The space shuttle Discovery is on its way home, and there probably aren't many people watching more closely than some Air Force personnel deep inside Cheyenne Mountain near Colorado Springs.
That's where members of the First Space Control Squadron of the 21st Space Wing use powerful radar and computers to track some 8,600 pieces of orbiting space junk. Some of the man-made debris travels at speeds fast enough to threaten the shuttle and other spacecraft.
Discovery undocked from the International Space Station early Saturday morning after a nine-day stay there that allowed the crew to complete unprecedented repairs to the shuttle.
The squadron helps guide manned and unmanned spaceflights to ensure they come no closer than six miles to orbiting debris, which ranges in size from paint flecks to pieces the size of a basketball court.
About once a year, a mission comes close enough to debris that the squadron sends a warning to the responsible company or nation, which can then change a craft's route to avoid a collision.
Thirty sensors around the planet send about 100,000 observations of space debris each day to Cheyenne Mountain, where the data is analyzed to predict the course of each piece.