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Comments on the meta question We have both electric-propulsion and ion-thruster tags, are they distinct? What would be good usage guidance for electric-propulsion? indicate that the term "electric propulsion" () may encompass one or more propulsion technologies beyond or outside of ion propulsion which for historical reasons we have captured as and not ion propulsion. See JPL Mission Manager/Chief Engineer Marc Rayman's discussion in the less-than-accurately named video How William Shatner Changed the World - Dr. Marc D. Rayman, Chief Propulsion Engineer, NASA, JPL for more on that, and answers to

Question: What are all the kinds of electric propulsion that don't qualify, or nicely fit under what's understood in standard spaceflight lingo to be ion propulsion"?

For example, are these examples of electric propulsion that are not necessarily ion propulsion?:

What about these for example, might the electric propulsion but not ion propulsion apply?

"EM drive"

Electromechanical

Other

uhoh
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    https://space.stackexchange.com/questions/16610/is-railgun-propulsion-being-researched – SF. May 01 '21 at 05:30
  • @SF. added and (partially) categorized, thanks! Please feel free to edit further. – uhoh May 01 '21 at 06:50
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    would you consider electric solid propellant valid here? Most of energy comes from combustion, but electricity does contribute. – SF. May 01 '21 at 10:18
  • @SF. It's worthy of consideration, let's see how answers address it. – uhoh May 01 '21 at 11:23
  • I would not consider e-sails/magsails to be electric propulsion, since the propulsion comes from an external mass flow. That might be an electrically-accelerated beam, but it's not powered by the vehicle's electrical supply...same as a laser-driven photon sail. Electrodynamic tethers would qualify though, and nothing's more electrical than an electrically powered photon thruster. – Christopher James Huff May 01 '21 at 13:53
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    I feel like thermalized electric thrusters aren't ion drive – ikrase May 01 '21 at 23:10

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You have come up with a good list of possibilities. Some see this as relatively straightforward, including me, though manufacturer marketing may cloud the issue.

  • Any kind of electrical augmentation, such as resistor jets or hydrazine arcjets, should count as electric propulsion because the satellite manufacturer has to factor in the power needed over and above the cold gas / catalytic N2H4 performance. I think this is the key feature that brings the name "electric propulsion". I've noticed that some in the modern EP community can be a bit dismissive of power augmented catalytic thrusters as their ISP isn't especially high, but I think that's a different matter.
  • It would be really neat and tidy if we could count types as ion propulsion when the ion production is a critical feature of the thruster operation. Thus gridded ion engines and hall effect thrusters both rely on plasma creation where as any ions produced in the frozen flow of a resistor jet are an unwanted bi-product. However, this is where we just have to accept that the community doesn't refer to the hydrazine arcjet as a type of ion thruster despite that the arc relies on ion production.
  • For all the more exotic forms of propulsion we could take the same theoretical definition based approach but still have the lexical definitions, i.e. actual usage, where by for example, neither the terms ion propulsion or electrical propulsion are used for solar sails. I'm less sure about the electro-spray type, I suspect both terms are used for it.
Puffin
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