ELECTRICAL BREAKDOWN CURRENTS ON LARGE SPACECRAFT IN LOW-EARTH-ORBIT

An experimental and theoretical investigation of an expanding plasma generated by an arc produced by biasing a conductor underneath a thin layer of anodized aluminum 160-V negative of a laboratory plasma that can produce large peak arc currents by discharging large surface areas is presented. A simple theory shows that the time scales and observed current magnitudes are consistent with the expansion of a discharge-generated plasma. The implication for large spacecraft in low Earth orbit, such as Space Station Freedom (SSF) which can store large amounts of charge, is that ares with the same amount of energy similar to those observed in the laboratory may occur. The energy in these arcs degrade the surface of the anodized aluminum thermal control coatings by producing large pits in the surface. These pits tend to increase the temperature of the spacecraft, and the material from the pits can become an additional source of contamination. The rise time and intensity of theses arc could produce significant EMI. To prevent the occurrence of these undesirable effects, SSF will utilize a plasma contactor that will control the structure to ambient plasma potentials.