Astronauts aboard Space Shuttle Discovery have closed the payload bay doors and started making final preparations for a landing in Florida this morning.
The crew is wrapping up a 13-day mission to the International Space Station.
NASA is aiming for a landing at 9:14 a-m, Eastern time, but forecasters are concerned that rain showers near the three-mile-long runway could violate flight safety rules.
If the shuttle can't land in Florida today, astronauts would get a bonus day in space and would attempt a landing tomorrow either in Florida or California.
The Discovery mission delivered supplies and a new crewmember to the space station and tested safety procedures for the shuttle developed since the "Columbia" disaster in 2003.