Posted on 02/15/2026 5:12:06 AM PST by TomEd
James Cobban Space Nerd since 19569h
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!
Liquid Hydrogen had nothing to do with the shuttle explosions. I am not sure what he means by touting the deaths of those astronauts.
When you are dealing with the smallest atoms in existence they are going to leak through EVERYTHING. We see things as “solid.” When you are an H atom, nothing is solid…there are spaces between everything.
NASA is reusing old technology since they seem unable to develop anything new. Liquid hydrogen has been used for a very long time because not only does it provide high thrust, but high specific impulse as well. And it’s clean burning. The problem is that it’s expensive, difficult to store, and prone to leak. SpaceX has wisely chosen to move away from it in favor of methane.
You’re two paragraphs contradict each other. Which is it?
“If you choose $20 why do you keep reelecting the thieves who insist on spending $1200?”
Like every other gummit kickback scam that put us $40,000,000,000,000 in debt and near collapse. Never forget that it is the uniparty in Congress that is ultimately responsible.
The external fuel tank, rather than the fuel it contained, was the weak link in the system. It was parked right next to the SRBs with their unreliable O-rings, and was cold enough to shed chunks of ice onto the fragile shuttle.
related, sort of:
Molecular solar thermal energy storage in Dewar pyrimidone beyond 1.6 MJ/kg
https://www.science.org/doi/10.1126/science.aec6413
The best feature (which is also the biggest problem) is that liquid hydrogen is light!
So rocket fueled by hydrogen do not weight as much as methane!
Which is good for rockets!
Why? Because the smallest molecule.
But then these mall molecules leak. The biggest hydrogen problem.
Plus hydrogen is expensive! It does not exists in pure form on the Earth and needs to be manufactured, using a lots of energy.
I can understand using hydrogen in space, but using it as a car fuel is the ultimate folly!
What does Hydrogen have anything to do with the loss of the Shuttles?? Weird.
Feynman made O-rings famous after his testimony before the investigative board, but if you read the final report it’s interesting to me they also noted the deletion of asbestos containing putty, used to seal off hot gases from the O-Rings. The “green” replacement putty never did work right, which should hardly be surprising. They did eventually change the joint configuration altogether obviating the problem. I guess.
Costs were not high on NASA’s list of concerns.
I don’t see that his paragraphs contradict each other. Hydrogen atoms are small enough to squeeze between pretty much anything.
I’ve read many places the reasons why Columbia was lost on re-ebtry. In early launches the tank was uninsulated meaning more fuel was lost to evaporation. The greenies then got involved and insisted the tank be insulated. So be it, foam was applied to external surfaces. A chunk of foam fell off during launch and struck the shuttle wing’s leading edge damaging it. Upon reentry the damaged edge allowed hot gases to enter the wing causing structural failures and the loss of the shuttle. It had nothing to do with hydrogen.
That is incorrect on several counts.
1) The external fuel tank was always insulated with foam.
2) During the first two (or three?) flights, white paint was applied over the orange/brown foam to reflect sunlight.
3) The paint weighed several hundred pounds, was determined to be unnecessary, and was deleted.
4) "Greenies" objected to the original foam, which used a freon to expand. The foam was changed to a different chemistry, but did not adhere quite as well as the original.
Understand. Just a comment about NASA. They may have used H2 to lower its carbon footprint to offset the perchlorate and rubber in the boosters. </s> The tile placement was quite complicated and statistically it’s not surprising some failed.
He knows his numbers but evidently not his chemistry. Liquid hydrogen and oxygen gives the needed specific thrust.
The molecules are too small to prevent leakage. That’s why methane is used.
1) Hydrogen + Oxygen
Reaction:
2 H2 + O2 -> 2 H2O
Energy released:
~286 kJ per mole of H2 (higher heating value, water liquid)
~242 kJ per mole of H2 (lower heating value, water vapor)
Energy per kilogram of hydrogen:
~120 MJ/kg (LHV)
~142 MJ/kg (HHV)
Key point:
Hydrogen has extremely high energy per unit mass, but very low density, so it has low energy per unit volume.
2) Methane + Oxygen
Reaction:
CH4 + 2 O2 -> CO2 + 2 H2O
Energy released:
~890 kJ per mole of methane (HHV)
~802 kJ per mole (LHV)
Energy per kilogram of methane:
~50–55 MJ/kg
Key point:
Methane has lower energy per kg than hydrogen, but much higher density, so better energy per unit volume.
Rocket-Relevant Comparison (Including Liquid Oxygen)
For rockets, you must include the oxidizer mass.
Hydrogen/Oxygen (hydrolox):
Highest specific impulse of chemical rockets (~450 s in vacuum)
Very high exhaust velocity
Requires very large tanks due to low density
Used in vehicles like NASA’s Space Shuttle main engines
Methane/Oxygen (methalox):
Specific impulse ~360–380 s in vacuum
Much denser propellant combination
Smaller tanks
Easier storage than hydrogen
Used in vehicles like SpaceX Starship
Energy Per kg of Combined Propellant (Fuel + Oxygen)
Hydrogen/Oxygen mixture ratio ~6:1 (O2:H2 by mass)
For 1 kg H2:
Requires ~8 kg O2
Total propellant mass = 9 kg
Total energy ≈ 120 MJ (LHV basis)
Energy per kg of propellant:
~13 MJ/kg
Methane/Oxygen mixture ratio ~3.5–4:1 (O2:CH4 by mass)
For 1 kg CH4:
Requires ~4 kg O2
Total propellant mass = 5 kg
Total energy ≈ 50 MJ
Energy per kg of propellant:
~10 MJ/kg
Bottom Line
Hydrogen has much higher energy per kg of fuel.
Methane is denser and easier to store.
Hydrogen gives maximum performance.
Methane offers better tankage efficiency and practicality.
When oxidizer mass is included, hydrogen’s advantage shrinks significantly. ChatGPT gets the research credit.
Yeah, talking about deaths in a discussion about H is misleading and conflation — a typical commie trash trick that he should be ashamed of.
As you say, H is horrid in that it penetrates everything. What is worse is that when you find something it can’t leak thru (there are metals) it gets part way in and then embrittles the material.
OTOHand, it is ubiquitous. Just crack some water and you have fuel. Solve the storage problem and you don’t need many power distribution infrastructures. E.g., set up a solar panel for the leccy to split some water out of your house’s hose tap — voila, fuel for your car.
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