XPS Investigation of the Source of GPS Arc Contamination

Abstract

Global positioning system (GPS) satellites are strongly suspected to arc into the space environment. Arcing on spacecraft due to differential charging can be blamed for a host of operational anomalies resulting in the loss of billions of dollars and productivity. In addition to anomalous behavior on spacecraft, arcing can be accused of an otherwise unexplained degradation in solar power production of GPS satellites while on orbit. In the study presented here, it will be shown that arcs on a GPS-representative solar array coupon under representative medium earth orbit/geosynchronous earth orbit (MEO/GEO)-like conditions result in contamination of solar panel coverglasses. This finding supports the argument that arc-induced contamination is a prime suspect in explaining the mysterious excess power loss of GPS satellites on orbit. Further, optical mapping suggests that this arcing occurs primarily at the edges of the sample panel where silicone adhesive with glass microspheres was exposed. X-ray photoelectron spectroscopy (XPS) reveals that the concentration of Si near the arc sites is increased, suggesting that the adhesive is ionized during the electrostatic discharge and coats the surface of the solar panel, resulting in reduced optical transmission through the coverglass and therefore reducing power production. X-ray depth profiling suggests that the silicon detected is due to surface contamination, and electrostatic simulations indicate that glass microspheres intended to reduce adhesive mass and produce a uniform bond-line may be exacerbating the arcing problem.