[jacquesm]

The masses you're talking about are such that you'd need to detect the asteroid well before impact (ideally: years) and that your efforts would not accidentally make matters worse rather than better. Even then it likely won't do anything at all. Calling Bruce Willis on line 3... But agreed on the smiley.

[sfink]

I'm not sure if we're talking about the same thing. The smiley drones would work fine hitting pretty close to Earth, even an hour or two out. And the mass shouldn't matter much, just the surface albedo.

Oh. You're probably talking about deflection. Yeah, deflection requires massive lead time, way more ballistic forecasting ability than I suspect we're capable of (isn't a clump of rocks going to heat up and throw things off as it comes in closer to the sun?), massively efficient engines to match velocity, and a whole lot of wishful thinking.

The smiley face might still be useful in that implausible scenario, I guess, if it changes the reflectivity enough to let the sun slowly nudge it out of the way? It at least avoids the velocity matching problem; you're intentionally crash "landing" anyway. And spinning is probably ok, as long as Galileo was right and the sun isn't orbiting around the asteroid. It's not likely to head straight at the sun.

But as you say, intervention seems just as likely to make things worse as better.