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Science & Tech

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Associated Press
In this image provided by the European Space Agency ESA, research satellite GOCE flies above earth at unknown date. The satellite crashed in the Atlantic Ocean on Monday.

Is falling space junk perilous?

European research satellite hits in Atlantic

– This time it splashed down in the Atlantic Ocean – but what about next time?

The European Space Agency says one of its research satellites re-entered the Earth’s atmosphere early Monday on an orbit that passed over Siberia, the western Pacific Ocean, the eastern Indian Ocean and Antarctica.

The 2,425-pound satellite disintegrated in the atmosphere but about 25 percent of it – about 600 pounds of “space junk” – slammed into the Atlantic between Antarctica and South America, a few hundred miles from the Falkland Islands, ESA said. It caused no known damage.

The satellite – called the GOCE, for Gravity field and Ocean Circulation Explorer – was launched in 2009 to map the Earth’s gravitational field.

The information is being used to understand ocean circulation, sea levels, ice dynamics and the Earth’s interior. The satellite had been gradually descending in orbit over the past three weeks after running out of fuel Oct. 21.

But how much space junk is out there? Here’s a look:

3,600 satellites in orbit

Some 6,600 satellites have been launched. Some 3,600 remain in space but only about 1,000 are still operational, according to ESA. Not all are still intact, and the U.S. Space Surveillance Network tracks some 23,000 space objects, ESA said. A lot of junk comes down unnoticed, said ESA Space Debris Office deputy head Holger Krag. Statistically, he said, “roughly every week you have a re-entry like GOCE.”

Tons of debris

About 110 to 165 tons of space junk re-enters Earth’s atmosphere each year, according to Heiner Klinkrad, the head of ESA’s Space Debris Office. In 56 years of spaceflight, a total of 16,500 tons of human-made space objects have re-entered the atmosphere.

How fast does it travel?

Space junk – mostly satellites and rocket stages or fragments – typically travels at about 17,400 mph shortly before re-entry at about 75 miles above the earth, according to ESA. It starts to slow down and heat up in the dense atmosphere. In the last 10 minutes, it hits a travelling speed roughly equal to that of a Formula One racing car –between 125 mph to 190 mph.

What’s the danger?

There have been no known human injuries or significant property damage caused by space junk, according to ESA. Unlike meteorites, which hurl into the Earth as solid chunks travelling about three times faster, space junk typically falls as fragments and is distributed over a fallout zone up to 600 miles long. Krag says fragments from a satellite came down in 2011 over the Netherlands, Germany and the Czech Republic but no pieces of that satellite were ever found.

Can it be redirected?

When systems are still functioning, spacecraft can be maneuvered to try to direct them to land in areas where there would be minimal impact, like into an ocean. In the case of uncontrolled re-entries, scientists are able to predict where the impact will be – but that can be a very wide swath. The GOCE satellite’s systems kept on working much longer than expected, providing data that Krag said will be invaluable in helping scientists figure out prediction models for future space junk descents.

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