Method and apparatus for establishing a reference potential on satellites in planetary ionospheres

摘要

A simple, nearly passive apparatus is disclosed that allows a spacecraft sensor to be driven to a potential close to that of a plasma where the ion concentration exceeds about 100 cm-3 even in the presence of a large vehicle potential. The apparatus includes a conductive reference surface insulated from all spacecraft elements. The reference surface is situated on the spacecraft such that it faces in the direction of motion, and collects ions thereon. There is developed on the surface a plasma potential. The reference surface is connected to the inverting input of an operational amplifier that is powered by floating voltages referenced to the potential at the noninverting input of the amplifier. Since the operational amplifier has to maintain equal voltages at both inputs, the amplifier will drive against spacecraft ground until the voltage at the noninverting input is substantially equal to the voltage at the inverting input. The reference potential established at the noninverting input is therefore the same as the potential on the reference surface.