A worker in the Payload Changeout Room, Launch Pad 39A, moves the Payload Ground Handling Mechanism away from the open doors of Space Shuttle Endeavour’s payload bay. The PGHM helped move the STS-100 mission payload into the bay. Visible above and behind the worker is the Multi-Purpose Logistics Module Raffaello, which carries six system racks and two storage racks for the U.S. Lab. Above Raffaello is the Canadian robotic arm, the SSRMS. Capable of handling large payloads and assisting with docking the Space Shuttle, the SSRMS is crucial to the continued assembly of the International Space Station. Launch of mission STS-100 is scheduled for April 19 at 2:41 p.m. EDT KSC-01pp0781

The Space Shuttle program was the United States government's manned launch vehicle program from 1981 to 2011, administered by NASA and officially beginning in 1972. The Space Shuttle system—composed of an orbiter launched with two reusable solid rocket boosters and a disposable external fuel tank— carried up to eight astronauts and up to 50,000 lb (23,000 kg) of payload into low Earth orbit (LEO). When its mission was complete, the orbiter would re-enter the Earth's atmosphere and lands as a glider. Although the concept had been explored since the late 1960s, the program formally commenced in 1972 and was the focus of NASA's manned operations after the final Apollo and Skylab flights in the mid-1970s. It started with the launch of the first shuttle Columbia on April 12, 1981, on STS-1. and finished with its last mission, STS-135 flown by Atlantis, in July 2011.