Discovery's astronauts woke up yesterday morning with hopes that a bank of storm clouds would not delay their return to Earth.
The weather forecast was mixed for yesterday morning at Kennedy Space Center in Florida, the only landing site NASA has called up for the day. Rain clouds to the north were forecast to dip south, and the big question was whether they would hold off in time for landing.
NASA had two landing opportunities yesterday at Kennedy: 9.14am EDT and 10.50am EDT.
The weather looked better for the first opportunity. The landing rules say rain has to be 50km away because rain could damage the shuttle's tiles.
NASA's spaceflight meteorology group predicted scattered Monday morning showers and storms, with worse weather today. The National Weather Service's forecast was for a 55 percent chance of rain at the shuttle landing strip as of early Monday morning.
Landing officials had to make a "go-no-go" decision for the first landing try at 7.47am EDT.
On that first landing attempt, Discovery would fly to Florida from the south. This would be the first landing at Kennedy in nearly four years. Last year's flight of Discovery, after weather delays, came down at Edwards Air Force Base in California, the backup site.
If Discovery was unable to land at Kennedy yesterday, NASA said it would call up Edwards and try to land at either location today, weather permitting, landing director Steve Stich said. The shuttle has to land no later than tomorrow because after that it will run out of oxygen for its fuel cells, he said.
Landing at Edwards costs NASA about US$1.7 million more because it has to get the shuttle back to Florida.
As he went to bed on Sunday, Discovery commander Steve Lindsey said he hoped that yesterday he'd wake up and be able to walk on the ground later that day.
The shuttle itself was cleared on Sunday for landing. After seven different inspection efforts, engineers and astronauts couldn't find any damage to the shuttle's heat shield. A small leak with one of three power units that control braking and maneuvering for landing did not appear to be a big deal, NASA mission managers decided on Sunday.
Discovery completed all its assigned tasks, including making sure repairs to the shuttle external tank were successful, fixing a rail car on the international space station, and bringing the station a new crew member.
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