In November 2021 the United States accused Russia of being the source of the orbital debris which passed so close to the ISS (International Space Station) that the seven personnel on board, including one Russian, got into their spacesuits and boarded their Soyuz capsules kept at the ISS for emergency return to earth in case the ISS was disabled, especially by an unexpected debris swarm.
Russia had conducted an unexpected ASAT (anti-satellite) test on November 15 using a “direct ascent” missile launched from Russia against Cosmos 1408, a 1.7-ton Russian electronic surveillance satellite that was sent up in 1982 and had a useful life of less than a year. Satellites of that era did not have a propulsion system on board that would move the satellite lower after it was no longer needed so that it could burn up in the atmosphere. Cosmos 1408 has been steadily moving lower since 1982 and was still years away from entering the atmosphere. The ASAT test was a success but it created 1,500 bits of debris large enough to be detected and tracked from earth. Some of that debris ended up on a collision course with the ISS, but missed.
Russia tried to avoid responsibility for the accident by pointing out that such ASAT weapons are legal and sometimes needed to destroy large satellites that might not completely burn up in the atmosphere. That’s not what happened to Cosmos 1408, whose explosive destruction while still 400 kilometers above the earth, sent many of those 1,500 fragments into higher orbits where they will remain a menace for years.
There are only four nations capable of carrying out direct ascent missions like this. In 2019 India carried out its first ASAT mission, using 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 very low (280-kilometer-high) orbit. Owners of satellites criticized the Indian test because it put more 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 most would drift lower and burn up within a few months because the destroyed satellite was already close to reentry. There was some danger from the fragments 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 increasing the odds of more collisions. The Russian ASAT test hit a satellite in a higher orbit and caused a debris field that would take more than a few months to descend into the atmosphere.
After sixty years of humans putting objects into orbit, there is a lot of dangerous junk still up there. Currently, over 300,000 dangerous objects 10 mm (.4 inch) in size have been identified. The smallest of these can disable a satellite, or damage 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 nearly a thousand commercial (mostly) and military satellites up there and the number is expected to multiply as more small satellites are put into LEO to provide global wideband Internet service as well as other forms of communication and monitoring of the climate and the earth surface, mainly for commercial uses. These smaller sats operate in swarms and at the low end of LEO, which extends from 300 to 800 kilometers above the earth. Debris disabling a few small sats in a swarm is no catastrophe. But damage to the growing number of space stations and manned space vehicles and larger satellites in LEO is another matter.
Efforts by the U.S. Space Command, Russia, China and many amateurs linked via the Internet to track this debris have provided a much more complete picture of the situation, and can usually determine who or what was responsible for new additions to the growing debris menace in LEO. The further out, there is a lot more orbital space and fewer satellites, usually larger ones equipped with a propulsion system to send them low enough to burn up in the atmosphere. There is growing a risk of SLVs (satellite launch vehicles) being hit by debris as they enter LEO to release their satellites or move on to higher orbits. Any effort to clean up LEO would be expensive and no one is volunteering to spend any money on that, at least not until the situation becomes critical.
This debris tracking effort has been under way for decades and has become quite sophisticated and open because of the large number of amateur observers who have better equipment and lots of help from fellow amateurs via the Internet. The effectiveness of the amateurs forced the major powers to be more open and even cooperate. This means that anyone who does something they would rather not become public knowledge is more restrained than in the past.