Endeavour's seven astronauts hoped to end their space station delivery and repair mission at the Kennedy Space Center in Florida, where their families were waiting. But Sunday morning, Mission Control informed the crew that dangerously high wind and possible thunderstorms were expected, not to mention moderate turbulence.
Good weather was predicted for the backup landing site in Southern California, Edwards Air Force Base. "It looks real nice out there," Mission Control radioed.
Flight controllers planned to make a decision on what to do later Sunday morning.
"Just keep us in the loop," replied shuttle commander Christopher Ferguson.
Although there are four landing opportunities - two in Florida and two in California - NASA managers only want to make three attempts Sunday afternoon before pushing the landing attempt to Monday.
Endeavour's astronauts have enough supplies to last until Tuesday, but NASA officials want them on the ground no later than Monday.
NASA managers would prefer to land in Florida since that's where Endeavour is housed, and it would spare the space agency the $1.8 million price tag of flying the shuttle to Florida on the back of a 747 airliner.
The last time a shuttle landed at Edwards Air Force Base was in June 2007. The runway at Edwards is about 3,000 feet shorter than the 15,000-foot runway at Kennedy. But NASA officials said that shouldn't be a problem since Ferguson and his co-pilot, Eric Boe, have made extensive practice landings on the runway in training aircraft.
The weather at Edwards for both days looks favorable. The weather at Kennedy Space Center on Monday isn't forecast to be a whole lot better than it's expected to be on Sunday.
"It's borderline," Lunney said. "It's not an easy day."
After examining images from a late inspection of Endeavour's protective heat shield, NASA managers on Saturday cleared Endeavour for a return home. The managers wanted to make sure there were no gashes which could allow fiery gases to penetrate the shuttle, like what happened to the doomed Columbia space shuttle in 2003.
"Endeavour looks to me and to the experts to be as clean or cleaner than any vehicle that we've flown," said LeRoy Cain, chairman of the mission management team.
If it lands Sunday, Endeavour will end a 16-day mission during which the shuttle flew to the international space station delivering a new bathroom, kitchen, exercise machine, sleeping quarters and recycling system designed to convert urine and sweat into drinking water.
The new equipment will allow NASA to double the size of the space station crew to six by June.
The Endeavour crew also took four spacewalks to unjam a joint which rotates in the direction of the sun to generate power. The mission also rotated out a crew member at the outpost, orbiting 220 miles above Earth. U.S. astronaut Sandra Magnus replaced U.S. astronaut Greg Chamitoff, who was returning aboard Endeavour after living for six months at the station.
"I'm really looking forward to seeing my kids and my family," said Chamitoff, who has two children.
Up at the space station, meanwhile, a Russian supply ship arrived Sunday morning with Christmas presents, food, clothes and other items for the three residents. Cosmonaut Yuri Lonchakov had to use manual controls inside the station to guide the craft in for a docking because of a last-minute technical problem.
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