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.

That could help move junk away from potentially dangerous orbits and ultimately to de-orbit it entirely. In fact, Mason and co say that the system could reverse the Kessler syndrome, so that the rate of debris removal once again exceeds its rate of creation.

They say their system could even be used for manoeuvring suitably-designed satellites, without the need for them to carry propellant. Such a system could be marketed as a commercial venture, thereby helping to pay for it.

Not that it need be terribly expensive. Mason and co estimate that a test device could be knocked up for a million dollars, which would have to be shared by many spacefaring nations, to avoid the inevitable legal issues that using such a device would raise.

Of course, the US (and obviously China), already have the technology to this kind of work, using their own antisatellite systems. Indeed, Mason and co say “it may be possible to perform a near-zero cost demonstration using existing capabilities such as those of the Starfire Optical Range at Kirtland AFB.”

It’s only a matter of time before a piece of space junk causes serious havoc in orbit, by threatening a crewed mission, for example. There’ll be plenty of interest in this kind of technology after such an incident. And then we’ll be asking why we didn’t invest in the technology when we had the chance to prevent this kind of disaster.

Ref: arxiv.org/abs/1103.1690: Orbital Debris-Debris Collision Avoidance

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Correction–15 March 2011
In response to this post, NASA Public Affairs Office sent the following:
James Mason, author from the Universities Space Research Association, would like a few points clarified about the following sentences:
1) “Today, James Mason at NASA Ames Research Center near Palo Alto and a few buddies…”
James Mason is of Universities Space Research Association (USRA). The work was a collaboration between USRA, Stanford University and NASA Ames: Mason and Marshall are funded by USRA. Stupl is funded by Stanford. Levit is a NASA civil servant.
2) “Focused onto a piece of junk for an hour or two every day, they calculate that a 5 KW laser could do the trick”
The “trick” is to only displace the object by a tiny amount, thereby preventing a collision. This laser’s effect would be far too weak to rapidly affect the decay of the object’s orbit. To actually de-orbit a debris object with a laser requires forces about 1,000 times more powerful. To “ultimately de-orbit it entirely” would take about the same amount of time as if we had not illuminated it - this may well take decades, depending on the object.
3) “Mason and co estimate that a test device could be knocked up for a million dollars”
The laser alone would cost about a million dollars (it is a commercially available industrial laser). The actual cost of an operation system (including telescope, adaptive optics etc) is unclear, but is likely to be at least tens of millions.
4) “Of course, the US (and obviously China), already have the technology to this kind of work, using their own antisatellite systems. Indeed, Mason and co say “it may be possible to perform a near-zero cost demonstration using existing capabilities such as those of the Starfire Optical Range at Kirtland AFB.”“
“antisatellite systems” may be too strong. The existing military technology is probably mainly for (at the moment) tracking and imaging other satellites. The Directed Energy Directorate at Kirtland probably has most of what would be needed to do a technology demonstration, however we stress in the paper that this system should be done as an international collaboration because of the obvious security implications.
Also, Jan Stupl, also an author from Stanford University, made a comment on the following sentence:
“Their idea is to zap individual pieces of junk with a ground-based laser, thereby slowing them down so that they eventually de-orbit.”
Our piece is about collision avoidance, not about de-orbiting. Same is true for the deadline: it is not about ‘removing’ space junk, but ‘moving’…