The Importance of Accurate Secondary Electron Yields in Modeling Spacecraft Charging
S-CUBED LA JOLLA CA
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Spacecraft charging has commonly been attributed to electrons with several kilovolts of energy impinging upon spacecraft surfaces. Recent experimental evidence from the SCATHA satellite has shown that charging correlates well with electrons of energies greater than 30 keV. In this paper it is shown that the SCATHA observations are consistent with the model of charging in which a satellite is immersed in a Maxwellian plasma, particle collection is orbit limited, and dominant surface effects are the emission of secondary and backscattered electrons. The energy dependence of the secondary yield for multi- kilovolt incident electrons determines the charging threshold. In the past, inadequate representations of the secondary yield have led experimenters to question the validity of the charging model. The accuracy of the secondary electron yield formulation based on electron stopping power, such as the one in the NASCAP and POLAR charging codes, gives good agreement with the SCATHA results. A Maxwellian representation of the magnetospheric plasma is justified by choosing effective temperatures and densities that minimize the error in calculated charging current densities.