Washington:
A six-ton NASA satellite that is on course to crash back to Earth on Friday is not expected to hit North America, the US space agency said in its latest update.
"Re-entry is expected sometime during the afternoon of September 23, Eastern Daylight Time. The satellite will not be passing over North America during that time period," NASA said in an update issued Thursday at 7:44 am (1144 GMT).
"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."
All but 26 pieces of the Upper Atmosphere Research Satellite (UARS) are expected to burn up on re-entry into Earth's atmosphere.
The surviving chunks will include titanium fuel tanks, beryllium housing and stainless steel batteries and wheel rims. The parts may weigh as little as two pounds (one kilogram) or as much as 350 pounds (158 kilograms), NASA said.
Orbital debris scientists say the pieces will fall somewhere between 57 north latitude and 57 south latitude, which covers most of the populated world. The debris footprint is expected to span 500 miles (800 kilometres).
UARS is the biggest NASA spacecraft to come back in three decades, after Skylab fell in western Australia in 1979.
The risk to human life and property from UARS is "extremely small," NASA said, adding that in 50 years of space exploration no one has ever been confirmed hurt by falling space junk.
There is a one in 3,200 chance that someone, somewhere in the world will be hit, according to NASA.
More frequent updates are scheduled for 12, six and two hours before it lands.