Divide and Collide

(Inspired by "Cutting asteroid in sections to save earth" by [SolarDon])

This idea is intended to reduce a large, solid iron asteroid on a collision course with Earth into many small chunks that will burn up in the atmosphere instead of hitting the ground. It needs a year or two to work, though.

An asteroid is going to be rotating in almost all cases. (I think I've read at least three different references to that (if something comes into view and it isn't rotating, it is most likely a spacecraft).)

A ship pulls up next to the asteroid, and fires a grappling hook/magnet onto the equator. The rotation carries the grapple around, until the grapple's cable is wrapped around the equator a few times. A team of intrepid robots equipped with mighty lasers (and magnetic treads) rides the end of the cable down to the asteroid. The team secures the end of the cable, girdling the equator.

The robots then use the lasers to slice the asteroid in half from pole to pole--into east and west hemis, not north and south--and the cable keeps it from splitting. (Solar power or nuclear power, it's going to take a while.)

The robots then cut the cable, letting the two halves of the asteroid separate at the right time, which causes them to go out from the trajectory, no explosives needed, just the centrifugal force of the rotation. (In some cases, the two halves could separate far enough to go on each side of the Earth, as in [SolarDon]'s idea.)

In this idea, half the robots go with each half of the asteroid. They use their lasers to blast away little bits of their respective asteroid halves, steering and accelerating them. And, of course, cutting grooves to weaken the asteroid and prepare it to break into chunks.

The two halves will theoretically come back together again after one orbit of the sun in their now-independent orbits. (Based on my understanding of orbital dynamics.) The speed of the collision would be the speed with which the two halves went away from each other, but the brave little robots have had a year to work. Their goal is to have the two halves collide as quickly and as accurately as possible, and in as fragile a state as possible.

The collision would reduce the asteroid into many small chunks, which would supposedly not reach the surface of the Earth.

The robots would bail before the collision, re-enter the Earth's atmosphere in a blaze of glory, and parachute down to their ticker-tape parade and beeping groupies.

(This goes halfbaked when you consider that a whole lot of small meteoroids will now be headed into the artificial satellites in orbit around Earth, but that's better than one big one hitting the planet. The meteoroid swarm could be in a slightly different orbit than originally, of course. Practically, the asteroid could be moved by the robots almost as well if it stayed whole. I just wanted to do something with my realization that the rotation would carry the two halves away, but they would come back together again.)