Re:A superconducting shield for astronauts
by jccooper on Friday August 07, 2015 @01:56AM
(#10021095)
Mars Direct uses suspiciously low boil-off rates for LH2. Certainly well past current state of the art. Best achievable (not flown, but could be) is 0.1%/day, and Mars Direct wants 0.1%/month. You don't lose a lot at 0.1%/day, but it adds up.
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.
A lot of Mars manned-mission proposals (starting with Zubrin's Mars Direct plan) depend on the use of a Sabatier reaction which would convert hydrogen brought from Earth into Methane and Oxygen. So the experts must think they can at least minimize boil-off over at least 8 or 9 months. [3]
[1] https://en.wikipedia.org/wiki/Spitzer_Space_Telescope
[2] http://www.spitzer.caltech.edu/news/436-ssc2009-12-NASA-s-Sp...
[3] https://en.wikipedia.org/wiki/In-situ_resource_utilization#M...