> space based laser
Lasers won't do squat. To move an asteroid you need nukes... either nuclear explosives or nuclear rocket engines. Bombs would be easier... we've got loads of 'em. If'n we could make the General Atomics "Casaba Howitzer" design of nuke, we'd *really* be in business here.
In any event, much as I'm a fan of the Rutans of the space world, this is the sort of thing that would require a Gubmint Mega Project. Build a whole armada of heavy lift launvh vehicles in the Saturn V class, launch a few hundred citybusters and a (probably manned) control system, and you'll be in business. Since I work for the company that makes the Shuttle boosters, I know what I'm going to be arguing for come the new year...