A discarded chunk of a rocket is forcing six space station astronauts to seek shelter in escape capsules.
Nasa spokesman Rob Navias said the space junk will barely be close enough to be a threat.
But if it hits the station it could be dangerous, so the astronauts - two Americans, three Russians and a Dutchman - will wake early and climb into two Soyuz vehicles ready to rocket back to Earth just in case.
It was not noticed until Friday, too late to move the International Space Station out of the way.
This is the third time in 12 years that astronauts have had to seek shelter from space junk.