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Nanoscale propulsion system that works in vacuum - or not?

  1. Feb 17, 2016 #1
    Moved this question from the quantum physics section to this section, since... Well it fits this section better since electrons apparently do obey conservation of momentum in the 'classical' sense.

    Why not produce thrust in microgravity with electrons? Plenty of harnessable electricity in space.

    While I'm on it, I bet you're exponentially better at solid-state physics than I am, so I have no pressure of making a fool out of myself. ;)

    http://imgur.com/i9jWmFE

    Imagine the crudely presented structure in 3D (a metallic torus confined within a dielectric sarcofage, with holes left in it for electric current input + the photon-electron input-output/nozzle/whatever you want to call it. A direct current is fed onto the torus (which is confined within an electrostatically-repellent dielectric structure), while electrons are expelled off the inner rim of the torus with energetic-enough photons, giving them momentum in the direction of the movement vector of the photons.

    Could this kind of nanoscale device be effective (mass to thrust ratio wise) at producing thrust - or is this an obvious fluke somehow?
     
    Last edited: Feb 17, 2016
  2. jcsd
  3. Feb 17, 2016 #2

    berkeman

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    So far your post is not making sense to me. Where does this DC current come from? When you eject electrons, your engine becomes positively charged, and attracts the ejected electrons back. And what is the photon/electron interaction you are alluding to? The photoelectric effect?
     
  4. Feb 17, 2016 #3
    DC current comes from example solar panels, and is conveyed to the torus with electrical conductors coming in through the dielectric from the sides of the torus (the outer 'rim', if you will). This should be conceivable from the sketch behind the link, the blue lines on the sides (these are electrical conductors), one of which is marked 'unidirectional flow of electrons' (so 2 dc inputs in the 2d picture, 1 from each side). Naturally, the torus would become positively charged, if there was no source that could provide a fresh supply of new electrons to replace the ejected ones.

    Yes, basically photoelectric effect, although I'm not sure if it is semantically correct to use that very term in this scenario. You expel electrons with photons interacting with the electron plasma (this interaction takes place on the inner lumen of the torus, or the inside edge of the 'doughnut', if you will), providing a gradient of momentary positive charge, which is constantly neutralized with a fresh supply of electrons jumping from the DC conductors in the immediate vicinity of the outer rim of the torus. A small gap between the conductors and the torus should be ok for electrons to move over of, since there is an electrical gradient present due to the photon-electron interaction expelling electrons from the torus.

    So, as clarification, the blue arrow-like shapes on the side (one dubbed unidirectional flow of electrons) bring the fresh electrons to the torus, and the ejected ones go in the direction of the green arrow (energetic photons).
     
  5. Feb 17, 2016 #4

    berkeman

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    I'm not understanding where this "fresh supply" of electrons comes from. A solar panel is a closed system -- you don't get a fresh supply of electrons from them....
     
  6. Feb 17, 2016 #5
    Point. An obvious fluke it is then, I was under the impression, that in a photovoltaic material the energy transfer results in excitons coupling into some kind of quantum spawning of an electron... Cursed facts!
     
  7. Feb 17, 2016 #6
    So basically, nothing wrong with the electron-momentum idea, except that it is perfectly unfeasible at the moment because of the obvious lack of new mass in form of electrons introduced to the system. Still, it's embedded in QED theory, that energy transform can occur via photon energies shifted into particles with rest mass (I'm referring to pair production). A little bit crazy, but are there any theories of for example metamaterials that would posess the ability to make positron-electron pairs at high rate, even perhaps being able to divert them from the inevitable annihilation process for other uses (non-canonical QED theory I suppose)?

    http://www.nature.com/nphoton/journal/v8/n6/full/nphoton.2014.95.html the only thing I found.
     
    Last edited by a moderator: May 7, 2017
  8. Feb 17, 2016 #7

    berkeman

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    Have you read about how Ion Thrusters work? https://en.wikipedia.org/wiki/Ion_thruster

    :smile:
     
    Last edited by a moderator: May 7, 2017
  9. Feb 18, 2016 #8
    Yes. I would assume that their level of optimization is more advanced than my (mis)conception. Heheh. I didn't bring them up because the need to have the physical propellant on board is obvious right off the bat.

    By the way, there are concepts of solar 'sails', or charged wires spread out into space that would catch drag off cosmic particle jets. Any ideas around of using them in combination with an ion thruster? As in capture high-energy particles flowing in interstellar space and store them to be used more efficiently with an ion thruster. Are there for example a lot of free electrons, or some heavier particles in greater amounts flowing through the interstellar medium by any chance? Or does the ball bounce off the post again? ;)
     
  10. Feb 18, 2016 #9
    The nearest (hypothetical) thing I can think of is a Bussard ramjet.
     
  11. Feb 21, 2016 #10
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