Actually, once in space and mostly free from the gravitational pull of another object, (I say mostly because you are never actually free completely) it takes very little energy to propel even an extremely heavy object due to the fact that the opposing force is very minimal. The extreme amount of force to, say, lift a rocket off of earth, is needed simply to break from the large amount of gravity present between the Earth and the rocket. Once the objects generate a greater degree of separation, the force needed to move the object becomes exponentially less. The more force you use to propel the object would merely determine it's acceleration once in space. That being said, it would be an unbelievable undertaking to have built something like this on a planet, then send into space, but it seems unlikely that if you had the technology to build this structure, you wouldn't just built it in space anyway.