The primary mirror of the telescope is mounted on its large, sturdy "backplane," which must support the 21-foot-diameter reflector as well as another 7,500 pounds of optics and instruments. It holds 12 segments in the middle part of the mirror and has two wings with three segments each. These wings fold back to help the mirror fit into a rocket. (There will be no mirror segment in the central hole, where the technician is standing; optical data will be sent through that aperture to the scientific instruments.) This photo actually shows a mock-up of the backplane, which engineers use to check practice handling, installation, and alignment procedures.