研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙飛翔工学研究系 教授総合研究大学院大学 物理科学研究科 宇宙科学専攻 教授
- 学位
- 博士（工学）(1995年3月 東京大学)
- J-GLOBAL ID
- 200901056190267532
- researchmap会員ID
- 1000253787
- 外部リンク
研究キーワード
4研究分野
3主要な経歴
18-
2020年 - 現在
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2019年 - 現在
学歴
2-
- 1995年
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- 1990年
委員歴
6-
2020年 - 現在
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2014年 - 現在
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2014年 - 2015年
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2014年 - 2015年
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2011年 - 2015年
受賞
3-
2014年
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2012年
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1999年
論文
272-
COMBUSTION AND FLAME 159(3) 1321-1338 2012年3月 査読有りWe developed a rotary valve for a pulse detonation engine (PDE), and confirmed its basic characteristics and performance. In a square cross-section combustor, we visualized a multi-shot of a pulse detonation rocket engine (PDRE) cycle at an operation frequency of 160 Hz by using a high-speed camera (time resolution: 3.33 mu s, space resolution: 0.4 mm) and a Schlieren method. The propellant filling process and the purge process were confirmed, and each process was modeled. Moreover, we confirmed the processes of detonation wave generation and burned gas blowdown. In addition, we investigated the impact of shortening the passage width of a combustor and negative-time ignition (ignition time is earlier than the end-time of the propellant filling process) on the deflagration-to-detonation transition (DDT) distance and time. The DDT distance did not depend on the passage width of a combustor and decreased under the negative-time ignition condition. With a passage width of 20 mm, the DDT distance decreased by 22% under the negative-time ignition condition to a minimum value (76 +/- 8 mm). The DDT time from spark time reached a minimum value (69 +/- 14 mu s) under the condition of a passage width of 10 mm and negative-time ignition. The detonation initiation time and the DDT distance were represented by the time until the flame expanded toward the tube-axis one-dimensionally from ignition (characteristic time). We also carried out thrust measurement using a PDRE system composed of a circular cross-section combustor and the newly developed valve. We obtained a stable time-averaged thrust in a wide range of operation frequency (40-160 Hz) and confirmed the increase of specific impulse due to a partial-fill effect. At a maximum operation frequency of 159 Hz, we achieved a maximum propellant-based specific impulse of 232 s and a maximum time-averaged thrust of 71 N. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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COMBUSTION AND FLAME 159(2) 859-869 2012年2月 査読有りThe detonation propagation phenomena in curved channels were experimentally studied in order to determine the stable propagation condition. A stoichiometric ethylene-oxygen mixture gas and five types of rectangular-cross-section curved channels with different inner radii of curvature were employed. The detonation waves propagating through the curved channels were visualized using a high-speed video camera. Multi-frame short-time open-shutter photography (MSOP) was developed in the present study to simultaneously observe the front shock shape of the detonation wave and the trajectories of triple points on the detonation wave. The detonation wave became more stable under the conditions of a higher filling pressure of the mixture gas and/or a larger inner radius of curvature of the curved channel. The critical condition under which the propagation mode of the detonation wave transitioned from unstable to stable was having an inner radius of curvature of the curved channel (r(i)) equivalent to 21-32 times the normal detonation cell width (lambda). In the stable propagation mode, the normal detonation velocity (D(n)) increased with the distance from the inner wall of the curved channel and approached the velocity of the planar detonation propagating through the straight section of the curved channel (D(str)). The smallest D(n) was observed on the inner wall and decreased with decreasing r(i)/lambda. The distribution of D(n) on the detonation wave in the stable mode was approximately formulated. The approximated D(n) given by the formula agreed well with the experimental results. The front shock shape of the detonation wave could be reconstructed accurately using the formula. The local curvature of the detonation wave (K) nondimensionalized by lambda decreased with increasing distance from the inner wall. The largest lambda K was observed on the inner wall and increased with increasing r(i)/lambda D(n)/D(str) decreased with increasing lambda K. This nondimensionalized D(n)-K relation was nearly independent of r(i)/lambda. