The 6 ½ ton satellite about the size of a school bus, which was slowly falling toward Earth after 20 years in space, finally came down around midnight.
The Upper Atmosphere Research Satellite fell back to Earth between 11:23 p.m. Friday and 1:09 a.m. Saturday, NASA said. The Joint Space Operations Center at Vandenberg Air Space in California said the satellite penetrated the atmosphere over the Pacific Ocean. The actual re-entry time and location of the satellite are not yet known, the agency said.
The risk to public safety or property is extremely small, NASA said.
UARS was brought into orbit in 1991 to collect measurements of ozone and other chemicals in the atmosphere. The mission ended in 2005. Since then the now-defunct satellite, which measures at 35-feet-long and 15-feet in diameter, has been slowly losing altitude as it is pulled back by Earth’s gravity.
Scientists expect the majority of the bus-sized spacecraft will be incinerated when it reenters the atmosphere, but around 26 pieces are expected to survive and fall somewhere on Earth. The smallest piece of debris could weigh as little as two pounds, and the largest piece could be about 300 pounds.
The debris will include titanium fuel, beryllium housing and stainless steel batteries and reaction wheel rims. NASA said that the chance a person will be hit with a piece of debris is about one in 3,200, and that it will most likely plunge into the ocean or land in an uninhabited region.
The agency did warn people who find parts of what they believe to be the satellite to inform local law enforcement and not touch it.
The last time a spacecraft as large as UARS fell back into Earth uncontrolled was when Skylab fell in western Australia in 1979.