Presumably, the fuel consumption with an aircraft like this is pretty constant, except maybe when taking off?

It could be fuelled immediately before take-off, and as long as its fuel consumption when cruising was higher than the natural boil-off rate, there wouldn't *be* much of a problem.

It's not like having a hydrogen-powered car, where having the fuel boil off in under a week would rather be a drawback, if not a bit of a safety issue.

It does seem obvious that, between the low temperature and pressure and the aircraft's fuel consumption, boil-off shouldn't be a problem, since hydrogen gas will rise to the top of the tank where you would be drawing hydrogen from the in the first place, using the hottest material first since it's easiest to burn.

Boys and their toys!