Venus has recently become a serious consideration for a potential manned mission – since it’s the closest planet, the journey would take less time, and there are more orbital windows of opportunity to go there. It has 81.5 per cent of Earth’s mass – versus 10.7 per cent for Mars – and its atmosphere would provide as much protection against radiation as Earth’s. But that atmosphere is also the reason no one has thought about going to Venus in a long time.