Assembly of the IXPE mirror modules

Expected to launch in December 2021, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Astrophysics Small Explorer Mission with significant contributions from the Italian space agency (ASI). Three identical x-ray telescopes combine to form the IXPE Observatory. Each is comprised of a 4-m-focal length mirror module assembly (MMA, provided by Marshall Space Flight Center) that focuses x-rays onto a polarization-sensitive, imaging detector (contributed by ASI-funded institutions). This paper describes the now-completed assembly process for the 3 flight and one spare mirror modules, and compares as-tested calibrated performance with as-built metrology data. Unexpected challenges and lessons-learned are also discussed.