An Unprecedented Space Collision

Feb. 12, 2009— -- When two satellites crashed in space Wednesday, it was unprecedented -- the largest orbital collision yet -- but it wasn't exactly unexpected.

"We knew this was going to happen eventually and this is it -- this was the big one," said Nicholas Johnson, chief scientist at the Orbital Debris Office at NASA's Johnson Space Center.

When the two large satellites crossing paths at hypervelocity -- each weighing more than 1,000 pounds and going 17,500 miles an hour -- collided Wednesday over Siberia at an altitude of 491 miles, it was the first time there had ever been such a crash in space.

No one knows yet why the Iridium communications satellite and an old Russian Cosmos satellite ended up on a collision course.

The military's Strategic Command -- Stratcom -- is monitoring the nearly 500 pieces of space debris left after the collision and analysts are working to plot the coordinates for each of the debris pieces, which will then be posted on the public Web site www.space-track.org so anyone with satellites in the sky can determine whether the new debris poses a risk to their objects.

Officials at Stratcom say they track 18,000 pieces of space debris larger than 10 centimeters. NASA tracks anything smaller than that -- those numbers run into the hundreds of thousands.

Johnson said what he is concerned about is whether anything will threaten U.S. spacecraft -- the space telescopes, earth observations satellites and of course the International Space Station. Mission Control has had to move the space station several times during the years to keep it from colliding with floating debris.

Teams are working around the clock to catalog and then track the debris from the satellites' collision Wednesday. When the junk settles, Johnson said, analysts will have a better idea what spacecraft might be threatened and then they will take measures to move those spacecraft into different orbits.

Space Debris from Satellite Crash

It is too early to tell, however, just how much is left of the two satellites because the debris is still clustered together in such big lumps, Johnson said.

It wouldn't take much to seriously damage the space station or the space shuttle. Orbital debris is considered the biggest threat to each shuttle mission, and every orbiter comes back with a number of small dings.

What are the odds of something like this collision occurring?

Pretty good, Johnson said. His office has tracked accidental collisions at the rate of one every five years.

Next week, the United Nations is holding its annual conference on orbital debris. Johnson said he will have quite the show and tell for his colleagues in Vienna, Austria.