The Importance of Secondary Electron and Backscattered Electron Emissions in Spacecraft Charging

Secondary electron and backscattered electron emissions are of central importance in determining the charging level of spacecraft charging. Traditionally, the Sternglass formula and the Sanders-Inouye formula are used for the secondary electron coefficient whereas the Prokopenko-Laframboise formula is used for the backscattered electron coefficient. A survey of the advances in secondary electron coefficient measurements in the past two decades shows that the results are all different. Surface contaminants, surface thickness, and space environment are factors affecting the secondary electron coefficients. These results affect spacecraft charging level calculations, especially at high levels above kilovolts. According to the Prokopenko-Laframboise formula, the backscattering electron coefficient approaches a small value as the primary electron energy approaches zero. Recent advances, however, have revealed that the backscattering electron coefficient approaches unity at zero energy. This result affects spacecraft charging level calculations, especially at low levels below about 50 volts.