On March 27th India became the fourth nation to carry out an ASAT (anti-satellite) mission. India used a 19 ton, three-stage missile. The final stage of the missile homed in on and collided with the target, an inactive Indian satellite in a 280 kilometer high orbit. Owners of satellites criticized the Indian test because it put debris into orbit. India pointed out that the debris was minimal and most would eventually enter the atmosphere and burn up. India admitted that there were a lot of large (enough to damage another satellite) fragments created by the test but contended those would drift lower and burn up within a few months. So there was some danger but not long enough to be significant. While true it is also the case that the number of large fragments still in orbit keeps growing and that increases the odds that more collisions will occur.
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 in 2004 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 with increasing frequency since the late 1990s. 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 a 2009 collision between Cosmos 2251 and the Iridium comsat,, nor some 2014 collisions, largely because the high speed of these objects, and slight instability of their orbits, can turn an expected near miss into a direct hit. The 2013 collisions involved three satellites damaged or destroyed after colliding with small bits of debris.
Meanwhile, it is getting easier and easier to develop and built ASAT weapons. These weapons are not new and back in the 1980s the U.S. developed and tested both ASAT missiles (ASM-135) and air-launched satellite launcher rockets (the Pegasus). Back then the U.S. Air Force developed the ASM-135 for knocking down low orbit satellites by using a 1.2 ton missile launched from a high flying jet fighter. This was done in response to news that Russia was developing a similar system. The Russian system relied on killsats and was never that effective. A successful test of ASM-135 was conducted in 1985, but the program was shut down three years later because the Air Force preferred to spend the money elsewhere.
A little later, in the 1990s, a civilian firm (Orbital ATK) developed, tested and built Pegasus air-launched (from a B-52 or modified large airliner) three-stage solid fuel rockets for putting small (up to half a ton) satellites into LEO (low earth orbit). The first version of Pegasus weighed 19 tons and the latest one 23 tons. So far (1990 to 2016) Pegasus has been launched 43 times and failed only 7 percent of the time. Most of the failed launches were early development models. In other words, Pegasus is still in use and the Air Force has admitted that the ASM-135 could resume production and be even more reliable, effective and cheaper because of advances in missile and guidance tech since the 1980s.
There have been losses to space debris, whether it was created intentionally by an ASAT or by accident. In early 2013, Russia reported that one of its satellites was hit and damaged by debris from a Chinese satellite that China had destroyed in a 2007 ASAT test. This was 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.
China has developed even more ambitious ASAT systems. American analysts believe China had conducted three tests of ASAT systems by 2013. One test apparently sought to put a KillSat (Killer Satellite) in a high enough (20,000 kilometers) orbit that could threaten the American GPS network. The first such test was in January 2007, when China successfully tested a satellite destruction system. They used a smaller rocket to put a KillSat in orbit that destroyed an old Chinese weather satellite that was about 850 kilometers up. That's at the upper range of where most reconnaissance satellites hang out. Three years later a second test was conducted but a satellite was not actually destroyed.
Back in 2008, Russia and China urged the UN to outlaw the development or testing of systems that can destroy space satellites. The impetus for was the February 22nd, 2008 destruction of a broken U.S. spy satellite by a U.S. warship firing an anti-aircraft missile modified to intercept ballistic missiles. What upset China and Russia was that this feat put all their satellites in a low earth orbit (160-2,000 kilometers up) at risk. The U.S. cruiser used its Aegis radar to locate the satellite some 220 kilometers above and then fired a single SM-3 missile to destroy the SUV sized satellite.
Where this is going is a major wartime use of ASAT weapons that could destroy over a hundred satellites and create a much larger threat to any surviving satellites or space vessels passing through orbital space.