> If we can make the effort to "tag" it, how much harder would it be to put something on it that would blow it to bits, when it goes away from Earth?
A lot. A tagging mission could be carried out similar to the NEAR mission... call it one Delta II launch, well under $100 million, launch it in less than 5 years. But a mission to deflect the asteroid away from an impact would require that very same mission to be launched anyway, with numerous additional missions to follow.
Deflecting the asteroid would be substantially easier than blowing it up enough to no longer pose any sort of risk... if you've got decades to do it. But either way would require a hell of a lot more launch capability than a single Delta II. Speaking as a "rocket scientist," I'd LOVE to see such a mission put together; it'd be great to build up the infrastructure. But it would nevertheless be a substantially longer-term and more costly mission than a simple transponder.
Are you telling me that we don't have the capacity to launch a nuclear warhead (or a sufficient combination of them) to an asteroid, with some sort of timing device that would let us blow the thing up, or at least deflect it? Or have I been watching too many Bruce Willis movies?
You'll need a LOT of mass at REaLLY high speeds to do this; right??