In an article in Spaceflight Now, it was reported that two satellites, a defunct Russian satellite and a commercial Iridium communications satellite, collided around 12:00 p.m. EST on February 10, 2009. The collision obliterated both satellites. Initial radar tracking has identified more than 600 pieces of debris.
Iridium Satellite model.
According to Air Force Brig. Gen. Michael Carey, deputy director of global operations with U.S. Strategic Command, there are about 18,000 objects in space that they routinely track. These include objects that they know about that are 3.9 inches across or larger. The collision between the two satellites occurred at an altitude of 491 miles over northern Siberia.  According to a 2008 report by an international monitoring group called the Space Security Index, before the latest incident, it is estimated that there were over 300,000 orbital objects measuring between 1 and 10 centimeters in diameter and “billions” of smaller pieces. Traveling at speeds that can reach many thousands of kilometers per hour, the tiniest debris can damage or destroy a spacecraft.
According to the article, in 1996, a French spy satellite was hit by a wheeling fragment left from an exploded Ariane rocket at 50,000 kilometers per hour. In June 1983, the windscreen of the US space shuttle Challenger had to be replaced after it was chipped by a fleck of paint measuring 0.3 millimeters, that impacted at four kilometers per second. The latest collision added an additional 600 pieces that will need to tracked.
If it is not self evident, one might ask, “Why it is important to track the objects?” Well, every time a rocket is sent into space, manned or unmanned, it is important that the rocket is not sent up in a collision course with something else already in orbit. Objects traveling 20,000 miles an hour on a collision course do not fare well, this included astronauts.
We take space walks almost for granted these days. When we ponder on the possibilities of a collision that might occur between a piece of space debris and an astronaut, the prospects of this are not good at all.
Back in school, we learned how a fusion reaction works. An atom splits sending out particles which split other atoms and they in turn do the same thing. The rate of atoms splitting continues to grow until the rate is enormous. Now let us ponder space satellites and space debris. What if satellites began to collide, producing hundreds of debris objects? These resulting objects then would collide with other objects producing even more objects. At what point do we reach a “critical mass” of space debris where it will be impossible to leave Earth and go into space without being struck by space debris? Something to ponder……
For more information about these articles, go to one of these the websites: http://spaceflightnow.com/news/n0902/11iridium/ oor
http://www.dailystar.com.lb/article.asp?edition_id=10&categ_id=2&article_id=99326