marked: 159th NASA crewed space flight 128th Space Shuttle mission since STS-1 37th flight of Discovery 30th shuttle mission to the ISS 103rd post-Challenger mission 15th post-Columbia mission 32nd shuttle night launch NASA's first Space Shuttle launch to take place during two calendar days 25th anniversary of Discovery's first flight, STS-41-D (August 30, 1984) Shuttle processing Discovery rolled out from the Orbiter Processing Facility to the Vehicle Assembly Building after the external tank was cleared for use and was mated with it. The foam insulation on the tank underwent stringent pull tests after the foam liberated and hit the orbiter during STS-127. The STS-128's tank initially exhibited no concerns while the STS-127 case was determined to be a one-off case due to surface contamination prior to foam application. The main change from previous missions is the change of the Ground Umbilical Carrier Plate (GUCP) vent housing. The quick release vents exhibited leaks during STS-119 and STS-127, which were determined to be due to a misalignment in the vent. This led to the one part rigid seal in the external tank being replaced with a two part flexible seal. Discovery later rolled out from the VAB to Launch Complex 39A on August 4, 2009, in a slow drive on the top of the Crawler-transporter. The rollout began at 02:07 EDT, and ended with the launch platform secured in place at about 13:50 EDT. The move took longer than expected due to adverse weather conditions, which included lightning warnings. The crawler also had to pause occasionally so mud could be removed from its treads and bearings. Technicians then quickly prepared the shuttle to host the crew's countdown dress rehearsal known as the Terminal Countdown Demonstration Test (TCDT). Discoverys seven astronauts flew to Kennedy on August 5, 2009, for the training activity which concludes later in the week with a complete practice countdown, minus liftoff, involving the crew and the launch team. Meanwhile, in an unprecedented operation, modifications were made to the left Solid rocket booster on the pad. The modifications involved replacement of a check valve filter assembly in the booster which was found to have broken. In a potentially delaying factor, in depth testing of the external tank with X-ray revealed voids in the foam which might have formed during the injection molding of the foam. This has also been decided as a suspect factor in the foam shedding during STS-127.