The SPEAR-1 experiment

As part of a program to provide new guidelines for the design of high voltage (HV) and high current systems in space the SPEAR-1 rocket payload was successfully flown on December 13, 1987. The payload exposed biased conducting spheres at potentials of 10's of kV to the ambient space environment at altitudes as high as 370 km (apogee) in the nighttime ionosphere. Previous large vacuum chamber tests of biasing from either a grounded payload, or a grounded mock-up, had produced volume discharges under both high vacuum and simulated ionosheric plasma conditions. Small chamber tests of the mock-up demonstrated the conditions for breakdown caused by sphere bias, magnetic field, chamber size, and secondary emissive properties of the chamber wall. In flight the failure to expose the payload's plasma contactor to the ionosphere caused a bipolar operation with interacting sheaths from both the payload body and the biased conducting spheres.