CAPECANAVERAL, Fla. - NASA's chances of launching the shuttle Atlantis toward the International SpaceStation (ISS) Sunday have dropped slightly due to impending thunderstorms,weather officials said Friday.
Shuttleweather officer Kathy Winters said Atlantis now has a 60 percent chance ofrocketing spaceward at 4:29:57 p.m. EDT (2029:57 GMT) Sunday, down from 70percent Thursday, because of stormy weather and thick clouds expected duringthe spacecraft's countdown.
"We'llprobably go red during the countdown," Winters said, referring the weatherstatus near Atlantis' Pad 39B launch site.
The mainconcern for launch involves anvil clouds, electrically charged cloudsassociated with thunderstorms, which could be within 20 nautical miles (37 kilometers),of the Kennedy Space Center (KSC). The clouds can spawn lightning duringshuttle flight and must be clear of NASA'sShuttle Landing Facility should Atlantis be forced to make an emergencylanding.
Weatherwilling, Atlantis' STS-115 astronaut crew will carry a new pairof solar arrays and a 17.5-ton set of trusses to be installed on the portside of the ISS.
NASA hasfour opportunities to launch Atlantis in five days beginning with the Aug. 27attempt. The shuttle's launch window extends through Sept. 7.
Winterssaid weather experts are also watching Tropical Depression 5, which is movingthrough the Caribbean. The storm may strengthen into Tropical Storm Ernestosoon and become a Category 1 hurricane by next week, as it builds strength inthe Caribbean. While the depression is not expected to impact the launch ofAtlantis, it could affect the KSC launch site or even NASA's Houston, Texas-basedshuttle and ISS mission control operations at Johnson Space Center.
"It couldbe a threat to any of those locations," Winters said, adding that the next fewdays will shed more light. "Everybody's just monitoring the situation."
Stormyweather has already impacted Atlantis' launch preparations, though it appearsto be the only concern facing launch controllers at this time.
"There areno smoking guns that I'm aware of, so to speak," NASA test director PeteNickolenko said during the briefing. "Technically, the vehicle is in greatshape."
Flightcontrollers began the shuttle's launch countdown sixhours early Thursday in order to load the cryogenic liquid oxygen andliquid hydrogen used to power the orbiter during its planned11-day mission. Engineers began pumping the super-cold propellant intoAtlantis' fuel tanks at about 9:30 a.m. EDT (1330 GMT) this morning, and hopeto finish by 2:00 p.m. EDT (1800 GMT), though afternoon thunderstorms - anever-present concern this time of year at the launch site - could delay theprocess.
Nickolenkosaid heavy rain, lightning and thunderstorms Thursday afternoon also preventedpad workers from closing Atlantis' payload doors - originally slated for noon -until about 9:45 p.m. EDT (0145 Aug. 25 GMT).
Aside fromweather, no technical issues have popped during the STS-115 launch countdown.One leftover item - final analysis of an auxiliary power unit (APU) glitch onAtlantis' sister ship Discovery - will be presented to the spaceflight'sMission Management Team (MMT) during a launch readiness review later today. Theissue is expected to be cleared at that time, shuttle officials said.
"All of ourteams are ready and their focused," Nickolenko said. "We're all looking forwardto launch on Sunday and the return to [ISS] assembly."
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