March 12, 2007: For the second time this year, there was an explosion in orbital space that put a large swarm of dangerous (at least four inches long) pieces of debris in orbit. Stuff this size can be detected by radars on earth. The ISS (International Space Station) has shields that will protect it from debris under four inches, but anything larger could cause damage. The radar observation can, some of the time, give the ISS warning, and the space station can be moved out of the way. But with a large swarm, like that produced in the two recent events, it may not be possible to move the ISS safely away. Some satellites can move as well, but many cannot.

The new swarm was the result of the accidental explosion of a Russian rocket on February 19th, that put over 1,100 dangerous fragments in orbit. Back on January 11th, China launched an anti-satellite system (a KillSat, or Killer Satellite) that destroyed an old Chinese weather satellite, about 850 kilometers up. That's at the upper range of where most reconnaissance satellites hang out. The KillSat hit the weather bird, and the result was several million fragments. Most of the pieces are tiny, at least 817 are truly dangerous (at least four inches long, wide or in diameter).

The Russian explosion occurred when the upper stage of the Photon rocket, which has been up there since it malfunctioned in February 2006, suddenly exploded. It was known that the rocket stage had lots of fuel still on board, but something set it off. This is a worse situation than the Chinese one, because the Russian debris swarm is in a elliptical orbit that varies from 500 to 15,000 kilometers. Thus it will take longer for those fragments to get pulled into the atmosphere and burned up.