Internal Charging of Indium Oxide Coated Mirrors

Optical solar reflectors of rigid and flexible type have been coated with Indium Oxide, a transparent conductive coating, in an attempt to eliminate surface charging resulting from electron bombardment that a spacecraft in a geostationary orbit may suffer. The grounding of the conductive layer to the spacecraft structure has previously been considered sufficient to prevent differential charging and subsequent discharging. Earlier tests on mirror tiles with electrons of low flux levels gave no discharges. During the current investigation however discharges were observed for electron energies above 20 KeV and flux levels above 3nA/cm2. The current pulses recorded varied in height from 30mA to 320 mA.