WASHINGTON — A lifeless satellite targeted for destruction by the United States has raised new concerns about the vast array of space debris — ranging from old rocket bodies to abandoned astronaut tools — that hurtle though the skies at thousands of miles an hour.
Since the Soviets launched Sputnik as the first satellite on Oct. 4, 1957, space has evolved into a cosmic junkyard. The Joint Space Operations Center at Vandenberg Air Force Base, Calif., is now tracking more than 18,000 manmade objects, including an estimated 850 functioning satellites, the international space station and debris from rocket launches dating to the dawn of the space era.
That tally reflects a 30 percent increase in the last 13 months, in large part because of debris created after the Chinese destroyed one of their satellites with a missile in 2007, said the center's director, Col. Stephen Whiting.
"At the speed with which debris orbits around the Earth, if two pieces were to hit each other, that would be a very catastrophic event," Whiting said.
President Bush has ordered the Navy to try to bring down the disabled spy satellite, which lost control after its computer failed almost immediately after its launch in 2006. Bush took the unprecedented decision out of fear that 1,000 pounds of highly toxic satellite fuel could endanger populous areas, military officials said.
Marine Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff, said Thursday that a Navy cruiser would try to hit the satellite with a Standard Missile 3, which is designed to bring down ballistic missiles.
Government officials, as well as many space experts, say that the satellite would be low enough so that debris from the blast would be destroyed almost immediately in the Earth's atmosphere. But some critics worry that the explosion could propel some marble-size debris upward into the path of the international space station.
"My concern is that some of it might go up to the altitude where the space station is," said David Wright, co-director of the Union of Concerned Scientists' Global Security Program. "Even though it might not stay up there, if it's up there for a week, what kind of risk would that pose for the space station?"
In addition to the hundreds of functional satellites and the space station — the largest manmade object in space — the skies are cluttered with nonfunctional spacecraft; old space parts; an array of other debris such as paint flakes, nuts and bolts; and abandoned paraphernalia from astronauts, including tools and gloves. Some space watchers say the debris field has even included coffee cups and toothbrushes that slipped out of the spacecraft hatch.
As depicted in a rendering by NASA's Orbital Debris Program Office (http://orbitaldebris.jsc.nasa.gov/photogallery/beehives.html), the debris field looks like a swarm of thousands of gnats encircling Earth.
Nicholas Johnson, NASA's orbital debris program manager, has long warned that space debris is a growing environmental problem. Space-faring nations agreed last year to a series of practices to lessen the chances for future debris — such as removing fuel from spent rockets — but have made no progress on calls to clear existing debris.
Given their blinding speed, even diminutive items can pack a wallop. Colliding with a 1-centimeter-sized aluminum sphere traveling at 22,320 mph would be like getting hit with a 60-pound safe going 60 mph, NASA says.
Richard Maurer, the author of "Junk in Space," compares the debris to the tire fragments, cans and other junk that motorists see every day along the roadside.
"Imagine that stuff, instead of safely being on side of the road, it's out there moving along with the traffic," he said. "That would be an incredible hazard."
While most objects burn up when re-entering Earth's atmosphere, a few large items have made it all the way to the surface. Parts from Delta II rockets, weighing more than 500 pounds, fell to Earth in Texas and in Cape Town, South Africa, between 1997 and 2000.
China's controversial destruction of one of its weather satellites on Jan. 11, 2007, spread additional space debris and raised fears in the United States that China was preparing weapons that could take down U.S. satellites. It was the first such destruction of a satellite since the anti-satellite tests that the United States and the Soviet Union conducted in the 1980s during the Cold War.
The Chinese test was in the upper ranges of the lower Earth orbit — which reaches up to 1,242 miles — and it scattered debris that will threaten space assets for more than 20 years, according to a study by the Congressional Research Service.
The report said that the test created a debris cloud that includes at least 950 pieces that are at least 4 inches long, plus thousands of smaller pieces, and threatens spacecraft in lower Earth orbit, including the space station, shuttle missions and reconnaissance and weather satellites.
U.S. officials say they see no chance for a similar debris spread from the impending U.S. shoot-down because the satellite will be at a very low altitude and the resulting fragments will be pulled downward by air drag. Most fragments will burn up within days, the military says.
Critics of the test, however, say that they worry about the international fallout, warning that China and Russia could be inclined to ramp up anti-satellite programs in response to what they see as U.S. aggression in space.
"The debris risk is fairly small, but the precedent is bad," said Theresa Hitchens, the director of the Center for Defense Information, a Washington think tank. "For a long time, nations like China and Russia have suspected that the U.S. missile defense program is about creating offensive weapons to kill a satellite. I don't think that's true, but we have just played into their fears."