The payload canister on its transporter sits beneath the payload changeout room on the rotating service structure.

The payload canister on its transporter sits beneath the payload changeout room on the rotating service structure (RSS) on Launch Pad 39A. The canister contains the S3/S4 integrated truss for mission STS-117 to the International Space Station aboard Space Shuttle Atlantis. Once inside the PCR, the S3/S4 arrays will be transferred into Space Shuttle Atlantis' payload bay after the vehicle has rolled out to the pad. The changeout room is the enclosed, environmentally controlled portion of the RSS that supports cargo delivery to the pad and subsequent vertical installation into the orbiter payload bay. The Atlantis crew will install the new truss segment, retract a set of solar arrays and unfold a new set on the starboard side of the station. Launch is targeted for March 15. Photo credit: NASA/Kim Shiflett