James Cobban Space Nerd since 1956.

Why is liquid hydrogen so challenging to handle when fueling rockets, and what special techniques are used to prevent leaks?

The most effective way to avoid the challenges of using liquid hydrogen is to not use liquid hydrogen. There is no galactic police officer holding a phaser forcing NASA to use liquid hydrogen. There is no law of physics which says rockets must use liquid hydrogen. What.there are is a bunch of collosally ignorant politicians being bribed to insist that NASA piss away billions of tax dollars on technology which killed fourteen American heroes.

One small example of this idiocy: each RS-25 hydrogen rocket engine costs NASA $145M. There are four on the SLS, so that alone is $580M of the cost of an SLS. And they are dumped in the ocean on every launch. The Blue Origin liquid methane engine costs less than $40M and has more thrust. The SpaceX Raptor 3 has about 25% higher thrust and weighs less than half as much as the RS-25, and costs Elon less than $1M each. Fuel for a rocket is merely a source of energy. The cost for a given number of Joules, or Kilowatt-Hours, or BTUs in the form of liquid methane (aka Natural Gas) is.1/60th of the cost of the same amount of energy in liquid hydrogen. So you drive up the rocket service station and the pump gives you a choice. You can buy $20 worth of methane or $1200 worth of hydrogen. Which one do you choose? If you choose $20 why do you keep reelecting the thieves who insist on spending $1200?

An old joke: Doctor, it hurts when I do this. Then don’t do that!