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Scientists design spacecraft to save Earth: A spacecraft capable of saving the world from a catastrophic asteroid collision has been designed by British space scientists.
The Telegraph
Richard Gray, Science Correspondent
29 August 2009
Heroic missions to stop life on Earth from being wiped out by an asteroid have become a favourite theme for Hollywood disaster films.
Now, a team of British engineers have designed a real-life spacecraft to save the world from destruction.
Their invention, called a "gravity tractor", would be deployed when an orbiting rock is detected on a collision course with Earth.
The spacecraft would intercept the asteroid and position itself to fly alongside it, just 160ft from its surface.
From this position, the 10 tonne craft is able to exert a small gravitational force on the rock, pulling the asteroid towards it.
By gradually modifying its course, over several years, the gravity tractor is able to slowly shift the asteroid's trajectory enough to ensure it misses the Earth.
Details of the planned craft come just weeks after an asteroid or comet was found to have ploughed into Jupiter, which is a giant gas planet, leaving behind a vast impact scar – estimated to be about the same size as the Earth – in its atmosphere.
Scientists believe it is only a matter of time before an asteroid comes close enough to the Earth to be a threat.
Nasa, the US space agency, is so concerned that it has established an expensive monitoring programme to track every object in the sky that might come close to the planet.
It estimates there are more than 100,000 asteroids orbiting near the Earth that are large enough to destroy a city. So far the agency has only been able to identify and track 6,363 of them.
Just one football pitch-sized asteroid would be capable of obliterating a large city and could cause widespread destruction by also throwing flaming material into the atmosphere and triggering tidal waves.
In 1908, a meteor of this size exploded above Lake Tunguska in Siberia, destroying 770 square miles of forest. Such collisions hit the Earth every 100 years.
To avoid such a disaster, engineers at space company EADS Astrium, which designs and builds spacecraft for Nasa and the European Space Agency, have designed the gravity tractor.
The team, who are based in Stevenage, in Hertfordshire, believe the craft could divert asteroids that are up to 430 yards across – big enough to release 100,000 times more energy than the nuclear bomb dropped by the United States on Hiroshima in 1945.
"Anything bigger than 30m (32 yards) across is a real threat to the Earth," said Dr Ralph Cordey, science and exploration business development manager at Astrium.
"Unfortunately it is a matter of when rather than if one of them hits us.
"The gravity tractor exploits the principals of very basic physics – every object with a mass has its own gravity that affects objects around it. It can move fairly large objects 300 metres (984ft) to 400 metres (1,312ft) across.
"These asteroids are hurtling around our solar system at 10km per second, so when you scale that up, you just need a tiny nudge to send it off course."
The 30m gravity tractor would need to be launched around 20 years before an asteroid is due to the hit the earth, giving it enough time to intercept the asteroid as it orbits the sun and change its trajectory.
The spacecraft would use four highly efficient low energy thrusters – known as ion thrusters which are often used on deep space probes – to gradually shift its position as it flies above the rock, causing the gravitational pull it has on the asteroid to "tug" it off the collision course.
With an asteroid around 300 yards across, the gravity tractor changes the angle it is travelling in by a fraction of an inch over a period of 15 years, creating enough of a change in the orbit for the asteroid to miss the Earth.
The team have designed the gravity tractor and planned the details of the mission. The craft could be built in a relatively short time, using existing technologies, if an asteroid was detected on a collision course.
It is likely it would require an international agreement to send a mission into space.
Christian Trenkel, who worked on the mission plans, said: "We have designed the mission using the technology that we currently have available, so it could be put into practice at any time."
Earlier this year, Nasa published a feasibility paper on using a gravity tractor to steer an asteroid, or near earth object as they are called, away from the Earth. It concluded that with enough warning it could be highly effective.
In 2004 an asteroid known as Apophis caused concern after it was calculated to pass alarmingly close to the Earth.
Projections of its path around the sun predicted it had a one in 37 chance of hitting the planet in 2029 – the highest threat in recorded history.
The threat of a 2029 collision was later ruled out but scientists fear that the asteroid could still pass through a key point in space known as a "keyhole" that would put it on course to collide with the Earth in 2036.
Kevin Yates, project manager for the UK Near Earth Object Information Centre which is responsible for warning UK ministers of risks from asteroids and comets, said: "Gravity tractors are a solution that are growing in popularity.
"There does need to be international agreements on how to tackle a threat from an asteroid.
"There are all sorts of political difficulties if, for example, a mission only managed to move the point of collision on the Earth from one country to another."
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