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition 34(2) 1939-1947 2012年Visualization experiments employing rectangular cross-section curved channels were performed in order to investigate the fundamental propagation characteristics of curved celluar detonation waves (CCDWs) stabilized in annular channels. A C2H4+3O2 mixture gas and five types of curved channels with different inner radii of curvature were used. The ratio of the inner radius of curved channel (ri) to the normal detonation cell width (λ) was an important factor determining the stability of the CCDWs. The detonation propagation mode in the curved channels transitioned from unstable to stable in the range 14 ≤ ri/λ ≤ 23. The shapes of the CCDWs stabilized in the curved channels became a specific curved shape. The normal detonation velocity (D n) on a CCDW stabilized in a curved channel was approximately formulated. The approximated Dn given by the formula agreed well with the experimental results. The front shock shapes of the stabilized CCDWs could be reconstructed accurately using the formula. The value of Dn nondimensionalized by the Chapman-Jouguet detonation velocity (DCJ) became a function of the curvature of the stabilized CCDWs (κ) nondimensionalized by λ, regardless of the type of curved channel, hence the front shock evolution of the stabilized CCDWs was controlled by this D n/DCJ- λκ relation. Self-similarity was seen in the front shock shapes of the stabilized CCDWs under constant ri/λ conditions. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
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48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit 2012 2012年Microwave rocket is an air-breathing Beamed Energy Propulsion (BEP) rocket, which use a gyrotron microwave oscillator as a beam source. Recently a reed valve air-intake was proposed to ensure air-breathing during the atmospheric flight from zero velocity to high flight Mach number. In this paper a conceptual design of the air-breathing microwave rocket is described. Then using an analytical model of the thrust produced by the air-breathing microwave rocket, launch simulations are discussed. As a result "maximal roads" of an altitude and Mach number are obtained. Additionally it is found that the vehicle can be accelerated to a velocity of 4 km/s in the air-breathing flight mode by the altitude of 60 km. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
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47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit 2011 2011年12月Some numerical wear tests are conducted for the carbon/carbon ion optics of a microwave ion thruster μ10 engineering model to evaluate the accuracy and precision of JAXA's ion optics code (JIEDI). Through comparisons with experiment, the JIEDI code showed good agreement with a real-time 18,000-hrs life test when incorporating the motion of eroded grid materials and a low-energy sputtering yield model for the energy below 300 V. Numerical error caused by the uncertainty of physical model is also studied and it is found that uncertainty in beam current and plasma parameters cause 10% or less error to estimate grid hole erosion profiles. The grid erosion profile is most sensitive to the uncertainty in sticking factor, which indicates what percentage of eroded grid material arriving at a grid surface will re-deposit onto the grid surface. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
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Proceedings of The 32nd International Electric Propulsion Conference, #IEPC-2011-033 IEPC-2011-033 1-11 2011年9月11日
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日本航空宇宙学会論文集 = Journal of the Japan Society for Aeronautical and Space Sciences 59(692) 229-235 2011年9月5日 査読有りMagnetic Sail is one of in-space propulsion systems using the interaction between the solar wind and an artificial magnetic field. In order to reveal thrust performance of Magnetic Sail which has feasible scale of magnetosphere, scale model experiment of Magnetic Sail was conducted in laboratory using Magnetic Sail ground simulator which was arranged in the space science chamber at JAXA. Magnetic Sail scale model obtains magnetospheric size of L = 0.07m, and 0.47 N-thrust in laboratory. Also, thrust is increased by increasing of the magnetic moment of a coil. The scale model corresponds to 30-N-class magnetic-sail which produces 80 km-size magnetosphere in space.
