Magnetic fields, man. Not just a great band but the key to space travel. What we want is a spaceship with a fusion reactor on it to power these magnetic fields that contain and direct its propellants: Antimatter to reach escape velocity and superheated hydrogen plasma for the ion engines that become useful in interstellar travel. The onboard fuel is going to have like a thousandth part of the mass of the ship. Much less if we stick a particle accelerator on there to let the ship make its own antimatter and really speed things up, but that's probably more of a built-in-orbit sort of feature that implies space elevators.
Strange conceptual kind of problem in reaching the stars, here: A rocket has to carry its own fuel, and an orbital elevator cable has to withstand its own weight. I wonder if the solution is taking a little of both. It would be a constant drain of energy on probably a type-1 civilization scale, but you could keep a simple lightweight wire of any length upright with some kind of rocket engines or, wait, how about some magnetic fields?
Once you reach space at ~100 km, I believe superconducting magnets could be used with little or no additional expense. Besides the energy production, the main problem I think will be finding enough magnetic iron and still have something left to make spaceships out of. Ever get the feeling that the universe is missing some kind of bank that could loan you a sum of energy or metals and things that you could easily pay back after you use it to build something?
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