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My space colonies are mainly located onto large, partialy terraformed moons in our solar system. They still travel using rockets but due to their vessels' large size they need very powerful propulsion system. Their fuel is metastable Helium. For this reason I need a way to store it for long period of time. Helium gas is monoatomic so it has a tendency to leak, plus my colonist would need extremely large tanks; cryogenic liquid storage is expensive and dangerous. I know Helium forms compounds despite it being a noble gas. Which of those (or hypothetical others) are stable liquid/solid in "non extreme" conditions for long storage onto the moons?

By non extreme I mean close to 1 atm and 20 °C, or the closest possible.

Thanks

EDIT: The stored Helium doesn't necesarily need to be in the metastable state.

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  • $\begingroup$ Welcome to the site, good question. $\endgroup$ – James Apr 18 '16 at 18:41
  • $\begingroup$ Why do you need to store Helium? Its the second most abundant nuclei in the verse. $\endgroup$ – Aron Apr 19 '16 at 8:04
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That may be one of the most unstable things I have ever heard of...

It is a combination of:

  • "Metastable Helium", a substance some times used in hard sci-fi as a rocket fuel. No ways are found of keeping the state stable. The extremely high energy content is what makes it suitable as a propellant. (This energy state of the helium atom exist in reality too.)
  • Helium compounds: "What is that?" Yes, some compounds can exist under insanely high pressures, exploding at even the gentlest disturbance.

You have now combined the properties of those two concepts. (Note to self, keep a huge distance to SilverCookie's ships.)

What I suggest instead:

Space is big. You have all the volume you need. At a reasonably scaled ship size, a giant balloon filled with helium is adequate storage. (When not doing things like combat or reentry.)

Upside: Works, cheap, does not spontaneously destroy your ship.
Downside: Makes your ship look like a giant ugly bladder, and definitely not cool.

Response to EDIT: As the clarification now states that the stored helium does not have to be in the metastable state, it makes things less impossible easier. I still hold on to my big ugly balloon though, but the gas can be more dense inside it.

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  • $\begingroup$ Sorry I didn't mean for the stored Helium to be in metastable state. The store helium is just helium. Also I know some helium compound can exist in very low pressure, though in minimal amounts. Will edit the question for clarity. Thanks $\endgroup$ – SilverCookies Apr 18 '16 at 19:02
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I don't think that storing Helium at 20° in space is the better idea you can have. Helium become liquid at about -269 °C, while space temperature is about -270 °C.

To store it at 20 °C you need to use a lot of energy and/or have a really good insulation in your tank.

A better idea can be to store the helium in liquid state since you just need to store it in a tank that is shadowed by some other structure, since vacuum is a good insulating.

The advantage is that, for a given volume, you can store a lot more helium and you are not using energy to store it.

The main disadvantage is that when you wnat to use the Helium, you need a LNG terminal, which can be tricky to run in space.

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  • $\begingroup$ Thanks for your input. My moons are partially terraformed, so conditions there are close to that of earth, and that's where I store my helium. I understand I should be more precise in my question, apologies. $\endgroup$ – SilverCookies Apr 18 '16 at 19:19
  • $\begingroup$ Oh well, this change everything... I then suppose you just need a structure that is air-tight and that it can sustain itself. A simple iron tank can store helium at a more higher pressure than 1 atm. A series of tank wagon can do the job in a very simple and cheap way $\endgroup$ – Gianluca Apr 18 '16 at 19:40

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