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APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 104(3) 935-940 2011年9月 査読有りFundamental investigations of plasma diagnostics of a forward laser plasma acceleration employing laser-foil interactions were conducted for an Al-foil target irradiated with an Nd:YAG laser of 1 J/pulse with pulse width of 10 ns. Temporal evolutions of electron temperatures and densities were evaluated with electrostatic probes and spectroscopic diagnostics. From the results, it was shown that an average speed of ions in a forward direction was about 40 km/s. Also, it was shown that the plasma temperature and density were about 2.5-8 eV and 10(10) cm(-3), respectively.
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32nd Int. Electric Propulsion Conf. IEPC-2011-079 2011年9月
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32nd Int. Electric Propulsion Conf. IEPC-2011-279 2011年9月
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32nd Int. Electric Propulsion Conf. IEPC-2011-56 2011年9月
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Journal of Propulsion and Power 27(5) 1149-1153 2011年9月 査読有りA study was conducted to accurately evaluate the momentum transfer process of magnetoplasma sail (MPS) in magnetohydrodynamic (MHD) scale. The flow and magnetic fields of an MPS spacecraft were numerically simulated based on the ideal MHD equations paying careful attention to the treatment of boundary condition near the MPS spacecraft. The solar wind was introduced through the inflow boundary at the beginning of the simulation run where the simulation started from a uniform initial condition and was continued until a steady state was achieved. The solar wind inflow boundary condition was implemented by fixing all physical states and the outflow boundary condition was implemented by linearly extrapolating all physical states. An MHD simulation was continued from an initial condition until a steady flow was established. Convergence was confirmed before terminating each simulation from the fact that the residual density fell by 3 orders of magnitude and that the mass and momentum conservation held within 0.5%.
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Theoretical and Applied Mechanics Japan 59 49-57 2011年8月 査読有り
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 54(184) 90-97 2011年8月 査読有りThe steady state of dipolar magnetic field expansion is examined by injecting a plasma jet from the center of the dipolar magnetic field (magnetic inflation). Using a two-dimensional hybrid particle-in-cell (PLC) code taking into account the finite Larmor radius effect, we examine the magnetic field inflation process when Argon (Ar) plasma is injected into a dipole magnetic field generated by a simple hoop coil: the plasma is injected within an angle of 30 degrees in the polar direction. Compared to ideal magneto hydrodynamics (MHD) results, the results obtained using the hybrid PIC code are more accurate since the finite ion Larmor radius effect decreases the flow of magnetic flux with respect to the flow of the plasma jet.
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42nd AIAA Plasmadynamics and Lasers Conference in conjunction with the 18th International Conference on MHD Energy Conversion 2011年6月
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The 28th International Symposium on Space Technology and Science 2011-b-09 2011年6月
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日本航空宇宙学会論文集 = Journal of the Japan Society for Aeronautical and Space Sciences 59(688) 126-131 2011年5月5日 査読有りThe magnetic sail is a spacecraft propulsion system using the interaction between the magnetic field and the solar wind. In this paper, to evaluate the propulsive force generated by a Pure Magnetic Sail spacecraft, a new numerical analysis model including the ion's finite Larmor-radius effect is proposed. In this analysis model, the trajectories of ion particles are solved based on the Flux-Tube model and electrons are treated as a plasma fluid under the assumption of quasi-neutrality and steady state. As for the electromagnetic field, the induction equation is employed to obtain a steady electromagnetic field. Using the Flux-Tube model, a 500-km-size magnetosphere was found to produce a thrust level of 1500N when a magnetic moment of the magnetic sail is set to 3.9×1016Wbm. This thrust level agrees well with the result obtained by magnetohydrodynamics model (1600N) and that by Hybrid particle-in-cell model including ion kinetic effects (1560N). Also, the computational cost of the Flux-Tube model is reduced to about 1/10 of that of Hybrid-PIC model.
