KENNEDY SPACE CENTER, FLA. - Early evening shadows glide across Space Shuttle Atlantis after rollback of the rotating service structure on Launch Pad 39B. The RSS provides protected access to the orbiter for changeout and servicing of payloads at the pad and then is rolled away before liftoff. In the background is the Atlantic Ocean. Extended from the fixed service structure at left is the orbiter access arm with the White Room at the end. The White Room provides entry into the orbiter. Seen above the golden 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. Atlantis is scheduled to launch Sept. 6 at 12:29 p.m. EDT on mission STS-115. During the 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 will provide one-fourth of the total power-generation capability for the completed station. This mission is the 116th space shuttle flight, the 27th flight for orbiter Atlantis, and the 19th U.S. flight to the International Space Station. STS-115 is scheduled to last 11 days with a planned KSC landing at about 8:03 a.m. EDT on Sept. 17. Photo credit: NASA/George Shelton