Opto-mechatronical analysis and outlook on potential improvements for Austria’s largest telescope system

Abstract

Astronomical telescopes enable high-quality imaging of distant objects, supporting applications in astronomy, satellite observation and optical communication. However, image quality is often degraded by wavefront distortions caused by alignment errors and structural deformations. In particular, thermal expansion and gravitational effects lead to relative displacements between the primary and secondary mirrors, necessitating active compensation strategies. This thesis investigates the opto-mechanical properties of the Leopold Figl-Observatory (LFO) to identify potential limitations and improvements. Using a small RC-telescope, a measurement system is developed and tested, which is then used to measure the relative positions of the mirrors of the LFO.The small RC-telescope has a 254 mm primary mirror and is equipped with a precision secondary mirror positioning system that operates independently of telescope light to reduce wavefront errors. An asymmetric temperature gradient of over 20 ∘C was ap- plied to simulate daytime operation. During heating, the RMS wavefront error improved from 185 nm to 46 nm, an improvement by a factor of 4.0. When considering only the compensated degrees of freedom - defocus and the tilting of the secondary mirror - the RMS wavefront error reduced from 167 nm to 13 nm, a factor of 12.8. In all measurements utilizing the compensation system a Strehl ratio (SR) exceeding 80% could be maintained, demonstrating its effectiveness in compensating for environmental disturbances.The measurement system was then successfully installed on the LFO (1.52 m primary mirror). The measurements show a slow, small drift behaviour for individual stationary positions with an average axial shift of 4.54 μm and almost no tilt. However, between different telescope positions, the relative position between the primary and secondary mirror varies considerably, with an average deviation of 45.08 μm and a maximum of 78.04 μm, which significantly affects the SR. Based on these results, an active compensation system, especially for the focus of the telescope, seems sensible. Further measurements on the LFO are needed to validate these results.