There’s a big piece of debris hurtling through space, and according to NASA, it’s heading right for the International Space Station. But the 13 astronauts on site aren’t in immediate danger: if necessary, NASA says it will fire thrusters to move the station and the shuttle Discovery to safety. The space junk, left over from part of Ariane 5, a European rocket launched three years ago, could pass within two miles of the complex. It is expected to float by on Friday at 3:06 p.m. GMT. Scheduled space walks will not be interrupted.