Payload Canister
The STS-135 payload canister's move to Launch Pad 39A began in the night of 16 June. The canister's lifting up of the pad structure to place it into the cleanroom happened on the next day. Technicians at the launch pad closed the Rotating Service Structure (RSS) back around Atlantis to gain access to the orbiter's payload bay. The payload bay doors were opened on the night of 18 June and the cargo was installed into the shuttle's payload bay on 20 June.
Read more about this topic: STS-135, Shuttle Processing