Collision

If this sort of thing continues, useful orbits will become unusable:

A RUSSIAN and a US satellite have crashed into each other in an unprecedented collision creating clouds of space debris.

A disused Russian military satellite, Kosmos 2251, collided with a US communications satellite about 800km above Siberia.

...The Pentagon acknowledged it had not anticipated the accident.

"We did not predict this collision," said spokesman Bryan Whitman, citing "limits" on the ability to track the thousands of man-made objects orbiting the Earth.

The debris from the defunct 900kg Russian satellite launched in 1993, and its 560kg US counterpart could be significant.

"We are looking at around more than 500 pieces of debris," said Navy Lieutenant Charlie Drey, a spokesman with US Strategic Command (STRATCOM), whose Joint Space Operations Centre tracks more than 18,000 man-made objects orbiting the Earth.

...Analysts are plotting the coordinates of each of the debris pieces, which will later be posted on the website space-track.org.

...Before the latest incident, there were over 300,000 orbital objects measuring between 1cm to 10cm in diameter and "billions" of smaller pieces, according to a 2008 report by the Space Security Index, a international monitoring group.

Travelling at speeds that can reach many thousands of kilometres per hour, the tiniest debris can damage or destroy a spacecraft.

In June 1983, the windscreen of the US space shuttle Challenger had to be replaced after it was chipped by a fleck of paint measuring 0.3 millimetres that impacted at 4km per second.