Discovery grounded over hydrogen valve glitch

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WASHINTON: NASA was planning to launch the space ****tle Discovery early Friday after thunderstorms and a hydrogen fuel tank valve postponed two previous attempts. The ****tle and its crew of seven astronauts were preparing for a 13-day mission to supply the orbiting International Space Station (ISS).Ahead of the next planned launch attempt, engineers will evaluate a liquid hydrogen valve that became problematic when technicians began fueling Discovery on Tuesday, mission management team chairman Mike Moses told reporters.It was the second scuttled launch in a 24-hour period. A first launch attempt early Tuesday was scrubbed due to stormy weather.Moses said detailed test data about the valve would be examined before the ****tle''s fuel tank is filled with propellant ahead of the planned launch shortly after midnight.If engineers cannot determine the exact nature of the problem or if the vlave must be replaced, he warned, "then we will probably not be in a position to launch 48 hours from now."Weather and hurricane risks could also prevent a Friday launch, he noted.Discovery can blast off until about Sunday, after which any attempts would have to be postponed until mid-October due to scheduling conflicts.US space agency officials said the problem valve cycles liquid oxygen from the external fuel tank to the ****tle''s main propulsion system, and technicians will attempt to fix it while Discovery remains at the launch pad, positioning it for a third launch attempt Friday at 12:22 am (0422 GMT).The delays were a reminder of turbulence that surrounded the previous mission, when space ****tle Endeavour''s launch was postponed five times by weather woes and technical glitches.The Discovery crew is scheduled to conduct three spacewalks of six and a half hours each during the mission.A key task during the spacewalks will be to replace an old liquid ammonia coolant tank, which will be substituted with a new, 1,760-pound (800-kilogram) replacement brought aboard Discovery.The new freezer will store samples of blood, urine and other materials that will eventually be taken back for study on the effects of zero-gravity.The seven ****tle astronauts also will be retrieving experiment equipment from outside the ISS and returning it to Earth for processing.A treadmill named after popular US comedy talkshow host Stephen Colbert will be the second aboard the ISS, where exercise is key for astronauts spending long periods of time in space because zero-gravity can result in muscle atrophy.The ****tle flight is to be the first with two Hispanic astronauts: veteran mission specialist John "Danny" Olivas, 44, of El Paso, Texas, and space3 rookie Jose Hernandez, 47, of Stockton, California. Veteran European astronaut Christer Fuglesang, 52, of Sweden, is also among the crew.Once the Discovery mission is complete, just six more ****tle flights remain before NASA''s three ****tles are retired in September 2010.The ISS is a project jointly run by 16 countries at a cost of 100 billion dollars -- largely financed by the United States.

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