It's plausible, but cryogenic fuels are currently only used on takeoff. This is because there's no way to keep your fuel cold; that plume of vapour you see from the top of rockets on the launch pad? That's fuel being vented because as the temperature slowly rises and the fuel boils. Once you reach orbit you typically switch to a different fuel, which will keep. Deep-space vehicles tend to use hydrazine. Voyager 1 still has hydrazine in its tanks which is 38 years old and it still works fine.

If you're capable of keeping cryogenic fuels cold in, say, the rings of Jupiter where such a shield would be useful, then you've probably got power to burn and don't need to resort to that sort of hack.

Hydrogen as well as methane and propane etc were looked at for Constellation's lunar module Altair some years ago. You save a lot of weight since it's much more efficient than hydrazine.

At least for the lunar descent you could use hydrogen, that's the most mass anyway and you don't need to worry about heat management at the surface anymore.

https://en.wikipedia.org/wiki/Constellation_program#Altair

Lockheed Martin has been working on lots of technologies for long term flights with Centaur stages. You could have onboard refrigerators etc.. It's not so strange nowadays as it was in the sixties.

A long-range spacecraft would probably not have LH2 on board. It evaporates quite quickly unless you want to install cryo cooling systems and the power to run them.

Boil-off is a bigger problem with LH2 than with liquid oxygen or liquid methane. However, I'm under the impression that it's a tractable problem out to months or maybe even years. Apparently the Spitzer Space Telescope maintained a supply of liquid helium for about five years [1][2].

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...

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.

That reminds me of the Arthur C Clarke story 2010, where he says they used ammonia instead to avoid the boil off.