Estimating Asteroids

A new NASA survey estimates there are around 4,700 Near-Earth asteroids bigger than 330 meters across.  That's large enough to cause at least regional disaster in the event of a collision.  The uncomfortable truth is that only about 30 percent of that populatiom has so far been found.

While this group holds the possibility for catastrophe, it also has great promise.  Many of those flying rocks are easier to reach than the Moon is in terms of energy requirements.  That makes them excellent targets for the first manned missions beyond the Moon, as well as for asteroid mining operations like those planned by Plannetary Resources.