The neighbourhood of Jupiter is also a high-radiation environment. Special types of cover glass are effective at reducing the steady and cumulative degradation of cell performance over the lifetimes of long missions. The susceptibility of standard silicon solar cells to radiation damage was recognised in the early years of space exploration and much effort has been put into design improvement to mitigate the effects and raise cell conversion efficiencies, presently approaching 20%. Although high-efficiency silicon cell are in widespread use, a major advance in recent years has been the development of multi-junction III-V cells based on gallium arsenide and related compounds,