The US space agency NASA has again postponed the launch of the space shuttle Discovery, saying it will not occur before February 27. The launch, initially scheduled for February 12, had already been delayed until February 19. NASA said Friday it will hold a news conference on February 20, following a review of space shuttle Discovery's readiness for flight and an assessment of shuttle flow control valve testing. The shuttle Endeavour had its flow control valve damaged during its mission in November.