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Would it make sense to use solid (aka red) oxygen as oxidizer instead of liquid oxygen? (Red oxygen: An allotrope of solid oxygen (O8))

J. Doe
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    Oxygen is not fuel. It is oxidizer. – Organic Marble Oct 10 '17 at 12:07
  • I'm afraid the speculations about using it as oxidizer in rockets will fall apart precisely for the same reason why ozone $O_3$ is not used - it's gonna be a very unstable explosive. – SF. Oct 10 '17 at 12:25
  • I thought this first as well but is it unstable? – J. Doe Oct 10 '17 at 12:26
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    @J.Doe: At pressures exceeding 10GPa, amounts possible to produce make determining that impossible. We don't have any macroscopic amount production capabilities for these pressures. – SF. Oct 10 '17 at 12:36
  • still, 10GP are at room temperature which very hot for an outer space factory – J. Doe Oct 10 '17 at 12:39
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    Outer space factories have trouble keeping cool. Just look at how much radiator area the ISS needs to keep room temperature even just for life support. Lower temperatures need even more radiator area. Space isn't cold in the way you seem to think :P – Luaan Oct 10 '17 at 13:54
  • "Lower temperatures need even more radiator area." please explain - far away from the Sun, behind a gas giant it would pretty cold or? anyway even absolute zero does not help here with O8. – J. Doe Oct 10 '17 at 14:21
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    Keep in mind that at these pressures even things we think of as non oxidizing might tend to do so, which makes containment that much more tricky. – Adam Davis Oct 10 '17 at 14:22
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    @J.Doe Things cool down when the heat within them is distributed to nearby molecules. In space, there are very few nearby molecules - thus, it's difficult to get rid of waste heat (generated by electronics, or by production facilities). – Tin Wizard Oct 10 '17 at 17:50
  • It would be very difficult to pump and inject solid oxygen into the combustion chamber. But the necessary pressure for solid oxygen is several orders of magnitude to high for a tank of a rocket. The tank would be so heavy that the rocket would never leave the launch pad. – Uwe Oct 10 '17 at 18:38

1 Answers1

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No. The pressure required to use red oxygen are insane, 10 GPa at room temperature, and still quite high otherwise.

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In order to use a solid part as a fuel, there are a few options. You can either burn it in place, or convert it to a liquid to pump. Burning it in place would mean that you would have to maintain that extreme pressure with a system designed to allow gas to flow through, which is very difficult, to say the least. Converting it to a liquid would be very difficult to do in the short term that a rocket needs to launch.

The only use case in rockets that I can imagine would be to store oxygen for a longish duration mission, something like a lunar mission, where you could convert a small amount of the oxygen to a liquid.

It should be noted that there is some hope that it can be stable at lower pressures once created. To my knowledge, this has never been demonstrated, however, it could still happen.

PearsonArtPhoto
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  • I was wondering about solid fuels; bind that oxidizer within some fuel that can contain it... but I bet the sort of technology to manufacture that is currently sci-fi. – SF. Oct 10 '17 at 12:37
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    10GPa are at room temperature! – J. Doe Oct 10 '17 at 12:39
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    8 GPA at absolute 0. I added the phase diagram. – PearsonArtPhoto Oct 10 '17 at 13:05
  • Wait! All this presumes that $\mathrm{O}8$ needs _sustained pressures above 10 GPa. But since it's actually a completely different allotrope, it would seem highly plausible that, once formed, it's actually stable at way easier-maintainable pressures, at least when the temperature is sufficiently low. (A static phase diagram can't express this kind of metastability.) Do you have any references that this wouldn't work? – leftaroundabout Oct 10 '17 at 15:56
  • There's no evidence to suggest it is stable at normal pressures. If there was such a method, then it could be a good oxidizer for use in fuel, but I haven't been able to find a single reference to someone actually having stable ε oxygen at "normal" pressures. – PearsonArtPhoto Oct 10 '17 at 16:17
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    Well, I suppose even if it is stable, the trouble of making it are too much for any large-scale use. If you need to produce it milligram by milligram, in a diamond anvil cell, you're not going to space today... – leftaroundabout Oct 10 '17 at 18:45