Measurement of threshold voltage during vacuum arc on satellite solar panel coupons in laboratory

Risk of arcing on external surfaces of satellites parked in geo-synchronous earth orbit due to the charged particles present in that environment should be minimized. Arcing on satellites´ solar panel is a crucial parameter for its proper functioning and life cycle. Considering the severe damaged caused by the arcs on the solar panel, a facility for simulating GEO environment and studying arc on its surface is developed in laboratory. Electron bombardment which results in secondary electron emission is responsible for differential charging of various materials on the solar panel´s surface. In laboratory a flood beam electron gun is used to produce electron shower of energy upto few KeV while the power generated by the solar panel coupon is simulated by an external power supply. All the satellite components are simulated according to the standards described in ISO 11221. The aim of the experiment is to find the threshold voltage. Threshold voltage is the voltage sustained by the solar panel coupon just before arc. An automatic arc detection and analysis system is developed for measuring arc current, arc voltage and arc image. A capacitive non-contact Trek probe carried by a two axis stage controller is used to measure surface potential on the solar panel coupon´s surface. It is observed through the experiments that the surface potential of the solar panel coupon increases continuously before the arc occurs. During the arc, complete coupon is discharged and surface potential fall to the bias voltage. As the occurrence of arc is unpredictable, coupon is scanned at regular intervals to measure surface potential. On the occurrence of arc, most recent scan helps to identify maximum surface potential. In one of the experiments, arc occurred while scanning the solar panel coupon and maximum potential was measured. Thus exact surface potential was obtained for the arc.