I’m a bit perplexed by the European Space Agency’s Mars500 mission, which just welcomed back its six “brave” volunteers, who spent 17 months in physical isolation — with a slight delay in electronic communications, to represent the lag when sending messages while en route to Mars.
Nuclear submarines routinely go out for three months at at time, and sometimes stay out twice as long. Antarctic bases don’t go anywhere, of course, but most members of their “crews” stay for a whole summer, while some stay as long as two winters and three summers — much longer than 500 days.
So we have plenty of experience with fairly small crews spending months and months away from home and the larger society, at normal gravity, without dangerous cosmic radiation.