March 20, 2013:
On March 7th Russia reported that on January 22nd one of its satellites was hit and damaged by debris from a Chinese satellite that China had destroyed in a 2007 anti-satellite weapon test. This is only the second time that an active (still operational) satellite was hit by orbital debris. The last time was in 2009, when an American satellite was hit by a dead Russian satellite. Since that incident owners of active satellites have paid more attention to where all the space junk (debris) is up there and it is more common for active satellites to move out of the way of oncoming concentrations of debris. This uses up precious fuel, which is normally used to maintain a low flying satellite in the proper orbit. When the fuel is gone, so is the ability to move and the usefulness of the satellite.
The 2009 loss was an American Iridium satellite, which supplies satellite phone service and was at an altitude of about 770 kilometers over central Russia. The Iridium satellite was hit by a dead Russian communications satellite (the one ton Cosmos 2251, equipped with a nuclear power supply, launched in 1993). The Russian bird could not be moved, nor could the Iridium (which, while active, was not equipped with thrusters for movement). The Iridium bird was one of sixty, so satellite phone services was not interrupted because of the spare capacity in the system. The collision turned the two satellites into 600 bits of debris.
The last time anything like this happened was in 1991, when a dead satellite ran into debris from another and created more debris. There have been two deliberate collisions since then. In 2007, China launched a "killsat" that maneuvered into the path of a dead Chinese weather satellite and destroyed it. In 2008, the U.S. Navy used one of its Aegis equipped warships to destroy a malfunctioning U.S. spy satellite with an anti-missile missile. Russia and China have since called for such U.S. activity to be outlawed.
After sixty years of humans putting objects into orbit, there is a lot of junk up there. Currently, over 300,000 dangerous objects 10 mm (.4 inch) in size have been identified. The smallest of these is capable of disabling a satellite, or damaging a spacecraft, mainly because these objects collide at very high speed (9-10 times faster than a bullet) when the two objects are coming from different directions.
There are nearly 22,000 objects 10 centimeters (4 inches) or larger in LEO (low earth orbit) and 500,000 smaller objects that are still large enough to cause damage. All of these can do some catastrophic damage to satellites or spacecraft. There are millions of objects smaller than 10mm, and these are responsible for many satellites failing early because of cumulative damage from getting hit by several of these micro objects. There are over 250 commercial satellites up there, plus nearly as many military ones.
There are a lot of people keeping an eye on this clutter. The U.S. Air Force Space Surveillance Network, which tracks objects 10mm and larger, stopped sharing all of its information nine years ago, for national security reasons. The Russian Space Surveillance System is known to use radar to track over 5,000 objects in low orbit. But the Russians have never shared this data completely or regularly. Filling in the gaps are two international organizations, IADC (Inter-Agency Space Debris Coordination Committee) and ISON (International Space Observation Network). IADC is a government operation, whose members include the U.S. NASA and the equivalents in Russia, China, and several other major nations. Like most government organizations, not all data is shared.
ISON is a non-government organization, and they come up with some of the most interesting stuff. ISON comprises 18 scientific institutions, 18 observatories, 25 telescopes, and over a hundred professionals. ISON does not, as far as anyone knows, withhold data because of any national security concerns. This is fairly certain because ISON work is monitored, and complemented, by the efforts of thousands of amateur astronomers and orbital addicts who connect via the Internet and constantly scour the orbital space for new objects and dangerous movements by existing ones.
ISON has already spotted nearly 200 larger (over 10mm) objects that have never been reported by any of the government organizations. The Internet based amateurs are often the first to spot a lot of this new activity, mainly because they have more eyeballs, and, in some cases, impressive optical equipment searching the skies.
When someone spots an object headed for a maneuverable satellite, the owner is alerted and the bird is moved. This has happened several times in the last few years. The number of dangerous objects up there increases 10-20 percent a year. That's even with many of them falling into the atmosphere and burning up each year. Apparently, no one was able to predict the collision between Cosmos 2251 and the Iridium bird, nor the recent collision, largely because the high speed of these objects, and slight instability of their orbits, can turn an expected near miss into a direct hit.