New Horizons faces an unusual challenge...

New Horizons faces an unusual challenge...  The New Horizons spacecraft is on its final approach to the Pluto/Charon system, which it will fly by on July 14th.  The unusual challenge derives from a simple fact: NASA doesn't actually know exactly where Pluto and Charon are!  The margin of error from Earthbound measurements is greater than the accuracy needed to aim New Horizons – so they're depending on frantic last-minute measurements from New Horizons itself (such as the imagery at right) to pin down the exact location of Pluto and Charon.

This is the first interplanetary mission where the aiming wasn't done entirely with Earth-bound metrics.  Unmentioned in the article is another interesting fact: none of this would have been possible until about 7 or 8 years ago, when the computing power required to model complex gravitational systems became routinely available...