Current and Voltage Thresholds for Sustained Arcs in Power Systems

In the late 1990s, satellites began to suffer multiple solar cell string failures, prematurely ending the satellite mission due to insufficient power. The root cause was determined to be sustained vacuum arcs triggered by electrostatic discharge, which in turn was caused by solar array charging in the ambient environment. The satellite industry reacted to the failures by adopting laboratory charging tests of solar array coupons as part of design qualification. Gradually over the decade since, researchers in industry, academia, and national laboratories have roughly delineated the current and voltage levels that put solar arrays at risk for sustained arcing. That decade of test results has reconfirmed what was previously established by the power industry research on vacuum arcs in the 1950s to 1980s: that sustained vacuum arcs are not possible at typical array string currents. However, conditions for sustained arcing exist in the solar array harness beyond the cathodes of the string blocking diodes where string currents are combined and routed to the main spacecraft power bus. Qualification tests should therefore focus on the array backside and harness, where the current levels are sufficient, and should include current sources representative of the main spacecraft power bus.