Starship Asterisk*

A tracking device (transmitter) placed on an asteroid would make them easier to track but not cost effective, yet.

Deep space radar is what is normally used. NEO's (near earth objects), that may be a future danger, are tracked and their orbits watched for any possible change in their paths that could bring them into earth contact. If such an object were to come into close proximity with another solar system body that body's gravity could effect the objects path changing the trajectory enough to bring it closer to earth on it's next path. Or, farther from earth.

Norval

If tracking instruments were planted on Earth aproaching asteroids; wouldn't that make them easier to track than observing them by telescope??? Or might it be too expensive??

Link http://antwrp.gsfc.nasa.gov/apod/ap050919.html

Just hoping that they will share all the data.
They do have some interesting experiments planed for the Hayabusa spacecraft. Link http://www.isas.jaxa.jp/e/enterp/missio ... ndex.shtml

Norval