| Summary: | Experiments in charge control were conducted on the P78-2 (SCATHA) satellite as part of a program on spacecraft charging at high altitudes. Experiments with the SCATHA ion gun were monitored by charged particle detectors and the electric field experiment. It was found that the electric field experiment could be used to measure satellite potential during ion beam emission in sunlight and eclipse. Unneutralized ion beam emission in high energy (1-2 KeV) and high current (1-2 mA) modes resulted in the satellite momentarily charging to a negative potential near the magnitude of the beam voltage and then rising to some less negative value, typically -500 to -800 v. The net emitted current was apparently limited by the formation of a virtual anode. Low current (20-30 microamp), high voltage (1 kV) resulted in -10 to -50 V satellite potentials. Trickle mode (20-80 microamp, no accel voltage) operations resulted in satellite potentials near zero volts. In sunlight the spacecraft potential exhibited a spin modulation, attributed to variations in the neutralization of the beam as it passed through the photoelectron cloud. Rapid fluctuations of the spacecraft potential occured which may be explained qualitatively by space charge instabilities. Theses. (JHD)
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