Ant wrote to mention a National Geographic article looking at the cluttered nature of Near-Earth Orbit. From the article: "Since the launch of the Soviet Union's Sputnik I satellite in 1957, humans have been generating space junk. The U.S. Space Surveillance Network is currently tracking over 13,000 human-made objects larger than four inches (ten centimeters) in diameter orbiting the Earth. These include both operational spacecraft and debris such as derelict rocket bodies. 'Of the 13,000 objects, over 40 percent came from breakups of both spacecraft and rocket bodies,'Johnson said."