Severe Electron Environment for Surface Charging at Geostationary and Medium Earth Orbits

Electron radiation environment with keV energies on medium earth orbit (MEO) is investigated around the times when worst-case severe environments for surface charging were detected at Los Alamos National Laboratory (LANL) satellites on geostationary earth orbit (GEO). The Inner Magnetosphere Particle Transport and Acceleration Model (IMPTAM) is employed to model 1-100 keV electron fluxes in the inner Earth's magnetosphere (inside 10RE) during four representative events selected out of 400 LANL worst-case severe environment events. Modeled fluxes are compared to the observed ones on GEO, and the peak electron fluxes are then extracted at L=4.6 which is considered as approximate MEO environment following the LANL events. IMPTAM generally reproduces the 10-50 keV electron fluxes on GEO but underestimates (of factor of 2 to 5) at energies above. It is found that the maximum electron flux on MEO is reached in about 1.5-2 h after the worst-case environment for surface charging was detected at GEO. Whereas the magnetic local time (MLT) location of the worst-case severe environments on GEO varies from 23 to 05, the maximum electron flux on MEO is located on 6-7.8 MLT. The maximum electron flux values on MEO can be 2 to 10 times higher than those observed on GEO and those estimated using European Cooperation for Space Standardization and National Aeronautics and Space Administration guidelines, which can be a significant increase of the risks in terms of surface charging.