How Much Junk is in Space?
The Galaxy 15 satellite is seen before its 2005 launch to geostationary orbit nearly 36,000 kilometers over the Earth's equator.
Credit: Orbital Sciences.

Space, a seemingly vast frontier, is actually pretty crowded with junk, and it's getting worse.

Just this week the communications satellite Galaxy 15 lost control and joined the growing ranks of debris crowding the space around Earth.

There are about 500,000 pieces of space junk ? down to items about 0.5 inches (1.27 centimeters) wide ? in orbit. Of those, about 21,000 objects are larger than 4 inches (10.1 cm) in diameter, and are being constantly tracked by the Department of Defense's U.S. Space Surveillance Network. These are items like spent rocket stages and broken satellites such as Galaxy 15.

Space junk ? even tiny pieces of it ? is dangerous because objects orbiting around Earth travel at speeds of about 17,500 mph (28,200 kph). At those velocities, any collision between two objects would cause serious damage.

However, this one new addition to the problem doesn't significantly increase the amount of space debris or the risk of a crash, said Nicholas Johnson, Chief Scientist for Orbital Debris at NASA's Johnson Space Center in Houston.

A major collision occurred last year, when the dead Russian Cosmos 2251 spacecraft accidentally slammed into the Iridium communications satellite over Siberia at an altitude of 490 miles (790 km). The collision broke up both craft into many tiny pieces.

Another major event occurred in 2007 when China intentionally destroyed a weather satellite about 528 miles (850 kilometers) above Earth, creating a massive cloud of flotsam in orbit.

"Those two events combined have increased the number of objects in low-Earth orbit that we track by over 60 percent," Johnson told Life's Little Mysteries, a partner. "And that's compared to everything which had accumulated over the past 50 years. These were dramatic, unprecedented increases."

Today, the highest concentrations of debris in space are at the respective altitudes of these two collisions, Johnson said.

Such crashes, and their ensuing additions to the swarm of junk in space, will only become more common as space gets even more crowded.