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Astronauts' tug aims to deflect asteroid threat</font size></center>
An artists impression of the gravity tractor
The Telegraph
By Roger Highfield, Science Editor
(Filed: 10/11/2005)
Two astronauts today unveil a method they claim could deflect asteroids away from a collision course with Earth.
Their move follows a warning by Britain's Natural Hazard Working Group that more must be done to prepare for devastating impacts that are thought to be responsible for extinctions such as the demise of the dinosaurs 65 million years ago.
Edward Lu and Stanley Love, of Johnson Space Centre, Houston, say in the journal Nature that it will not be necessary to send for the likes of Bruce Willis or Ben Affleck when disaster looms.
Instead they will launch their gravity tractor.
Such a machine has advantages over other scenarios. Blowing up an asteroid could still leave the Earth vulnerable to incoming fragments, as shown in the film Deep Impact.
Even a nuclear device might not work, despite the big screen efforts of Harry S Stamper (Bruce Willis) and his crew in Armageddon, because a low density asteroid might absorb the impact and carry on its way.
And, despite the success of Nasa's Deep Impact probe and a comet this year, the astronauts say that attaching a spacecraft to an asteroid and pushing on it directly could be tricky as they tend to be little more than spinning collections of rubble.
Instead, they propose that a nuclear-powered "tugboat" spacecraft be sent to a threatening near-Earth object to gently alter its course.
The tug would be a heavy rocket that could hover over the asteroid's surface and rely on its tiny gravitational pull.
The tractor's thrusters would be angled outwards so they do not blast the asteroid's surface and reduce the towing force.
The authors calculate that a 20-ton gravity tractor could safely deflect an asteroid 200 metres across in about a year.
Visitors to the Science Museum in London today will be able to listen to an interview with Dr Lu.
• The US patent office has granted a patent on a design for an antigravity device that, if it worked, would allow perpetual motion, breaking its resolution to reject inventions that defy the laws of physics.
The patent, issued to Boris Volfson, of Indiana, is based on a space vehicle propelled by a superconducting shield.
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