Editor's Update: On February 10, 2009, two satellites collided in orbit, destroying a working communications spacecraft owned by Iridium Satellite LLC. At the time this article was published, no such major collision had ever taken place.
From This Story
It's happened only three times, as far as we know: three occasions when two sizeable objects in Earth orbit have accidentally collided at high speed. The first, or the first to be clearly identified, was in July 1996, when a fragment from a long-disintegrated Ariane rocket stage hit a French military satellite called Cerise at nine miles a second. The impact cut in half a 20-foot boom extending from the spacecraft, thereby adding another bit of junk to the 12,000 pieces currently being tracked in space. Cerise kept operating, which was lucky. Lab tests conducted last year in Japan, of impactors striking smaller satellites at much slower speeds, smashed the targets into smithereens.
Another collision happened five years earlier, although it wasn't understood until recently. A defunct Russian navigation satellite (Cosmos 1934) ran into a fragment from another Cosmos while both were circling in similar 600-mile-high orbits. Tracking networks soon noticed two new pieces of debris produced by the collision.
The third occurred in January 2005, when a fragment from a Chinese rocket struck a U.S. rocket stage that had been orbiting for 31 years, breaking off three pieces of debris from the larger object. Lucky again.
Most experts on space debris say that in terms of both the frequency of these events and their severity, our luck will soon run out. Collisions among pieces of debris in space beget more debris, and certain orbits—particularly the polar orbits favored for weather satellites and other Earth observers—will eventually become hazard zones. It's not an emergency yet, says Nicholas Johnson, the chief scientist at NASA's orbital debris program office at the Johnson Space Center in Houston. But it's time to act.
In an influential article published in Science magazine in January 2006, Johnson and his NASA colleague Jer-Chyi Liou argued that only "the removal of existing large objects from orbit" can keep the problem from getting worse.
The scientists used computers to simulate the proliferation of debris in Earth orbit over the next 200 years, assuming no more satellite launches—a hypothetical best case. Their models predict that, up until 2055, the creation of new debris from collisions will be balanced by the disappearance of old junk, which burns up in the atmosphere as its orbit decays. After 50 years, though, as more collisions occur, the creation of debris will start to predominate. The simulations predict 18 collisions over the course of 200 years, each yielding hundreds or thousands of fragments that exacerbate the risk. Even if we never launched another satellite—and of course we will—Johnson and Liou wrote, "The current debris population in [low Earth orbit] has reached the point where collisions will become the most dominant debris-generating mechanism."
Although the scientists conclude that it's time to start cleaning up, they also acknowledge that "no single [cleanup] technique appears to be both technically feasible and economically viable."
Two years later, that's still the case: No one knows how to begin removing orbital debris. "No easy or cheap solutions have yet been identified," Johnson says flatly. It isn't for lack of ideas. Well-meaning inventors have come forward with all kinds of schemes for clearing out space junk: space flypapers, sweepers, robot garbage scows. Take, for example, U.S. patent no. 4,991,799, filed in 1990, for a propeller-like sweeper that would ram into small particles and knock them from a threatening orbit. Or patent no. 6,655,637, filed in 2002, for a robot that could grab space junk with "inflatable fingers."
"Some of the ideas are technically outlandish, some are technically feasible," says Johnson. The problem, almost always, is cost. "If you want to spend tens of millions to retrieve a single rocket body, you can do it," he says. "But it doesn't make any sense economically."
So Johnson and other debris experts from Europe, the United States, and Japan are working on a comprehensive study for the International Academy of Astronautics that will evaluate cleanup options. Results are due next year.