Space solar cell edge, interconnect, and coverglass designs and their effect on spacecraft charging and plasma interactions

One of the principal design drivers for space solar arrays is solar cell arcing into the plasma due to spacecraft charging. The amount of spacecraft charging and the resulting differential voltages on space solar cell edges and interconnects is related to the cell edge, interconnect and coverglass designs. For example, the International Space Station (ISS) did not charge up to expected levels because of its closely spaced solar cells, wrap-through interconnects, and coverglass overhangs, which serve to choke off electron collection and prevent the concomitant negative charging that would otherwise occur on its high voltage solar arrays. Secondly, the occurrence of sustained arcing on solar arrays is related to the cell spacing and coverglass overhang. In this case, closely spaced solar array strings with little coverglass overhang may allow primary electrostatic discharges (ESDs) to transition into arcs between strings, which may continue until the entire solar array power is shorted. Thirdly, even primary ESDs have been shown to produce damage to some high efficiency triple junction solar cells by producing contaminants that can provide a conductive path between cell junctions, acting as a partial shunt resistance. Recently, novel solar cell types have been invented with structures at the cell edge, including buried junctions and stepped cell edges that may prevent damage from ESDs and sustained arcs. It is important that these designs be evaluated by spacecraft charging and current collection models to determine their effect on electron current collection, spacecraft charging, and solar array arcing. In this paper, we model standard, ISS-type, and new cell designs to determine whether the new cells help ameliorate solar cell arcing and/or damage due to the arcs.