Method for estimating spontaneous pulse rate for insulators inside spacecraft

High energy electrons that penetrate the thin surface materials on spacecraft can be stopped in insulated materials inside spacecraft and thereby generate spacecharge-caused electric fields and high voltages inside the spacecraft. The fields are large enough to induce spontaneous pulsing by insulating materials. Realistic estimates of pulse rates are currently lacking. The frequency of electrostatic discharge pulsing can be estimated by extrapolating the pulse rate measured for insulators on the CRRES spacecraft. The extrapolation is based upon CRRES data which show that: (1) The pulse rate scales with high energy electron flux, and with the area and type of insulator. (2) Samples must be soaked in vacuum for at least six months before being tested so that the results are not biased by species such as water and free radicals that eventually outgas. (3) Insulators containing many large imperfections such as the glass fibers in epoxy fiberglass circuit boards produce the most frequent pulsing. (4) Some insulators pulse only rarely. (5) We have not yet determined a high energy electron flux below which no pulsing occurs.