Suppose there is an electric sail in LEO, do the electrons coming out of the gun produce an additional thrust? to produce a net thrust the electrons should NOT return to the satellite (which is at a typical positive potential of 20kV). enter image description here

source of the image: Mengali, G., A. Quarta and P. Janhunen, Electric sail performance analysis, J. Spacecr. Rockets, 45, 122-129, 2008 via electric-sailing.fi more info available on other pages there, in Wikipedia's Electric Sail and at

note: The function of the electron gun is to eject electrons from the wires to maintain it at a high positive potential.

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    $\begingroup$ What's the source of the image? $\endgroup$ Commented Dec 9, 2020 at 0:13
  • $\begingroup$ To have the sail at positive potential you just need to make sure more electrons are leaving than are coming in to set the potential (charge the system), then keep the two in balance. Yes, you will get some thrust from the electrons leaving, just like an ion thruster, just much much less because an electron is really (really really) light. $\endgroup$
    – Jon Custer
    Commented Dec 9, 2020 at 16:19
  • $\begingroup$ @JonCuster the question is, electron will return to the satellite? if so if the then the net thrust is 0 $\endgroup$ Commented Dec 10, 2020 at 14:16
  • $\begingroup$ If the sail is at, say, 20kV relative to outer space, you send out the electrons at 30kV and they will not return. And you send enough to hold the potential of the sail relative to empty space relatively constant. $\endgroup$
    – Jon Custer
    Commented Dec 10, 2020 at 15:31
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    $\begingroup$ @uhoh edited ........ $\endgroup$ Commented Dec 11, 2020 at 0:08

1 Answer 1


In short the existing particles from the gun would exert force in the opposite of the forward force you would want... that is unless you could bounce the particles and angles that are not perpendicular to either your desired trajectory or the source trajectory - something like mirror box for lasers but maybe resembling more of Nautilus structure. Each "bounce" of the particle would create some force- the trick would be create enough bounces from each particle so that more-than cancels the momentum of it's own creation.

  • $\begingroup$ Why not point it in the other direction or from the tips of the sails rather than the center? $\endgroup$
    – uhoh
    Commented Dec 11, 2020 at 3:11

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