Early Studies of Deep-Dielectric Charging at Geostationary Orbit

Many spacecraft operational problems in Earth's magnetosphere are due to intense, transient radiation phenomena. Early work at the Los Alamos National Laboratory placed particular emphasis on highly relativistic electrons (3-10 MeV). Electron fluxes and energy spectra were measured by two high-energy electron sensor systems at 6.6 R_E from 1979 through the 1980s. Large, persistent increases in this population were found to be relatively infrequent and sporadic in 1978-81 around solar maximum. During the approach to solar minimum (1981-1985) it was observed that the highly relativistic electrons occurred with a regular 27-day periodicity, and were well associated with observed high-speed solar wind stream structures. Through a superposed epoch analysis technique it was shown that energetic electron enhancements typically rise on a 2- to 3-day time scale and decay on 3- to 4-day scale at essentially all energies above ~ 3 MeV. Key early spacecraft operational anomalies were seen to correlate closely with the electron enhancements. The analysis suggested that these electrons have a very deleterious influence on spacecraft systems due to deep dielectric charging and low-dose susceptibility effects. These discoveries have greatly informed subsequent space weather thinking.