[Baron Munchausen]

Originally posted by narf poit chez BOOM:
your post stired up a thought...what if the heat generated by interstellar dust was used to pre-heat the reaction mass?

A fascinating thought. But any 'reaction' drive suitable for interstellar travel is going to need to have a very high impulse (thrust per weight units of fuel) ratio. This means something with very high energy like a fusion reactor with an opening pointing out the back. It sounds good in theory to run your coolant around the spaceship skin and then route it to some sort of 'converter' to preheat the fuel -- but how are you going to convert plain old radiant heat carried by a 'coolant' medium into the extremely intense sort of energy needed for fusion reactions? A pelet of fuel (probably hydrogen in a little glass 'bubble') has to be heated to thousands of degrees in a tiny fraction of a second -- probably by lasers. If this extreme conVersion can be done at all it looks likely to be very involved and complex. And once you figure out all the tricks necessary to do this, are you gonna have any space left in your ship for cargo between all those heat-exchanger coils and electrical generators and what not? So though it sounds good on its face I wonder if it can be done in practice.

This sort of reminds me of the idea of putting generators on the wheels of an electric car. Yeah, it should work (and some electric cars do recover a small amount of energy this way) but the inherent inefficiencies put some pretty steep limits on its effectiveness.

Maybe there are simpler ways to do it? Do thermocouples actually 'use up' energy and reduce their heat levels by generating electricity? A ship with a skin made of thermocouples is an interesting concept. Peltiers reduce temperature by moving the heat around but you still have to dispose of it somewhere, somehow and the Peltier effect USES energy and creates more heat.

It's a very difficult problem.

[ March 27, 2004, 04:02: Message edited by: Baron Munchausen ]