CAPE CANAVERAL, Fla. — Atlantis astronauts are waiting for the weather to clear over Florida so they can try to land on Saturday after thunderstorms forced them to stay in space an extra day.
Shuttle commander Scott Altman and his crew will make a second attempt to land on a runway here at NASA's Kennedy Space Center, where the weather has been dismal for days and looks to continue that streak.
The shuttle is slated to land at 9:16 a.m. EDT (1316 GMT) to end the crew's successful repair mission to the Hubble Space Telescope. But if Mother Nature doesn't cooperate, there are other chances to touch down in Florida and at a backup runway in Southern California.
Mission Control told the Atlantis astronauts that the final decision on when and where to land will depend on actual weather conditions on Saturday.
"We'll stand by," Altman radioed back. "We're enjoying the view."
Altman and his crew are returning to Earth after what is now a 12-day mission to overhaul the Hubble Space Telescope for the last time. They blasted off from a seaside launch pad here on May 11.
The astronauts performed five back-to-back spacewalks to install a new wide-field camera and super-sensitive spectrograph, replace aging gyroscopes, batteries and other gear, and successfully repair two long-dead instruments that were never designed to be fixed in space.
Hubble scientists have said the upgrades have left the 19-year-old space telescope more powerful than ever. They should extend Hubble's mission flight for at least five or 10 more years, they added.
Atlantis actually has three separate chances to land on Saturday, but would have to choose between landing sites for the last two. The Florida runway is available for all three opportunities, with a backup landing strip at Edwards Air Force Base in California online for the final two chances.
If Atlantis misses its first landing target, it could aim for either a California touchdown at 10:45 a.m. EDT (1445 GMT) or another Florida landing a few minutes later. A similar choice is available at 12:24 p.m. EDT (1624 GMT), when the first of the final two opportunities comes up.
Atlantis has enough supplies to stay aloft until Monday, so the weather on Sunday — as well as Saturday — will play a key factor.
NASA prefers to land space shuttles at the Kennedy Space Center, since it is their launch site and homeport. Florida landings save a week of time and $1.8 million in transport costs to ferry shuttles back to the spaceport from California atop a modified 747 jumbo jet.
Set to return to Earth on Atlantis with Altman are shuttle pilot Greg H. Johnson and mission specialists Michael Good, Megan McArthur, John Grunsfeld, Michael Massimino and Andrew Feustel.
While they waited out the extra day in space, the astronauts gazed at their home planet through Atlantis' windows and attempted to watch DVD movies. But software glitches on the shuttle's laptop computers prevented the movie screenings in space.
Grunsfeld, an astrophysicist-astronaut who made his third trip to Hubble, told Mission Control not to worry about the computer glitch.
"We'll be home tomorrow and we'll go to the movie theater," he said.
Atlantis' mission is NASA's fifth and final flight to Hubble before its shuttle fleet retires next year. The agency's capsule-based replacement — the Orion capsule — is designed to ferry astronauts to the International Space Station and on to the moon, but does not have a robotic arm to grab Hubble or the large cargo bay to store extra parts.
NASA once cancelled the mission a year after the 2003 Columbia disaster because of its risk. But Hubble repair flight was reinstated in 2006 after NASA successfully resumed shuttle flights and tested vital repair tools and techniques.
For this flight, NASA also primed a second shuttle — Endeavour — as a rescue ship in case Atlantis was damaged in space. No rescue was required and Endeavour is now slated to fly a space station construction mission in June.
SPACE.com is providing continuous coverage of NASA's last mission to the Hubble Space Telescope with senior editor Tariq Malik in Cape Canaveral, Fla., and reporter Clara Moskowitz in New York. Click here for landing coverage, mission updates and SPACE.com's live NASA TV video feed. Live coverage begins at 6:00 a.m. EDT.