Shuttle Atlantis prepares for final flight
7 July 2011 Last updated at 21:34 BST
The final space shuttle lift-off is expected to be attended by 500,000 people at Florida's Kennedy Space Center on Friday.
The Atlantis orbiter is due to lift off at 1126 local Florida time (1526 GMT) on a mission to haul critical supplies to the International Space Station.
But forecasters believe there is a 70% chance now that stormy weather will prevent the shuttle getting away on time.
David Shukman reports.