HIGH-VOLTAGE INTERACTIONS IN PLASMA WAKES - RESULTS FROM THE CHARGINGHAZARDS AND WAKE STUDIES (CHAWS) FLIGHT EXPERIMENTS

Data from the charging hazards and wake studies (CHAWS) flight experim ents on board space shuttle missions STS-60 and STS-69, during which a negatively biased, high-voltage (0-5 kV) probe was placed in a plasma wake in low Earth orbit, are presented. For these experiments the sou rce of the wake was the 4-m-diameter Wake Shield Facility (WSF), which was operated both as a free-flying spacecraft and attached to the shu ttle orbiter's robot arm. Current collection by the biased probe is in vestigated as a function of the density and temperature of the ambient plasma and the probe's location in the plasma wake. Current collectio n behavior is determined by the expansion of the high-voltage sheath i nto the ambient plasma stream. Consistent with preflight predictions, current collection on the probe is highly nonuniform, varying by more than 5 orders of magnitude across the surface of the probe. The onset of current collection, however, begins at voltages that are an order o f magnitude lower than anticipated. This is likely due to the low-ener gy, turbulent plasma (typically 2-5% of the ambient density and up to 40% on occasion) observed in the ambient environment. This important m inority constituent of the plasma was observed in the vicinity of the shuttle Orbiter and observed while the WSF was free-flying.