The launch countdown began 10 June 2009, but on 13 June 2009, as tanking was underway, a gaseous hydrogen leak on a vent line near the Ground Umbilical Carrier Plate was observed, and the 13 June 2009 launch was scrubbed at 00:26 EDT. As liquid hydrogen fuel is pumped in, some of it boils off as the extremely cold liquid enters the warm external tank. The vent line valve controls the resulting buildup of gas pressure by allowing excess gas to escape into a ground-side vent line, which leads to a flare stack at a safe distance away from the pad. A similar leak situation was seen during the first launch attempt of STS-119. NASA managers met on 14 June 2009 and 15 June 2009 and evaluated the leak, discussed steps that had to be taken, and set a new launch date of 17 June 2009, at 05:40 EDT.