(Related news: "Terrorist Use of Google Earth Raises Security Fears" [March 12, 2007].)
A U.S. official confirmed that the spy satellite is designated by the military as US 193.
The satellite, launched in December 2006, carried a sophisticated and secret imaging sensor, but its central computer failed shortly after launch.
The official spoke on condition of anonymity because the information is classified as secret.
Sky Show
The satellite includes some small engines that contain a toxic chemical called hydrazine—rocket fuel. But Renuart said they are not large booster engines with substantial amounts of fuel.
Video images of the satellite captured by John Locker, a British amateur satellite watcher, show it to be about 13 feet to 16.5 feet across (4 meters to 5 meters across).
He believes it weighs a maximum of 10,000 pounds (4,536 kilograms). Locker calculated its size with data on its altitude and location provided by other amateur satellite watchers, using the International Space Station as a yardstick.
Satellite watchers have been plotting the satellite's degradation for a year. They estimate it is now at an altitude of about 173 miles (278 kilometers), and Locker believes it is dropping about 1,640 feet (500 meters) a day.
When the satellite burns up, flares will be visible from the ground, said Ted Molczan, a Canadian satellite tracker. From that point on, he said, it will take about 30 minutes to fall.
In the past 50 years of monitoring space, 17,000 human-made objects have re-entered the Earth's atmosphere.
Copyright 2008 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
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