The U.S. space agency says pieces of a decommissioned satellite will crash into the earth in the coming hour. NASA says the risk to public safety from the falling debris is very remote.

NASA has further narrowed the window for the re-entry of the bus-sized Upper Atmosphere Research Satellite to just one hour between late Friday and early Saturday Washington time .

Most of the satellite is expected to burn up as it re-enters the Earth's atmosphere. It will pass over Canada, Africa and Australia, as well as vast areas of the Pacific, Atlantic and Indian oceans.

The satellite is expected to burn brightly enough to be spotted during daylight hours and break apart into 26 pieces. NASA says since the beginning of the Space Age in the late 1950s, there have been no confirmed reports of an injury resulting from re-entering space objects. The space agency also says there is no record of significant property damage resulting from a satellite re-entry.

NASA has warned people not to touch any of the debris, which could be scattered along a path more than 800 kilometers long.

NASA launched the research satellite in 1991 on a three-year mission to study ozone levels in the atmosphere. NASA took it out of service in 2005.

The satellite was placed into a lower orbit to avoid any collision with the International Space Station. The satellite is the largest piece of space debris to fall to the planet since NASA's Skylab space station crashed in western Australia 32 years ago.