1. Introduction In parallel with the enhancement of human activities in space, larger electrical power is required. Space power issues are acquisition, storage, transmission, conversion and waste, which may impose constraints on space activities. Associated with large electrical power, efficient generation and transmission can be made by high voltage, which has been familiar on the ground. Skylab in 1973 adopted about 30 V as bus voltage, and the NASA Space Station will employ 250 V. The higher the voltage becomes, however, the stronger the impact imposed on the spacecraft by the interaction with space plasma [1]. Especially in low earth orbit (LEO), this seems to be severe for a high voltage solar array (HVSA), of which the interconnects between the solar cells are exposed to the ionospheric plasma. The interference of the HVSA can be viewed as follows. Ions and electrons are collected by the HVSA through the space charge sheath which is formed around the conductive surface of the HVSA at some potential based on the plasma potential. A potential distribution in the HVSA relative to the ionospheric plasma adjusts itself so as to collect no net plasma current. The difference of the current densities between ion and electron makes the potential in almost all the parts of the HVSA lower than the plasma potential, and ions are collected in accordance with the drift probe characteristics. Ion collection is essential to the interference of the HVSA with the ionospheric plasma. This plasma current results in leakage of power from the HVSA. Occasional discharge at the negatively polarized portion causes electromagnetic interference with onboard electronics. These above interactions are predicted by many investigators [2] and verified by a ground experiment [3] and a short-period rocket experiment [4]. The Two Dimensional High Voltage Solar Array (2D/HV) Experiment [5], as shown in Fig. 1, onboard the Japanese reusable spacecraft. Space Flyer Unit (SFU), is under development in order to determine the upper operational voltage of the solar array in LEO in early 1993, when solar activity is near its maximum, so that a stringent environment will exist. The 2D/HV system consists of a deployable array of 6.4 m length square, and solar cells which are furnished on a small part of the 2D array with restriction of the SFU resources. Arrangement of the solar cells on the 2D array will be determined. This is designed to generate optional voltages up to 570 V with constant power in a series-parallel connection of the solar cells. This is a key technology for the versatile power control system to supply directly high-power equipment with its required voltage, no dc-dc converters, and no loss in them. We have revealed new interference phenomena by numerical simulation [6] and a ground experiment [7]. The momentum exchange between the HVSA and the plasma induces spacecraft drag. The surface of the solar cell is eroded by frequent particle collisions so that their erosion or re-adhesion to themselves may cause damage to power generation. A ground experimental simulation using a real-scale HVSA is not realistic if you consider the dimensions of the available space chamber, uniform plasma
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