STS-119 is a space shuttle mission by NASA using the Space Shuttle Discovery, that was launched on 15 March 2009. Space Shuttle Discovery moved from its Orbiter Processing Facility to the Vehicle Assembly Building on 7 January 2009. The payload of the S6 truss segment, solar arrays and batteries were delivered to Launch pad 39A on 11 January. Discoverymoved to the launch pad 39A on 14 January 2009. The move began at 05:17 EST, and was completed at 12:16 EST.
The STS-119 crew was at Kennedy Space Center from 19–22 January 2009 for the Terminal Countdown Demonstration Test. On 21–22 January 2009, mission managers met for the program level Flight Readiness Review (FRR). Following the FRR, mission managers recommended evaluating the hydrogen flow control valves on Discovery, and set a new target launch date of 19 February 2009.
Due to the breakage of one of three flow control valves on the previous flight, STS-126, the flow valves of all orbiters were subjected to tests to determine if Discovery was safe to fly. These valves are used to synchronize the flow of gaseous hydrogen between the external fuel tank and the Space Shuttle Main Engines, creating an even flow. Following the testing of the valves, mission managers decided to postpone the launch, and engineers were asked to replace the suspect flow valves with valves that had less flight time.
Following the replacement of the valves, the Mission Management Team gave the approval for launch, and scheduled it for 11 March 2009. The astronauts arrived at the Kennedy Space Center on 8 March 2009 to prepare for launch. The 11 March 2009 launch was scrubbed due to a leak in a liquid hydrogen vent line between the shuttle and the external tank. On 15 March 2009, the shuttle successfully lifted off from pad 39A. The leak problem manifested itself again during STS-127 which led to a thorough test. The root cause was found to be a misalignment in the GUCP (Ground Umbilical Carrier Plate) which was set right leading to a successful flight.