fuel tank and solid rocket boosters, already in place atop the mobile launcher platform. The mating of the Orbiter to the stack occurred on February 12, 2007. The rest of the pre-launch preparations also continued to proceed according to plans, with the payload canister, containing the S3/S4 Truss and a set of solar arrays, arriving at the launch pad at 02:54 EST on February 12, 2007. The canister lift began at 05:40 EST the same morning, ready for transfer of the ISS truss segments and other cargo into the Payload Changeout Room on the newly refurbished rotating service structure of pad 39A. Atlantis was originally scheduled to begin her rollout to launch pad 39A (the first shuttle launch at 39A in four years) on February 14, 2007, however due to erratic chamber pressure readings on one of the Operational Pressure Transducers (OPTs) on the forward skirt area of the right-hand SRB, the rollout was delayed to 07:00 EST on the morning of February 15, 2007. Various problems, including a generator transfer issue to the mobile launcher platform, meant that first movement of the stack was delayed from the scheduled rollout time and did not occur until 08:19 EST. The , six-hour journey to the launchpad concluded that afternoon, with Atlantis arriving at the launch pad at 15:09 EST. It was decided that the issue with the OPT would be solved on the launch pad, a task which may require all six transducers on the STS-117 stack being removed and replaced. On February 21, 2007, the STS-117 crew traveled from Houston to the Kennedy Space Center (KSC) to participate in the Terminal Countdown Demonstration Test (TCDT). The astronauts were at KSC from February 21 to 23, 2007, during which time they practiced launch activities, carried out safety exercises, inspected the payload and concluded the test with a simulated main engine cut-off exercise. They then returned to Houston via T-38 jets, planning to return to KSC a few days before launch. The next milestone in the launch preparations was the Flight Readiness Review from February 27 to 28, 2007, during which time managers, engineers and contractors examined the readiness of the Space Shuttle, flight crew and payloads to determine whether everything was set to proceed for launch. Hail damage Following a hailstorm at KSC on February 26, 2007, inspections of the stack found damage to the shuttle and the external tank. Hailstones