On an asteroid that has a diameter larger than eight kilometers, an astronaut who jumps will probably come back to the surface, Carr said. But if the asteroid is smaller than that, the astronaut may float away.

http://www.spaceref.com/news/viewpr.html?pid=23616

I imagine that to visit a small asteroid is a very risky mission since that some boulders is not fixed on asteroid and after roping it, this might also float away along with the astronaut.

How is this related to Cassini?


EDIT: TOPIC MOVED

This article has an interesting point. The next manned space mission after the moon would be targeted on an asteroid before than Mars.