In the payload changeout room or PCR workers stand on part of the mechanism or PGHM.

In the payload changeout room, or PCR, on Launch Pad 39A at NASA's Kennedy Space Center in Florida, workers stand on part of the payload ground-handling mechanism, or PGHM. The PGHM will be used to transfer the cargo in the payload canister into the PCR. The cargo comprises 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 Replacement Unit Carrier and the Super Lightweight Interchangeable Carrier. The PGHM removes payloads from a transportation canister and installs them into the shuttle. It is essentially NASA’s largest fork-lift. Atlantis is targeted to launch Oct. 10. Photo credit: NASA/Jim Grossmann