I've been kicking around an idea for spaceship for exploring deep space. If I have the math right, it ought to be able to reach nearby stars within a few years. I might have slipped a couple of decimal places somewhere along the way, in which case your wouldn't be able to reach the stars, but you should be able to reach most any of the planets in our solar system within a few months.
The the ship would be composed of three basic parts - the active part with would contain the crew quarters and the propulsion system and a fuel tank. The active part would be roughly the size of an Ohio class nuclear submarine. The fuel tank would be roughly the size of super tanker that we use for transporting crude oil across the surface of the oceans on Earth.
The fuel tank would be filled with iron in some form. The propulsion system would be a linear accelerator powered by the nuclear reactor. I imagine we could use iron rods a foot in diameter and a thousand feet long. The back end of the rod would be fed into the nuclear reactor which would melt it and then inject the liquid iron into a linear accelerator that would pump the iron out the back at some ridiculously high velocity. The rod might be a foot in diameter going into the reactor, but it would be stretched and elongated into a stream of atomic size particles by the time it reached the exit.
It might be possible to achieve a constant one G of acceleration with such a system, but even if it did, when we reached our destination, whether it's Mars or Sirius, we would probably want to spend some time there, and for that we would want some kind of rotating structure to provide a semblance of gravity. So we've got a nuclear submarine pushing a super tanker and around the junction we are going to have a donut maybe a thousand feet in diameter rotating at several RPM.
Problem here is we are going to need a method to get from the rotating donut into the rest of the ship. That means you are going to need some kind of super heavy duty bearing along with a rotary seal. That would be a bit of a design challenge, but it will probably be the least of the problems we would encounter trying to build such a monster.
We would probably want to build this thing in orbit around the moon. We might be able to build it here on Earth, but I am not sure just how much damage the exhaust would do to the ground. It would certain ly burn a hole wherever it touched. There are places on the planet where this might not matter, like the Sahara desert, but I don't know how deep a hole it would burn, or how radioactive it would be. Might go right thru the crust and unleash a volcano. Cool special effects though, if you wanted to make movie.
