The GMT Telescope metrology system: Easing the complexity of initial and operational alignment and increasing observing efficiency

The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory. The optical design consists of 7 8.4-m primary mirror segments that reflect light to 7 secondary mirror segments in a doubly-segmented direct Gregorian configuration. Each mirror pair must be coaligned and co-boresighted. During operations, the alignment of the optical components will deflect due to variations in temperature, gravity-induced structure flexure of the mount, and, on a scale relevant to phasing, vibrations. The doubly-segmented nature and size of the GMT will create a novel set of challenges for initial assembly, integration, and verification and maintaining high-precision alignment of the optical elements during operations. GMT is developing a Telescope Metrology System that uses 3D laser metrology systems to decrease the complexity of alignment and increase observatory efficiency. This paper discusses the 4 subsystems of TMS as well as their operational modes.