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Classical and Quantum Gravity 28(9) 094011-094011 2011年5月 査読有り
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日本航空宇宙学会論文集 = Journal of the Japan Society for Aeronautical and Space Sciences 59(686) 70-75 2011年3月5日The plasma plume of a 1-MW-class quasi-steady magnetoplasmadynamic (MPD) arcjet is studied to reveal the plume plasma fluctuations in a downstream plume region (150–900mm away from the MPD arcjet). By using a double probe and a time-of-flight method, the averaged velocity distribution along the centerline of the plasma plume is found to be almost constant (∼38km/s), and the average ion saturation current is inversely proportional to the square of the distance from the MPD arcjet. The power spectrum density (PSD) of the ion saturation current is proportional to 1/f 1.6 (f : frequency) in 50–200kHz range and it is proportional to 1/f 2.6 above 200kHz. However, fluctuations are dominant in the lower frequency region of 50kHz, where PSD vs. f curve is flat. The spectrum analysis of the fluctuations shows that the MPD arcjet plume in the downstream region is isotropic turbulent flow.
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2011 IEEE MTT-S International Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems, and Applications, IMWS-IWPT 2011 - Proceedings 185-188 2011年An air-breathing pulse-detonation engine powered by microwave energy beaming, "Microwave Rocket" is considered as a future mass transportation system to space. A key to realize Microwave Rocket is to achieve high air-breathing performance. We are now developing the system using side-wall reed valves which is expected to minimize ventilation period. A test chamber equipped with a reed valve was fabricated and the ventilated volume flow rate was measured. CFD was also conducted. As a result, it came out that pressure oscillation frequency inside the thruster was approximately in inverse proportion to the thruster length. It was also found that there is minimum thruster aspect ratio where complete ventilation can be accomplished. © 2011 IEEE.
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Plasma and Fusion Research 6(1) 2406103-1～2406103-4 2011年 査読有りAnalytical thrust model for the Lissajous Helicon Plasma Accelerator (LHPA) is developed by extending previous works [1,2] in order to guide experiments for achieving feasible value of the thrust. In the LHPA, a rotating transverse electric field in an external divergent magnetic field drives azimuthal currents via electron E × B drift then the thrust is produced due to the Lorentz force. One dimensional (1D) analytical model is developed which includes the electric field penetration into the plasma and the E × B current estimation based on a trajectory analysis. Thrust as a function of parameters of the plasma density and the magnetic field is studied. The penetration of the electrical field into plasmas is examined by 1D particle in cell (PIC) simulations whose results are consistent with those of the 1D analytical model. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research.
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49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition AIAA-2011-1073 2011年1月
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Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan Vol. 8, pp.Pb_109-Pb_114 2011年 査読有り
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Transactions of JSASS Space Technology Japan 8 .Pb_19-Pb_25 2010年12月 査読有り
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Transactions of JSASS Space Technology Japan 8 Pb_33-Pb_38 2010年12月 査読有り
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VACUUM 85(5) 574-578 2010年11月Thrust performance tests were conducted for an arrayed multi-plasmajet structure consisting of rectangular nozzle elements each with an exit height of 05 mm and length of 05 mm To evaluate the thrust characteristics of the arrayed micro-multi-plasmajet the thrust was measured using a calibrated cantilever-type thrust stand in vacuum Using 3 x 3 nozzle elements the micro-plasmajet array showed stable DC operation Compared to conditions with cold-gas flow the application of a DC discharge showed a significant improvement in thrust performance of at least 20% for thrust and specific impulse Typical values achieved for thrust specific impulse and thrust efficiency at an Input power of 6 3 W were 8 5 mN 77 s and 021 respectively (C) 2010 Elsevier Ltd All rights reserved
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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 58(10) 3282-3288 2010年10月The ionized exhaust plumes of solid rocket motors may interfere with RF transmission under certain flight conditions. To understand the important physical processes involved, we measured microwave attenuation and phase delay due to the exhaust plume during sea-level static firing tests for a full-scale solid propellant rocket motor. The measured data were compared with the results of a detailed simulation performed using the frequency-dependent finite-difference time-domain (( FD)(2)TD) method. The numerically derived microwave attenuation was in good agreement with experimental data. The results revealed that either the line-of-sight microwave transmission through ionized plumes or the diffracted path around the exhaust plume mainly affects the received RF level, which depends on the magnitude of the plasma-RF interaction.
