The morning sky lightens behind Space Shuttle Atlantis while lights still illuminate the orbiter on Launch Pad 39B.

The morning sky lightens behind Space Shuttle Atlantis while lights on the fixed service structure (FSS) still illuminate the orbiter on Launch Pad 39B. 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. Seen poised 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. Extending from the FSS to Atlantis is the orbiter access arm with the White Room at the end. The White Room provides entry into the orbiter through the hatch. At right is the 300,000-gallon water tank that releases its contents onto the mobile launcher platform during liftoff to aid sound suppression. 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/Troy Cryder