The space shuttle Discovery ended its 13-day mission to the international space station on Friday with a Florida landing that was almost literally under a cloud until the final hour.
"You've got seven thrilled people right here," Discovery commander Mark Polansky told Mission Control after the sunset touchdown at 5:32 p.m. ET. "We’re just really proud of the NASA team that put it together. ... We think it’s going to be a great holiday.”
There was an air of suspense surrounding the buildup to Discovery's holiday homecoming: Throughout the day, NASA managers debated the weather conditions at the shuttle's Kennedy Space Center home base as well as two backup landing sites.
NASA passed up Friday's first opportunity for a Florida landing, due to concerns about showers and clouds in the area. However, the weather forecast turned more optimistic as the afternoon wore on.
“The stuff that built up earlier has dissipated,” radioed chief astronaut Steve Lindsey, who checked out the weather at Kennedy in a shuttle training plane. That led the mission managers to give the green light for the day's second and last opportunity for a Florida landing.
"We have worked this one as hard as we can, and we’re confident we’re going to keep you clean of clouds and rain," astronaut Ken Ham in Mission Control told Discovery’s astronauts.
With that, Discovery fired its engines and descended toward its Florida landing.
The other sites under consideration had been Edwards Air Force Base in California, where strong crosswinds prohibited a landing, and White Sands Space Harbor in New Mexico, which hasn’t been used for a shuttle landing since 1982.
Kennedy was NASA’s first choice because it would spare the space agency the cost of transporting Discovery back to its home in Florida. That cost has been estimated at $1 million or more. Shipping the shuttle back from California atop a modified Boeing 747 generally takes at least a week, and it could have taken much longer in the event of a New Mexico landing.
Discovery needed to be on the ground by Saturday — otherwise it could have run out of the fuel that powers its electrical system. The shuttle originally had been scheduled to land on Thursday, but the flight was extended to allow a fourth spacewalk to fold up an accordionlike solar array on the space station.
During Discovery’s successful eight days at the space station, astronauts rewired the orbiting outpost, installed a new $11 million section, retracted the solar array and rotated out a space station crew member. American Sunita Williams replaced German astronaut Thomas Reiter, who spent six months aboard the space station.
‘Land White Sands’?
If Florida had been taken out of the picture for Friday's second opportunity, NASA could have gone with California or New Mexico later in the day — and there were additional opportunities for landing at any of the three sites on Saturday.
During the 25 years of the shuttle program, there have been 63 landings at Kennedy, 50 at Edwards and one at White Sands.
Even though the White Sands runway regularly is used for practice landings by astronauts, NASA does not like to use it for the real event. It could take as long as two months to get the shuttle back to Florida from New Mexico, compared with a week from Edwards, threatening NASA's ability to get Discovery ready to fly again next October.
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," the lyrics said.
This report includes information from The Associated Press and MSNBC.com.