NASA
How will humanity keep enormous, Earth-obliterating meterors away? In 2005, two NASA scientists proposed a gravitational tractor. Stick a 20-ton, nuclear-powered ion-drive space ship next to an asteroid, they said, and through methodical maintenance, the two objects will attract each other -- so much that the asteroid's course will be shifted, and it won't hit our planet.
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This article available online at:
http://www.theatlantic.com/technology/archive/2012/07/picture-of-the-day-how-we-might-keep-killer-meteors-at-bay/259557/