The Upper Atmosphere Research Satellite is in the grasp of the remote manipulator system end effector above the payload bay of the Earth-orbiting Discovery during STS-48 pre-deployment checkout procedures.
Credit: NASA Johnson Space Center
This story was updated at 8:27 p.m. ET.
A huge, dead satellite tumbling to Earth is falling slower than expected, and may now plummet down somewhere over Canada, Africa or Australia late tonight or early Saturday, NASA officials now say.
The 6 1/2-ton Upper Atmosphere Research Satellite (UARS) was expected to fall to Earth sometime this afternoon (Sept. 23), but changes in the school bus-size satellite's motion may push it to early Saturday, according to NASA's latest observations of the spacecraft.
"Re-entry is expected between 11 p.m. Friday, Sept. 23, and 3 a.m., Sept. 24, Eastern Daylight Time (3 a.m. to 7 a.m. GMT)," NASA officials wrote in their latest update. "During that time period, the satellite will be passing over Canada, Africa and Australia, as well as vast areas of the Pacific, Atlantic and Indian oceans. The risk to public safety is very remote." [Complete coverage of NASA's falling satellite]
NASA expects about 26 large pieces of the UARS spacecraft to survive re-entry through Earth's atmosphere and reach the planet's surface. The biggest piece should weigh about 300 pounds. The spacecraft is the largest NASA satellite to fall from space uncontrolled since 1979. [6 Biggest Spacecraft to Fall Uncontrolled From Space]
NASA officials have said the the chances that a piece of UARS debris hits and injures one of the nearly 7 billion people on the planet are about 1 in 3,200. However, the personal odds of you being struck by UARS satellite debris are actually about 1 in several trillion, NASA officials have said.
As of 7 p.m. EDT (2300 GMT) today, the UARS satellite was flying in an orbit of about 90 miles by 95 miles (145 kilometers by 150 km), and dropping. NASA launched the UARS satellite in 1991 to study Earth's ozone layer and upper atmosphere. The satellite was decommissioned in 2005.
Earlier today, officials reported that solar activity is no longer affecting the satellite's rate of descent.
The sun has had an extremely active week, one that has included several solar flares. High solar activity can cause the Earth's atmosphere to heat and expand, which can increase drag on a low-flying satellite like UARS, making it fall faster.
But exactly where the UARS spacecraft will fall still remains anyone's guess. NASA orbital debris experts have said the satellite could fall anywhere between the latitudes of Northern Canada and Southern South America, a region of Earth that encompasses much of the planet.
NASA officials have said that, since 75 percent of the Earth is covered with water, it is likely that the UARS satellite could fall over an ocean.
Editor's note: If you snap a photo or observe the re-entry of NASA's UARS satellite and want to share it with SPACE.com for a story or gallery, contact managing editor Tariq Malik at: firstname.lastname@example.org.