Three-dimensional calculations of charge neutralization by neutral gas release

Summary form only given. There have been numerous observations of high rocket or spacecraft potentials, both positive and negative, and both naturally and artificially induced, being neutralized during thruster firings. Two current studies, CHARGE-2B (positive polarity) and SPEAR-3 (negative polarity), attempt a more systematic exploration of this phenomenon. Calculations performed in support of the SPEAR-3 program are discussed. Conventional phenomenology of breakdown is applied to the 3-D system formed by the electrostatic potential and plume density fields. Using real cross-sections, the paths along which the nozzle plume can support breakdown have been calculated. This leads to a recommendation that the higher flow rate on SPEAR-3 be 2 g/s of argon, equal to the CHARGE-2B flow rate. In a laboratory chamber, conditions favor breakdown of the positive (electron-collecting) sheath for SPEAR-3 geometry.