Structural analysis and design of a four meter class altazimuth telescope with a meniscus mirror.

Abstract

Structural analysis and design of a four meter class altazimuth telescope was performed using the finite element program MSC/NASTRAN. Optical performance of the mirror was evaluated using the program FRINGE. Structural and optical performance was optimized based on reduction of the root mean square (rms) wavefront deflections of the mirror surface and minimization of the self weight of the telescope using natural mode shapes of the finite element model. A procedure to optimize the support locations for the primary mirror using the piston frequency from the free vibration analysis was proposed. Finite element models for the mirror were automatically generated by a special purpose pre-processor developed for this study. Optimized support locations and the support systems are presented for a four meter meniscus mirror. Preparation of an input data file for the optical performance evaluation program FRINGE from the NASTRAN structural deformation data was achieved using a post-processor which was developed for this specific case study. Procedures to achieve the optimum criteria are presented. Analysis and design of mirror cell, secondary mirror, optical support structure, and fork are presented. Both static and free vibration analyses were performed on all the components of the telescope. Comparisons were made wherever approximate solutions were available. Also, primary mirror handling analysis, mesh refinement study, effect of grid pattern of the finite element model on the FRINGE analysis are presented.