The International Space Station may have to fire its thrusters to avoid a piece of space junk that is on course to pass within two miles of the orbiting complex and its 13 astronauts. Nasa 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...