Satellite crash: A briefing on the 6.5-ton NASA bird falling to Earth

Satellite crash facts and fiction: How big are the risks? NASA says satellite debris could be spread across 500 miles.

Sometime in late September or early October, a 6.5-ton Upper Atmosphere Research Satellite, or UARS, is going to come tumbling to Earth.

Should you worry, Chicken Little?

The short answer is no.

Yes, NASA says that some pieces of its satellite will make it to Earth, while most of it will burn up upon reentry. Satellite debris could be scattered across an area 500 miles long. NASA figures that about 1,170 pounds of the 6.5-ton research bird (decommissioned 6 years ago) will get sprinkled across the planet.

Where will that 500-mile danger zone be?

Well, NASA isn't sure yet. It's too soon to tell. The rate of decay of the orbit is affected by solar flares, the gravitational pull of the Moon and the Earth, as well as gravitational anomalies. NASA says now that the satellite is likely to come down somewhere between 57 degrees north latitude and 57 degrees south. That's not a lot of help. At this point, that's a swath that covers most of the inhabited areas of the planet (from roughly Alaska and Denmark in the north to the tip of South America in the south).

But consider this from NASA's UARS update:

"Since the beginning of the Space Age in the late-1950s, there have been no confirmed reports of an injury resulting from re-entering space objects. Nor is there a record of significant property damage resulting from a satellite re-entry."

There has been one confirmed report of an individual struck by space debris. Lottie Williams of Tulsa, Okla., was hit on the shoulder by a piece of a Delta rocket while she was walking in a park in 1997. But the six-inch long fragment didn't injure her, so the NASA statement is correct.

In 1979, NASA brought Skylab (the manned orbiter that was the forerunner to the International Space Station) down to Earth. They were aiming for the debris to land in the Indian Ocean, but some of it scattered across Western Australia. Seventeen-year-old Aussie Stan Thornton found a small piece of Skylab debris on the roof of his house, and collected a $10,000 reward offered by the San Francisco Examiner.

Another reason that it's unlikely that any of the UARS debris will cause significant damage or injury: About 71 percent of the Earth's surface is covered by oceans.

But if you want to stay on top of this, NASA plans weekly updates, until four days before the expected re-entry. Then, as satellite reentry timing becomes more certain, NASA plans daily updates, "until about 24 hours before re-entry, and then at about 12 hours, six hours and two hours before re-entry."