RELATIONSHIP BETWEEN ELECTROSTATIC DISCHARGES ON SPACECRAFT P78-2 AND THE ELECTRON ENVIRONMENT

The relationship between the energetic electron environment and electrostatic discharges on the P78-2 (SCATHA) spacecraft has been examined. Internal discharges occur near perigee, whereas surface discharges occur uniformly over the radial range covered by SCATHA from 5.5 to 8 R(e). Surface discharges peak at local midnight and decrease toward local morning, whereas the internal discharges have a broad occurrence maximum centered on local noon. Both types are far more likely to occur when the Earth's magnetic field is disturbed. Although few surface discharges occur when the planetary magnetic index Kp is < 4, a modest number of internal discharges occur under these quiet to normal conditions. Surface discharges have a strong tendency to occur when the flux of electrons with energies of tens of keV is high, whereas internal discharges occur when the flux of electrons with energies of hundreds of keV is high and the flux of tens of keV electrons is low. A significant correlation has been found between the occurrence of discharges on SCATHA and an estimate of the energetic electron fluence at geosynchronous orbit obtained from a neural network model of the relativistic electron flux al geosynchronous orbit. The incidence of internal discharges at predicted daily fluences above 10(10) electrons/cm2 is sufficiently high to warrant the use of this predictor to issue warnings for real-time satellite operations. The statistics of nine years of surface discharges on the SCATHA spacecraft are dominated by the single charging event on September 22, 1982.