Determination of SPEAR-1 rocket body potential during high-voltage experiments

Abstract

The Space Power Experiment Aboard Rockets (SPEAR) 1 payload was launched on December 13, 1987. It had a primary objective of providing guidelines in designing high-voltage (HV) systems for use in Low-Earth Orbit (LEO). The experiment consisted of 24 HV bias operations using two 20 cm diameter spheres attached to the rocket by booms. The SPEAR-1 rocket charged to substantial negative potentials during the flight when the spheres were biased positive with respect to the rocket. This thesis uses the electrostatic analyzer ion data to determine the charging response of the rocket body. The peak potential was reached during a 45 kV sphere bias sequence resulting in a -17.4 kV rocket body potential at 361 km altitude. The rocket body potential varied between 7 and 38 percent of sphere potential. Geomagnetic orientation, vice altitude, had greater effect on rocket body potential. The flight data also indicated that neutral gas emissions from the rocket attitude control system (ACS) triggered transient discharge currents that effectively grounded the rocket body potential. ACS firings resulted in an order of magnitude change in the rocket body potential.