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Metallic hydrogen is probably the best possible chemical rocket fuel. It would make single-stage-take-off possible. The trouble is the stuff is extremely hard to contain, and requires exotic fuel tanks.

Can we contain metallic hydrogen entirely with magnetic fields rather than physical pressure?

In particular, could magnetic fields actually compress hydrogen in the first place or could they just contain it? I was thinking this might be an interesting way to have dropships that have to effectively charge up before launching back to orbit.

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  • $\begingroup$ Why would magnetic fields interact with hydrogen? $\endgroup$
    – AlexP
    Nov 14, 2022 at 0:48
  • $\begingroup$ The idea would be that metallic hydrogen is a metal and so can be influenced by electric and magnetic fields. But I suppose you're right that this would never work to synthesize the fuel in the first place. You'd have to just keep it contained in the first place and damn the safety issues. $\endgroup$
    – Adam Reynolds
    Nov 14, 2022 at 3:06
  • $\begingroup$ You might want to ask this over on the physics Stack Exchange. $\endgroup$
    – Salda007
    Nov 14, 2022 at 6:44

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It's been hypothesized that metallic Hydrogen would be a superconductor, so if you had some way to produce it, I suppose you might be able to then keep it contained in some sort of high-powered magnetic bottle, but I don't have the physics Ph.D needed to estimate how strong a magnetic field you might need.

I don't think that you could use the magnet to compress the hydrogen, though, since it'd be in its molecular H2 form until it was sufficiently compressed to transition to the metallic form.

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    $\begingroup$ The other things to remember is that trapping and squishing things with magnetic fields is hard. If it weren't, fusion wouldn't have taken nearly so long and produced so little power. Even if it were possible to have a metallic hydrogen confinement bottle, you might find that it still boils off and escapes over time. $\endgroup$
    – Starfish Prime
    Nov 14, 2022 at 18:19
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Feasibility of containing it or not, the real problem is upstream

metallic hydrogen is probably the best possible chemical rocket fuel one could make

it makes little sense to make it and then burn it, because the energy you'd get out would be (at best) the energy you'd have put into making it. It's like saying you synthesize coal and then burn it.

The only way for this to make sense is either:

  • you have somewhere where you can mine metallic hydrogen (as far as we know, it occurs naturally only in the core of gas giants like Jupiter)
  • you have an (almost) free energy source which produces it without your intervention (like it happened with the sun and the coal stored underground)
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    $\begingroup$ I think this answer takes too narrow a view. Converting energy into other forms of energy has utility even though it always incurs losses. Rocket fuel today is made & stored at a net loss. We can't launch rockets on raw sunlight (yet), so we convert other forms of energy at a loss. Feasibility of metallic hydrogen hinges on its economic viability, which OP hasn't specified. $\endgroup$
    – BMF
    Nov 14, 2022 at 4:34
  • $\begingroup$ As @BMF said. Are rechargeable batteries pointless because you get less energy out than you put in? No, because the object isn't to obtain more energy, it's to store energy for later use. $\endgroup$
    – Christopher James Huff
    Nov 14, 2022 at 5:26
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    $\begingroup$ "it makes little sense to make it and then burn it" - You do realize that's how every single rocket fuel in common use works? Cryogenic H2 needs to be cracked out of water or methane and super-chilled; kerosene needs refinement from crude oil, methane needs to be collected, purified, and super-chilled; UDMH and N2O4 need to be produced via assorted chemical pathways, etc... The whole point of a rocket is that you take a lot of energy that you can easily produce over a long period of time and put it into a form which you can get all that energy out of very, very quickly. $\endgroup$
    – Salda007
    Nov 14, 2022 at 6:17
  • $\begingroup$ @Salda007 et al, you are just rewording what I stated in the second bullet. $\endgroup$
    – L.Dutch ♦
    Nov 14, 2022 at 6:25
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    $\begingroup$ "it makes little sense to make it and then burn it" That's because you don't understand what the point of metallic hydrogen as a rocket fuel actually is. It is mentioned in that context because it has insanely high specific impulse value, far higher than any other known fuel. And specific impulse is a property that is extremely importat for a rocket fuel, as it determine the mass ratio of fuel to rocket that makes it still possible for reaching escape velosity. $\endgroup$
    – Negdo
    Nov 14, 2022 at 9:31

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