Inception and Prevention of Sustained Discharges on Solar Arrays

Sustained arc between adjacent cells is certainly a catastrophic event that results in significant loss in the power delivered to spacecraft systems. In order to prevent this kind of discharges, the threshold magnitudes of voltage and current should be determined in ground tests and compared with respective operational parameters. It is necessary to demonstrate that the results of ground tests depend on solar array designs but do not depend on the simulated environment and the electrical circuitry arrangement. A thorough analysis of about 20 tests performed in different laboratories has been conducted in this work. Sustained arc current thresholds were established for a variety of solar array designs and confronted with well-known magnitudes for vacuum arcs. If both voltage and string current magnitudes exceed the threshold values, the gaps between adjacent strings can be filled in with insulating material (RTV). Comprehensive ground tests demonstrated a high efficiency of this method. However, the lifetime of modern spacecraft spans for 10-15 years, and aging of RTV due to space radiation and temperature variations may cause critical changes in insulator properties. Thus, it seems reasonable to prepare a sample with RTV-grouted gaps, to undergo it proton fluence and thermal cycling equivalent to a few years in the geosynchronous orbit, and to test the sample against sustained arc inception. This program was also realized in the test described in this paper.