ORIGINALLY PUBLISHED ON 11/23/09
Every. Single. Rocket. Engine. That's. Ever. Flown. has been conventionaly powered. Well, ok, not *EVERY* rocket engine - there have also been a few Ion engines. Those aren't conventional because they're electrical. They are, however, EXTREMELY low yield - 18 months to the moon - and not really practical for our considerations. The point is that (nearly) every rocket engine that's ever flown in space is a conventional liquid-fueled rocket.
Someone is finally developing a Nuclear alternative, and - big surprise - it's not the US that's doing it.
A little background before we begin: Rockets function by combining a fuel, an oxidiant, and an electrical charge to get Fwoom - Fwoom being, of course, the pillars of fire and smoke that generate thrust that put the rocket in space, and move it about once it's up there. Solid rockets work the same way, except that the fuel and oxidiant are in solid form. They still require the electric charge. There's also what they call a "Hypergolic" engine, which is exactly the same except that it dispences with the electrical charge. Instead they use fuels that just naturally hate each other, and when they're combined they go Fwoom of their own accord. Ion engines don't do this at all, but they are also wussie as heck, and we'll just table them to be discussed on another day, shall we?
This is great and good and as it should be, but the various space agencies of the world have long wondered if, maybe, there was a way to simplify things, or at least get a little more bang for their buck, and this - as was the spirit of the times - immediately led to the concept of Nuclear Rocket Engines.
In the US, we worked on the NERVA - "Nuclear Engine for Rocket Vehicular Applications" - the concept being that we could dispence with the oxidiant altogether and pass the fuel through a nuclear reactor, which would not only cause it to go "Fwoom," but it would also generate electricity for the spacecraft without all that mucking about with fuel cells or solar pannels. The Soviets, meanwhile, were working on the same concept, which resulted in this http://www.astronautix.com/engines/rd0410.htm
Now, to be honest, NERVA had problems. They tested it for the better part of a decade, irradiated a hell of a lot of the Jackass Flats area, and it never performed the way they thought it should. Given relatively disappointing fuel yields, the anti-Nuclear naysayers who couldn't tell a bomb from an MRI had it shut down, and that was the end of American's attempts at a Nuclear interplanetary engine.
The Soviets, meanwhile, continued to forge ahead. As is typical for them, they had a smaller budget, and much more focused research, and as is typical of them, they never really sealed the deal. Their project was canned during the ongoing Russian financial crisis of the mid-90s.
However, they've announced they're back at it: http://spacefellowship.com/2009/10/28/russia-develops-spaceship-with-nuc... and, of course, we're not. Rather than stepping up to meet the challenge the way a shattered, poor country like Russia is, we're actually debating whether we even want to have a manned space program at all anymore.
Gee, thanks, President Obama.