Growing junk yard in space imperils satellites, astronauts

Fresh evidence shows orbiting debris poses increasing risk of

In the market for some used rocket parts? Skip the trip to Watto's scrap heap on Tatooine. Near-Earth space may have just what you're looking for.

And that troubles a growing number of people who see the path to living and working in orbit strewn with space-age litter.

Roughly 10,000 objects large enough to track from the ground - from old satellites and spent upper stages to fuel tanks, lens caps, tie-down straps, and bits of explosive bolts - encircle the planet. And that doesn't include the millions of smaller bits of orbital debris ringing Earth.

Only four collisions between a spacecraft and debris have occurred since spaceflight began. But concern is growing that as the number of satellites multiplies - along with Earthlings' reliance on them for everything from cell phones to digital directions to grandmother's house - so are the chances that orbiting flotsam could knock out key satellites and threaten human presence in space.

"Is this something people should worry about? Yes it is," says Scott Pace, a science-policy analyst with the RAND Corp. in Washington.

Earlier this month, for example, a derelict Russian rocket booster hurtled toward an uncomfortably close encounter with the unoccupied International Space Station. And in 1997, a close encounter between the Russian space station Mir and a US satellite forced Mir's crew to strap themselves into their escape capsule until the satellite had passed.

Scientists are also concerned about the potential for chain-reaction collisions if a piece of space junk slams into a satellite that is part of a larger constellation of spacecraft.

In the current issue of the journal Nature, Alessandro Rossi of the Italian National Research Council and two colleagues from the University of Trieste looked at the collision risk to the Iridium project, a global phone and paging network designed around a fleet of 66 satellites (plus six spares).

Dr. Rossi's team estimates that the risk of a catastrophic collision is about 10 percent over a 10-year period. If that happens, debris from the first collision has a 10 percent chance of taking out another Iridium satellite over the next five years.

Such events, the team concludes, could set up chain-reaction collisions that would generate debris for a century - too slow to affect phone service, perhaps, but three to five times faster than previous estimates.

The space-junk problem has become sufficiently acute that orbital debris has for the first time found a place on the agenda for the United Nation's Conference on the Exploration and Peaceful Uses of Outer Space, which will be held in Vienna in July.

Space junk's appearance results largely from a change in attitude on the part of the United States, which had kept the issue off the table at previous meetings, according to John Logsdon, director of the Space Policy Institute at George Washington University in Washington, D.C.

When the Defense Department dominated the launch US launch scene, "it didn't want to expose its issues and craft to international debate," Dr. Logsdon explains. The US argued that space junk was a science and technology issue, not a legal problem.

These days, however, private companies launch more hardware than the federal government, bolstering economic arguments for controlling space debris. The US, Logsdon says, bowed to the inevitable - with hopes of steering the discussion.

For now, the best hope for controlling the cosmic clutter seems to lie in spacecraft and mission design, researchers say, rather than in cleanup technologies.

"Basically, we've got to live with it," says Kyle Alfriend, who heads the aerospace engineering department at Texas A&M University. "Let's not increase the amount of stuff we leave up there, and let's let the atmosphere help clean it out."

A few years back, the National Aeronautics and Space Administration conducted a study on using ground-based lasers to hit small pieces of debris. "But that idea raised significant political problems," Dr. Alfriend says, noting that one nation's laser "broom" is another's antisatellite weapon. Even if lasers were used benignly, he adds, it's still possible to zap another country's satellite by mistake.

Faced with little prospect of clearing space with an orbiting Hoover, researchers are focusing efforts on improving computer programs that calculate debris orbits. Such improvements, researchers say, can lead to more accurate and more timely warnings of potential collisions.

"We do not have a good set of knowledge about what's up there," says William Kainard, senior research scientist at the NASA Langley Research Center in Hampton Roads, Va. "Before you can do too much, you need to understand the population of millimeter- to centimeter-size objects, get their sources, and orbital lifetimes."

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