March 24, 2015:
An American space satellite exploded in orbit on February 3rd. This one was a twenty year old weather satellite that experienced an equipment failure that 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. At this point the air force is still trying to find any additional pieces of the satellite in orbit so that these can be tracked and the owners of other satellites warned if the debris will get too close.
While rare, satellite unexpectedly exploding is not unknown. It is more common for mishaps to occur as the satellite is put into orbit. Thus 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, meaning that they will soon fall towards earth and burn up.
The space junk situation is getting worse. 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. This call began when China 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, in early 2007 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.
In late 2007 the U.S. Terra environmental satellite was in an orbit that indicated a seven percent chance of hitting debris from the Chinese KillSat test. So controllers adjusted Terra's orbit slightly, to reduce the risk to zero. Similar adjustments have become more frequent since 2007 and have become more common as more satellites are put into orbit.
The IADC (Inter-Agency Space Debris Coordination Committee) 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. 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.