Incoming! Space Station Takes Evasive Action, Again

Astronauts aboard the International Space Station Sunday were forced to change the orbit of the station -- and the Space Shuttle Discovery that is currently docked to it -- to avoid an estimated 4-inch piece of space junk that may have been on a collision course.

It's the third time in three weeks that astronauts on the space station have had to worry about space debris , but it's the first time they have deemed the threat serious enough to change the orbit.

The trouble with space is all the junk up there -- there's so much junk that it is now becoming routine for NASA to repeatedly have to calculate whether manned spacecraft will need to take evasive action to avoid a collision on orbit.

On Sunday, shuttle Cmdr. Lee Archambault used Discovery's steering jets to change the position of the shuttle and space station. The move created drag, which would lower their orbit, and reduced their speed around Earth by half a foot per second, to prevent a close encounter with the debris.

Millions of Pieces of Space Debris

The threat, according to Maj. John Morgan of the U.S. Strategic Command, comes from a small piece of a Chinese satellite launch in 1999.

"We notified NASA on March 19 that this object had the potential to cross paths with the space station and the space shuttle."

No one knows the exact size of the junk -- a few inches -- but it wouldn't take much to damage a spacecraft on orbit.

It's a huge headache for space station flight director Kwatsi Alibaruho.

"Adjusting the orbit of the space station is a big deal. It requires a lot of planning. It's very resource intensive. When we do not have a shuttle there, it requires a great deal of coordination and analysis between Mission Control in Houston and Mission Control in Russia. ... It's a big deal. It's very tiring. But at the same time, we accept it as a necessary part of our business," Alibaruho said.

At the U.S. Strategic Command, located at Offutt Air Force Base in Nebraska, officials monitor more than 13,000 pieces of junk at more than 30 feet long that are orbiting in space.

There are at least an additional 100,000 hunks of junk that measure less than 4 inches. The number of pieces smaller than 1 centimeter orbiting Earth is in the millions.

NASA Orders Discovery and the International Space Station to Change Orbit to Avoid Space Debris

NASA is still waiting for the analysis of a potentially bigger threat.

Hundreds of pieces of debris were created in February when two satellites collided over Siberia -- debris that will soon be drifting into the orbit of other spacecraft like the Hubble Space Telescope.

The Space Shuttle Atlantis is scheduled to launch in May for the final service mission to repair and upgrade the space observatory.