What's the risk from space junk?

Last update: February 20, 2008 - 9:39 PM

Giant chunks of manmade space junk regularly fall to Earth. Yet no one has ever been reported hurt by them.

Chunks of debris weighing 2 tons or more from satellites and rocket parts fall uncontrolled every three weeks or so, said an analysis by a Harvard University astronomer. And that's just based on the past three years.

Go back a decade or so when countries didn't try to control these falling objects. Back then, 2-ton chunks fell to Earth much more frequently, said Jonathan McDowell, who runs Jonathan's Space Report, which tracks the world's space launches and satellites.

It's likely that 50 to 200 "large" pieces of manmade space debris return to Earth every year, said the Center for Orbital and Reentry Debris Studies. In the past 40 years, about 12 million pounds of manmade space junk has survived reentering Earth's atmosphere, the center said.

Yet experts know of only one report of a person being hit. Lottie Williams of Tulsa, Okla., was hit on the shoulder in 1997 by a small piece of debris from a Delta rocket. She was unhurt.

The reason space junk doesn't regularly hit people is simple: About 70 percent of the Earth is water. So the odds of anyone being hurt by any piece of re-entering space junk, said the orbital debris center that studies the issue: one in a trillion. You are far more likely to get hit by lightning, it said.

That doesn't take into account toxic fumes from the hydrazine rocket fuel, which is the reason Pentagon officials said they needed to shoot down the satellite.

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