Space is mostly empty, but sometimes it isn't empty enough.
Two days ago a pair of orbiting satellites collided 480 miles (780 km) up over Siberia. One was Cosmos 2251, a defunct communications satellite launched in 1993 by the Russian Ministry of Defense. The other was named Iridium 33, one of several dozen spacecraft in a globe-girding commercial communications network.
It's not yet clear exactly how many satellite shards the smashup created; more than 600 have already been logged by the U.S. military's worldwide satellite-tracking network. A more accurate debris census — and, more importantly, how they're distributed in orbit — will take a week or so to sort out.
This unplanned meeting in orbit is unprecedented, but it was bound to happen sooner or later. Ground-based cameras and radar currently keep tabs on more than 13,000 orbiting objects, everything from fragments the size of tennis balls to the International Space Station.
Speaking of ISS, it doesn't appear to be in imminent danger. It orbits quite a bit lower, typically 220 miles (350 km). There's a little more worry concerning the Hubble Space Telescope, currently circling at a height of 350 miles (565 km). Both of the colliding spacecraft had high-inclination orbits (Cosmos 2251 at 74°, Iridium 33 at 86°), and depending on their post-crash speeds, some of the 1½ tons of fragments might end up either much higher or much lower.
The February 10th collision was an accident: the Russian craft was inoperable, and the Iridium, though apparently equipped with a maneuvering rocket, hadn't known it was going to be hit. As worrisome as all this might seem, it totally pales compared to an intentional space smashup that occurred two years ago.
Let's not forget that on January 11, 2007, the People's Republic of China launched a ballistic weapon that struck and destroyed Fengyun 1. The resulting fragments created more space shards than any other event in the history of satellite exploration, creating a hazardous cloud that has spread to altitudes ranging from 300 to 2,500 miles.
According to a recent newsletter from NASA's Orbital Debris Office, pieces of Fengyun 1 and its annihilator now total nearly 2,400, accounting for more than 25% of all the objects being tracked at low orbital altitudes. And the estimated count of smaller bits, 1 to 5 cm across, exceeds 150,000. Some of these will remain aloft for decades, others for more than a century.
Accidents will happen, but to knowingly put so many other spacecraft at risk is unconscionable. Remarkably, five years earlier China's National Space Administration (CNSA) had signed a United Nations agreement to help reduce the amount of space debris.