- Gravitational tractor
In asteroid deflection, a gravitational tractor is a way to use the
gravitational attraction between a spaceship and an asteroid to modify its trajectory to prevent it from colliding with the Earth. In the plan, the spaceship hovers above the asteroid's surface using thrusters, and gravitational attraction deflects the asteroid. The thrusters must not point directly at the asteroid, else the effect would be voided by momentum transfer between exhaust gas and the asteroid's suface.Writing in Nature, physicists
Edward T. Lu andStanley G. Love ofNASA 'sJohnson Space Center show that a gravitational tractor is a reasonable proposition: it is robust to the asteroid's structure and rotation rate, and a technologically feasible plan (such as a 100 W nuclear electric propulsion system) could impart adelta v of a few millimeters per second to an asteroid with a diameter of 200 meters over the course of several years, sufficient to prevent an Earth impact.References
Gravitational tractor for towing asteroids, Edward T. Lu and Stanley G. Love, [http://www.nature.com/nature/journal/v438/n7065/abs/438177a.html "Nature" 438 (10 November 2005), 177–178, doi:10.1038/438177a] ; also, see [http://arxiv.org/abs/astro-ph/0509595 astro-ph/0509595] in the arXiv.
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