A Novel Coverglass System with Enhanced Radiation Resistance

The service life of coverglasses used to protect photovoltaic cells on spacecraft is limited by darkening caused by ionizing irradiation. This decline in transmissivity significantly reduces solar-cell power output toward the system's end of life (EOL), which ranges from 15 years for satellites in geosynchronous orbit (relatively low radiation doses), to 10 years for those in low Earth orbit (moderate radiation). Coverglasses with improved radiation resistance are required to reduce or eliminate darkening at EOL for satellites in intermediate orbits that are subject to high levels of irradiation. Cerium, commonly used to impart radiation hardening to glasses, functions by absorbing protons and electrons by redox type reactions. Its effect is limited by practical constraints on the maximum doping concentration, as well as by constraints imposed by redox equilibria. A program to determine the feasibility of using alternative glass types in a novel coverglass system with enhanced radiation hardening properties is proposed here. The glass will accommodate increased amounts of radiation absorbing dopants that provide concurrent oxidation and reduction pathways. Further, the new glasses can be engineered to broaden band gaps and so further enhance performance of modern, high-efficiency III-V solar cells. (P040286)