Internal EMU Resistance Impact on Suit Arcing During EVA

A significant electrical potential exists between the pressurized elements of the American segment of the International Space Station (ISS) and its surrounding ionosphere environment. At ISS complete this voltage will be as high as 50 Volts and under off nominal conditions as high as 80 Volts. Therefore, a crewman could be presented with a shock hazard during extra vehicular activity (EVA) if an electrical arc occurs on exposed anodized areas of the space suit. In particular, a concern exists that an arc on the neck ring, arm ring or other anodized metal parts on the suit surface could provide a current path through the crewman's body between various internal metallic contact points. A numerical model, developed for this study, helps to illuminate specific physical features such as the discharge current and equivalent resistance of the crewman during an EVA. These model results are compared with currents and voltages from an equivalent plasma chamber arcing experiment and it is concluded that for any resistance equivalent to a crewman's body, arc currents are biologically unacceptable to the ISS program.