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In 1978, the NASA scientist Donald Kessler predicted that a collision between two pieces of space junk could trigger a cascade of further impacts, creating dangerously large amounts of debris.
Kessler pointed out that when the rate at which debris forms is faster than the rate at which it de-orbits, then the Earth would become surrounded by permanent belts of junk, a scenario now known as the Kessler syndrome.
By some estimates, the Kessler syndrome has already become a reality. In January 2009, a collision between the Iridium 33 and Cosmos 2251 satellites created just this kind of cascade. Two years earlier, the Chinese military tested an anti-satellite weapon by destroying one of its own satellites called Fengyun 1C. Both incidents took place at altitudes of about 800 km.
Today, the European Space Agency's Earth observing satellite, Envisat, orbits at about this height and is regularly threatened by potential impacts. Over 60 per cent of these threats can be traced back to the Iridium/Cosmos collision or the Fengyun incident.
But while space junk threatens most space operators, few have a real incentive to do anything about it. If a significant threat arises, it's usually possible to move a satellite out of the way. That's much cheaper than actually clearing the junk.
The result is a "tragedy of the commons" situation, where a common resource is exploited to the point where it becomes unusable.
Which is where a government agency like NASA comes in. Various ideas have been floated for removing space junk, most of them hugely expensive.
Today, James Mason at NASA Ames Research Center near Palo Alto and a few buddies describe a much cheaper option. Their idea is to zap individual pieces of junk with a ground-based laser, thereby slowing them down so that they eventually de-orbit.
Of course, laser removal isn't entirely new. In the 1990s, the US Air Force studied the idea, thinking that a powerful enough laser could ablate an object, creating a force that could be used to de-orbit it. The trouble with this idea is that such a powerful laser has an obvious dual purpose, which is unlikely to please other space faring nations.
So Mason and pals have studied the possibility of using a much less powerful system which uses the momentum of photons alone to decelerate the junk. Focused onto a piece of junk for an hour or two every day, they calculate that a 5 KW laser could do the trick and that such a device could tackle up to ten objects a day.
Complete Story
Kessler pointed out that when the rate at which debris forms is faster than the rate at which it de-orbits, then the Earth would become surrounded by permanent belts of junk, a scenario now known as the Kessler syndrome.
By some estimates, the Kessler syndrome has already become a reality. In January 2009, a collision between the Iridium 33 and Cosmos 2251 satellites created just this kind of cascade. Two years earlier, the Chinese military tested an anti-satellite weapon by destroying one of its own satellites called Fengyun 1C. Both incidents took place at altitudes of about 800 km.
Today, the European Space Agency's Earth observing satellite, Envisat, orbits at about this height and is regularly threatened by potential impacts. Over 60 per cent of these threats can be traced back to the Iridium/Cosmos collision or the Fengyun incident.
But while space junk threatens most space operators, few have a real incentive to do anything about it. If a significant threat arises, it's usually possible to move a satellite out of the way. That's much cheaper than actually clearing the junk.
The result is a "tragedy of the commons" situation, where a common resource is exploited to the point where it becomes unusable.
Which is where a government agency like NASA comes in. Various ideas have been floated for removing space junk, most of them hugely expensive.
Today, James Mason at NASA Ames Research Center near Palo Alto and a few buddies describe a much cheaper option. Their idea is to zap individual pieces of junk with a ground-based laser, thereby slowing them down so that they eventually de-orbit.
Of course, laser removal isn't entirely new. In the 1990s, the US Air Force studied the idea, thinking that a powerful enough laser could ablate an object, creating a force that could be used to de-orbit it. The trouble with this idea is that such a powerful laser has an obvious dual purpose, which is unlikely to please other space faring nations.
So Mason and pals have studied the possibility of using a much less powerful system which uses the momentum of photons alone to decelerate the junk. Focused onto a piece of junk for an hour or two every day, they calculate that a 5 KW laser could do the trick and that such a device could tackle up to ten objects a day.
Complete Story
