A commercial satellite collided with a Russian satellite over Siberia on February 10th. This yielded a cloud of fragments, according to a NASA scientist tracking space debris.

The collision between the commercial satellite, belonging to Iridium, and a defunct Russian satellite, was the first event of this kind, says Nicholas Johnson, chief scientist at the NASA Orbital Debris Program at Johnson Space Center in Houston. "In the past almost 20 years, there have been three other accidental collisions between objects in orbit, but they've all been very minor," Johnson says.

According to Johnson, the military sky-watchers who track satellites in orbit picked up the collision 490 miles (790 kilometers) above Earth on Tuesday. "One of the things that they discovered yesterday afternoon ... was all of a sudden, where two satellites used to be, there were two clouds of debris," he says. The actual crash appears to have occurred just minutes before noon, Eastern Standard Time. Johnson says NASA has already determined that the debris cloud poses "no significant new risk to the International Space Station." The next space shuttle mission, which may launch as early as February 22nd, should be in the clear as well, according to the space agency. Most, if not all, of the satellite debris should burn up in atmosphere re-entry.

Such a collision between two intact spacecraft may be unprecedented, but it is not completely unexpected. "There are no rules of the road in space," Johnson says. "Anybody can fly anywhere they want." Even concerted efforts to track and guide spacecraft in orbit are subject to some uncertainty in trajectory estimates. At seven miles (11 kilometers) per second, Johnson says, "a little error means a lot."

In an Iridium statement concerning the crash, the Company stated nothing so catastrophic as this incident has occurred before, with only three other accidental collision between catalog objects. In their statement, Iridium acknowledges the loss of their satellite as the result of a collision with a non-operational Russian satellite that's been orbiting for ten years. The Iridium constellation remains healthy due to its design to withstand events of this nature. The necessary steps are being taken to replace the lost craft with one of the Company's in-orbit spare satellites.

(Image: Iridium satellite over Earth. Source: Scientific American, John Matson)