July 20, 2007: Last month, the
United States became the first nation that had to change the orbit of one of
their satellites to avoid the cloud of debris created when China tested an
anti-satellite weapon earlier this year. China had launched an anti-satellite
system (a KillSat, or Killer Satellite) that destroyed an old Chinese weather
satellite, about 850 kilometers up on
January 11th. 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, but at least 817 are
truly dangerous (at least four inches long, wide or in diameter). There are
many such debris swarms up there, that have to be watched and avoided. But
these other debris swarms are the result of accidents. For example, on February
19th, a new swarm was created because of the accidental explosion of a Russian
rocket, that put over 1,100 dangerous fragments in orbit. Those two incidents
increased the dangerous debris in orbit by about fifteen percent.
The U.S. Terra environmental
satellite was in an orbit that indicated a seven percent chance of hitting
debris from the Chinese KillSat test. So controllers adjusted Terra's orbit
slightly, to reduce the risk to zero.
The IADC (Inter-Agency Space
Debris Coordination Committee) is an international organization that
coordinates the exchange of information, and space operations, as they relate
manmade and natural debris in orbit around the earth. Every year, some of this
stuff falls into the atmosphere and burns up, but there are always new
accidents, or deliberate operations,
that add more junk to the spaceways.
