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How would one go about sending a probe on an orbit that goes around the Sun in the opposite direction as most planets? Specifically, a rather high orbit - something like Pluto's. What happens to possibility of gravity assists and Obereth maneuvers? Would using planetary fly-bys make turning harder? Would it necessitate excessive fuel budget?

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Plutinos are dwarf planets in 2:3 mean-motion orbital resonance with Neptune. There's a large number of Plutinos, and to examine them better, a fly-by mission would be very helpful. Now to examine a number of objects roughly scattered around a single orbit, a craft in the same orbit would be best - except flying in the same direction as Pluto, chasing them all would take a very long time. One flying head-on, would pass all of them in half their orbital period (123 years) in unpowered flight, much shorter if using gravity assists for "shortcuts" to skip from one to another.

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  • $\begingroup$ Check The Use of Gravity Assist Flybys in Plane Change Maneuvers, D. B. Reid, University of Colorado at Boulder, 2012. Specifically the parts about “orbit pumping” and “orbit cranking”. $\endgroup$ – TildalWave Dec 2 '14 at 18:24
  • $\begingroup$ Probably a better solution to the particular problem you propose would be to launch multiple probes ~simultaneously. $\endgroup$ – pericynthion Dec 2 '14 at 18:56
  • $\begingroup$ The fact that they are in resonance just means they have a particular semimajor axis. There are many orbits with that parameter. It depends on how close you want to get with your flybys-because of the other orbital parameters, particularly inclination and eccentricity, you might be far away when you make closest approach. $\endgroup$ – Ross Millikan Dec 4 '14 at 5:30
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You can use one or more Jupiter flybys, as needed, to crank the orbit around. Ulysses used a Jupiter flyby to get into an orbit over the poles of the Sun.

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  • $\begingroup$ Yes, turning around is quite doable. The question is - what then? Will gravity assists work if you rush against oncoming traffic? $\endgroup$ – SF. Dec 4 '14 at 8:25
  • $\begingroup$ I don't understand your question. $\endgroup$ – Mark Adler Dec 4 '14 at 14:13
  • $\begingroup$ Gravity assists can be used to increase or decrease speed, and the outcome is dependent on approach and departure angle, but I don't quite tackle how it depends on them. About all probes moving away from the Sun traveled in protograde direction and used gravity assists to increase speed, but I'm not sure if that's an essential correlation or just accidental one; can you speed up by using gravity assist to speed up when passing a planet in the opposite direction it travels? $\endgroup$ – SF. Dec 5 '14 at 9:14
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It would be foolish to attempt a complete orbit reversal starting from earth as the delta V would be enormous. For a comparison, if the delta V to reverse orbit at earth's orbital speed is a 1, out there at pluto's speed it would be 0.16. Factor in the lighter craft after having presumably expanded fuel to get there in the first place, it is now much cheaper to reverse the orbital direction once at the outer orbitals, near your target.

Edit: Forgot to mention, since you haven't completed the Hohmann to circularize once you yet at the right orbit, and if you calculated your transfer right, you should shave off a big part of the pro-grade speed you need to cancel.

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  • $\begingroup$ You should be able to reverse the direction through Oberth maneuver around any mass, - this is the least of concerns. Just pick the exit angle right, making a lowercase-gamma shaped orbital pass. This will be difficult though if the speed is very high already, and I'm worried if gravity assists in the retrograde direction will be viable at all. $\endgroup$ – SF. Dec 2 '14 at 16:42

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