wheelontour t1_je105fr wrote
Reply to comment by Sagybagy in The Swiss hypersonic hydrogen jet aiming to fly between Europe and Australia in 4 hours by mancinedinburgh
hydrogen contains a lot of energy per kg but its density is extremely low, so you need a huuuge and heavy high pressure container to hold it. That mostly negates all its advantages, at least for the aeronautics industry and the contemporary space industry.
It would be a different story for spaceflight if one had the capability to fuel up a hydrogen rocket in orbit. In that case one could (mostly) take full advantage of all the benefits of hydrogen over other propellants.
D_Ethan_Bones t1_je1wpg0 wrote
In spaceflight there's a conflict between delta-V and thrust to weight ratio - solid rocket boosters give a lot of thrust or 'muscle' so they are used for getting things off the ground while the lighter fuels would be in a later smaller stage that thrusts to get you in transit from Earth to Mars.
Refueling could be a thing, but without space manufacturing it won't be much of a useful thing. The staged design we use will get you to the moon and back because blasting off from the moon isn't nearly as hard as blasting off from Earth.
Getting to Mars and back could hypothetically be done by parking a huge orbital fuel tank around Mars, but getting it there would be an unprecedented achievement. Payload is expensive and it takes a lot of heavy fuel to provide enough thrust for an earth->mars or mars->earth transit. If you want a human crew and a ship capable of holding them then the fuel tank is going to be ridiculous, and the heaviest stage to get it off earth's surface would be terrifying.
Shot-Job-8841 t1_je2i86v wrote
It does make sense if battery costs don’t drop as much as we hope. Really, I view Hydrogen Fuel Cells as the backup to if battery tech doesn’t have a major breakthrough.
Xeroque_Holmes t1_je4gazv wrote
Plus there's a lot of inefficiency in generating, transporting and storing hydrogen.
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