Implementation of a laser-truss based telescope metrology system at the Large Binocular Telescope

Abstract

Large ground-based telescopes are prone to perturbations caused by environmental factors that affect the mechanical structure of the telescope that can cause collimation loss and image quality degradation. The Telescope Metrology System (TMS) is a metrology method under development at the Giant Magellan Telescope (GMT) and prototyped on the Large Binocular Telescope (LBT) to monitor and maintain collimation and pointing. TMS measures the precise position and orientation of a telescope's primary mirror in relation to other telescope elements. Currently, prototyping has progressed to TMS operation at prime focus between LBT's two 8.4m primary mirrors and the Large Binocular Camera (LBC), a pair of prime focus correctors and wide-field detectors. TMS utilizes a multi-channel absolute distance measuring (ADM) interferometer to create a laser truss by determining the distance between fixed points on the primary mirror and the LBC. By performing a kinematic analysis of the ADM data, the relative position and orientation of the primary mirror and LBC can be determined. With knowledge of the position of the telescope, an optical layout model can be created using TMS data as input. This allows for iterative simulation of field aberrations and loss in image quality due to misalignment of the telescope. This will allow for collimation and pointing to be actively monitored and maintained during an observation. This paper will discuss the process of implementing TMS on LBT and the challenges that arose.