This story was updated at 12:58 p.m. EST.
CAPECANAVERAL, Fla. - NASA is once more preparing to launch the shuttle Discovery and itsseven-astronaut crew tonight after low clouds thwarted a Thursday evening liftoff.
NASA mission managers decided earlier today to continue preparations for today's planned space shot, though fueling operations for Discovery's external tank were been delayed from this morning to midday.
"We haven't started tanking yet, we'll be doing that in in the next few minutes, but we are going to make an attempt tonight," NASA spokesperson Bruce Buckingham said here at the Kennedy Space Center.
Launch is currently scheduled for 8:47:34 p.m. EST (0147:34 Dec. 10 GMT), though threatening weather could prevent liftoff. Weather permitting, the launch may be visible to viewers along the U.S. eastern seaboard [Map].
Led bycommander MarkPolansky, the five-man, two-woman crew of STS-116are tasked with delivering a new portsidepiece of the InternationalSpace Station (ISS) and rewiringthe orbital laboratory's electrical grid.
Launchcontrollers decided to forgo a Friday attempt to loft Discovery after a bleakweather forecast of low clouds, rain showers and high crosswinds gave only a1-in-10 chance of the shuttle lifting off.
"Wehave high winds on Friday that will not allow us to launch, so the decision hasbeen made to perform a 48-hour turnaround and the next launch attempt will beon Saturday," NASA launch commentator Bruce Buckingham said after Thursdaynight's launch scrub.
Low clouds,showers and crosswinds are still predicted for tonight's launch attempt, butchances of favorable conditions are slightly better at 30 percent. The weatheroutlook continues to improve for Sunday, with a 40 percent favorable forecast.
If NASAdecides to attempt launches both tonight and on Sunday, they will have to standdown on Monday to top off liquid oxygen in the shuttle's fuel cells, whichevaporates if not used, NASA officials said. Under this scenario, launch attemptswould resume again on Tuesday, Dec. 12.
NASA'sstandard approach is to try two launch attempts and then stand down for one torefuel either the liquid hydrogen or liquid oxygen, NASA spokesperson JuneMalone told SPACE.com.
"Sometimesyou can try three in a row, but a lot of that has to do with the fuel cells andhow much fuel we have on board," Malone said. "Also, ground crew restis an issue, so you don't overtax the organization of the people."
Tuesday'sweather forecast is the most favorable yet, with a 60 percent chance thatconditions will permit the shuttle to lift off. After Tuesday, another coldfront is expected to move into central Florida, possibly bringing with it thickcloud cover and showers that could once again hinder launch.
Threespacewalks are scheduled for the 12-day spaceflight. One of them will bededicated to the installation of a new piece of the station's portsidetruss. The other two are set aside for a complicated rewiringtask of the space station's electrical grid that will involve a heavilychoreographed power-down of its different sections, as well as the activationof the orbital laboratory's thermal cooling system.
"We'regoing to do the largest power down of the space station during thisflight," NASA launch director Michael Leinbach told reporters in aprelaunch news briefing. He added that during the two space station rewiringspacewalks, NASA ground control will send an excess of 4,500 commands to thespace station, compared to only about 800 commands on a normal day.
"That'sthe most we've ever done," he said.
Set to rideinto space with Polansky today are: Discovery shuttle pilot WilliamOefelein and mission specialists RobertCurbeam, NicholasPatrick, JoanHigginbotham, SunitaWilliams and European Space Agency (ESA) astronaut ChristerFuglesang, Sweden's first spaceflyer to bound for orbit. With exceptions ofPolansky and Curbeam, all five STS-116 astronauts are making their spaceflightdebut today.
Williams willrelieve European Space Agency astronaut, ThomasReiter, who has been aboard the orbital laboratory since July. Reiter willride back to Earth aboard Discovery in Williams' place.
Discovery'slaunch window currently runs from Dec. 7 to 17. Additional flight opportunitiesexist through Dec. 26, but only if mission managers approve the shuttle forflight over the year-endswitch from 2006 to 2007.
NASAwill broadcast Discovery's launch countdown and planned liftoff on NASATV beginning at about 2:30 p.m. EST (0730 GMT). You are invited to followthe countdown's progress using SPACE.com's feed, which is available by clickinghere.
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