6th Rocky Mountain NASA Space Grant Consortium Symposium
Over the last decade, high-powered spacecraft have been designed that will operate at voltages greater than 100 V. At these voltages, the solar arrays can undergo both destructive arcing at negative biases, and plasma electron current collection at positive biases. Furthermore, above some critical positive bias voltage (~100 V), the electron current collected by the array interconnects increases dramatically through a phenomenon termed Asnapover@. During snapover, large portions of the solar array cover glass charge positively, and begin to draw electron current from the plasma as if it were a conducting surface. This leads to substantial power losses for the spacecraft. We describe the results of an experimental investigation aimed at examining the importance of conducting material, insulating material, size and shape of the conductor, sample history, biasing rate, plasma density, and condition of the dielectric surface (contamination and smoothness) to the onset potential and magnitude of the parasitic snapover current. Theoretical investigations and computer simulations have proposed that the fundamental physical process underlying snapover is secondary electron emission from the dielectric. Our attempts to confirm the importance of secondary electron emission in the mechanism responsible for snapover were not conclusive, but in general did not support previous simple interpretations of the SE model. In addition, we observed much larger current jumps at biases from 350 V to 1000 V attributed to gas discharges. Both surface roughening and surface coatings were found to substantially inhibit snapover and gas discharge.
Clint Thomson and JR Dennison, “Snapover: Anomalous Plasma Current Collection by Positively Biased Conductors when Surrounded by a Dielectric,” 6th Rocky Mountain NASA Space Grant Consortium Symposium, Salt Lake UT, May 2000.