Measurement of Degradation Properties of Dielectric Materials Used on Spacecraft Power Systems

Abstract

This paper reports the results of tests and measurements made on Kapton type H films of varying thicknesses. The quantities measured are capacitance, dissipation factor, surface resistivity and volume resistivity. The test variables are voltage, temperature, frequency and pressure. The electrical insulating materials suffer degradation primarily due to the interaction of high energy protons, electrons and space plasma. Furthermore, the degradation is brought about by the thermal cycling due to the extreme temperatures to which the spacecraft is subjected when the spacecraft is facing the sun or eclipsed from the sun. The properties of the insulating materials targeted for measurement are Volume Resistivity, Surface Resistivity, Capacitance and Dissipation factor. The volume resistivity is used to indicate, indirectly, the uniformity of an insulating; material either with regard to processing or to detect conductive impurities which affect the quality of the insulating material. It is often used as an indirect measure of moisture content, mechanical continuity and deterioration of various types. The surface resistivity is used to indicate the level of the contamination that happens to be on the surface of the sample at any time. It is often used as a measure of moisture absorption and contaminant deposition on the surface (1) and deterioration, which affect the materials insulating properties. The capacitance is used to indicate the property of a dielectric which permits the storage of electrically separated charges when potential difference exists between the dielectric surfaces. The change in capacitance or dielectric constant indicates the changes in the bulk molecular properties of the material. The dissipation factor is used to indicate the A. C. power loss. The change in dissipation factor is a measure of the stability of the insulating properties, where as the value of the dissipation factor is a measure of the quality of the insulating properties under specified service conditions.