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It's going to be another year before all of the data that New Horizons gathered is finally transmitted to Earth, but based on current science return, does what's been received so far warrant an advanced orbiter with multiple flybys mission that would navigate the Pluto-Charon system for an extended period of time, the way Cassini is navigating at Saturn?

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    $\begingroup$ Howard hi, welcome to Space Exploration! I took the liberty to rewrite your question somewhat to remove invitation for opinions and general discussion, since we're a Q&A and not a discussion forum. I'm not sure I entirely succeeded in that. Hopefully, it can now be answered with some authority. Please review and see our About and How to Ask pages for more info on what our site is all about. $\endgroup$ – TildalWave Oct 24 '15 at 3:56
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    $\begingroup$ Also see Requirements to orbit Pluto. Problem with an advanced orbiter mission to the Pluto-Charon system isn't so much in lack of scientific interest in it, as it is in difficulties in achieving something as sophisticated like that in any reasonable time frame. In any case, it would be a class A mission with current technology and competing for budget with likely higher priority ones. $\endgroup$ – TildalWave Oct 24 '15 at 4:19
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    $\begingroup$ Since every encounter with a new celestial object offers big surprises, there are good reasons to visit a new one instead of revisiting an old one again. $\endgroup$ – LocalFluff Oct 24 '15 at 7:48
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    $\begingroup$ Those same 'big surprises' are a good reason to go back and study them in more detail, with instruments designed to answer the questions raised by the flyby. $\endgroup$ – Hobbes Oct 24 '15 at 8:19
  • $\begingroup$ @Hobbes One could of course argue both ways. I think that we are just beginning to make a survey of the strange things out there, and can't make an informed pick to peek closer at. Need to increase the sample to begin with. Maybe one day, two things which are similar are found, and a systematic can be founded. $\endgroup$ – LocalFluff Oct 24 '15 at 10:22
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We simply don't have the launcher system to accomplish that (see below).

EDIT (hat tip to Mark Adler for an answer to a related question - although please have a look at his criticism of my answer here before judging for yourself and voting):

That means a mission that can achieve Pluto orbit insertion (POI) after being launched from the Earth on a single rocket... and take less than 10 years or thereabouts from launch to first scientific results. ESA's mission study from Mark Adler's answer had transfer lasting 18 years. In 18 years Principal Investigators will most likely go senile, retire, or die, and their replacement will lack critical knowledge to troubleshoot payload instruments. (See also this question for more information on this very problem)

Source: PERFORMANCE REQUIREMENTS FOR A NUCLEAR ELECTRIC PROPULSION SYSTEM - 2002*

An orbiter mission is only practical with high-performance propulsion at Pluto. For reasonable trip times, as described below, the encounter velocity at Pluto is about 12 km/s. Pluto does not have enough atmosphere for aerocapture, and its gravity well is of low potential. Therefore, the entire encounter velocity must be removed propulsively. SEP does not work so far from the Sun, thus unless nuclear electric propulsion is available, one is left with chemical propulsion (jet velocity about 4 km/s, optimistically).

The practical mass ratio (total mass/payload mass) is about 40 to 50. A reasonable mission spacecraft mass is about 500 kg, leading to a trans-Pluto mass requirement about 20,000 kg. Not since the Saturn V has the U.S. possessed such a launch capability. Nor does any other nation presently possess such large launch capability. NEP is the only propulsion option that can reasonably perform a Pluto orbiter mission.

NEP - Nuclear Electric Propulsion.

SEP - Solar Electric Propulsion.

In addition, you have to choose among scientific missions to maximize their marginal scientific results. Titan, Enceladus, and Europa all look much more promising #, and are much easier to get at with reasonable payload masses.


* Despite the source being 13 years old, nothing has really changed as far as heavy launchers are concerned. Sigh. We don't have nuclear propulsion, either.

# Liquid something yadda yadda wanna see clash of the titans and the snakes at enceladus ALL THESE WORLDS ARE YOURS—EXCEPT EUROPA ATTEMPT NO LANDING THERE.

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    $\begingroup$ Enceladus, the moon of Saturn, has fascinated me ever since the first photos came back from Cassini, even before the geysers were discovered. We really need a follow on mission, one with cubesats we can risk for etremely close passes to ring objects, and landers with enough oomph to take off and land several times. $\endgroup$ – Howard Miller Oct 24 '15 at 14:00
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    $\begingroup$ Incorrect. You can have nuclear electric propulsion with RTGs. It is plausible that it can be done with existing launchers and technology. I posted a link to a study of such a Pluto orbiter in another answer here. Also the question was not whether we could or how we would do it, but rather would it be justified. $\endgroup$ – Mark Adler Oct 24 '15 at 17:52
  • $\begingroup$ @MarkAdler - we can, in principle, send a two- or three-launch Earth-orbit rendezvous mission with a chemical POI engine. It is definitely possible, but we'd lose two missions with greater payload to other bodies of interest. $\endgroup$ – Deer Hunter Oct 24 '15 at 18:38
  • $\begingroup$ Found it. See this answer. $\endgroup$ – Mark Adler Oct 24 '15 at 18:53
  • $\begingroup$ Will the SLS have enough performance to launch such a mission? $\endgroup$ – 2012rcampion Oct 24 '15 at 19:15
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There are definitely some interesting questions resulting from the Pluto flyby, that I'm sure scientists would love to study. However, there are a number of objects that are higher in the priority to study in the outer solar system. Here is what I think the expected priorities would be, for an orbiter class mission:

  1. Europa, with other observation of Jupiter's moons if possible
  2. Enceladus
  3. Titan (Might require a dedicated mission just to study this moon)
  4. Neptune (Triton in particular is of interest)
  5. Uranus
  6. Flybys of other major KBOs
  7. Pluto

The bottom line is, while Pluto is a very interesting body, it is only a small body, and not of particular interest such that it would justify an orbiter, particularly in terms of how difficult it is to get there. It is with little doubt the most fascinating KBO, but I just can't see an orbiter for some long period of time, owing to the difficulty in achieving orbit, as well as the fact that there are fewer bodies to study than the moons of any of the giant planets. Mars is more interesting, and closer. Pluto is probably the most interesting rocky object in the outer solar system after Titan, Europa, and Enceladus, but it still doesn't quite beat those 3 objects.

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    $\begingroup$ This is the correct answer. With infinite money, sure, a Pluto orbiter is justified and we would send one. However with finite money, there are other priorities. $\endgroup$ – Mark Adler Oct 24 '15 at 17:54

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