Flight Model Discharge System.

Abstract

Abstract : The Flight Model Discharge System (FMDS) Program is an autonomous system that detects both absolute and differential charging of high-altitude satellites and actively discharges the associated potentials before hazardous arcing levels are reached by emitting a low-energy inert-gas plasma. FMDS operating principles are based on empirical results from the Air Force SCATHA (P78-2) and NASA ATS-6 satellites, both of which successfully demonstrated the principle of safely reducing spacecraft charging levels by the emission of a low-energy space-charge-neutral plasma - effectively 'grounding' the spacecraft frame and dielectric surfaces to the potential of the ambient space plasma. FMDS uses a xenon plasma source capable of igniting within one second and of emitting a flow of space-charge-neutral plasma containing more than 1 mA of Xe(+) ions. The spacecraft charging level is detected by sensors similar to those that operated aboard SCATHA (i.e., ion and electron electrostatic energy analyzers and surface-potential monitors). This report describes the development details for the breadboard and flight models of the FMDS instrument. Operational characteristics of the electrostatic analyzers, surface-potential monitors, transient-pulse monitor, plasma source, microprocessor-based controller, and software architecture are described. Results of vacuum-chamber testing under simulated geosynchronous environmental conditions are also presented. Keywords: Spacecraft charging; Charge control system; Autonomous discharge system; Xenon plasma source; Geosynchronous charge control.