By Irene Klotz
CAPE CANAVERAL, Florida (Reuters) - A defunct NASA satellite the size of a bus that is expected to fall to Earth on Friday will likely miss North America, NASA said.
The agency's 13,000-pound (5,900 kg) Upper Atmosphere Research Satellite, or UARS, has been slowly tumbling from orbit since its mission ended in 2005. It is expected to re-enter Earth's atmosphere and break apart on Friday.
Most of the debris will incinerate as it plows through the air, but about 26 pieces, weighing a total of about 1,100 pounds (500 kg), are expected to survive the fall and land somewhere on Earth.
Because the science satellite is tumbling, NASA and the U.S. Air Force, which tracks space debris, are not yet able to make an exact prediction about when and where UARS will return to Earth.
With 75 percent of the planet covered by water and vast regions of desert and other uninhabited regions, NASA said the odds that a person will be hit by a piece debris from UARS are about 1-in-3,200.
The satellite flies over most of the world as it orbits between 57 degrees north and 57 degrees south of the equator. Its altitude on Thursday was about 115 miles above the planet.
NASA said on its website on Thursday that re-entry was expected sometime Friday afternoon.
"The satellite will not be passing over North America during that time period. It is still too early to predict the time and location of re-entry with any more certainty, but predictions will become more refined in the next 24 to 36 hours."
The 35-foot-long, 15-foot diameter (10.6-metres long, 4.5-metres diameter) satellite was launched into orbit aboard a space shuttle in 1991 to study ozone and other chemicals in the planet's atmosphere.
Websites offering real-time tracking of UARS include Heavens-Above.com and Space-Track.org.
(Editing by Kevin Gray and Anthony Boadle)