NASA Moves Shuttle Launch Target Up to March 11

Thisstory was updated at 7:02 p.m. EST.

NASA?sspace shuttle Discovery is now set to launch no earlier than March 11 - one dayearlier than previously planned - after nearly a month of delays due to suspectfuel valves, the space agency announced late Wednesday.

Missionmanagers set the new launch target after reviewing the status of Discovery?snew fuel control valves, which were replacedlast week. The shuttle is now slated to launch toward the InternationalSpace Station on March 11 at 9:20 p.m. EDT (0120 March 12 GMT) pending a finaldiscussion by top NASA officials on Friday.

KyleHerring, a NASA spokesperson at the agency?s Johnson Space Center in Houston,told SPACE.com that Discovery?s new launch target - up one day from March 12 -is feasible because mission managers opted to forgo an extra modification tothe shuttle?s engine plumbing that would take more time to develop.

?All of theother analysis, the impact testing and the fact that we?ve got poppets and fuelcontrol valves that are essentially crack-free, gave everyone comfort that wecould fly without a modification,? he said.

Discovery?stwo-week construction flight to the International Space Station has beendelayed since Feb. 12 due to concerns with the shuttle?s threefuel control valves. The valves, one for each main engine, are designed towork in concert to maintain pressure in the shuttle's liquid hydrogen reservoirinside its attached external tank.

To maintaina stable pressure during launch, metal poppets in the valves pop up as needed -much like lawn sprinkler heads - to route gaseous hydrogen from the shuttle'saft-mounted engines through a set of plumbing lines and into the external tank. 

When NASA'sshuttle Endeavour launched last November, one of its fuel valves crackedand chipped. The spacecraft's two other valves compensated for the damagedone and the shuttle reached orbit without incident.

But NASAwanted to be sure that a similar problem, if it occurred during Discovery's launch,would not cause catastrophic damage by puncturing the shuttle?s vital plumbinglines or overpressurizingits hydrogen tank. A plumbing line break near the shuttle's aft could cause anemergency engine shutdown, while an overpressurized tank could end up venting the flammablegas overboard during launch, according to a NASA document.

Last week,NASA set a tentative March 12 launch target for Discovery as engineers replacedthe shuttle?s fuel valves with newer ones that had flown fewer times.

NASA mustlaunch Discovery by about March 13 in order to complete its 14-day missionbefore the arrival of a previously scheduled Russian Soyuz spacecraft carryingthe space station?s next crew later this month. If Discovery does not launch bythen, NASA would stand down until April 7 to launch after the space stationcrew change.

Commandedby veteran astronaut Lee Archambault, Discovery?sSTS-119 crew will deliver the final segment of the space station?sbackbone-like main truss and the last pair of U.S. solar wings for the outpost.Four spacewalks are scheduled for the two-week mission.

Discoverywill also ferry Japanese astronaut Koichi Wakata to the space station to jointhe outpost?s three-person crew. Wakata will replace NASA astronaut SandraMagnus as a flight engineer for the Expedition 18 mission, then joint theincoming Expedition 19 crew when it arrives in late March.

Magnus, whohas lived aboard the station since last November, is due to return to Earthaboard Discovery after four months living and working aboard the orbitallaboratory.

Discovery?sSTS-119 mission is the first of up to six NASA shuttle missions scheduled tofly in 2009. The others include the final shuttle mission to overhaulthe Hubble Space Telescope ? slated to launch no earlier than May 12 ? anda series of space station construction flights.

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