Importance of Surface Conditions for Spacecraft Charging

摘要

This paper studies the importance of secondary and backscattered electrons in spacecraft charging. Thensecondary and backscattered electron yields from surface materials are affected not only by the energies of thenincoming electrons but also by the surface condition. Some typical parameters characterizing the surface conditionnare the surface smoothness, thickness, surface composition, and surface contamination. By using the publishednformulae of secondary and backscattered electron yields, the critical temperature values for the onset of spacecraftncharging are calculated. The results found are different for different yield formulae. The yields are not onlynimportant in governing the current balance at equilibriumand the onset of spacecraft charging, but also in affectingnthe accuracy of model calculations of the spacecraft potential. This paper suggests that, for predicting spacecraftncharging or in spacecraft design, it is inadequate to look up published tables of the yields for a given type of surfacenmaterial. It is necessary tomeasure the secondary electron and backscattered electron yields of an actual piece of thensurface material, because the thickness, smoothness, surface composition, and so forth can affect the yields and, innturn, spacecraft charging.