Pointing algorithms for binocular telescopes

Abstract

When two telescopes share a single telescope mount, as is the case for the Large Binocular Telescope, the control system has to both position the mount and adjust the alignment of the two optical systems if the telescopes are going to point and track the way a single telescope is expected to do. The alignments of the two systems depend on the flexure models, target position and observing wavelength all of which may be different for the two telescopes. Furthermore these differences change as the telescope tracks. This paper describes how the pointing algorithms for a single telescope have been adapted to calculate the optimum position for the telescope mount and the necessary adjustments to the optical alignments of two telescopes. It also shows how the same algorithms can be used to support the rather more common case of a chopping secondary (or other mirror) where the tips and tilts for the chopping mirror are generated by treating the two (or more) chop states as if they were independent telescopes. This delivers a chop throw that takes into account differential refraction and all other similar effects.