QUOTE (djellison @ Dec 22 2005, 04:00 PM)
I'd have thought, if you were intent on doing a misssion out to near 100AU then you're going to have to go with Ion or even more interesting propulsion ( A solar powered Ion 'stage' to the spacecraft, ejected once prop is exhausted after perhaps 12 months of thrusting adding a few km/s to the velocity of the RTG powered spacecraft )
I was wondering about the feasibility of a weak ion engine that would be powered off the surplus energy from an RTG during most of the cruise. How feasible would it have been for NH to have included a 100 watt ion engine that would slowly accelerate during 8 years or so of (otherwise dormant) interplanetary cruise? What cumulative delta-Vee could we expect from that on a 500 kilogram probe? A fast kick-start would still be needed during Jupiter injection, but if the long thrusting period shaved a year off the trip time, it might just have been worthwhile. Have any studies been done on that?
Of course, a very reliable ion engine would be needed, possibly similar in design to Hayabusa's microwave driven one? As I gather there is no weardown of the electrodes in that case which would make it very convenient. Then there's the problem of the drive failing and the achieved final trajectory would probably not reach Pluto but fell short.
I wonder if a thrust angle profile could be set up so that at any point if the engine was cut-off the Pluto fly-by geometry would be set up, yet only the arrival date varied by continuing thrusting onward? In other words, the engine would continually move the aimpoint to earlier arrival times, keeping the C/A distance pretty much constant. Orbital dynamics probably don't allow for that, though.