NASA managers cleared space shuttle Discovery to return home Friday, but are unsure where the spacecraft will touch down.
Showers and clouds were forecast at Kennedy Space Center in Florida and crosswinds were expected at NASA's next-best option, Edwards Air Force Base in California's Mojave Desert. That may rule out both sites because of landing rules.
If they are ruled out, NASA will be left with the White Sands Space Harbor in New Mexico, a site that has not been used for a shuttle landing for 24 years, as the best option for favorable weather.
"I have a lot of things to worry about on this flight that I can control and the weather is something I can't," Discovery commander Mark Polansky told reporters from space. "I'm ready to land at any of the three sites."
NASA managers shipped a crane for lifting the shuttle, equipment that purges gases and cools and heats the shuttle on the ground, thruster plugs and 60 workers from the Kennedy Space Center to the New Mexico landing site in preparation for the shuttle landing.
They then hoped the weather would clear at the other two sites.
"As we get closer, we'll have much more certainty on what we're really faced with," said entry director Norm Knight, who will direct the landing.
The first landing opportunity was at 3.56p.m. EST (2056GMT) at Kennedy Space Center. Other opportunities were 1Ѕ hours later at all three sites followed by two opportunities at Edwards and White Sands 1Ѕ hours after that. NASA managers were considering a last try at 8:36 p.m. EST (0136GMT Saturday) at Edwards.
NASA has seven more opportunities to land the shuttle on Saturday. Discovery needs to be on the ground by Saturday because it will run out of the fuel that powers its electrical system.
Discovery had originally been scheduled to land on Thursday, but the flight was extended a day to allow a fourth spacewalk to fold up a stubborn, accordion-like solar array on the space station.
On Thursday afternoon, the space agency pronounced Discovery safe to return after analyzing images from an inspection of the ship's heat shield. Shuttles are now routinely inspected in flight for any damage of the sort that doomed Columbia in 2003.
During the 25 years of the shuttle program, there have been 63 landings at Kennedy, 50 at Edwards and just the single landing at White Sands in 1982.
Even though the White Sands runway is regularly used for practice landings by astronauts, NASA does not like to use it for the real event because it lacks the equipment to service the shuttle.
It could take as long as two months to get the shuttle back to Florida from New Mexico, compared to a week from Edwards, threatening NASA's ability to get Discovery ready to fly again next October, reports AP.
Flight controllers in Houston, trying their hand at holiday songwriting, sent the Discovery crew in their daily messages lyrics to their version of the song, "Let it Snow."
"Oh the weather at KSC is frightful. But at White Sands it's so delightful. And since we have to land. Land White Sands. Land White Sands. Land White Sands," it said.
"There should be no Russian who goes to sleep without wondering if they're going to get their throat slit in the middle of the night,” Milley said