Also posted at: http://www.gn.apc.org/cndyorks/yspace/articles/debris.htm.
A new eye in the sky is about to take the measure of a pollution problem that is out of this world. A US satellite to be launched today will count bits of cosmic debris 500 miles above the Earth's surface.
Some of the microscopic fragments will be stardust, left behind by passing comets. And some will be specks of paint, splinters of glass and shards of metal - part of the growing cloud of pollution from 40 years of investment in space.
There could be 150,000 objects in orbit, most between l cm and 10cm across, bits of litter left behind by the cold war and the growth of communications and navigation by satellite.
There are perhaps 10,000 larger objects - spent satellites, rocket stages and so on - systematically catalogued and tracked by radar. But the real hazards come from particles too small to see but which travel at five miles a second with the explosive power of a bullet.
Teams from the National Aeronautics and Space Administration have several times had to replace space shuttle windows, pitted by flying fragments. One satellite exploded in 1995 after a hit. A splash of urine, jettisoned by astronauts long ago, was found on the skin of a spacecraft recovered from orbit.
Into the swelling cloud of rubbish, the US Air Force has placed Argos: advanced research and global observation satellite. It carries a huge number of experiments - scientists have called it a "Swiss army knife in space" - and one of these is Spadus, a space dust monitor devised by the University of Chicago.
Scientists now have an instrument that can distinguish between the natural dust of space - the micrometeorites that pepper the planet all year round - and the litter from an industry that began with Sputnik 1 in 1957.
"We will be able to tell whether the debris is uniformly distributed or in clouds around the Earth, and even whether there is a ring around the earth, like Saturn's, but very weak," said John Simpson, one of the Chicago team. Space is huge, and spacecraft are small: for decades US and Russian military and business corporations assumed that they had the ultimate dump on the doorstep. But commercial investment in space is increasing dramatically. Old launch vehicles and satellites have collided, or exploded, or detached into pieces which have then collided with other pieces.
Astronauts have left behind spanners, cameras, and plastic bags full of excrement. Russian nuclear powered spycraft "parked" at high orbits have begun to leak irradiated fuel. Space has become a shooting gallery. The cost of "armour-plating" the International Space Station - the size of a football field and now being assembled in orbit against man-made rubbish travelling far faster than any bullet has added at least $5 billion (£3 billion) to its bill.
The concern is not limited to America: Europe is now a big player in space, and Britain has a huge share in the satellite industry. Richard Crowther, of Britain's Defence Evaluation and Research Agency, is one of a group of scientists who have campaigned for action for years. Argos is a step towards better understanding of the problem.
"The idea is to get snapshots of the environment an altitude at a time," he said. "When you add these snapshots together you will get an overall picture of the environment.
"Spadus handles dust from two millionths of a metre to 200 millionths. From Earth with radar, we can see objects as small as lcm. We can't track them but we can see them. Objects the size of a portable phone or larger you can track with radar, so you can work out where they are and where they will be in future."
The United Nations was just coming to the end of a three year review of the problem, he said. "Until now we have been trying to agree just how bad the problem is and which are the most effective measures. This year we will have to decide how we are going to deal with it.
We would expect in future that when people do use space they would leave the environment almost as they found it."
Where just a grain of sand can become a potent danger
Even if humans clean up their act in space, there will still he hazards.
A large comet or asteroid probably hits the planet once in 100,000 years but smaller meteors burn up in the sky every night. Most never fall to Earth - but even a grain of sand rushing in from outer space at 25,000 mph is a danger to anything in the way.
The Americans put in orbit a long duration exposure facility - a kind of deliberate target - and left it for six years to see what ,would happen. They found that a piece of aluminium debris less than lmm cross smashed through an aluminium wall 2.5cm thick. But they also found evidence that satellites were literally being "sandblasted" by millions of little impacts, mostly from spacedust; enough, in Nasaspeak, to "degrade mission performance or cause mission denial".
Some of this dust has been spilled by comets as they careered around the Sun: one of these, Comet Tempel-Tuttle, delivered a cloud of particles into which the Earth crashes each year. Every 33 years, it goes through the heart of the dust-storm: the Leonid meteor shower last November was supposed to light up the skies. It was a disappointment, but this year, it could deliver the long promised meteor spectacular, with hundreds of shooting stars every hour. The Spadus experiment has instruments sophisticated enough to distinguish between comet dust and satellite fragments. It will also look for comet trails. "There are 15 or 16 streams that are possible candidates for detection, based on how close we come to them," said one scientist. "There are a lot of things to look for."