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 53(180) 84-90 2010年8月To propel a spacecraft away from the Sun, a magneto plasma sail (MPS) spacecraft produces an artificial magnetic cavity to block the hypersonic solar wind. To make a large magnetic cavity sufficient to obtain significant thrust, the MPS spacecraft increases the magnetic cavity size using an onboard coil with assistance from a plasma jet. This process is called magnetic field inflation. In this study, we performed ideal and resistive magnetohydrodynamic (MHD) analyses to investigate the magnetic diffusion effect on the magnetic field inflation process. Our results indicate that a dipole-like magnetic field is drastically deformed by a plasma jet; when the magnetic Reynolds number R. was 10 or more, the magnetic field lines were nearly identical to the streamlines of the plasma jet. Hence, no magnetic diffusion effect appeared for R(m) > 10. Meanwhile, when Rn, is an order of unity, the magnetic diffusion effect was remarkable in the current sheet formed around equatorial region. For example, when the divergence angle of a plasma jet in the polar direction was 30, the magnetic field strength at 40m from the spacecraft (calculated by resistive MHD model) was 19% smaller than the ideal MHD model (R(m) = infinity).
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JOURNAL OF SPACECRAFT AND ROCKETS 47(4) 627-633 2010年7月 査読有りUnder certain conditions during rocket flight. ionized exhaust plumes from solid rocket motors may interfere with la transmission. To understand the relevant physical processes involved in this phenomenon, measurement of microwave attenuation and phase delay caused by rocket exhaust plumes was attempted in a sea-level static firing test for a full-scale solid propellant rocket motor. The measured data were analyzed by comparing them with simulation results for an exhaust plume flowfield. The results revealed that the change in the shock structure in the plume affects the microwave attenuation level, since it significantly affects the plasma density at the measuring location. When the plasma density in the plume is low, the microwaves can penetrate the plume. The plume plasma properties were successfully estimated for that situation in which the numerically calculated attenuation level agreed well with the experimental results. On the other hand, high-density plasma in the plume does not allow penetration. Therefore, microwaves bypass around the plume and the diffraction effect becomes dominant.
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CLASSICAL AND QUANTUM GRAVITY 27(8) 084010 2010年4月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.
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JOURNAL OF PROPULSION AND POWER 26(1) 159-166 2010年1月Magnetic sail is a propellantless propulsion system proposed for an interplanetary space flight. The propulsive force is produced by the interaction between the magnetic field artificially generated by a hoop coil equipped with the magnetic sail and the solar wind. Three-dimensional hybrid particle-in-cell simulations are performed to elucidate the plasma flow structure around the magnetic sail and to measure the propulsive force of the magnetic sail. We report the characteristics of the magnetosphere, such as the profile of the magnetic field, the thickness of the magnetopause current layer, and the predicted thrust value obtained by simulations, which agree well with laboratory experiment when simulations are carried out by considering the ion-neutral collision effect. The hybrid particle-in-cell simulation carried out without considering the collisional effect gave a thrust value of 3.5 N, which can be applied to the thrust evaluation of the magnetic sail in a magnetosphere with size of 300 kin in a collisionless interplanetary space.
