a total of 47 kg Xenon propellant. Total duration of powered spaceflight is 25590 hours which provided a delta-V of 2.2 km/s and a total impulse of 1 MN·s, approximately. Finally, the spacecraft returned to Earth. Its reentry capsule, which may contain samples from asteroid Itokawa, was retrieved from the Australian outback according to plan. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

A completely new concept, the Air Breathing Ion Engine [1] (ABIE), has been proposed for spacecraft drag compensation at a super low earth orbit. ABIE enables progress of aeronomy, accurate gravity / magnetic field mapping, and high-resolution earth surveillance. The ABIE takes in and uses the rarefied atmosphere surrounding the satellite as a propellant. Therefore ABIE is a promising propulsion system for aerodynamic drag free missions longer than two years. Feasibility and performance of the ABIE depend on the compression ratio and the air intake efficiency. A laboratory environment which imitates the orbital conditions on such a super low earth orbit is necessary to study ABIE on ground. The purpose of this paper is to simulate the environment in super low Earth orbit using an ECR plasma source. An atomic oxygen beam was realized by de-ionizing an atomic oxygen ion. We achieved a flux of 5E14 atom/cm2/sec, which is similar to the orbital velocity.

A study on the post-HINODE Solar Observation Mission has been started in the Solar physics community. One candidate of the mission targets on the observation of the Solar polar region from the orbit largely inclined with the ecliptic plane. Following the paper presented in the previous meeting, this paper focuses on the mission design option which uses the Solar electric propulsion. The design is refined and optimized based on the further analyses on the sensitivity to parameters and the additional consideration of practical constraints. The newly obtained mission baseline and its features are discussed as well.

DECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECihertz Interferometer Gravitational wave Observatory), which is a future space gravitational wave antenna. DECIGO is expected to provide fruitful insights into the universe, particularly about dark energy, the formation mechanism of supermassive black holes and the inflation of the universe. Since DECIGO will be an extremely challenging mission, which will be formed by three drag-free spacecraft with 1000 km separation, it is important to increase the technical feasibility of DECIGO before its planned launch in 2024. Thus, we are planning to launch two milestone missions: DPF and pre-DECIGO. In this paper, we review the conceptual design and current status of the first milestone mission, DPF. © 2009 IOP Publishing Ltd.

Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency (ISAS/JAXA) successfully developed and operated the microwave discharge ion engines “µ10” onboard Hayabusa asteroid explorer. The µ10 ion engines feature the cathode-less plasma generation in both the ion sources and neutralizers with the results of long life and high reliability in space. Based on the space achievements of µ10 ion engines with 8mN thrust, 3,000sec Isp and 350W consumption power, the µ10HIsp is under development for deep space missions to such as Jupiter and Mercury. The integrated test with the plasma sources, a propellant isolator, a microwave DC block and a high Isp grid system established the thrusting operation with 9,600sec Isp using 15kV acceleration voltage, 25mN thrust, 12mN/kW thrust power ratio, and 2.1kW power consumption.

DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will consist of three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by a differential Fabry-Perot interferometer. We plan to launch DECIGO in middle of 2020s, after sequence of two precursor satellite missions, DECIGO pathfinder and Pre-DECIGO, for technology demonstration required to realize DECIGO and hopefully for detection of gravitational waves from our galaxy or nearby galaxies. © 2009 IOP Publishing Ltd.

Neutral particles play an important role in the physics of the upper atmosphere, which expands and shrinks depending on solar activity. We have been investigated that remote sensing of the upper atmosphere structure via artificial Energetic Neutral Atoms (ENAs) generated by the charge exchange (CEX) collision between upper atmosphere atoms and the artificial ion beam. In our previous study, a krypton ion has high CEX cross-section, which calculated by the Impact-parameter method theoretically, than other noble gas to atomic oxygen. We started to some fundamental experiments for the krypton ENAs detector. We have been investigated to solid particle detector as a simple ENA particle detector. Avalanche Photodiode (APD) which has a self-amplification effect was selected as a solid detector. As a result of the heavy particles (ion and ENA) irradiation experiments to APD, APD is sensitive to the heavy particles with 1∼2keV drift energy, and its multiplication ratio is about 50 ∼ 100 times. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

The Hayabusa spacecraft launched in 2003 is now completing its round trip to a near Earth asteroid Itokawa, to which it accessed in 2005. Hayabusa suffered from a fuel leak and eruption incidents after its successful descent, touch-down and lift-off at the end of November in 2005. Hayabusa lost two reaction wheels among three aboard and the chemical propulsion. The only means left for Hayabusa are the ion engines and xenon gas reserved for them as well as a single reaction wheel. Hayabusa project team devised the use of xenon gas for cold gas propulsion, and also developed the new attitude control strategy taking the advantage of solar radiation pressure. The spacecraft started the delta-V maneuver using the ion engines from 2007 and will continue it by next February. It is scheduled for Hayabusa to reenter into the atmosphere and land in middle of Australia in June of 2010.