The operation of high voltage equipments inside a satellite may trigger electric discharge if the pressure around them is above the threshold. In a thermal vacuum test, high voltage equipments are turned on after the vacuum gage outside a satellite indicates a safe level —below the threshold— to avoid electrical discharge. However, since a satellite has quite a few outgassing sources in it, along with the limited conductance, the internal pressure is higher than the external pressure. So there is a possibility that the internal pressure is still above the threshold even after the external pressure has gone below it. To find out if it is safe to judge when to turn on high voltage equipments solely from the gage outside a satellite, we measured the pressure of both inside and outside a satellite, by placing a vacuum gage in both places. Measurement results showed that the internal pressure remained above the threshold even after the external pressure had fallen below it. As a consequence, it is confirmed that in a thermal vacuum test the power supplying point is better to be judged upon the internal pressure for the case of a satellite with high voltage equipments.