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61st International Astronautical Congress 2010, IAC 2010 13 11061-11068 2010年Magnetic sail is one of efficient and high thrust propulsion systems. The thrust force of the magnetic sail is subjected to the interaction between solar wind momentums with the artificial magnetic fields from an excited superconducting coil. Because solar wind is usually changing its velocity and density, we must regulate current through the superconducting coil to control the thrust force. Thus, we need a power supply and a current regulation system on the spacecraft. A lightweight regulation system and power supply system onboard the spacecraft can cause steep change of output voltage and current, including voltage ripple in output of the power supply. The ripple voltage and steep change of the output voltage and current locally bring about transition from superconductivity to normal conductivity, resulting in burning or break-up of the superconducting coil. In this paper, we proposed four power supply circuit. From the comparison of four systems, Thermoelectric Circuit, Capacitor Circuit and DC/DC Converter Circuit are light-weight. So, it is possible these circuits to be installed onboard the magnetic sail. However, there is no precedent that the superconducting coil is excited by these power supply circuits. So before adopting these power supplies, we must investigate the effect of ripple voltage and steep change of output voltage and current to the superconductivity.
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INTERNATIONAL SYMPOSIUM ON HIGH POWER LASER ABLATION 2010 1278 191-+ 2010年A fundamental study of a newly developed rectangular pulsed laser-electromagnetic hybrid thruster was conducted. Laser-ablation plasma in the thruster was induced through laser beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration only by using a laser beam. The performance of the thrusters was evaluated by measuring the mass shot and impulse bit. As results, significantly high specific impulses up to 7,200 sec were obtained at the charge energies of 8.6 J. In addition, typical thrust efficiency varied between 11.8% and 21.3% depending on the charge energy.
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INTERNATIONAL SYMPOSIUM ON HIGH POWER LASER ABLATION 2010 1278 184-+ 2010年The micro-Newton thrust generation was observed through low-power continuous-wave laser and aluminum foil interaction without any remarkable ablation of the target surface. To evaluate the thrust characteristics, a torsion-balance thrust stand capable for the measurement of the thrust level down to micro-Newton ranges was developed. In the case of an aluminum foil target with 12.5 micrometer thickness, the maximum thrust level was 15 micro-Newtons when the laser power was 20 W. It was also found that the laser intensity, or laser power per unit area, irradiated on the target was significantly important on the control of the thrust even under the low-intensity level.
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61st International Astronautical Congress 2010, IAC 2010 13 11049-11054 2010年The aim of this paper is to investigate the thrust force of the magnetic sail spacecraft equipped with a superconducting coil by an experiment and a computer simulation. We designed the experimental system to measure the force on the hanged superconducting coil in the external magnetic field. For this experiment system, we analyzed the thermal design to keep the hanged superconducting coil at a sufficiently low temperature. In result, this system can refrigerate the superconducting coil at 20K, and we can pass a current at 100A. We concurrently analyze the current distribution of the superconducting coil in the presence of an external magnetic field using the Bean model that is the critical current model of the soft superconductors. By this computer simulation, the mechanism that an external field applies force on the superconducting coil is calculated. Copyright ©2010 by the International Astronautical Federation. All rights reserved.
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46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit AIAA-2010-6773 2010年Research status of spacecraft propulsion using the energy of the solar wind in Japan is overviewed. Experimental and numerical studies showed that moderately sized magnetic sails in the ion inertial scale magnetosphere (∼100 km) could produce Newton-class thrust. In the same scale length, magnetic cavity size was successfully controlled in the laboratory experiment of magnetic sail with a plasma jet (Magnetoplasma sail, MPS), but so far, no significant thrust increment was observed in the experiment. On the contrary, MPS concept was tested in MHD scale by numerical simulation, and thrust increment from pure MagSail to MPS as much as 90% was obtained. Currently, we are continuing our experimental and numerical efforts to make a feasibly sized Magnetoplasma sail (10∼100 km magnetosphere) in a transitional regime between ion scale and MHD scale by optimizing the magnetic field inflation process of MPS. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
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IEEE TRANSACTIONS ON PLASMA SCIENCE 37(12) 2390-2398 2009年12月Comprehensive comparisons of the numerically simulated results of plasma flow fields in a 100-kW-class 2-D magneto-plasmadynamic thruster with the available experimental data are conducted. The propellant is argon of 1.25 g/s, and the discharge current is varied from 8 to 12 kA. The physical model includes a nonequilibrium single level of ionization and a collisional radiative model for argon ion to assess the reaction processes in detail. The data we mainly compared are the current path, electron number density, and electron temperature. There is qualitative agreement between the calculated and experimental results except for the electron temperature. In order to explain the disagreement of the electron temperature, we estimate the excitation temperature from the distributions of the excited ions in 4s and 4p states, the radiation of which was employed to determine the electron temperature in the experiment. As a result, it is found that the calculated excitation temperature becomes close to the measured result and that the plasma deviates from the partial local thermodynamic equilibrium near the anode surface. Regarding the thrust and thrust efficiency, their features against variation of the discharge current are well captured by the simulation, although they are slightly overestimated compared with the measured values.
