Click to play videoCape Canaveral (Florida): NASA officials on Thursday put off the much-anticipated launch of space shuttle space shuttle Discovery due to bad weather.
According to the officials at the agency, low clouds forced them to delay the rare nighttime launch of the space shuttle.
Astronauts were strapped in and the countdown clock was at five minutes when the decision was taken. "We gave it our best shot," said one controller.
Discovery and its seven-member crew are likely to try again on Saturday to begin a mission to rewire the international space station.
However, there has been no word yet on a possible re-attempt.
It would be the first nighttime launch in four years.
Despite just a 40 per cent chance of favorable weather at the 2135 hrs (ET launch time), Discovery's seven astronauts donned their orange spacesuits and strapped into the shuttle. Earlier in the afternoon, the astronauts - five of whom are going to space for the first time - toasted one another with water at a pre-launch meal.
The hatch was closed about two hours before the planned launch.
Indian-origin Astronaut Sunita Williams, who will live at the space station for six months, seemed especially excited. While her crewmates suited up, she did bodybuilder poses for the camera and waved a "Go Red Sox" sign before boarding the shuttle.
Not to be outdone by their crewmate, Joan Higginbotham held up a "Hi Mom" sign and Robert Curbeam, who will spacewalk three times during the mission, flashed a "Go Colts" sign and then one that said "Hi Eva" to his daughter.
As dusk arrived, launch controllers grew more concerned about high winds, although they were slightly more optimistic about getting a break in the clouds.
If the space shuttle didn't get off the ground Thursday night, NASA likely would wait until Saturday before trying again. The Friday forecast was even worse, with only a 10 per cent chance for launching.
"Unless the weather changes, which in case you haven't noticed has been observed to occur in Florida from time to time ... I doubt we would even try to tank tomorrow if we don't make it for today," NASA Administrator Michael Griffin said on Thursday.
Not only was the sky thick with clouds over Kennedy Space Center, but the weather also wasn't favorable at the shuttle's three emergency landing sites in Spain and France.
NASA won't launch unless one of those sites has good weather.
Too many clouds prevent the necessary observation of the shuttle during its ascent, and the shuttle commander needs visibility if an emergency landing is required.
The best opportunity for launching over the next several days was Tuesday, said shuttle weather forecaster Matt Timmermann.
At the beginning of next week, "we see an improving trend," he said. "The winds get lighter and it gets drier."
During the 12-day mission, Discovery's astronauts will rewire the space station, bring up a new two-ton addition to the space lab and rotate out one of the station's three crew members.
NASA had required daylight liftoffs for the three launches after the 2003 Columbia accident to make sure the agency could get good daytime photos of the external fuel tank in case debris fell from it during launch.
Foam breaking off the tank and striking Columbia's wing at liftoff caused the damage that led to the disaster that killed seven astronauts.
But NASA officials were comfortable with the acceptable levels of foam loss during the last two liftoffs and believe radar will be able to spot pieces falling from Discovery's tank.
Griffin said he felt no pressure to stick to the launch schedule, despite NASA's desire to go up before December 17 so that Discovery is back on the ground for the new year.
Shuttle computers aren't designed to make the change from the 365th day of the old year to the first day of the new year while in flight. The space agency has figured out a solution for the New Year's Day problem, but managers are reluctant to try it if they don't have to.
If Discovery is still grounded by December 18, NASA may decide to keep trying anyway through December 26.
"We've got days and days, and we're not even worrying about the clock problem," Griffin said. "The clock problem is an annoyance but it's not a real problem in the sense that we know how to deal with it."
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