Since then, UARS has been one of more than 20,000 pieces of space junk tracked by the Air Force - and a large one at that. The satellite, which has 10 science instruments, is 15 feet in diameter and weighs 13,000 pounds.
"Although the spacecraft will break into pieces during re-entry, not all of it will burn up in the atmosphere," says NASA.
The risk to public safety and property is extremely small, scientists say.
Space debris has been falling back on the planet since the dawn of the space age 50 years ago, with no confirmed reports of an injury resulting from re-entering space objects, NASA said in a statement.
Nor is there a record of significant property damage resulting from a satellite re-entry, it added.
"It is too early to say exactly when UARS will re-enter and what geographic area may be affected," NASA said.
Regular updates will be posted here.
Image: What goes up ... UARS before being released by the shuttle Discovery crew in September 1991. Credit: NASA