Storm clouds roll across Launch Pad 39B Space Shuttle Atlantis still sits on the pad.

Storm clouds roll across Launch Pad 39B where Space Shuttle Atlantis still sits on the pad. Atlantis was originally scheduled to launch Aug. 27, but a scrub was called by mission managers due to a concern with fuel cell 1. Towering above the shuttle is the 80-foot lightning mast. 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 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 landing at KSC. Photo credit: NASA/Ken Thornsley