Who'll Take Out the Space Trash?

The Growing Mess of Orbital Debris Threatens Satellites, Space Missions - and your Roof

As Adam Rogers mulls launching his own satellite , he's got more than just the half-billion dollar price tag to worry about. There's also the vast gyre of human-made space trash floating around in orbit, which poses a growing threat to satellites, manned space missions and even us down here on Earth.

In fifty years of shooting objects into space, we've generated a huge amount of what's known as orbital debris: everything from spent rocket stages and burned-out satellites to the shrapnel created when such castoffs collide or explode. The list even includes lost items like lens caps, a camera, a glove and a putty knife dropped by spacewalking astronauts.

The US government's Space Surveillance Network currently counts more than 17,000 bits of debris larger than 10 centimeters - big enough to cause serious damage to a satellite or craft like the International Space Station. NASA estimates there are over 100,000 more between 1 and 10 cm in diameter - and if you throw in particles smaller than a centimeter, the figure is in the tens of millions. Those numbers jumped up in January of this year, when China fired a missile into one of its defunct satellites, smashing it into more than 2,000 fragments the size of a tennis ball or larger. (The US and Soviet Union ran their own tests of anti-satellite weapons from 1968 to 1986 that also generated countless shreds of orbiting scrap metal.)

What's the big deal about trash that tiny? All that junk isn't just floating around - it's zooming through space at staggering speeds. Debris in low Earth orbit travels at an average speed of 21,600 miles per hour. At that velocity, the impact of a 10 cm chunk of aluminum is comparable to 25 sticks of dynamite. Even a 1 millimeter scrap hits like a rifle bullet. "Things that size won't kill a spacecraft, but they can cause a lot of trouble," says Dr. William Ailor, director of the Air Force-affiliated Center for Orbital and Reentry Debris Studies. They could damage sensitive gear like the Hubble Space Telescope's mirrors, or protective sun shields. A window on a space shuttle was once cracked when a stray flake of paint smacked into it, Ailor points out.

Sure, there's a lot of room in space, and such collisions are so far exceedingly rare. But they do happen. In 2005, an engine from a 31-year-old derelict American rocket and a fragment from an exploded Chinese rocket - each about the size of a microwave oven - slammed into each other. In 1996, a knapsack-sized piece of an Ariane rocket smashed into a French satellite at 31,500 mph, breaking off a stabilizing boom. Space agencies have had to make in-flight adjustments to the course of space shuttles and various satellites several times in recent years to steer them clear of threatening orbital debris.

Space junk could conceivably also do damage down here on Earth. Many of those thousands of bits of debris will eventually be pulled down out of orbit by our planet's gravity. In fact, according to NASA, that happens about once a day. Most burn up in the atmosphere, or fall into oceans, deserts or other unpopulated areas. But in 1997, a 550-pound piece of a Delta 2 rocket crashed down in the front yard of Texas farmhouse. And just last May, an orange-sized chunk of stainless steel alloy that may have been a satellite fragment careened through the roof of a home in New Jersey.

Scientists and governments of the dozens of nations with satellites in orbit are increasingly concerned. The US and other major spacefaring nations have developed guidelines to limit debris creation, by doing things like building systems into satellites that will jettison propellant left over at the end of the machine's useful life to eliminate the chance of explosion. Last June, a United Nations panel adopted similar guidelines to cover the many smaller countries that are planning to launch satellites.

Still, such measures will at best only stabilize the problem. No one is likely to clean up the space trash that's already there. What few solutions have so far been proposed - from debris-zapping ground-based lasers to using robots to attach rocket engines that could push defunct spacecraft out of orbit - are too technically difficult or expensive.

Depending on how high up it is, a piece of space junk can remain in orbit for decades or even centuries. "What's up there now is going to be there for a long time," says Ailor. That means more and more of those castoff bits and pieces are bound to collide with each other, generating still more dangerous debris.