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While most applications of ion thrust involves long "burns" with either a tiny, slow rotation or none, in the case of this question: Thrust strategy to circularize a standard GTO orbit using ion propulsion? you might want to rock the satellite back and forth every orbit (for a fixed ion engine) to optimize for least time to circularization with a fixed solar panel area. (ion engines are typically powered in real time by the solar panels).

edit: You might be in a hurry to get away from low orbiting debris for example - and depending on space weather - trapped radiation like this:

https://en.wikipedia.org/wiki/File:Van_Allen_Belts.ogv

If you orient a satellite with fixed panels for maximum power, you may wish you could vector the ion thrust. This is just an example of a situation where you might want to do this, it's not the subject of the question, nor the only possible reason.

Charged particles are deflected all the time, naturally and artificially, by either (or both) magnetic and electric fields. One could vary a DC bias on electrostatic deflector plates or even adjust positions of some permanent magnets to steer the thrust without doing (too much) work.

Of course, one could just gimbal the entire engine.

None of these are simple, and they'll surely have design, cost, complexity, risk and performance impact.

My question is: are there any stated plans or research to vector ion thrust?

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The ion engines on Deep Space 1 and Dawn were gimbaled. If you are going to operate one engine, it pretty much has to be gimbaled or vectored to direct the thrust, on average, through the CG (center of gravity). That seems unavoidable to me. If you didn't have a way to direct the thrust, then the thrust could not be assured to be through the CG as, for example, propellant is expended, moving the CG. Then the ion engine would act as an extremely efficient attitude control thruster applying torque to the spacecraft, that the hydrazine attitude control thrusters would have no hope of countering.

I suppose you could try to electromagnetically vector the thrust, but plasma physics is complicated whereas gimbals are pretty darned simple. I think you would just reduce the efficiency of the engine with electromagnetic vectoring, not getting all the ions to go in the same direction. A gimbal doesn't have that problem.

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    $\begingroup$ You could also dynamically shift the CG. A movable weight inside the craft (or even multiple propellant tanks, depletable in regulated proportions) would be able to maneuver the CG of the craft, to allow desaturation of the reaction wheels. Is it more robust/efficient than a gimbal? I don't know. $\endgroup$ – SF. Jun 13 '16 at 10:27
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    $\begingroup$ @uhoh: Your hunch is right. $\endgroup$ – SF. Jun 13 '16 at 11:11
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    $\begingroup$ OK this makes complete sense. If there is but one engine, you need a rudder no matter it's a plane, boat, or deep space probe, to avoid going in circles. Gimbaling is now a proven solution. There is plenty of experience with gimbaled articulation of other things (solar panels, antennae) and since these engines have such low thrust, the gimbal won't know it's pointing an engine rather than a more passive device. Sounds like you don't expect a lot of active research in ion thrust vectoring by E or B fields, due to lack of an urgent need for it. $\endgroup$ – uhoh Jun 13 '16 at 11:24
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    $\begingroup$ note to self: CG = center of mass $\endgroup$ – uhoh Jun 13 '16 at 12:33
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I don't know if there are any plans or developments in vectoring thrust from a single ion thruster, be that by gimballing or deflecting the ion stream, but LISA Pathfinder (a prototype for planned eLISA mission) is testing two sets of ion thrusters - colloid and field emission - for ultra-precise attitude control. These are installed and act as RCS thruster blocks - sets of multiple tiny thrusters of minuscule thrust aimed in various directions, able to provide both arbitrary rotation and translation to the craft.

They are extremely important in the interferometer experiment, where the distance and orientation between the probes located millions of kilometers apart must be maintained with sub-micron precision. The Pathfinder mission is to determine which ones fulfill the task better.

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  • $\begingroup$ It simultaneously makes complete sense to me and totally blows me away that to get ultimately sub-micron (and ya, way below) precision, one moves to spacecraft traveling at kilometers per second. Optics and space were made for each other! $\endgroup$ – uhoh Jun 12 '16 at 13:59
  • $\begingroup$ This is definitely an easier way to do it if you can use small thrusters. But for a single large one for major propulsive maneuvers, either thrust vectoring or attitude control seem to be the only options. $\endgroup$ – uhoh Jun 12 '16 at 15:21
  • $\begingroup$ @uhoh: Attitude control is necessary regardless. It's not like you can perform any rapid maneuvers with some 4N of thrust anyway, so if you want to dodge asteroids, chemical RCS would be a better option. $\endgroup$ – SF. Jun 12 '16 at 15:25
  • $\begingroup$ Sounds good! I just wanted to thank you for your answer but vector the subject back to the question. $\endgroup$ – uhoh Jun 12 '16 at 16:00
  • $\begingroup$ @uhoh Well, somebody else will have to fill in. I believe slight vectoring should be perfectly viable, bending the ion beam the same way electron beam is bent in CRT monitor, but that's just me, no clue if it's being done, researched or anything. $\endgroup$ – SF. Jun 12 '16 at 16:29

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