At NASA's Kennedy Space Center Launch Pad 39A workers open the doors of the payload canister.

Inside the payload changeout room, or PCR, at NASA's Kennedy Space Center Launch Pad 39A, workers open the doors of the payload canister. Inside are four carriers holding various equipment for the STS-125 mission aboard space shuttle Atlantis to service NASA’s Hubble Space Telescope. From top to bottom are the Multi-Use Logistic Equipment carrier, the Flight Support System carrier, the Orbital Replacment Unit Carrier and the Super Lightweight Interchangeable Carrier. The payload will be moved into the PCR. The PCR is the enclosed, environmentally controlled portion of the rotating service structure that supports cargo delivery to the pad and subsequent vertical installation into the shuttle’s payload bay. Launch of Atlantis is targeted for Oct. 10. Photo credit: NASA/Jack Pfaller