The Multiutility Spacecraft Charging Analysis Tool (MUSCAT), a spacecraft charging analysis software, has been developed as a collaboration work between Japan Aerospace Exploration Agency and Kyushu Institute of Technology. Laboratory experiments for fundamental code validation were carried out in both facilities' plasma chambers. MUSCAT is a particle simulation code based on particle-in-cell (PIC) and particle tracking (PT) algorithms capable of calculating the floating-body potential of a spacecraft with respect to the plasma potential. Three experiments were carried out regarding spacecraft-plasma interaction phenomena important in LEO and PEO. A Langmuir probe was used to measure the current collection and potential distribution in static plasma to validate the PIC and PT schemes. The floating potential of an object in plasma with an energetic electron component was measured to validate the floating-body calculation as well as the PT scheme. Current collection and potential distribution in the wake structure were measured to validate the PIC and PT scheme in flowing plasma condition. The experimental results and the simulation results agreed very well in all the three experiments, validating the accuracy of the MUSCAT solver.
Space development has been rapidly increasing, and a strong demand should arise regarding the understanding of the spacecraft-plasma interactions, which is one of the very important issues associated with the human activities in space. To evaluate the spacecraft-plasma interactions including plasma kinetics, transient process, and electromagnetic field variation, the authors have started to develop a numerical plasma chamber called Geospace Environment Simulator (GES) by making the most use of the conventional full particle-in-cell plasma simulations. For the development of a proto model of GES, the authors have used the Earth Simulator, which is one of the fastest supercomputers in the world. GES can be regarded as a numerical chamber in which space experiments can be virtually performed and temporal and spatial evolutions of spacecraft-plasma interactions can be analyzed. In this paper, the authors have briefly introduced GES in terms of its concept, modeling, and research targets. As one of the research topics of GES, the authors have investigated the impedance variation of electric field antenna onboard scientific satellites in the photoelectron environment in space. From the preliminary simulation results, the large change of reactance of the antenna impedance below the characteristic frequency corresponding to the local plasma frequency determined by the photoelectron density could be confirmed.
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