Space Charging Currents and Their Effects on Spacecraft Systems

The range and limits on the space charging electron currents available in the near-geosynchronous orbit have been identified from a large SCATHA satellite data base. The most intense current densities observed were 0.8 nA/cm2 at 1 keV and 0.5 pA/cm2 at 1 MeV. The effects of these currents on both surface and internal charging of dielectrics have been modeled. In exposed dielectrics radiation-induced effects significantly increase the conductivity within the first few ¿m of the surface, produce permanent radiation damage, and affect the final potential of the sample. The calculated electric field profiles and surface potential of a 127 ¿m Kapton® sample are found to be consistent with the voltage measured aboard the SCATHA satellite during a charging event. The calculated field strength of 2×105 V/cm is below the spontaneous breakdown level. Transient electrical pulses observed in association with the charging may therefore be due to capacitive coupling effects rather than to breakdown. The electric fields and voltage internal to both plane-parallel and coaxial geometries containing a Teflon® dielectric enclosed between two conductors have also been modeled. Electric field strengths of a few x 105 V/cm and internal potentials of several kV are calculated for these typical configurations when exposed to the direct electrons in unusually energetic events.