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Are there any ion thrusters which could conceivably provide thrust inside the atmosphere?

Not that they'd have enough thrust to take off under their own power, of course; I'm just wondering whether all ion thruster designs require a vacuum to operate, or if any could be theoretically designed to operate at ambient pressure. I know about electrohydrodynamic thrusters; thinking more about something which actually ejects a propellant stream of its own.

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  • $\begingroup$ thrusters which actually eject their own high-velocity propellant stream. Resulting pressure of that high velocity propellant stream should be above air pressure. And that means if pressure inside engine chamber is 10 times lower, than air pressure outside, high velocity should be, let say 10M, or 3 km/s. If inside pressure is 10Pa, it means 3000 km/s jet. So yes, they possible, but way beyond current state of art. $\endgroup$ – MolbOrg Feb 27 '16 at 19:18
  • $\begingroup$ @MolbOrg: Why keep the chamber pressure 10 times lower than ambient? Let the propellant be at >1 bar; sure that will be wasteful - much higher propellant flow than in space-faring engines - but that thing is not flying anywhere anyway, so mass is not really a concern, nor do we need to skimp on electricity as it will likely be powered off the grid anyway. $\endgroup$ – SF. Feb 27 '16 at 19:33
  • $\begingroup$ @SF.problem is how OP considers it to be. I find that your answer to op question covers it 100%. $\endgroup$ – MolbOrg Feb 27 '16 at 20:17
  • $\begingroup$ @SF Yes, indeed some one may use propellant at ambient pressure and will get the same as in that nice video, you have posted. Totally valid. I talked about pure plasma, actually keeping in mind thermonuclear engine, which not exists(yet), but may be possible.Be at ambient pressure in that case is hard, but not necessary. And it may work as OP wish. $\endgroup$ – MolbOrg Feb 27 '16 at 20:25
  • $\begingroup$ @Uwe has a good point, but I wonder, at 100km (Karman line) the drag will be low(er) and the mean free path high enough that you can probably get some efficiency, this might have some kind of chance if you are in a neutral buoyancy craft (balloon). The problem is that the wind can be so darn fast up there this kind of thrust won't really be relevant. $\endgroup$ – uhoh Jun 13 '16 at 14:37
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Yes, you can even easily build your own. And it uses atmospheric air as propellant too!

There's nothing inherent about ion thrusters that demands vacuum - of course there are engineering concerns like the size of spark gap, so that you don't have an arc between the electrodes, or pressure of the propellant and giving it a clear path to move, and so on - so ion engines designed for vacuum may, or may not operate in air. But designing one that works in air is definitely possible - if not quite practical, for the reasons you have mentioned.

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  • $\begingroup$ I was thinking more along the lines of the thrusters which actually eject their own high-velocity propellant stream. From what I've read, the necessity of a vacuum to prevent arcing is a critical element. Wondered if there were Coulomb or Lorentz thrusters that didn't require this. $\endgroup$ – sevenperforce Feb 26 '16 at 19:47
  • $\begingroup$ @sevenperforce: of course you can supply your own propellant. Arcing is a problem you must overcome by increasing the air gap, and ambient air will impair the flux, but these are not problems that make it impossible, just concerns to be taken into account and possibly impair performance. $\endgroup$ – SF. Feb 26 '16 at 19:59
  • $\begingroup$ What type of thruster would be least affected by ambient air? Something electrostatic, or something like a magnetic plasma thruster? $\endgroup$ – sevenperforce Feb 26 '16 at 20:46
  • $\begingroup$ @sevenperforce: In one hand, I dont know. On the other hand, why not exploit the totally free propellant? $\endgroup$ – SF. Feb 26 '16 at 21:41
  • $\begingroup$ Ya, but they even admit it won't go to alpha-Centari any time soon. What good is any propulsion system if it can't at least do that? :) $\endgroup$ – uhoh Jun 13 '16 at 14:33

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