LOW-EARTH-ORBIT DURABILITY OF PROTECTED SILICONE FOR REFRACTIVE PHOTOVOLTAIC CONCENTRATOR ARRAYS

Photovoltaic power systems with novel refractive silicone solar concen trators are being developed for use in low Earth orbit (LEG). Because of the vulnerability of silicones to atomic oxygen and ultraviolet rad iation, these lenses are coated with a multilayer metal oxide protecti ve coating, The objective of this work was to evaluate the effects of atomic oxygen and thermal exposures on multilayer coated silicone. Sam ples were exposed to high-influence ground-laboratory and low-fluence in-space atomic oxygen. Ground testing resulted in decreases in both t otal and specular transmittance, while in-space exposure resulted in o nly small decreases in specular transmittance, A contamination film, a ttributed to exposed silicone at coating crack sites, was found to cau se transmittance decreases during ground testing. Propagation of coati ng cracks was found to be the result of sample heating during exposure . The potential for silicone exposure, with the resulting degradation of optical properties from silicone contamination, indicates that this multilayer coated silicone is not durable for LEO space applications where thermal exposures will cause coating crack development and propa gation.