On October 27th the ISS (International Space Station) had to burn some of its fuel (which has to be brought up by cargo rocket at great expense) to move out of the way of a swarm of debris. This “debris field” missed the ISS by about 320 meters. This hazard was created in 2009 when wreckage from an old Russian satellite hit an American Iridium communications satellite.
Without the warning of the approaching swarm the ISS would have been in great danger. Those warnings are often provided by the IADC (Inter-Agency Space Debris Coordination Committee). This is an international organization that coordinates the exchange of information, and space operations, as they relate manmade and natural debris in orbit around the earth. What is up there and where it is constantly changes. Every year some of this stuff falls into the atmosphere and burns up but there are always new accidents or deliberate operations that add more junk to the spaceways. There is currently over 500,000 pieces of manmade debris, weighing about 6,000 tons, in orbit. More is being added faster than existing debris falls back into the atmosphere and burns up. Proposals to destroy a lot of this debris are stalled because any solution is very expensive and there is no agreement on who would pay for it.
Meanwhile there are agreements to equip satellites with the capability to leave orbit and enter the atmosphere (and burn up) at the end of their useful lives. But a lot of old and useless satellites still up there did not have this function and are a continuing menace. Even some of the new satellites with the self-destruct feature find that this feature does not work when enabled and so yet another dead satellite is left in orbit.
Some countries are deliberately doing things to make the space junk situation worse. This became news in 2007 when 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 the year. China had launched an anti-satellite system (a KillSat or Killer Satellite) on January 11th that destroyed an old Chinese weather satellite, about 850 kilometers up. That's at the upper range of where most reconnaissance satellites hang out. The KillSat hit the weather bird, and the result was several million fragments. Most of the pieces are tiny, but at least 817 are truly dangerous (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. But these other debris swarms are the result of accidents. For example, a month after the KillSat incident a new swarm was created because of 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.
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. Thus 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 collision situation. For a satellite costing several hundred million dollars to build and put into orbit, this is considered a prudent way to operate.
Currently some 900 active satellites are in orbit, and nearly half of them are American. About 75 percent of all satellites are non-military (most of them commercial, the rest government non-military birds). The Russian Sputnik was the first satellite ever put in orbit, in 1957. The U.S. followed in 1958. Since then, ten other nations have done the same. France launched its first satellite in 1965, Japan and China in 1970, Britain in 1971, and India in 1980. Israel launched its first satellite in 1988. Ukraine did so in 1995. Iran claims to have put a satellite in orbit recently, but there is no conclusive proof. North Korea put a dead (non-responsive) satellite up in December 2012, and South Korea followed with a successful launch of a very active satellite a month later.
Not all the debris comes from collisions. 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 (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 are large and in a low orbit, so these will soon fall towards earth and burn up.