Deep dielectric charging effects due to high-energy electrons in earth's outer magnetosphere

Abstract

Many spacecraft operational problems in the earth's outer magnetosphere appear to be due to intense, transient radiation phenomena. Three types of naturally occuring, and highly variable, hostile particle radiation environments are encountered at, or near, the geostationary orbit: (1) high-energy protons due to solar flares; (2) energetic ions and electrons produced by magnetospheric substorms; and (3) very-high-energy electrons of uncertain origin. In this paper, particular emphasis is given to highly relativistic electrons (3–10 MeB). Electron fluxes and energy spectra are shown which were measured by two high-energy electron sensory systems at 6.6 R E from 1979 through 1984. 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-present) it is observed that the highly relastivistic electrons occur with occur with a regular 27-day periodicity, and are well associated with the re-established solar wind stream structures. Through a superposed epoch analysis technique we show that an energetic electron enhancement typically rises on 2- to 3-day time scale and decays on 3- to 4-day scale at essentially all energies above ca. 3 MeV. The present analysis suggests that these electrons have a very deletrious influence on spacecraft systems due to deep dielectric charging and low-dose susceptibility effects.