An out-of-control NASA satellite that is dead in space will plunge back to Earth in the next few weeks, but exactly when and where the spacecraft will fall are still a mystery, space agency and military officials said today.

The spacecraft, called the Upper Atmosphere Research Satellite, is about the size of a school bus and is expected to re-enter Earth's atmosphere sometime between late September and early October, NASA officials said. The nearly 12,500-pound (5,668-kilogram) satellite will fall over a stretch of land more than 500 miles (804 kilometers) long somewhere between northern Canada and southern South America.

But NASA and U.S. military officials tracking the defunct UARS satellite won't have a better idea of where the spacecraft will fall until around two hours before it happens.

Johnson said 26 large pieces of the UARS satellite are expected to survive the re-entry and reach the Earth's surface. The largest piece of debris could weigh nearly 300 pounds (150 kg).

Great work guys. Good plan.