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I am wondering if a canister of pressurized oxygen could be used as a fuel source for an ion thruster.

To show how this could work on a conceptual basis, please reference the following drawing:

enter image description here

I believe if this would work, it would be a more cost effective way of generating thrust since it would not require the hardware to generate magnetic fields nor the use of an electron gun, both of which are needed for a standard ion thruster.

Could pressurized oxygen be used as a fuel source for an ion thruster?

EDIT

I realize now that neutral oxygen atoms would not work. It would have to be a pressurized canister of ionized oxygen with a negative charge, or if ionized oxygen with a positive charge is used, then the electric field grids' polarity would have to be reversed. I have learned that there are machines that produce either ionized oxygen with a negative charge or with a positive charge, yet whether it can be pressurized within a canister, that I do not know. Reference: http://www.drkaslow.com/html/inhaled_ionized_oxygen_iiot.html

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    $\begingroup$ Without anything to ionize the oxygen, how does the O2 molecule become oxygen ions? No. With the drawing shown this won't work. $\endgroup$
    – uhoh
    Sep 5, 2020 at 13:34
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    $\begingroup$ And if it was ionized, it would be really hard not to run a very engine-rich mix. Ionized oxygen is ludicrously reactive. $\endgroup$
    – SF.
    Sep 5, 2020 at 15:04
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    $\begingroup$ I’m voting to close this question because the concept is impossible to realize. The reason can be explained in Physics SE or Chemistry SE, but this is off-topic here in Space Exploration SE. $\endgroup$
    – uhoh
    Sep 5, 2020 at 22:21
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    $\begingroup$ oxygen ions are much lighter than xenon or krypton ions, not heavier, but either way you have to ionize them in a plasma using some combination of electrical discharges, radio frequency excitation and heavy magnets. $\endgroup$
    – uhoh
    Sep 5, 2020 at 22:23
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    $\begingroup$ @uhoh, that's for pointing that out about oxygen ions, I had thought the oxygen ion was the heaviest. $\endgroup$
    – user35148
    Sep 5, 2020 at 22:25

1 Answer 1

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No, that's impossible.

You can't compress an ionized gas and put it into a cylinder like that.

All familiar ordinary matter, including gases, is not ionized, or else only slightly ionized.

If you try to squish a large amount of ionized oxygen atoms together to reach a dense gas, let alone a super-compressed one, the following will happen:

  • The oxygen will be strongly repelled from itself, and try to escape containment any way it can.

  • It will require massive amounts of energy to overcome the forces pushing the ions apart -- the force will be far more than any physical pressure vessel can contain.

  • The intense electrostatic field will try to strip any nearby electrons (such as those making up the atoms that make up the spacecraft) to neutralize the intense positive electrical charge of all those oxygen ions -- and this will probably happen with explosive force.

  • All that change will attract any random ions or electrons in the space environment, basically putting the spacecraft in the middle of its own particle accelerator.

For a humorous look at the consequences of doing this kind of thing on a rather larger scale, take a look at this XKCD whatif: the universe is destroyed.

If you actually could make a quasi-magical force field to compress charges down like that, you'd have a wonderful power storage mechanism -- and rocket engine -- without even needing the charged plates of the ion engines. (make sure to bring some compressed electrons as well, to balance things out.)

(Note: insulating the cylinder makes little difference - this level of charge will have enough voltage to just burn through nearly any conceivable insulation.)

Real ion engines either ionize a tiny whiff of diffuse gas in the vacuum of space (such as gridded ion thrusters), or make a neutral plasma where electrons are stripped from the atoms but it all evens out to just being "hot, electrically conductive, magnetically-responsive gas" (such as VASIMR thrusters).

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  • $\begingroup$ "to neutralize the intense positive electrical charge of all those oxygen ions" - normally oxygen ionizes to $O^-$. Can one even make $O^+$? $\endgroup$
    – SF.
    Sep 8, 2020 at 8:39
  • $\begingroup$ I think the answer depends on "chemistry or physics". $\endgroup$
    – ikrase
    Sep 8, 2020 at 10:24
  • $\begingroup$ @ikrase, I have been thinking about your answer and if there could be any solutions to the issues you've brought up. One thought is that both the inner lining and the outside surface of the canister could be coated in rubber (5mm thickness) to stop any flow of electrons trying to enter the canister. Another thought is to reverse the polarity on the grids in order to keep the ions from escaping the canister, then reverse the polarity again to allow the ions to escape the canister and to then be accelerated by the grids like a standard ion thruster. $\endgroup$
    – user35148
    Sep 8, 2020 at 13:03
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    $\begingroup$ That is like trying to contain a thermonuclear explosion in an oil drum. The energy levels are just way too high for what you're considering. Common high-voltage electricity, which is nothing like this monster you're proposing, will blow through 5mm, or 50mm, of rubber like it isn't there. This question is solidly in "magical forcefield" territory. $\endgroup$
    – ikrase
    Sep 8, 2020 at 20:14
  • $\begingroup$ @SF. It is certainly physically possible to ionize oxygen atom to $\text{O}^+$; such ions definitely exist in oxygen plasma. I am not sure of a chemical way of achieving $\text{O}^+$, but an ionic compound dioxygenyl hexafluoroplatinate, which contains a rare dioxygenyl cation $\text{O}_{2}^{+}$, exists. BTW, normally oxygen does not ionize to $\text{O}^{-}$ but to $\text{O}^{2-}$ instead. In oxygen difluoride oxygen technically has a $+2$ oxidation state, but {continues} $\endgroup$
    – user47149
    Jun 7, 2022 at 0:44

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