Clouds and rain from a fast moving storm from the Atlantic are seen behind the Vehicle Assembly Building (VAB) at the Kennedy Space Center in Florida. (Photo/AP)
HOUSTON, Texas 鈥?Thunderstorms and high winds forced NASA to abandon its first two attempts to land the space shuttle Discovery, with the next bid for a high-speed descent to Earth set for Friday.
"We know everyone worked it as hard as they could," shuttle commander Rick Sturckow told mission control when informed of the decision. "We will look forward to trying again tomorrow."
Fresh bids to bring Discovery home were penciled in for late Friday, but with stormy conditions again forecast for Florida's Kennedy Space Center, Edwards Air Force Base in California was ready to become an alternative landing site if required, the US space agency said.
"The weather was simply unstable, very unpredictable," said NASA commentator Rob Navias. "Mother nature had the upper hand today."
NASA said it has four landing opportunities Friday, the first two -- 2148 GMT and 2323 GMT -- in Florida and two more later Friday night in California, at 0053 GMT and 0228 GMT Saturday.
Favorable conditions at Edwards on Friday night local time were forecast to worsen the following day due to winds kicked up by Hurricane Linda in the Pacific ocean. The shuttle is equipped with enough provisions to remain in orbit through Sunday.
Earlier Thursday, the crew fired up Discovery's engines and carried out a 14-second evasive maneuver to prevent the shuttle from hitting a piece of debris that had apparently drifted away from the shuttle during a spacewalk Saturday, mission control said.
When all was clear, shuttle commander Sturckow and his crew were given the green light to close the doors on Discovery's big cargo bay and begin other preparations for the planned descent.
Discovery's return marks the end of a successful mission to the orbiting International Space Station during which the crew installed new scientific equipment, overhauled the orbiter's cooling system and gathered up external experiments to be returned to Earth for analysis.
On Wednesday, NASA mission managers finished an evaluation of the shuttle's heat shielding, concluding that the fragile thermal barrier was in good shape for the high-velocity de-orbit.
Sturckow and Discovery pilot Kevin Ford tested the spacecraft's steering and communications systems as well, finding no problems.
It was during the steering tests that one of the astronauts noticed and captured photographs of a three to four-inch-long (seven to 10-centimeter) strip of material floating near the shuttle.
The unidentified object apparently drifted away during a spacewalk on Saturday while Discovery was docked at the space station, according to mission control.
Discovery returns to Earth with American astronaut Tim Kopra, who is ending a 57-day mission to the space station, and just over 5,200 pounds (2,300 kilos) of research gear, discarded equipment and trash.
"This experience has completely exceeded anything I thought it would be like, just in sights and sounds, the experiences," said Kopra. "It's been absolutely phenomenal."
He was replaced on the station by American Nicole Stott, who is due to remain aboard the outpost with five Russian, European and Canadian astronauts through late November.
Discovery's mission, which featured three spacewalks, left the 220-mile (354-kilometer) high space station better equipped to house crews of six astronauts as NASA prepares to retire its aging space shuttle fleet by early 2011.
A half-dozen shuttle missions remain, each intended to gradually complete the assembly of the 15-nation space station.
(Agencies)
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