Originally posted by: jjones
Only an imminent colision with a planet-killing asteroid could hope to achieve what you suggest.
How imminent? Might-hit-in-50-years imminent, or "I can see it in broad daylight, it's going to hit tomorrow" imminent?
In the former, the "might hit" - we don't do anything about it, and hope that the silly little doomsday scientists are wrong with their trite calculations. Then when it can be seen in broad daylight, we all riot and blame the scientists for either not warning us, or for not making sure something effective (end probably expensive) was done in time.
Right now, our ability to deflect asteroids is very limited. Even a "small" asteroid is still incredibly massive. We launch little tin cans into space weighing a few hundred tons, or even a few thousand. An asteroid a few hundred meters in diameter will probably have a mass many thousands or even millions of times greater than that of the shuttle, which is around 2 million kilograms. Hit it with every nuke on the planet, and you'll just ablate a bit off of the surface, and it'll keep coming.
Our best hope for moving a threat is to catch it early, maybe launch a probe or two to really nail down its exact orbial parameters, and then somehow nudge it slightly off course so it will miss Earth. Such a thing would be completely untested, expensive, and would be countering a threat decades off - most people wouldn't see that as a priority.