In article ,
Richard Riley wrote:

There's more energy available in a pound of liquid hydrogen than in a
pound of any conventional hydrocarbon like jet fuel. The LE (Long
Endurance) part of HALE is the basic design goal.

A pound of LH2 has about 2.6 times as much energy as a pound of
gasoline.

The temperature at 65k isn't significantly different from 50k - jet
fuel would work fine.


But when you weigh in with the tanking required to keep the stuff, the
net system energy (fuel + tank) gets out of hand. Hydrocarbons are
orders of magnitude more dense than LH2 and do not require special
containers or special purging of fuel lines to get rid of air, nitrogen
and water. LH2 will freeze all of the above and reacts violently with
FROX (frozen oxygen).

Hydrogen leaks burn clear and hot, too!

To purge LH2 lines, you first flush with dry nitrogen, followed by a
helium flush, to get rid of the nitrogen, then gaseous H2.

It not an inexpensive process, and widespread use would severely impact
the world supply of helium.