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The trick is figuring out exactly when the asteroid will be in the exact place where such a modest bump would be effective.

I wonder if the author of this piece ever heard of Deep Impact? You know...the rendezvous and intentional collision with a moving comet on July 4th, 2005?

It's not a "trick." It's called rocket science.

radio beacon?? whats wrong with telescopes?? do they expect an asteroid to run around changing course unpredictably??

Apophis huh?

A singularly ominous and inappropriate appellation.

There is an excellent 5 page article on this, the asteroid originally known as "2004 MN4" in the July/August 2005 issue of The Planetary Report of The Planetary Society. Unfortunately it is not available online. This is the 320m diameter asteroid that at the end of last year briefly looked like it might hit us 4/13/2029. Best data now is that it will be a very close miss then, coming closer than the geosynchronous satellites. However such a close flyby will change its orbit; by how much depends on precisely how close it comes. One possible distance results in it hitting earth in 2036. That risk is currently estimated as 1/12,000. One website estimates 850MT energy for that collision - think Krakatoa times 4; although the risk is small its energy is high enough to average out at 70KT predicted energy.

Even though we have quite a bit of data on it we can't yet predict the orbit to the needed precision to rule in or out a 2036 hit. We need to predict the miss distance within 600 meters. Best current predictions are that the available earth based (Hubble can't help here) future observations probably won't improve our orbit enough to know before the 2029 pass whether 2036 will be a hit. Placing a radio beacon on it would give us enough data to know before 2029. In any case we will know soon after the 2029 pass whether the 2036 pass will hit. Moving the asteroid to avoid a 2036 collision would be much easier before the 2029 pass than after it, requiring just 0.01% as much energy. The early fix is likely possible in time; the late fix may be beyond our ability then.

Timing may become an issue. Can we expect NASA and the rest of the government to pull off a massive emergency space mission in seven years? From JFK to the moon took nine. First, I'd advise letting the astronomers firm up their predictions. If they expect enough data from earth based sources to arrive in time, than wait for that. If there's a good chance we won't learn enough that way than this looks like a great target for one of the unmanned space missions that NASA would likely budget anyway. Tag it with a radio beacon and do whatever other science can be added to the mission for a reasonable price. Than we'll know whether or not to panic while we can still move the dang thing out of our way. In parallel (I hope) to the above I endorse efforts to develop, and test on some orbitally safe asteroid, the technology needed to move a bad one. We're sure to need it someday, our technology is probably up to it and the cost is cheap by the standards of pork on Capital Hill.