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.