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Management team clears Discovery for launch BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: August 28, 2009 
NASA's Mission Management Team cleared the shuttle Discovery for a fourth launch try Friday night, approving a waiver to pre-launch flight rules allowing engineers to cycle a liquid hydrogen valve, if necessary, to confirm it is closed. Launch is targeted for 11:59:37 p.m. EDT, roughly the moment Earth's rotation carries the launch pad into the plane of the International Space Station's orbit. Fueling was scheduled to begin at 2:34 p.m., but it was held up about 10 minutes because of concern about the possibility of lightning within five nautical miles of the launch pad. The forecast for launch calls for a 40 percent chance of unacceptable weather, with a chance of thunderstorms within 20 nautical miles. Discovery's crew - commander Frederick Sturckow, pilot Kevin Ford, flight engineer
Jose Hernandez, Patrick Forrester, John "Danny" Olivas, European Space Agency
astronaut Christer Fuglesang and space station flight engineer Nicole Stott - plans
to begin strapping in around 8:40 p.m., weather permitting.
NASA flight rules prohibited engineers from cycling the valve under cryogenic conditions out of a concern about a possibly unknown problem that could cause it to fail in the closed position, making it difficult to drain the tank after a delay. Launch was tentatively rescheduled for early Friday. During tests Wednesday night, after Discovery's tank was drained, the valve and its position indicator both worked normally, cycling open and closed five times at ambient temperatures. A pressure decay test also indicated the valve closed normally. Discovery had two launch opportunities Friday roughly 23-and-a-half hours apart. During an MMT meeting Thursday, NASA managers opted to pass up the first opportunity in favor of the second to give engineers more time to review the valve issue. During today's meeting, a waiver was processed that will allow engineers to cycle the valve twice during fueling, if required, to confirm closing. In addition, engineers developed plans to use alternate cues to verify the valve's position. The MMT also discussed a hydraulic system failure Thursday that delayed the test firing of a new five-segment solid-fuel booster intended for use in post-shuttle rockets. The hydraulic system in the test rocket is virtually identical to equipment used by Discovery's solid-fuel booster, but NASA managers found no problems with the shuttle hardware and cleared Discovery for flight.
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The official crew patch for Discovery's flight to deliver and research gear to the space station
