It is getting crowded in orbital space and it is critical in LEO (low earth orbit) space. Higher orbits are also suffering from crowding but the situation there is much less critical than at LEO. Over the last sixty years nearly 10,000 satellites have been launched, about 6,000 are still up there and most are dead with only about 40 percent operational to one degree or another. The number of new ones is rapidly growing because of the greater use of smaller cubesats and new applications that call for thousands of cubesats in orbit to be effective. By the end of the 2020s about a thousand new satellites will be put in orbit each year.
Currently about 87 percent of functioning satellites are commercial or non-military government birds. About 60 percent of the commercial satellites, and at least half the non-commercial ones are used for communication. Another 27 percent of commercial birds are for earth observation (weather, land use and so on). The majority of the military/government satellites are communications and earth observation. The United States owns about half the operational satellites, China about 15 percent, Russia about seven percent and Britain has five percent. These five nations control 76 percent of operational satellites and that percentage will increase. A growing number of other nations now control their own satellites but American firms are largely responsible for the rapid growth of satellites launched, especially the swarms of cubestats used for communication, including worldwide cellphone connections or high-speed Internet access.
In the early days most of the satellites were military. That slowly changed and now a growing percentage of satellites in orbit are commercial. The more numerous commercial communications, scientific and observation satellites are growing in number and soon most of them will be cubesats. The biggest threat to these cubesates are the more numerous clouds of space debris. This is especially true for satellites that cannot move themselves to a different orbit. Most of these fixed orbit satellites are cubesats.
Monitoring and tracking these debris swarms has become a business because commercial satellite operators will pay for information that indicates where the growing number of debris swarms are and where the swarm will be. Most of the debris is in LEO space and those tiny objects regularly fall into the atmosphere and vaporize. Because of this, making maps of space debris map is a never-ending process.
This problem has been seeking a solution for some time. A decade ago, commercial satellite operators formed the Space Data Association and established the Space Data Center which collected all unclassified data on space debris. More powerful computers, analytic software and graphic display systems enabled new firms to be formed that could analyze and deliver all this data to commercial customers as a real-time service that can also predict what the situation will look like in the next few years. This enables commercial satellite operators to move expensive satellites out of the way when a debris swarm appears to be on a collision course. Future swarm activity is useful for planning where to put new satellites, especially the new networks containing thousands of smaller satellites that cannot move themselves out of the way.
While the debris is a danger, it should be put into perspective. Orbital space is actually quite large. Each “layer” of orbital space is over 600 million square kilometers. A layer is anything you want it to be (say a kilometer) between orbits. Even in low orbit (500-2,000 kilometers) you have 1,500 such layers. Orbits lower than 500 kilometers will rapidly drag debris back into the atmosphere. While this amounts to two billion square kilometers of orbital space for half a million bits of dangerous debris, most satellites occupy a small portion of these orbits and move through an orbit every 90 minutes. Most of the debris is concentrated in a small number of debris swarms, but these swarms tend to be in the most heavily used orbits. Bottom line is that current chances of any live satellites getting hit by debris are low but as more debris accumulates the chances of getting hit increase. It has reached the point where satellite operators take precautions, like equipping their satellites with the ability to move (until the fuel runs out) and paying people to constantly monitor the debris collision situation. For a satellite costing several hundred million dollars to build and put into orbit, this is considered a prudent way to operate.
This space debris is moving at high velocity meaning that objects as small as one cm (0.4 inch) can damage satellites and larger stuff (at least 10cm) can destroy satellites and seriously damage the ISS (International Space Station). While there are millions of fragments in orbit, most of the pieces are tiny. At least a thousand bits of debris are truly dangerous and these are the one that are at least 10 cm (four inches) long, wide, or in diameter. There are many such debris swarms up there that have to be watched and avoided. Not all the debris swarms are the result of accidents. For example, in 2007 a Chinese KillSat test put a huge debris swarm in orbit followed by another new swarm created by the accidental explosion of a Russian rocket that put over 1,100 dangerous fragments in orbit. Those two incidents increased the dangerous debris in orbit by about fifteen percent.
The most common time for orbital debris to be created occurs as a satellite is put into orbit. For example, in late 2012 the third stage of a Russian satellite launcher unexpectedly exploded after it failed to put two satellites into orbit. Launched via a Proton rocket, there was some kind of problem in the final stage and apparently the remaining fuel in that stage caused an explosion. This created a debris field of several hundred new bits of space junk, mainly pieces of the third stage and the two satellites. This prompted satellite (and space station) operators to check their orbits and make adjustments if there might be a collision with this new cloud of deadly (at high speed coming from the opposite direction) debris. On the bright side, many of these new bits of junk were large and in a low orbit, meaning that they would soon fall towards earth and burn up. That also has to be tracked, so you know what debris is gone and what is not.
A less common cause of orbital debris is stable satellites that explode in orbit. In early 2015 an American space satellite did this. This one was a twenty-year-old weather satellite that experienced an equipment failure which showed up to ground monitors as a rapid increase in internal temperature followed by the satellite exploding into 43 pieces. This was not catastrophic for weather monitoring since this satellite, because of its age, was relegated to backup duty in 2006. Eventually, when it failed, it would have been maneuvered into a lower orbit where it would eventually burn up in the atmosphere and leave no debris in orbit. As soon as signs of malfunctioning in the satellite were detected plans were made to maneuver the satellite into the lower orbit, but the satellite soon became uncontrollable and exploded. While rare, a satellite unexpectedly exploding is not unknown. The space junk situation has been getting a lot worse in the 21st century. In 2007 the United States became the first nation that had to change the orbit of one of their satellites to avoid the cloud of debris created when China tested an anti-satellite weapon earlier in 2007.
Most of the dead satellites are on higher (than LEO) orbits and that means it will take a long time for them to enter earth atmosphere and burn up. But the higher orbits are larger and the satellites up there are fewer than those in LEO with lots of empty orbital space to use without endangering other satellites. The real and future problems are in LEO space, where all those cubesats are.