How to design discharge-free equipment for space applications

With the increase of high voltage for space applications to 500 V or more, there is a need to design equipment in order to avoid the occurrence of electrical discharges. At very low pressures such as 1 mbar or less, the equipment works under conditions which are at the minimum of Paschen’s law. Hence conventional techniques, like field optimization, materials grading or insulation reinforcement, are not sufficient to be discharge-free. A disruptive approach is then needed. This paper proposes a novel methodology, in order to eliminate electric discharges in a closed volume at a very low pressure, like in space equipment. Firstly, based on Townsend theory, an analysis of discharges extinction is done in the case of a closed volume. The notion of “distance” in Paschen law is clarified, by considering the potential evolution along the curvilinear abscissa along electric field lines. It is then demonstrated that the conditions of discharge extinction can be reached whatever the low pressure and the voltage. Secondly, an analysis, based on a numerical tool, which combines an electrostatic solver to Paschen law, allows us to confirm this hypothesis. We demonstrate that the field lines’ highest length is the first order parameter on the discharges extinction pressure. Numerical results are compared to experiments in the case of two simplified mock-ups, for which the breakdown voltage is recorded, as a function of pressure, until no breakdown occurs anymore. An excellent agreement is obtained. This confirms that the physical phenomenon is well understood and controlled. Lastly, the developed methodology is transposed to equipment for space application. By skillfully controlling the way electric field lines are distributed in the closed volume, it is shown that, at the working conditions, no discharge higher than 5 pC is detected. Hence the equipment is intrinsically discharge-free, which guarantees its reliability and its dependability.