I wasn't thinking anything this ambitious. We can keep people alive in the crushing depths of the oceans for weeks/months/years at a time; the real limits ther

I wasn't thinking anything this ambitious. We can keep people alive in the crushing depths of the oceans for weeks/months/years at a time; the real limits there seem to be economic. We could do the same thing for tens or hundreds of people on Mars if we really wanted to. Living indoors/underground most of the time, dependent upon certain things being supplied from Earth (but otherwise some kind of closed cycle or local production for anything bulky), etc.