Secondary electron emission causing potential barriers around negatively charged spacecraft

Abstract

Low-energy secondary electrons have been observed to be reflected back to the spacecraft during eclipse conditions. It has been argued that the presence of negative potential barriers can be caused by the secondary electron emission space charge and may play a role in the spacecraft charging process. The barriers turn back the lowenergy spacecraft-emitted electrons and prevent the low-energy ambient electrons from reaching the detector. Two numerical methods previously presented by Whipple and by Parrot et al. in the literature have been used to study the effect of secondary electrons on potential barriers negatively charged spacecrafts. The former method provides an upper bound for the potential barriers when the sheath is large compared to spacecraft dimension. The latter one provides in principle the exact sheath profile subject to accurate integration of the density distribution over the energy. The application of the methods to data provided by the ATS6 and Freja spacecraft suggests that the high level negative charging is not due to barriers induced by secondary electron emission space charge