Statistical properties of the surface-charging environment at geosynchronous orbit

Based on 13 years of data from the Magnetospheric Plasma Analyzers on six Los Alamos National Laboratory (LANL) geosynchronous satellites, the statistical behavior of environmental conditions that cause strong surface charging on the satellites is examined. Analysis of the Magnetospheric Plasma Analyzers data reveals the electron energy range (similar to 5-10 keV) and threshold flux (1.4x103 cm-2 s-1 sr-1 eV-1 at 8 keV) that are most closely associated with satellite surface charging. We also find that the average ambient electron temperature in the plasma sheet correlates with the observed magnitude of the surface potential on the LANL satellites. Analysis of the statistical occurrence rates of (1) the observed surface potential on the LANL satellites, (2) 8 keV electron fluxes above the threshold, and (3) elevated values of the average electron temperature all reveal that an enhanced surface charging probability exists (a) during higher values of Kp, (b) in the local time range from premidnight through dawn, (c) during equinox seasons, and (d) during the declining phase of the solar cycle. With the exception of the solar cycle dependence, these are the same statistical dependences found by Choi et al. (2011) in the satellite anomaly database they examined. The local time dependence of those anomalies is a particularly strong diagnostic of surface charging as a probable cause of a significant number of them.