Pianosorplanets wrote:
When NH passed Jupiter it accelerated to 14.2mps. When it left Earth, I believe the speed worked out to about 10.1mps. When it reached Pluto, we're getting quoted around 10mps again. So some retrorockets must have fired around here someplace?... Space dust doesn't slow your speed down that much over that short a distance. If they could drop 14,000 mph as a part of this mission, I find it hard to believe that it would have been THAT expensive to drop more. The thing only is the size of a Grand Piano and weighs a lot less. I rebuild grand pianos for a living and can pick up the corner of a concert grand by myself...
Escape velocity at Jupiter's orbit is still ~11.5 mps
so no retrorockets or space dust were needed to slow down after Jupiter.
A Steinway grand piano weighs about 450 kg;
New Horizons weighs roughly the same: 395 kg plus 77 kg of hydrazine monopropellant fuel
Hydrazine monopropellant has an exhaust,
ve ~ 2.2 km/s; therefore,
in order to lose all of its 13.78 km/s velocity at Pluto NH would have required
over
200 tonnes [=395 kg x exp(13.78/
2.2)] of hydrazine monopropellant fuel.
The
Ares V might be able to deal with a 5 tonne NH but not a
200 tonne one.
An ion propulsion system (such as that on the Dawn spacecraft) would be feasible
but that would require continuous deceleration from Jupiter flyby and a ~20 year voyage.