The Gravity Tractor

In this artist's impression by Dan Durda, a gravity tractor near an asteroid uses an ion engine to hover above its surface. The asteroid feels the gravitational pull of the tractor and accelerates slightly towards it. Calculations by NASA astronauts Ed Lu and Stan Love show that with several years warning, such a device would be capable of changing a dangerous asteroid's orbit by enough to make it miss the Earth.

For more information see Nature, Vol. 438, 177 (2005)

Ed Lu, co-inventor of the gravity tractor, was a solar physicist at the University of Hawaii prior to becoming an astronaut.