What ever happened to nuclear candles? Have they been classified?

Sort of like a fusion reactor then?

Not really… At least I think not.

I think you’re probably talking about either fission-powered rockets or – possibly, but unlikely – ion engines.

I’ve never heard of a nuclear candle before, and Google only turns up ideas for small, lightweight fission reactors, not interplanetary/interstellar propulsion concepts.

Link was helpful, I was thinking of a nuclear pulse design using a steady stream of excitable materials. I still can’t find the actual concept though…

For a moment there, that sounded like the most badass decoration gadget ever.

Man it’s not like I’m looking for it because it wasn’t badass :D

It’s “risk becoming Curie” badass :D

It sounds like you’re describing the Orion Nuclear Propulsion System. The only difference being Project Orion proposed to pulse detonate nuclear material rather than try to do it continuously. The problem becomes maintaining critical mass in a continuous flow of nuclear material so that only the material you want to explode does. I have a feeling that the detonation of part of a continuous flow would compress parts of the flow in such a way that it would naturally become discontinuous. I’d be concerned about what kind of modes of vibration such a flow might have. However the proposed vehicle is designed with a tremendous damping system so if it was designed right it might not be such a problem.

Already read that article, not it.
I think it was similar to a chemical rocket but using fissionable fuel regulated with some other gas.

I don’t think that’s possible – fissile material is solid and pretty dense. I suspect (and I wish I had the skills in physics to actually check myself) that maintaining critical mass would be impossible, in the practical sense. Certainly, any material unstable enough to engage in fission in a gaseous form would not be… fun to be around.

A fusion rocket sounds closer to what you are talking about.

Nuclear powered engines make quite a bit of sense in submarines (which are surrounded by water for cooling, and conversion to steam for propulsion) but they really no sense for spacecraft propulsion. Far more promising are laser/solar sails, particularly if a laser base were set up on the moon where laser propulsion wouldn’t have to travel through Earth’s propulsion.
http://en.wikipedia.org/wiki/Laser_propulsion