The Effects of Material at Arc Site on ESD Propagation

In the past few years, the Aerospace Corporation and other labs have been exploring how electrostatic discharges propagate over the surface of a positively charged dielectric surfaces, like solar arrays, on a spacecraft. One goal of these explorations is ultimately to aid in the extrapolation of transient currents measured on coupons in the laboratory to currents expected on full-scale spacecraft assemblies. In the popular plasma bubble model, the electrostatic discharge plasma is expected to expand radially from a single arc initiation point at the ion sound velocity, which depends on the composition of the conductor at that initiation point. In this paper, we examine how changing the conductor material at the arc initiation site affects propagation on a positively charged Kapton surface. By measuring current flowing into a series of concentric electrodes beneath this Kapton surface, we can monitor surface neutralization as a function of time and radial distance from the arc site. Results will be presented for a selection of cathode materials, and implications for existing and future models will be discussed.