The continuing challenge of spacecraft ESD

The threat of spacecraft electrostatic discharge (ESD) arises primarily from the energetic charged particles (electrons and ions) present in the magnetospheric plasma of the earth, at the altitudes of geo-synchronous satellites. The charged particles in the energy range, less than 50 keV, give rise to surface charging and those in the higher energy range (> 100 keV) penetrate into the interiors of the spacecraft and give rise to deep dielectric (internal) charging. Under certain circumstances, the charge accumulation continues until the dielectric breaks down electrically, producing effects such as material destruction, contamination of nearby surfaces, or electrostatic discharge. The discharge may induce transient electromagnetic interference (EMI) in the electronic circuitry and may give rise to switching anomalies or failure of the system under severe environmental condition. This paper describes the spacecraft charging, surface charging as well as internal charging studies that have been carried out. Techniques of hardening the spacecraft subsystems against on-board ESD are outlined. The point made is that spacecraft ESD threat has not gone away, and the relevant satellite specifications are becoming increasingly stringent, constituting a continuing major challenge for spacecraft designers and system integrators.