The U.S. space agency NASA is preparing to launch the space shuttle Discovery Friday, after two other attempts this week were postponed.
The shuttle is now scheduled to blast off late Friday instead of earlier in the day.
NASA originally planned to launch the shuttle from the Kennedy Space Center in Florida early Tuesday, but postponed that attempt because of stormy weather.
The launch was moved to Wednesday, but that attempt was scrubbed because of a bad fuel valve. Engineers said a so-called fill-and-drain valve in the shuttle's engine compartment was not opening and closing properly.
The seven-member Discovery crew is to deliver a new freezer and other instruments for future experiments in space.
The cargo also includes a treadmill named after American comedian and television show host Stephen Colbert, who lobbied on television to have a piece of the space station named after him.
NASA mission management chair Mike Moses said one problem engineers are continuing to watch is foam falling off the shuttle's fuel tanks during launch. The issue has plagued several recent shuttle flights, and is blamed for causing damage that led to the break-up of the shuttle Columbia in 2003, killing all seven astronauts aboard.
Discovery is expected to spend 13 days in orbit.