The astronauts on the US space shuttle Atlantis closed their ship's cargo bay doors on Friday, hoping for good weather that would allow them to return to Earth after two weeks in orbit.
The first opportunity to land at the shuttle's home port at the Kennedy Space Center in Florida will be at 2:18 pm EDT (1818 GMT) but thick clouds and nearby rain could prompt flight directors to divert the spaceship to a backup landing site in California.
The first opportunity to land at Edwards Air Force Base in California would occur at 3:49 pm EDT (1749 GMT). NASA had planned to end its first shuttle mission of the year on Thursday but the spacecraft and its seven astronauts were told to stay in orbit an extra day due to summer thunderstorms at the Florida space port. Although the shuttle has enough fuel and supplies to remain in orbit until Sunday, NASA intends to bring it back to Earth on Friday.
"The mindset is we're going to land you safely some place today," astronaut Tony Antonelli from Mission Control in Houston radioed to Atlantis commander Frederick Sturckow. Atlantis was returning from a nine-day stay at the International Space Station, a $100 billion project of 16 nations that is a little more than half finished.
The shuttle carted a third pair of power-producing solar wing panels to the outpost and its crew conducted four spacewalks to install them, fold up another older wing that will be moved to a new location and install equipment needed to prepare for the arrival of additional laboratories. The astronauts also were called upon to repair a hole in the heat shield on Atlantis, which arrived in orbit with a corner of an insulating blanket torn loose.