[quote=Abefroeman]
I am going off of my experience with playing planetary annihilation, but, moving celestial objects is just a matter of setting up the massive engines required to move it. I think FTL for these is sheer crazyness, if not impossible. But, attaching ship engines onto an asteroid and just programming it to fly on a set course doesn't seem out of the picture. It would look to be mainly a single system weapon, on able to attack targets within the same gravity well of the local sun. But, yes, defenses could be set up, but, even if you did manage to break up the comet/asteroid it would still rain down smaller fragments. Just a thought.
[/quote]

My idea of accelerating a giant object is gravity. If you can manipulate gravity, you could just make the asteroid 'fall' towards wherever you want it.

The use of engines on an asteroid, even FTL or sublight drives, would require insane amounts of fuel to power up, keep powered up, and continue to keep powered up, including constant maintenance due to the stress of moving such a large, solid object.