Image: Earth shown from space surrounded by debris
Electro Optic Systems  /  AFP - Getty Images
An image created by Australia's Electro Optic Systems (EOS) aerospace company shows a view of the Earth from geostationary height depicting swarms of space debris -- approximately 50,000 of the half-million or more debris objects greater than 1cm -- in Low Earth Orbit (LEO).
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updated 7/30/2010 12:12:49 AM ET 2010-07-30T04:12:49

A piece of Chinese space junk passed harmlessly by the International Space Station on Thursday after worries that the outpost's crew of six might have to take shelter in their Russian lifeboats as a precaution.

The potentially threatening space debris was part of the defunct Fengyun 1C weather satellite that was intentionally destroyed by China in a 2007 anti-satellite test. The debris made its closest pass by the space station at 1:47 p.m. ET Thursday, but came no closer than 5 miles (8 kilometers), NASA said.

Earlier in the day, Mission Control had alerted the space station crew that the Chinese space junk posed a potential threat, one that could have forced the astronauts and cosmonauts to wait out the debris pass inside the two three-person Soyuz spacecraft docked at the space station.

But about an hour before the flyby, Mission Control radioed good news to the station crew.

"All three of our tracking passes show a consistent green miss distance, so at this time we think there is no probability of conjunction and we are not going to be sheltering in place," Mission Control told the space station crew.

"OK, we understand, Houston," a station crew member replied.

NASA typically moves the space station if the odds of a space junk impact are within a 1-in-10,000 chance and there is sufficient time to plan a debris avoidance maneuver.

The agency also prefers to keep a pizza box-like buffer around the station free of any debris. That safety zone extends about 15 miles (25 kilometers) around the space station, as well as about a half-mile (0.75 kilometers) above and below it. The station flies in an orbit about 220 miles (354 kilometers) above Earth.

NASA space junk experts tracked the Chinese satellite remnant this week and thought at first that it would pose no threat to the station, agency spokesman Kelly Humphries told Space.com from Johnson Space Center in Houston. After further analysis, the uncertainty in the object's orbit prompted flight controllers to alert the station astronauts that they may need to take shelter.

"This has been a hard object to get a precise fix on," Humphries said.

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The space station is home to six people. Three are American astronauts with NASA, and three are cosmonauts representing Russia's Federal Space Agency. They arrived in two teams of three people each on the Russian Soyuz spacecraft, which remain docked at the station throughout their mission.

Space junk has been a growing concern for satellites and astronaut-carrying spacecraft in orbit. NASA keeps close watch on any pieces of debris that may fly close enough to the space station to pose an impact risk and endanger its crew.

NASA works with the U.S. military's Space Surveillance Network to track potentially dangerous space debris flying in low-Earth orbit. To date, there are more than 21,000 pieces of space junk that are tracked in Earth orbit by the SSN, though a NASA document states that up to 500,000 pieces of debris are currently circling the planet.

The last time astronauts sought refuge from space debris in their Soyuz spacecraft was in March, when a small piece from an old satellite rocket motor flew within 2.4 miles (4 kilometers) of the space station. That debris also did not impact the space station.

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