KENNEDY SPACE CENTER, FLA. - Huge clouds roll over Launch Pad 39B where Space Shuttle Atlantis still sits after the scrub of its launch on mission STS-115. Atlantis was originally scheduled to launch at 12:29 p.m. EDT on this date, but a 24-hour scrub was called by mission managers due to a concern with fuel cell 1. Towering above the shuttle is the 80-foot lightning mast. At left is the rolled-back rotating service structure with the payload changeout room open. Just above the orange external tank is the vent hood (known as the "beanie cap") at the end of the gaseous oxygen vent arm. Vapors are created as the liquid oxygen in the external tank boil off. The hood vents the gaseous oxygen vapors away from the space shuttle vehicle. During the STS-115 mission, Atlantis' astronauts will deliver and install the 17.5-ton, bus-sized P3/P4 integrated truss segment on the station. The girder-like truss includes a set of giant solar arrays, batteries and associated electronics and wil