"NASA will hold a news conference Friday, Feb. 20, following a review of space shuttle Discovery's readiness for flight and an assessment of shuttle flow control valve testing. An official launch date for the STS-119 mission has not been set, but for planning purposes, liftoff now is targeted for no earlier than Feb. 27. The new planning date is not expected to affect the launch dates for missions that will follow Discovery's flight, STS-125 to NASA's Hubble Space Telescope and STS-127 to the International Space Station."
NASA retargets Discovery launch for February 27, Reuters
"Initially slated for launch this week, NASA wanted more time to review analysis and test results of potentially troublesome valves needed to keep the shuttle's fuel tank properly pressurized during the 8.5-minute ride into space."