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Wednesday, 17 June 2009

Endeavour fueling delayed due to lightning concern

Stormy weather around the Kennedy Space Center will delay, at least temporarily, this evening's fueling of space shuttle Endeavour at launch pad 39A. NASA hopes the weather clears and activities can resume for a liftoff at 5:40 a.m. EDT tomorrow (10.40 BST).

Mission Status Center:

Countdown ticking for Endeavour's predawn launch:


Engineers pulled a protective gantry away from the shuttle Endeavour and restarted the orbiter's countdown Tuesday, setting the stage for launch Wednesday on a delayed space station assembly mission.

Endeavour awaits tomorrow's launch. Credit: NASA Countdown clocks at the Kennedy Space Center began ticking backward at the T-minus 11-hour mark at 1:15 p.m. EDT, setting the stage for a launch attempt at 5:40:52 a.m. Wednesday, roughly the moment Earth's rotation carries launch complex 39A into the plane of the space station's orbit.

There are no technical problems of any significance and forecasters are predicting an 80 percent chance of good weather at launch time.

Because of a conflict with NASA's Lunar Orbiter Reconnaissance mission, Endeavour's crew will only have one shot at getting off the pad. If the weather or some other problem delays launch, the shuttle team will stand down to give the LRO team a launch opportunity Friday at 6:41 p.m.

Endeavour's normal launch window closes on June 20 and even if the LRO mission took off on time Friday, Endeavour would not get another launch opportunity until July 11, after a so-called "beta angle cutout" defined by the angle between the sun and the plane of the space station's orbit. During beta cutouts, temperature constraints can be violated when the shuttle is docked to the lab complex.

Hoping for the best, engineers plan to begin loading a half-million gallons of liquid oxygen and liquid hydrogen rocket fuel into Endeavour's external tank starting with transfer line chill down at 8:15 p.m. The remotely-controlled fueling procedure should be complete by around 11:15 p.m.

It was during fueling overnight last Friday that a significant leak showed up in an umbilical where a vent line attaches to the shuttle's external tank. The vent line is used to carry hydrogen gas from inside the tank to a flare stack well away from the shuttle where it can be safely burned away before launch.

The leak occurred as the hydrogen section of the external tank was nearing a full load late Friday and the umbilical plate that connects the vent line to the side of the tank was subjected to extremely low temperatures. A similar problem grounded the shuttle Discovery for four days last March.

Engineers are not sure what caused either problem, but in this case they suspect an internal seal might have been damaged when the umbilical was connected, disconnected and then reconnected when Endeavour was moved from pad 39B to 39A last month. In any case, the seal in question was replaced and engineers are hopeful the quick-disconnect fitting will be leak free the second time around.

If all goes well, commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra will begin strapping in around 2:20 a.m. Wednesday to await liftoff.

The goal of Endeavour's 16-day mission is to attach a sophisticated experiment platform to a Japanese research module, to replace aging solar array batteries, to store critical spare parts on the space station for future use and to replace one of the lab's six crew members. Kopra will remain behind aboard the station when Endeavour departs and Japanese astronaut Koichi Wakata, launched to the complex last March, will return to Earth in his place.

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