Imagine half a million marbles circling Earth -- an obstacle course in space for satellites, rockets, and the International Space Station...
Orbiting space debris is becoming a problem. The pieces vary in size -- 500,000 are larger than a marble, and 20,000 larger than a softball. However, size doesn't matter because when debris travels 17,500 or more miles per hour, even a paint flake can chip a space shuttle window. It already happened on one mission.
"It's almost like it's being sandblasted by these very small pieces of space debris," said Roderick Heelis from the Hanson Center for Space Sciences in Texas
The shuttle and space station travel in low Earth orbit where debris has increased 60% since 2006. This includes 3,000 pieces of debris from 2009 when China destroyed a old satellite. 2,000 more bits were created when two satellites collided this year.
As for the space station, its trash is loaded into the Russian Progress vehicles, which ferry supplies up. After the Progress is filled with junk, it is sent hurtling toward Earth, where much of it burns up in the atmosphere.
Large trash that doesn't fit into the Progress comes back in Discovery's payload bay. When Discovery recently returned to earth, it carried 20,000 pounds of trash and equipment.
"Space is like the Wild West used to be," said David Wright from the Union of Concerned Scientists. The first explorers of the new frontier "didn't feel like they needed laws. They dumped their trash anywhere."
New international agreements are needed for space activities and the rubbish that gets left behind, Wright said. Otherwise, "all the great things you want to use space for beneficially could be much, much more difficult to use."
In today's world, satellites are crucial to the military, communications, and monitoring the weather. Satellites orbit higher in space where debris travels even faster and cause more damage. Since the debris is farther from earth, it may take decades or centuries to destroy it.
Meanwhile, space debris is being tracked using telescopes and computer modeling. Bob Plemmons from Wake Forest University does some of the tracking for the Air Force. The problem is getting worse as countries put up more satellites. "With technology today, it's essential to have good communications satellites."
The U.S. and other countries have begun focusing on the problem of space junk. This includes new satellite designs.
"Space is large, so the chances of [debris] hitting you are very small," Heelis said. "But if it does hit you, the consequences are very large."