Weather Concerns Increase for Sunday Shuttle Launch

On Launch Pad 39B, Space Shuttle Atlantis' payload bay doors are being closed for launch. Inside is seen the orbiter's cargo, the 17-and-a-half-ton P3/P4 truss segment for the International Space Station. CREDIT: NASA/Jim Grossmann.

CAPE CANAVERAL, Fla. - NASA's chances of launching the shuttle Atlantis toward the International Space Station (ISS) Sunday have dropped slightly due to impending thunderstorms, weather officials said Friday.

Shuttle weather officer Kathy Winters said Atlantis now has a 60 percent chance of rocketing spaceward at 4:29:57 p.m. EDT (2029:57 GMT) Sunday, down from 70 percent Thursday, because of stormy weather and thick clouds expected during the spacecraft's countdown.

"We'll probably go red during the countdown," Winters said, referring the weather status near Atlantis' Pad 39B launch site.

The main concern for launch involves anvil clouds, electrically charged clouds associated with thunderstorms, which could be within 20 nautical miles (37 kilometers), of the Kennedy Space Center (KSC). The clouds can spawn lightning during shuttle flight and must be clear of NASA's Shuttle Landing Facility should Atlantis be forced to make an emergency landing.

Weather willing, Atlantis' STS-115 astronaut crew will carry a new pair of solar arrays and a 17.5-ton set of trusses to be installed on the port side of the ISS.

NASA has four opportunities to launch Atlantis in five days beginning with the Aug. 27 attempt. The shuttle's launch window extends through Sept. 7.

Winters said weather experts are also watching Tropical Depression 5, which is moving through the Caribbean. The storm may strengthen into Tropical Storm Ernesto soon and become a Category 1 hurricane by next week, as it builds strength in the Caribbean. While the depression is not expected to impact the launch of Atlantis, it could affect the KSC launch site or even NASA's Houston, Texas-based shuttle and ISS mission control operations at Johnson Space Center.

"It could be a threat to any of those locations," Winters said, adding that the next few days will shed more light. "Everybody's just monitoring the situation."

Stormy weather has already impacted Atlantis' launch preparations, though it appears to be the only concern facing launch controllers at this time.

"There are no smoking guns that I'm aware of, so to speak," NASA test director Pete Nickolenko said during the briefing. "Technically, the vehicle is in great shape."

Flight controllers began the shuttle's launch countdown six hours early Thursday in order to load the cryogenic liquid oxygen and liquid hydrogen used to power the orbiter during its planned 11-day mission. Engineers began pumping the super-cold propellant into Atlantis' fuel tanks at about 9:30 a.m. EDT (1330 GMT) this morning, and hope to finish by 2:00 p.m. EDT (1800 GMT), though afternoon thunderstorms - an ever-present concern this time of year at the launch site - could delay the process.

Nickolenko said heavy rain, lightning and thunderstorms Thursday afternoon also prevented pad workers from closing Atlantis' payload doors - originally slated for noon - until about 9:45 p.m. EDT (0145 Aug. 25 GMT).

Aside from weather, no technical issues have popped during the STS-115 launch countdown. One leftover item - final analysis of an auxiliary power unit (APU) glitch on Atlantis' sister ship Discovery - will be presented to the spaceflight's Mission Management Team (MMT) during a launch readiness review later today. The issue is expected to be cleared at that time, shuttle officials said.

"All of our teams are ready and their focused," Nickolenko said. "We're all looking forward to launch on Sunday and the return to [ISS] assembly."

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