“Just the basic premise of a hydrogen fuel tank makes the extent of the challenge apparent. Packing the molecules together in liquid form and keeping them that way requires extremely low temperatures — at least minus 253 degrees Celsius. This in turn calls for a multilayer tank that needs, for long-distance flights, an active cooling system that basically works like a refrigerator by circulating cryogenic fluid such as helium gas through high and low pressures.
All these extra parts, of course, would add more weight to a design and reduce the amount of fuel that can be carried.
“Looking at tank mass, there’s been discussion of composite tanks versus metallic tanks,” says Wesley Johnson, a NASA engineer whose focus is on cryogenic technologies. In the past, NASA has used cryogenic tanks made from composites for various spacecraft, “but there’s different requirements on the airplane side that may drive how you design and develop those.” Hydrogen tanks for aviation must endure multiple uses, for example.”