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I have a question about neutralizing the ion thruster, why simply does not put a positive potential on the satellite to prevent the emitted ions from returning to the satellite? is the ion current so large that it would take several kV to repel that current?

edit: forget to mention that in the solar wind there are electrons to neutralize the ions at some point

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  • $\begingroup$ Is there really a problem with returning of emitted ions? $\endgroup$
    – CallMeTom
    Jul 23, 2020 at 4:24
  • $\begingroup$ yes... if the ions accelerate out of the satellite and then return to it, the net thrust is zero since they accelerate and then decelerate, also by erosion you end up destroying the satellite $\endgroup$
    – Ricardo Casimiro
    Jul 23, 2020 at 4:30
  • $\begingroup$ @RicardoCasimiro: sry, my question was not clear. I am not asking, why it is bad, when ions return. I wanted to ask: is there a significant amount of ions from thrusters actually returning, so that the problem you mention is really a problem? $\endgroup$
    – CallMeTom
    Jul 23, 2020 at 4:36
  • $\begingroup$ yes, because when xenon is ionized it produces the same amount of ions as electrons, if the electrons stay in the satellite then it will be negatively charged in the same magnitude as the ions that come out, therefore most will return to the satellite $\endgroup$
    – Ricardo Casimiro
    Jul 23, 2020 at 5:10
  • $\begingroup$ I just looked in the Wikipedia-Article for Ion Thruster because I couldn't imagine, this problem really exists. And in deed, see my answer: the Ions are neutralized again with the "spare" electrons so the "exhaust" gas become neutral. $\endgroup$
    – CallMeTom
    Jul 23, 2020 at 5:34

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It is always important to keep the charge of a spacecraft close to zero and to never get too large. This is true no matter if you are using ion propulsion or not.

A charged spacecraft can suffer from several failure modes. So when a spacecraft emits positive ions it also must use an electron gun to emit electrons to keep the spacecraft close to neutral.

Rather than reproduce all the reasons and problems here, I'll direct you to the excellent discussions in the following posts:

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    $\begingroup$ Thank you sir, I think the answer to my question is that when you ionize the xenon it produces an ion (which comes out of the satellite) and an electron, so if the excess electron is connected to the mass of the satellite and the ion comes out, the satellite will be charged negatively and the positive ion will attract, the best way to get rid of that excess electron is emitting them close to the emission of ions $\endgroup$
    – Ricardo Casimiro
    Jul 23, 2020 at 5:03
  • $\begingroup$ @RicardoCasimiro I don't know much about that actually, so I've asked a follow-up question: Is there any possible reason to direct the electron gun specifically towards the ion trail behind an ion thruster? $\endgroup$
    – uhoh
    Jul 23, 2020 at 6:59
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The Problem you are assuming, is actually none:

Temporarily stored electrons are finally reinjected by a neutralizer in the cloud of ions after it has passed through the electrostatic grid, so the gas becomes neutral again and can freely disperse in space without any further electrical interaction with the thruster.

Source: Ion Thruster Wiki, just in the introduction

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