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Transactions of the Japan Society for Aeronautical and Space Sciences,Space Technology Japan Vol. 7(No. ists26) pp.Pb_65-Pb_69 2009年9月
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Effects of Nozzle Geometries on Thrust Performance Improvement of Micro-Multi-Nozzle-Array ThrustersTransactions of the Japan Society for Aeronautical and Space Sciences, Space Technology Japan Vol. 7(No. ists26) pp.Pb_77-Pb_82 2009年9月
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The 31th IEPC-2009 IEPC-2009-229 1-12 2009年9月
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日本航空宇宙学会論文集 = Journal of the Japan Society for Aeronautical and Space Sciences 57(666) 287-294 2009年7月5日The steady state of dipolar magnetic field expansion is examined by injecting a plasma jet from the center of the dipolar magnetic field (magnetic inflation). An effective magnetic inflation is essential for the realization of a magneto plasma sail (MPS), which produces a propulsive force by the interaction between the solar wind and an artificial dipolar magnetic field that is inflated by the plasma jet injected from the spacecraft. During the process of magnetic inflation, the finite Larmor radius effect is of practical significance since rL/LB is considerably greater than unity in a region far from the center of the dipolar magnetic field. The simulation result obtained using the ideal magnetohydrodynamics (MHD) model is overestimated, namely, it shows that the inflated magnetic field decays according to |B| ∝ r -2.0 since the magnetic field is frozen into the plasma jet. In comparison with the MHD result, the results obtained using the hybrid particle-in-cell code are more accurate. These results show that the inflated magnetic field decays according to |B| ∝ r -2.3 under the condition βin = 1 since the finite ion Larmor radius effect decreases the flow of magnetic flux with respect to the flow of plasma jet.
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Transactions of the Japan Society for Aeronautical and Space Sciences, Space Technology Japan Vol. 7(No. ists26) pp.Pb_17-Pb_22 2009年6月 査読有り
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Transaction of the Japan Society for Aeronautical and Space Sciences,Space Technology Japan Vol. 7(No. ists26) pp.Pb_159-Pb_162 2009年6月 査読有り
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Transactions of the Japan Society for Aeronautical and Space Sciences, Space Technology Japan Vol. 7(No. ists26) pp.Pb_11-Pb_16 2009年5月 査読有り
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CLASSICAL AND QUANTUM GRAVITY 26(9) (9 pages) 2009年5月 査読有りDECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECi-hertz 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.
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JOURNAL OF PROPULSION AND POWER 25(2) 397-405 2009年3月A self-field magnetoplasmadynamic thruster is numerically studied for an argon mass flow rate of 0.8 g/s. We focus on the plasma behavior around the critical current, at which full propellant ionization is theoretically expected. At a discharge current higher than the critical current, the flail parameter is large at the anode surface, which leads to an obliquely skewed current profile. This skewed current profile, together with the voltage-current characteristics, show that the Hall effect plays an important role around the critical current. When operating the magnetoplasmadynamic thruster above the critical current, it is shown that the current concentration and the gas density depletion at the anode edge induce a shortage of current carriers. To circumvent the carrier shortage at high discharge currents, we employ a segmented anode. It is found that a segmented anode is effective for suppressing the current concentration and the plasma density depletion on the anode surface without degrading the performance of the thruster.
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