Comments on: Compact, Cheap Nuclear Space Power

By: John Mansfield

John Mansfield — Fri, 30 Nov 2012 00:36:44 +0000

Ion thrusters were used to carry a European craft from GTO in ever growing orbits that after two years reached the moon. NASA's Dawn orbited Vesta for a year and left a couple months ago for Ceres under ion thrust. It's effective exhaust velocity is 30 km/s, an order of magnitude better than liquid rocket engines.

By: Adam G.

Adam G. — Thu, 29 Nov 2012 20:39:18 +0000

Anon,
ion thrusters are already used for station-keeping in satellites. Their exhaust leaves at c*, so hyper speeds is about right, and their exhaust is ions, so yes, very small amounts of matter is also about right.

But while there have been proposals for scaling up to make ion thrusters large enough for in-space travel, to my knowledge it hasn’t been done yet.

Because ion thrusters require so little exhaust mass, they can accelerate for very long times. However, because their exhaust at any one time is so small, they can’t accelerate very fast. What this means is that they can’t be used for launch but could be used for in-space travel.

*duh, not at c. Ionized atoms, not photons or some such. See below.

By: anon

anon — Thu, 29 Nov 2012 16:50:21 +0000

Is this device just for generating electricity or also for propulsion?

I remember reading something years ago about a theoretical space engine designed to eject small amounts of matter, but at such hyper speeds, that the reaction was sufficient to accelerate the craft. I forget if it was science fiction, or a serious real-world, though speculative, design.