Analysis of electron retarding potential analyzer measurements of vehicle skin potential in the PRECEDE experiment

A 2 kW electron accelerator was launched as the initial launch in the EXCEDE series of artificial auroral experiments. The launch, designated PRECEDE, was supported by a number of ground based optical systems to record the electron induced atmospheric emissions as a remote diagnostic technique of accelerator performance in addition to recording emissions of aeronomic interest in a controlled artificial aurora. The electron source, square wave modulated at 0.5 Hz, was initiated at 95 km on payload ascent and continued through apogee (120 km) to a descent altitude of approximately 80 km providing a total of 90 pulses of the 2.5kV 0.8 ampere electron beam over a period of 180 seconds. A rocketborne retarding potential analyzer provided a measure of the vehicle potential due to a net positive charge build up on the electron emitting payload. A steady-state vehicle potential of less than 30 volts was indicated at apogee with substantially smaller values at lower altitudes. Langmuir probe theory is shown to accurately model the altitude dependent steady-state vehicle potential.