NASA satellite to crash into earth, but where?

It’s coming but everyone is clueless about its destination. A defunct NASA science satellite is expected to fall back to Earth on Friday, showering debris somewhere on the planet although scientists cannot predict exactly where.

The 6.5-ton bus-sized Upper Atmosphere Research Satellite, or UARS, was carried into orbit during a space shuttle mission in 1991. It operated for 14 years, collecting measurements of ozone and other chemicals in the atmosphere.

Since completing its mission in 2005, UARS has been slowly losing altitude, tugged by Earth's gravity. On Friday, the 35-foot-long, 15-foot diameter (10.6-metres long, 4.5-metres diameter) satellite is expected to plunge into the atmosphere, NASA reported on its website.

On re-entry the satellite is expected to break into over 100 pieces out which 26 may survive the burn and crash onto earth’s surface.

The largest chunk may weigh around 136 kilograms. The satellite's orbit passes over most of the planet, from as far north as northern Canada to the southern part of South America.

However, the debris spread area would be around 805 kilometres, the location of which would be determined by the precise time at which the spacecraft will make the re-entry.

Assuaging fears about its impact on earth, NASA said the chance a piece of UARS debris will strike a person is about one in 3,200. The debris will mostly likely fall into an ocean or land in an uninhabited region of Earth.

Satellites as large as UARS re-enter Earth's atmosphere about once a year.

NASA said there have been no reports of any deaths or injuries to people from falling debris.

Nasa: US satellite may crash back to Earth

A 20-year-old satellite that measured the ozone layer is expected to crash back to Earth late next week, but NASA said Friday it still does not know where it will fall.

The US space agency stressed that the risk to public safety from the Upper Atmosphere Research Satellite (UARS) is "extremely small," and said that most, but not all, of the gear will burn up on re-entry into Earth's atmosphere.

"Re-entry is expected Sept. 23, plus or minus a day. The re-entry of UARS is advancing because of a sharp increase in solar activity since the beginning of this week," NASA said in a brief update on its website.

"Safety is NASA's top priority," it added, noting that throughout history, there have been "no confirmed reports of an injury resulting from re-entering space objects."

The decommissioned satellite could land anywhere between 57 degrees north latitude and 57 degrees south latitude, a vast swath of populated territory. Predictions will only get more precise as the landing approaches.

The UARS satellite was sent into orbit in 1991 by the space shuttle Discovery.

The 35 by 15 foot (three by 10 meter) spacecraft weighed 13,000 pounds (5,900 kilograms) and toted 10 scientific instruments for measuring wind, temperature and ozone chemistry. It was officially decommissioned in 2005.

"Although the spacecraft will break into pieces during re-entry, not all of it will burn up in the atmosphere," NASA said.

"It is impossible to pinpoint just where in that zone the debris will land, but NASA estimates the debris footprint will be about 500 miles (800 kilometers) long," the space agency said.

It also urged anyone who comes across what they believe may be space debris not to touch it, but to call authorities for assistance.