LSST Telescope Mount & Pier Design Overview

The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the summit of Cerro Pachon in Chile. The survey mission requires a short slew and settling time of 5 seconds for a 3.5 degree slew. This is significantly faster than similar aperture telescopes. Since the optical system does not include a fast steering mirror the telescope has stringent vibration limitations during observation. Meeting these requirements is facilitated by the compact mount riding on a robust pier which produces high natural frequencies, an advanced control system to minimize vibration excitation and reaction mass dampers. The telescope mount design is an altitude over azimuth welded and bolted assembly fabricated from mild steel. It supports the primary / tertiary mirror cell assembly, the secondary mirror cell assembly and the camera assembly. The mount design enables the removal of these optical assemblies for servicing and recoating. Retractable / deployable platforms have also been provided for accessing the camera on telescope. As a result of the wide field of view, the optical system is unusually susceptible to stray light consequently the mount must incorporate substantial light baffling. The dynamic characteristics of the steel reinforced concrete pier were enhanced by utilizing two different wall thicknesses, an unusually large diameter of 16 meter and anchoring the foundation in unweathered bedrock. The entire pier and mount assembly has been designed to be invariant with azimuth and elevation angle to enhance the effectiveness of the advanced control system.