NASA Aims To Launch Discovery March 12

NASA just set March 12 as a new tentative launch date for Discovery -- a target that provides time to replace suspect main propulsion system valves and complete engineering analyses aimed at making certain the shuttle is safe to fly.

Liftoff time would be around 8:54 p.m. EDT. The agency is leaving open an option to move the launch up to March 11 if work between now and then goes well.

NASA in any case would have a back-up launch day on March 13 before the agency stood down for an already scheduled crew rotation at International Space Station.

NASA established the tentative date after putting in place a safety plan that should enable the agency to launch Discovery and a crew of seven astronauts safely.

NASA is replacing three suspect valves that control the flow of gaseous hydrogen into the shuttle's external tank during flight. The valves are key to keeping pressure within the giant tank at proper levels as propellant is exhausted by the ship's three main engines in flight.

One of three valves failed during Endeavour's launch last November, routing gaseous hydrogen into its external tank at a higher than normal rate. Post-flight inspections showed a piece of the lip of the valve - which is the size and shape of a small pop-up lawn sprinkler - cracked off during flight.

Engineers fear a cracked valve could create shards that could rupture a gaseous hydrogen line, resulting in a loss of pressure to the external tank. That could trigger an engine shutdown in flight.

Too much pressure in the tank could force open a separate relief valve that would dump combustible gaseous hydrogen overboard - a potentially explosive fire hazard.

NASA engineers have determined that valves that have been used on fewer flights are less susceptible to failure, so managers ordered up the replacement of the three now on Discovery. Those valves each have flown 12 flights. Technicians are removing them tonight.

Two of the replacement valves have flown four missions; the third replacement has flown five times. They will be delivered to Kennedy Space Center next week and then installed in the orbiter.

If need be, engineers also could shore up gaseous hydrogen lines in places where bends make them more vulnerable and susceptible to damage.

Extensive testing, meanwhile, is continuing at several NASA centers around the country. The tests are aimed at determining how large a piece of debris might be created during a valve failure and how much damage that debris might do to gaseous hydrogen lines. Managers then must determine whether the valves present an unacceptable risk to Discovery and its astronaut crew.

Shuttle program managers will meet next Wednesday to gauge progress, and if all is going well, a formal flight readiness review would be held March 6.

As it stands, Discovery would have to launch by March 13 for its astronauts to complete a mission to deliver a new set of solar wings to the station and then depart the outpost before the March 28 arrival of a fresh resident crew.

Expedition 19 commander Gennady Padalka, flight engineer Michael Barratt and space tourist Charles Simonyi are slated to launch March 26 from Baikonur Cosmodrome in Kazakhstan.

Current station commander Mike Fincke, flight engineer Sandra Magnus and Simonyi then would return to Earth on April 7.

Should Discovery still be on the ground March 14 or later, NASA could negotiate with the Russian Federal Space Agency for a delay in a planned March 26 launch of Padalka and his crew. Or NASA could shorten the 14-day Discovery flight by scrapping one of four planned spacewalks. Either option might gain the agency an extra launch attempt.

ABOUT THE IMAGE: Click to enlarge and save this awesome photo of shuttle Endeavour hurtling toward orbit after launch on the STS-118 mission in 2007. The water near launch pad 39A captures both the setting sun and Endeavour as it rumbles off on the 22nd shuttle mission to the International Space Station. Photo credit: NASA/Sandra Joseph, Tony Gray, Robert Murray.