Theoretically, being no friction in space, a constant emission of energy should result in a constant rate of acceleration but for some reason this doesn't work as the speed approaches that of light. The graph of energy required vs speed attained produces a curve which never reaches light-speed. The spatial dimension in the direction of travel reduces, and time slows, proportionally to said curve so that, in theory, infinite energy is required to reach light-speed at which point you'd be 2-dimensional and time would stop. That's also why they reckon going faster than light would send you rocketing back in time, but nobody's ever done it.
I think it was Steven Hawking or somebody who actually said that if you could match the vibrational frequency of a craft with the frequency of a point in spacetime, you'd transport there instantly, which is what Swerdlow & others have said too.