Ok, I'm not sure if all of you get Discover magazine, but if you do, in the August 2003 issue (Can we rocket to another star?), it talks about the idea of a Fusion Ramjet.
Basically, it is an inverted cone, leading to a reactor, the cone being a couple ten thousand miles wide (if a i read correctly), and as the Fusion Ramjet goes through space, it picks up hydrogen particles which are funneled to the reactor, and by some combustion process (dont ask me how...) it shoots the Ramjet to near light speeds due to a lack of fuel tanks to weigh it down..so the article says. (a rough estimate by its creator: it would take 25 years to get to Alpha Centrui and 90 years to 55 Cancri (41 light years away). Kinda fast if you ask me. The pros of the Ramjet: near-light speed;unlimited interstellar travel in any direction
Cons?: requires major advances in physics and engineering knowledge.
Though one problem is drag. With fusion particles shooting out the back, the interstellar particles of hydrogen used as fuel start piling up in front of it, slowing it down. Also, at denser parts of the galaxy, the ship might grind to a stop, but Robert Zubrin (engineer who runs Pioneer Astronautics) suggested using a magnetic field as a brake to slow the ship down without wasting fuel.
The biggest problem? Deuterium and Tritium, used in modern experimental fusion reactors are rare in space. Interstellar hydrogen is the regular variety with a single proton. And no one has a clue how to fuse together pure hydrogen. But we do know it happens everyday: The sun.
So, do you guys think it is possible to use a fusion ramjet to travel between stars if we make the right advances in physics and engineering? :-?