This story was updated May 22 at 4:53 a.m. EDT.
CAPE CANAVERAL, Fla. — Atlantis astronauts are hoping for a break in the weather for their planned Friday landing as they prepare to wrap up their successful mission to tune up the Hubble Space Telescope.
Atlantis is slated to touch down on the runway here at NASA's Kennedy Space Center (KSC) Friday just after 10:00 a.m. EDT (1400 GMT), but only if the weather allows. The forecast is grim, with the potential for rain showers and thunderstorms near the landing strip may keep the shuttle in orbit longer than planned, NASA officials said.
"The weather for KSC on Friday, I'll tell ya, doesn't look great," said entry flight director Norm Knight. "We expect it's going to improve over the next couple of days, but again we'll just have to wait and see."
Atlantis has two chances to land Friday, with the second arising at 11:39 a.m. EDT (1539 GMT). But the shuttle could also try again Saturday and choose either its Florida runway or a backup landing strip at Edwards Air Force Base in Southern California. The shuttle has enough supplies to remain in space until Monday, Knight said.
Atlantis commander Scott Altman and his seven-astronaut crew are finishing up an 11-day mission to the 19-year-old Hubble, where they plowed through five exhausting spacewalks in as many days to leave the iconic observatory more powerful than ever. It was NASA's fifth, and last, mission to Hubble before retiring its three-shuttle fleet next year.
Returning to Earth with Altman are shuttle pilot Gregory H. Johnson and mission specialists Michael Good, Megan McArthur, John Grunsfeld, Michael Massmino and Andrew Feustel.
The weather for the crew's landing is dynamic. Mission Control radioed the astronauts to say that there's a chance the sky may clear in time for at least one landing attempt, but they'll know more later today.
"There are a lot of issues against us, however it's a very dynamic situation and we're going to keep an eye on it closely," Mission Control said.
NASA prefers to land space shuttles at the Kennedy Space Center here because it is the home port and launch site for the fleet. It also saves about a week of time and $1.8 million by avoiding the need to ferry a shuttle from its backup runway in California to Florida using NASA's modified 747 jumbo jet transport craft.
Hubble's new lease
Despite a series of unexpected hitches — like stuck bolts, handrails and balky gyroscopes — that slowed their work, the astronauts labored tirelessly through to repair Hubble. Their efforts should extend the space telescope's cosmic scans of the sky through at least 2014 or longer.
The Atlantis astronauts installed two new instruments in Hubble and fixed two long-broken ones that were never designed to be fixed in space. They also replaced several vital components, like batteries and gyroscopes, to upgrade Hubble's systems.
Grunsfeld, the mission's spacewalking chief and a self-described "Hubble hugger," said he expected to be sad when Atlantis left Hubble in space Tuesday, but felt pride instead.
"Everything worked, we deployed Hubble and it's at the apex of its capabilities," said Grunsfeld, a five-time spaceflyer who made his third trip to Hubble. "We pulled it all off. It was a very hard mission."
The new instruments are expected to push Hubble's vision deeper into space and peer back to a time when the universe was just 500 million years old. The universe is currently 13.7 billion years old. Hubble scientists will start calibrating the telescope's instruments next week and plan to resume science observations by the end of summer.
Atlantis' final flight to Hubble cost about $1.1 billion, about one-tenth the total $10 billion invested in the beloved observatory.
Triumph at Hubble
Lead flight director Tony Ceccacci said that there were some people who had little faith in the spaceflight, which was once deemed so risky that it was canceled. NASA called the service call off five years ago after the Columbia disaster and studied a potential robotic service call before reinstating the manned mission in 2006.
To deal with the added risk of space debris damage and Hubble's already high 350-mile (563-km) orbit, which put Atlantis out of range of the lower International Space Station and its different 220-mile (354-km) orbit, NASA made an unprecedented decision.
It kept the shuttle Endeavour and a crew of four astronauts on standby, ready to launch a rescue mission within a week of an emergency. No rescue was needed and Endeavour stood down from rescue status on Thursday.
"There were folks who thought we couldn't do this," Ceccacci said before landing. "They always told us 'you're too aggressive, you're going to get in trouble.'"
But the more than two years of training, planning and preparation paid off for the Atlantis astronauts and their flight control team on Earth. Not only did the tireless astronauts overhaul Hubble, but they pushed through all of Hubble's unexpected obstacles to hit all their mission goals.
"I don't want to tell you I told you so, but I told you so," Ceccacci said with a smile.
It wasn't always easy going. The astronauts spent more than 36 hours working on Hubble, at times tackling intricate repairs that had no guarantee of success. Then flight controllers powered the long-dead instruments back up to the delight of the astronauts and scientists on Earth.
The Atlantis crew also gave Hubble one extra addition: a docking ring to allow a future robotic spacecraft to latch on and send it plunging into the Pacific Ocean when its mission is over sometime after 2020.
Mission Control roused the astronauts early Friday with "The Galaxy Song," a tune from the film "Monty Python's The Meaning of Life."
"Atlantis, we hope that soon you'll remember what it's like to stand on the planet," Mission Control radioed the crew.
"And Houston, thanks for that," Altman replied. "We're looking forward to that as well."
SPACE.com is providing continuous coverage of NASA's last mission to the Hubble Space Telescope with senior editor Tariq Malik at the Kennedy Space Center and reporter Clara Moskowitz in New York. Click here for mission updates and SPACE.com's live NASA TV video feed. Live landing coverage begins at about 6:30 a.m. ET.