CAPE CANAVERAL, Fla.--Despite two opportunities for a morning landing, the space shuttle Discovery is still in orbit after cloud cover prevented the orbiter from returning to Earth Monday.

Unpredictable weather--pop-up rain showers and a broken cloud deck at approximately 1,000 feet (304 meters) above the Kennedy Space Center's Shuttle Landing Facility--forced flight controllers to wave-off both of today's two landing opportunities for the space shuttle Discovery. The landing was originally scheduled for 4:47 a.m. EDT (0847 GMT).

"The only word that describes all this is "unstable"," astronaut Ken Ham, spacecraft communicator at Mission Control, informed Discovery's crew. "We regret not getting you guys home today."

"You guys made the right decision," Discovery's STS-114 commander Eileen Collins said. "We're going to enjoy another orbit."

The added day extends an already extended mission for Collins and her six fellow astronauts. Mission controllers lengthened the STS-114 flight's stay at the International Space Station (ISS) by one day to allow more time for cargo transfer between the two vehicles. The astronauts will have spent 14 days in orbit - they were slated for only 12 days - after tomorrow's planned landing.

LeRoy Cain, NASA's ascent/entry flight director for Discovery's STS-114 mission, said the orbiter has supplies to stay in orbit until Wednesday. While KSC will still be the primary landing target for Tuesday's attempts, alternative landing sites at Southern California's Edwards Air Force Base and Northrup Strip at White Sands Missile Range in New Mexico will also be prepared to host a shuttle arrival, he added.

"We will attempt to land somewhere tomorrow," Cain said after Monday's landing wave-offs.

STS-114 flight controllers hope to try for a KSC landing again Tuesday at 5:07 a.m. EDT (0907 GMT), but have a total of six opportunities to land tomorrow, shuttle officials said. In addition to the initial opening, there is a second KSC landing opportunity at 6:43 a.m. EDT (10:43 GMT) and two windows each for Edwards or Northrup, they added.

The weather forecast at KSC is very similar to what was seen today, whereas the outlook for Edwards is favorable all week, Cain said. Weather predictions for Northrup are not as promising, though that airstrip is Cain's third choice for a landing after KSC and Edwards, the flight director said.

Clad in their orange pressure suits, Collins and pilot James Kelly were prepared to guide the 100-ton Discovery orbiter back to Earth, with STS-114 mission specialists Stephen Robinson - serving as flight engineer - and Andrew Thomas on the flight deck, when the descent was called off. Mission specialists Wendy Lawrence, Charles Camarda and Soichi Noguchi, an astronaut with the Japanese Aerospace Exploration Agency (JAXA), prepared for landing in Discovery's middeck.

John Madura, manager of KSC's weather office, said shuttles require a cloud ceiling of 8,000 feet (2,438 meters) to land. Both landing attempts today had cloud ceilings of 1,000 feet (304 meters) or lower, which would have caused visibility problems. NASA prohibits shuttles from flying through rain because of the damage it can cause to the orbiter's exterior, they added.

"They want to be able to see the runway," Madura said. "They don't want to fly in on instruments."

During Discovery's second landing opportunity Monday, flight controllers reported that conditions were technically go for landing, but they still had concerns.

"It was a close thing," Cain said. "I just couldn't get quite comfortable with the overall day."

Astronauts on hand for Discovery's landing said that a wave-off is not necessarily bad, since it gives shuttle crews time to reflect on their mission - especially one as busy as STS-114.

"We were delayed four days coming home," said astronaut John Herrington, who served as mission specialist aboard Endeavour during STS-113, NASA's last shuttle to land at KSC. "[The delay] is a chance to sit back and really take a deep breath to look out the window."

The STS-114 astronauts are NASA's first shuttle crew to fly since the loss of the seven STS-107 crewmembers aboard the Columbia orbiter, which broke apart over Texas on Feb. 1, 2003 during reentry. Columbia was damaged during launch when a 1.67-pound piece of external tank foam pierced its heat shield, which later allowed hot gases into the orbiter's left wing that destroyed the vehicle, killing its astronaut crew.

NASA's spent more than two years and $1.4 billion dollars to prevent such foam loss from endangering a shuttle again, only to find a 0.9-piece foam chunk fall from Discovery's external tank - but not strike the orbiter - during its July 26 launch. At least three other pieces too large for NASA's new safety standards also separated from Discovery's tank, prompting shuttle officials to suspend future shuttle flights until the problem is solved.

Discovery's external tank foam loss cast a cloud over what shuttle officials and STS-114 crew tout as a wildly successful spaceflight. 

"These 13 days have gone by so quickly," Robinson said Sunday. "There've been a lot of challenges, but rewarding challenges."

The STS-114 astronauts tested a series of new tools developed as a direct response to the Columbia accident, including a laser camera-tipped 50-foot (15-meter) boom that they attached to Discovery's robotic arm to scan the shuttle's heat shield for damage. A suite of wing leading edge sensors, designed to detect impacts and measure temperature during launch, far outlasted their anticipated 36-hour battery lifetimes and were still functioning as the STS-114 crew prepared for landing, shuttle officials said.

"We have definitely accomplished all our mission objectives," Collins told reporters before Monday's landing attempts.

Discovery's crew delivered about six tons of food, water, science equipment and spare parts to the ISS - the first shuttle resupply to the station since December 2002 - and returned about three tons of trash, unneeded or broken equipment and more than 10 Russian-built Kurs navigation systems used aboard Russian Soyuz and Progress spacecraft to dock at the space station, shuttle officials said.

Robinson and Noguchi, STS-114's spacewalking duo, staged three extravehicular activities from Discovery's airlock to test heat shield repair techniques, replace a broken ISS gyroscope and add a spare parts platform to the exterior of the orbital laboratory among other tasks. During their final spacewalk, Robinson also conducted the first-ever repair of the shuttle's belly heat shield when he plucked two gap-fillers jutting out from between the orbiter's heat-resistant tiles.

Robinson said he and his crewmates were looking forward to getting home and looking over their mission's launch video, which relatives told them was amazing.

"We're going to get to see this mission from a whole new perspective," he added.

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