The first of the 8.4 m off-axis segments for the primary mirror of the Giant Magellan Telescope is being manufactured at
the Steward Observatory Mirror Lab. In addition to the manufacture of the segment, this project includes the
development of a complete facility to make and measure all seven segments. We have installed a new 28 m test tower
and designed a set of measurements to guide the fabrication and qualify the finished segments. The first test, a laser-tracker
measurement of the ground surface, is operational. The principal optical test is a full-aperture interferometric test
with a null corrector that includes a 3.75 m spherical mirror, a smaller sphere, and a computer-generated hologram. We
have also designed a scanning pentaprism test to validate the measurement of low-order aberrations. The first segment
has been cast and generated, and is in the process of loose-abrasive grinding.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.