[JasonC]

Well, the best idea so far about deflecting these is, you send a ship up and just park it in the right location near the asteroid, and the gravitational attraction of even the wee little ship, pulls the asteroid ever so slightly off its previous trajectory. (This is called a gravitational tether, incidentally. No physical hook-up required).

If you do it in the most sensitive direction before a near gravitational slingshot past a larger body, you change its course through the deeper gravity well. Effectively, the course correction to put in before, is amplified by the next interaction. The best time to get one is several years before a close pass, letting the ship sent (which can be robotic of course) hover over it for several years. Even a small mass can do the job with enough lead time.

So no, don't wait to see if it is too close after the pass, calculate well and deflect years before the 2029 pass.

[strategofr]

"So no, don't wait to see if it is too close after the pass, calculate well and deflect years before the 2029 pass."

Burp.

[KC Burke]

I have also herd talk of chaulking an asteroid -- basically covering it or it's sunward side with white dust. The difference in how that reflectivity interacts with solar wind can make a continuous push over a period of years and alter the orbit in a precalculated manner.