Study of Surface Degradation of Spacecraft by Energetic Oxygen Ions

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Spacecraft with high power utilities, such as the Solar Power Satellite, will use a high voltage in the power system. Exposure of a high voltage more than 100 V in space plasma causes ion bombardment to the negative side, resulting in an enhanced power loss, material degradation and pollusion in its vicinity. We have made an experiment on the sputtering effect of energetic oxygen ions of 7.1x10^<13> ions/cm^2・sec irradiated onto alluminized polymide. The irradiation rate is approximately 1000 times larger than that on an satellite at the height of 500 km. The mass loss rate of the alluminum layr is estimated by measuring its optical transmittance. The secondary ions generated at the alluminum surface are detected by an ion mass spectrometer. The energy distribution of the secondary ions are measured by a Faraday cup. For 1 keV oxygen ions, the sputtering rate has been found to be typically 0.8 to 1.0 at 1000 eV.The production rate of the secondary ions is 0.02-0.04% and their energy ranges from 30 to 40 eV.These results have been used to estimate power loss, mass loss and pollusion rate for a satellite exposing a high voltage in the ionosphere. In case of a sphere with 1 m diameter biased at -1000 V located at the height of 500 km, alluminum surface will be degraded by 16mum each year while the vicinity will be contaminated by the secondary ions to be accumulated up to 30* per year. The power loss is calculated as 5 watt for this case.