German ROSAT Satellite Has Fallen to Earth, Say NASA Sources

Oct. 22, 2011— -- The German ROSAT satellite fell back to Earth Saturday evening, U.S. time, NASA sources told ABC News.

DLR, Germany's scientific research agency, said the satellite re-entered the atmosphere between 9:45 and 10:15 p.m. ET.

It was the second time a satellite large enough to for debris to reach the Earth's surface has fallen from orbit in the past month, an occurence that typically happens only once per year.

Last month NASA's UARS re-entered the atmosphere. ROSAT, an orbiting telescope designed to map X-rays in the sky, was launched on a Delta 2 rocket from Florida in 1990.

While functioning in space, ROSAT found roughly 110,000 stars, supernovas and cosmic rays emitting X-rays.

The German Space Agency put the chances at one in 2,000 that someone would be struck by a piece of ROSAT. That works out to odds of about one in 14 trillion that any particular one of the 7 billion or so people on Earth would be whacked by a piece of the satellite.

The threat of someone being hit by a piece of UARS was one in 3,200. The remnants ended up falling in the remote Pacific Ocean.

Engineers said ROSAT would likely end up in the sea as well, since 75 percent of Earth is covered by water.

NASA orbital debris scientist Mark Matney told ABC News there is a lot of junk up in space waiting to come down on us.

"The U.S. Space Surveillance Network has catalogued 16 thousand things in Earth orbit, many of them are quite small pieces of debris, but about 7,000 of those are large objects, spacecraft and large rocket bodies, we have made quite a mess up there," Matney said.

Germany's ROSAT X-ray astronomy satellite is smaller than UARS but was considered a bigger threat because more of the satellite was made of heat-resistant components, including its 880-pound primary mirror.

the German space agency estimated that up to 3,750 pounds of the decaying satellite could survive re-entry.

ROSAT was turned off in 1999 and its altitude gradually dropped from 350 miles above the Earth to 149 miles Saturday morning. The satellite's orbit took it 53 degrees north and south of the equator.

ABC News' Ned Potter contributed to this report