boil-off

Given the chance, liquid hydrogen will "boil-off" and escape as a gas - potentially becoming a hazard.

Likewise, while current MRI machines do use up to 1000 liters of helium in their cryostats, "they do not let it evaporate as they did a decade ago; they recycle it. Therefore there is no need to regularly fill these scanners," which are known as "'zero boil-off' magnets."

ULA will also get $2 million for technology to reduce cryogenic fuel boil-off and $1.9 million to demonstrate the midair retrieval of a vehicle coming back to our planet from orbital velocity.

This is a zone where there can be sufficient solar heating to cause the ‘boil-off’, or sublimation, of solid ice into the vacuum of space.

The current data seem to suggest that this boil-off, like that of a cometary nucleus, is the more likely culprit for Ceres’s watery outbursts – coinciding with its closest approaches to the Sun.