Comprehensive Tolerance Analysis and Improvement Strategies for the Final 6.5 m Wide-field MUltiplexed Survey Telescope

Abstract To fulfill the urgent requirement for large-scale spectroscopic survey telescopes with wide field of view in modern astronomy, the 6.5 m MUltiplexed Survey Telescope (MUST) has been presented by Tsinghua University and the final optical design consisting of a Ritchey–Chretien system and a 1.6 m five-element wide-field corrector has been determined after abundant iterations and communications with vendors. This optical system guarantees excellent performance with the 80% enclosed energy diameter not greater than 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>″</mml:mi> </mml:mrow> </mml:mover> </mml:math> 524 within 2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> </mml:math> 8 field of view over 55° zenith angle. However, there will be various errors in fabrication and assembly and more dynamic errors induced by environmental temperature and gravity during sky survey, all causing unexpected performance deterioration. To get rid of those errors, the corresponding improvement strategies are proposed and verified. The aberrations caused by fabrication and assembly errors can be optimized by adjusting the position of the secondary mirror and adding spacers between optical components, while the thermal-induced and gravity-induced errors can be compensated by dynamically adjusting the position of the secondary mirror and modifying the surface figure of the primary mirror during tracking. The improvement strategies showing satisfactory results are significant and referenceable for the subsequent construction of MUST.