Polar-Auroral Charging of the Space Shuttle and EVA (Extravehicular Activity) Astronaut

Abstract : The same conditions needed for spacecraft charging at geosynchronous orbit are also found at times in the low-altitude polar-auroral environment. The required conditions are high fluxes of energetic electrons, low plasma densities, and darkness. The energetic electrons are found in very bright active auroras. Plasma densities are occasionally low enough in polar regions but, more importantly, a large body such as the Shuttle sweeps out the ambient ionospheric plasma to produce a cavity in its wake. The POLAR charging code has been used with measured parameters for energetic auroral electrons and plasma densities to evaluate polar orbit charging. The Shuttle can be expected to charge at times to thousands of volts while the astronaut during EVA can charge to hundreds of volts. The multibody charging problem of the astronaut in the wake of the Shuttle, a more complicated problem, is being evaluated. Laboratory test results are presented that confirm charging and subsequent arc discharge of EVA equipment material samples. Induced current and radiated radio frequency EMI were measured from the arc discharges. Such EMI could cause potentially dangerous EVA equipment anomalies. Ground tests of subsystems and the complete EVA equipment system are needed.