At 0.1% per day, I get 30% boil-off in 1 year (0.999 ^ 365 ==> 0.694), which is expensive but probably still a net win. I don't think boil-off is a problem onc

At 0.1% per day, I get 30% boil-off in 1 year (0.999 ^ 365 ==> 0.694), which is expensive but probably still a net win. I don't think boil-off is a problem once you're on Mars because you can probably just use the hydrogen gas as feedstock into the Sabatier process. Which is not to say that Mars Direct isn't overly optimistic, possibly about many other things as well.