Particle generation by silicone potting compound of returned Mir solar cells

A solar panel with more than ten years space exposure was returned to Earth in January 1998. Methy-phenyl silicone was used for both the adhesive between the coverglasses and silicon wafer, and for the potting compound between individual solar cells. Glass fiber scrim was used for structural integrity of the panel. Atomic oxygen in low-Earth-orbit interacted with the exposed silicone and converted the outermost layer (several microns thick) to oxidized silicon, i.e. SiOx, where x~2. This brittle SiOx served to protect underlying silicone from oxidation, unless the film was removed by some means. There is much evidence of microeruptions within the potting compound and spewing of silicone and SiOx film debris across the solar cell coverglasses. Ten of 409 solar cells of a returned panel have been scanned with a 50x brightfield microscope. This paper presents measurements of millimeter size SiOx particles and, glass fibers on the returned solar cell coverglasses. Erosion of the potting compound is also discussed.