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Countdown sequence begins again for shuttle Endeavour BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: July 8, 2009 
Engineers started a fresh countdown for the shuttle Endeavour Wednesday, targeting a Saturday night launch to kick off a 16-day space station assembly mission. Running a month late because of a now-repaired hydrogen vent line leak, there are no technical problems of any significance at launch complex 39A. But forecasters are predicting a 60 percent chance of afternoon and evening thunderstorms that could trigger a launch delay.
Engineers started Endeavour's countdown at 10 p.m. EDT Wednesday. Launch is targeted for 7:39:35 p.m. EDT Saturday, roughly the moment Earth's rotation carries the launch pad into the plane of the space station's orbit. But shuttle weather officer Kathy Winters said afternoon thunderstorms and associated electrical activity could cause problems. "The weather has really been an issue for us this week," she said. "We've had afternoon thunderstorms each day and we're also expecting that we'll see some afternoon thunderstorms in the area around launch time on launch day as well. Another concern is the (electrically charged) anvils that blow off from the top of those thunderstorms. So with that, we are forecasting a 60 percent chance of KSC weather prohibiting launch." The forecast for Sunday calls for better conditions, but Winters said she still expects a 40 percent chance of thunderstorms and nearby anvils. The forecast improves to 70 percent "go" on Monday.
The Progress can "loiter" in orbit for five days, but it must dock by July 29. And that means Endeavour must take off by July 14 to complete its mission in time to undock by July 27, making way for the Progress. The goal of Endeavour's five-spacewalk mission is to deliver a Japanese experiment platform, to replace aging solar array batteries, to store critical spare parts and to deliver supplies. The shuttle crew also will bring Japanese astronaut Koichi Wakata back to Earth after five months in space, leaving NASA flight engineer Timothy Kopra behind in his place. Kopra, commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy and Thomas Marshburn flew to the Kennedy Space Center from Houston Tuesday to prepare for launch. "I would just like to take a moment to recognize the outstanding work that was done by the workforce here and at the other NASA centers to go ahead and correct the problems that we encountered last month," Polansky said. "Now it's ready for STS-127 to carry out its mission, and I can tell you this crew and the entire operations team are both eager and ready to get to work. So hopefully we will get a chance to do that come this Saturday evening." Endeavour was grounded June 13 and 17 because of a gaseous hydrogen leak where a vent line attaches to the side of the shuttle's external fuel tank. After the second launch scrub, engineers discovered the vent port housing built into the side of the tank was misaligned. The leak only occurred when the vent line hardware was chilled to ultra-low temperatures. To fix the problem, engineers substituted a different type of internal seal and used shims to compensate for unwanted motion when the hardware contracts slightly under cryogenic conditions. During a fueling test July 1, the vent line was leak free and engineers are confident the system will work properly the next time Endeavour is fueled for launch.
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The official crew patch for Endeavour's flight to finish building Japan's section of the space station is available in the Spaceflight Now Store.
