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New Horizions just reached Pluto after almost a decade in space. That means it was launched with technology that is well over a decade old (when you factor in planning and construction time).

If we had a new probe with modern technology on the launch pad today, how long would it take to get to Pluto? Would it be significantly faster? Would it depend heavily on the alignment of the planets (ie the Jupiter slingshot maneuver)?

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    $\begingroup$ It actually would be slower, for a number of reasons. Pluto is further out than it was previously, and there won't be as good of a slingshot (I believe) as there was for New Horizons. $\endgroup$ – PearsonArtPhoto♦ Jul 15 '15 at 16:59
  • $\begingroup$ @PearsonArtPhoto Do you know approximately how much further out it is? $\endgroup$ – David says Reinstate Monica Jul 15 '15 at 17:03
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    $\begingroup$ I would think if it had ion thrusters that could still make a big difference. $\endgroup$ – kim holder Jul 15 '15 at 17:06
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    $\begingroup$ Ion thrusters could work actually, it helps if you will be in transit for a long time. I'm toying with the idea of making an ion powered craft simulator, will have to play with it some... $\endgroup$ – PearsonArtPhoto♦ Jul 15 '15 at 17:09
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    $\begingroup$ space.com/18566-pluto-distance.html $\endgroup$ – PearsonArtPhoto♦ Jul 15 '15 at 17:11
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Modern technology doesn't change the major constraints of rocket propulsion significantly.

In the absence of a gravity assist, the most fuel-efficient route from Earth to Pluto is approximately a 45-year journey. Bringing that down to 9 years already represents a large investment in propulsion fuel; New Horizons set the record for the highest launch speed of a human-made object from Earth (~16 km/s); the Jupiter flyby increased its speed by another ~4 km/s.

If NH had an ion thruster capability similar to that of the Dawn spacecraft, with enough fuel for an additional 4km/s of maneuvering, it could have managed roughly the same travel time without the Jupiter assist, or, with both the ion drive and the gravity assist, managed more like a 7-8 year trip.

That kind of capability would come at the cost of something else; NH's very high launch speed was only possible because the spacecraft was so small (about half a ton), and the fuel needed for such an ion thruster would be about a third the mass of the craft. Either a much larger launcher would be needed, or the science package on the probe would have to be much reduced.

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For a launch to Pluto, a Jupiter gravitational slingshot opportunity occurs once every 12 years or so (one Jupiter orbit + 12/248, to account for Pluto's movement in those 12 years). The next one is ~2-3 years away.

Then there's the rocket. You want the fastest launch possible. The Atlas V 551 used by New Horizons can put 18 tons into LEO. As a first approximation, more weight to LEO = faster launch of a New Horizons-class probe on its way to Pluto. So going through this comparison list, the Proton M does a little better at 21 tons, but the real improvements are still in development, notably the SpaceX Falcon Heavy (53 tons) and the SLS Block II (130 tons).

Those rockets also give the freedom to use an ion engine, and to design better upper stages than the Centaur and STAR-48. I'll leave the number crunching on those to others.

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  • $\begingroup$ Why only one rocket to LEO, though? Launch one science package, one (or several) propulsion units, mate them in orbit. $\endgroup$ – jamesqf Jul 15 '15 at 19:19
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    $\begingroup$ That adds a huge amount of complexity and cost to the mission. $\endgroup$ – Russell Borogove Jul 15 '15 at 19:38
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    $\begingroup$ And I think it's understating it to say "huge amount of complexity". More like "HUUUUUUUGE amount of complexity". $\endgroup$ – Thane Brimhall Jul 15 '15 at 20:29
  • $\begingroup$ @Russell Borogove: I don't see how. Automated docking is pretty bog standard stuff these days, with the ISS. Lots less complex than building a new large launch vehicle that'd only be used for a few missions. $\endgroup$ – jamesqf Jul 15 '15 at 20:49
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    $\begingroup$ Docking itself is not a huge challenge. The logistics to enable docking add a huge amount of complexity to the probe: suddenly the probe and everything that docks to it need independent power and attitude control systems (can't dock to a tumbling object) and the active side of docking needs its own propulsion system. After docking that redundant power/attitude control becomes dead weight that you're dragging out to Pluto. Also, everything has to work flawlessly during and after years of travel in space, which is why they were trying to get rid of complexity (scan platform) originally. $\endgroup$ – 1337joe Jul 15 '15 at 21:55
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Hobbes and Russell Borogove gave good answers. I'd like to add another factor: distance from the sun. Pluto's perihelion is 29.64 AU. Aphelion is 49.12 AU. Last perihelion was in 1989. Pluto's orbital period is about 246 years. So next perihelion is in the year 2,235. During our lifetimes Pluto is only going to get more distant.

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