Falling space junk is common

February 22, 2008 6:10:20 AM PST
An Ivy League astronomer who tracks satellites and space debris says giant chunks of manmade space junk - like the dead satellite that the U.S. government is trying to shoot down - regularly fall to Earth.Jonathan McDowell of Harvard University runs Jonathan's Space Report, which tracks the world's space launches and satellites. He says no one has ever reported being hurt by falling space debris.

Chunks of debris weighing two tons or more from satellites and rocket parts have been falling uncontrolled every three weeks or so over the last three years, according to McDowell's own analysis.

A decade ago, countries who owned wayward satellites didn't try to control them. Two-ton chunks fell to the Earth far more frequently.

The Center for Orbital and Reentry Debris Studies says 50 to 200 large pieces of manmade space debris fall to Earth every year. The Center also says about 12 million pounds fell over the past 40 years.

Experts in the field know of only one person who was struck by space debris.

Lottie Williams of Tulsa, Oklahoma was hit on the shoulder in 1997 by a small piece of debris from a discarded piece of a Delta rocket. Williams was not hurt.

The reason why space debris tends to miss humans is because they are unlikely targets. More than two-thirds of the planet is covered in water.

There are about 130 people per square mile of land on Earth, and people don't take up that much space. In fact, a Columbia University researcher says more than 99.9 percent of the land on the planet is not occupied by a human being at any given time.

However, there are areas at higher risk - particularly the land areas that are below the common orbital paths of satellites. Even so, McDowell, the Harvard astronomer, says the chance of someone getting struck by space debris in these higher-risk areas could be as high as one in a million.

That doesn't take into account toxic fumes from the ton of frozen and dangerous hydrazine rocket fuel, which is the reason Pentagon officials said they needed to shoot down the dead satellite. The Centers for Disease Control and Prevention put out a notice to local public health officials warning of the toxicity of the fuel.

McDowell is skeptical of any actual public health threat due to falling space debris.

"My gut reaction is that this is just completely bogus," McDowell said. He doesn't completely discount the danger of the rocket fuel, however.

This is the type of risk that shouldn't be reduced to mere numbers, said David Ropeik, a Boston risk communications expert who has consulted with the Bush White House and Department of Homeland Security.

"It's the nature of the risk, not the number," said Ropeik, co-author of the book "Risk." "A good question can be asked whether it is the public's worry that is driving this or whether the government is concerned about the harm that it can cause, even though the chances of that are low."

WEB LINK: Jonathan's Space Report