In the payload changeout room on Launch Pad 39B, one of the doors of the payload canister is open, revealing its cargo, the Port 3/4 truss segment for mission STS-115. The payload will be removed from the canister and later installed in Space Shuttle Atlantis' payload bay. Atlantis' launch window begins Aug. 28. During its 11-day mission to the International Space Station, the STS-115 crew of six astronauts will install the truss, a 17-ton segment of the space station's truss backbone. Photo credit: NASA/Jack Pfaller