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

An experimental and theoretical investigation of an expanding plasma g enerated by an arc produced by biasing a conductor underneath a thin l ayer of anodized aluminum 160-V negative of a laboratory plasma that c an 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-ge nerated plasma. The implication for large spacecraft in low Earth orbi t, such as Space Station Freedom (SSF) which can store large amounts o f charge, is that ares with the same amount of energy similar to those observed in the laboratory may occur. The energy in these arcs degrad e the surface of the anodized aluminum thermal control coatings by pro ducing large pits in the surface. These pits tend to increase the temp erature of the spacecraft, and the material from the pits can become a n additional source of contamination. The rise time and intensity of t heses arc could produce significant EMI. To prevent the occurrence of these undesirable effects, SSF will utilize a plasma contactor that wi ll control the structure to ambient plasma potentials.