By Chris Baltimore
HOUSTON (Reuters) - The International Space Station might have to fire its thrusters to avoid a piece of space junk that could pass within two miles of the orbiting complex and its 13 astronauts, NASA said on Wednesday.
The U.S. space agency is tracking debris from a portion of a European rocket, the Ariane 5, that was launched more than three years ago. The debris could pass close enough to require astronauts to fire thrusters to move the station and shuttle Discovery that is docked there out of the way, NASA officials said at a briefing.
The debris posed no immediate danger to the station or the shuttle, the agency said.
The debris, which is in an oval-shaped orbit that makes it difficult to track, will make its closest approach to the station at 11:06 a.m. EDT (3:06 p.m. GMT) on Friday, NASA said.
The debris will not force NASA to delay the second of three spacewalks planned outside the station on Thursday. NASA might decide to take no action, or could "reboost" the station from its current orbit 220 miles above the Earth after astronauts complete their second space walk, it said.
Discovery arrived at the station on Sunday to deliver more than seven tonnes of food, supplies, equipment and spare parts to the $100 billion, 16-nation orbital outpost.
Space junk is not uncommon -- about 19,000 objects larger than 10 centimeters are known to exist, according to NASA's Orbital Debris Program Office.
China's intentional destruction of a weather satellite in 2007 and the accidental collision of American and Russian communications satellites in 2009 have greatly increased the number of large debris in orbit, the office said.