The Optical Telescope Element (OTE) consists of a 6.6 m, all-reflective, three-mirror anastigmat. The 18-segment
primary mirror (PM) presents unique and challenging assembly, integration and alignment verification requirements.
Each mirror segment is mechanically integrated with the Primary Mirror Backplane Support Structure (PMBSS) using
compound angle shims to compensate for global alignment and local co-planarity errors. The processes used to
determine the mechanical shim prescription, primary mirror alignment and integration, and placement verification are
discussed. In an effort to reduce process uncertainty and program risk, the JWST program recently conducted a PMSA
Integration Demonstration at ITT. Through this activity, full scale demonstrations of the Ground Support Equipment
(GSE) and critical integration processes were successfully completed. The results of these demonstrations indicate that
the equipment, processes, and procedures developed by ITT meet the critical requirements for PMSA placement.