Space Junk

Cosmos 2251 was an ordinary satellite designed to transmit signals across the vast Russian landmass. Launched in 1993, it would appear every 90 minutes or so over the northern skies, relay electronic blips of information among a network of satellites and ground stations like a hockey player passing the puck, and disappear over the southern horizon.

Iridium 33, launched for Motorola in 1997, did something similar, though it took a slightly different orbit that brought it closest to Earth during its pass over North America. For years the two satellites circled the planet, minding their own business, never coming within a thousand kilometers of one another.

Then something happened to Cosmos. It may have sprung a small leak; perhaps it struck a tiny asteroid or a piece of debris. Nobody knows for sure, but for one reason or another, Cosmos drifted off course. T. S. Kelso, an aeronautics expert at Analytical Graphics, which provides satellite-tracking services to NASA, noticed that the orbits of Cosmos and Iridium were bringing the two satellites closer to each other all the time. In February he issued a warning that they would pass within a kilometer of one another. He was right. On Feb. 10, Motorola lost track of Iridium's signal. Over the next few days, Kelso and others surmised that what many had feared for years had finally come to pass: two intact satellites had collided head on.

The consequences go far beyond merely the loss of two pieces of property. Each satellite weighed more than half a metric ton and was moving at 7.5 kilometers per second. The resulting explosion was catastrophic, generating a massive cloud of cosmic debris—perhaps 100,000 pieces of junk bigger than one centimeter in diameter, estimates David Wright, a space expert at the Union of Concerned Scientists. In one stroke, the accident increased by nearly a third the number of stray objects in the crucial 700-to-900-kilometer band known as low Earth orbit (LEO). The junk cloud will eventually disperse around the entire planet, like a shroud.

The event served as a wake-up call to space planners. Insurance rates for the $18 billion worth of active commercial satellites now in orbit have ticked upwards by 10 to 20 percent since the accident. Governments, too, have grown to rely on networks of satellites to gather intelligence, direct weapons systems, forecast climate and weather changes, monitor agriculture, and operate communications and navigation systems. Experts calculate that debris will now strike one of the 900 active satellites in LEO every two or three years. For the first time, junk is the single biggest risk factor to equipment in some orbits. Among the orbital threats are two former Soviet nuclear reactors. Even the International Space Station may one day be at risk, as debris slowly descends to its 350-kilometer orbit.

Many experts now believe that even if all space littering were to stop completely, the number of stray objects would continue to increase for centuries. The reason: debris is now so dense that objects will continue to crash into each other, creating even more objects, expanding the rubbish cloud geometrically. "We've been saying for years that these things are going to happen," says Nicholas Johnson, head of NASA's Orbital Debris Program Office. "Until they happen, it's hard to get people's interest."

NASA engineer Don Kessler predicted the current situation with uncanny accuracy back in 1978. At the time, rockets carrying astronauts or communications satellites would discard upper stages like empty beer cans, often without having completely burned up their fuel. Several rockets exploded spontaneously in orbit, with no immediate consequences except to add to the orbiting debris. Each time an astronaut lost a bolt or a wrench, the object would take its place in the debris cloud. The Soviet Union may have been the most egregious polluter. In the 1970s and '80s, it launched 32 radar satellites, designed to track the positions of U.S. Navy ships, each powered by its own nuclear reactor.

Kessler ran the calculations, and the results came as a surprise. When one object slams into another, he found, they splinter into hundreds of pieces, each moving like a projectile at high speed. "Everybody had had this concept, probably from science fiction, of things floating together in space," he says. "People just hadn't thought about it." By about 2000, he predicted, collisions between satellites would start to outpace other forms of space accidents.

To avert what came to be known in the trade as the Kessler Syndrome, NASA formed its Orbital Debris Program Office, made Kessler the head, and gave him a staff of 20 or so engineers and scientists to tackle the problem. The group, headquartered at the Johnson Space Center in Houston, led a quiet and successful effort to reform the more wasteful practices of spacefaring nations. Now, discarded rocket stages are routinely angled to disintegrate in the atmosphere, or at the very least they're left with empty fuel tanks.