[Curmudgeon]

I don't see any sensors listed. If you're depending on naked eye sightings of the impactors, it's going to be pretty close to the habitat already. Depending on how close to lightspeed the impactor is, you may be taking about a minute between sighting the impactor and the collision, which won't let you change your velocity by much, so it'll depend on how big the impactor is both absolutely and relative to the habitat.

You can probably slow the habitat down or speed it up enough to generate a miss for a 5-mile diameter impactor aimed at the very end of the habitat, OTOH, if the impactor is targeting the habitat dead amidships, you probably aren't going to be missed, and a 5 mile diameter impactor, even at the speed of most objects in our own solar system would be an extinction level event for Earth. I don't see the habitat faring better. And on the gripping hand, unless your hostiles strap their own Captain Kong onto the impactor with a steering mechanism, they're going to have a hard time targeting an orbiting planet much less a habitat.