DESIGN STUDY OF STRESSED MIRROR POLISHING (SMP) FIXTURE FOR SEGMENTED MIRROR TELESCOPES

Alikhan Basheer, T. Krishna Murthy

Abstract: Stressed Mirror Polishing (SMP) is a technique developed for the fabrication of off-axis aspheric mirror segments in a rapid and cost effective manner. In SMP, the polishing of the mirror is carried out along with specific loads which are capable of deforming a spherical mirror into any desired aspherical shape and thus reducing the difficulty of aspheric mirror polishing. When the blank is removed from SMP after spherical polish and metrology, the blank will relax to the required aspherical surface with-in desired PV & RMS surface figure accuracies. This paper discusses the different FEM approaches that can be adopted for simulating the deformations in the mirror blank. For preliminary study purpose, a 36-cm diameter off-axis, meniscus shaped parabolic roundel and a Spherical roundel mirror blanks are taken and required deformations are achieved through various FEM approaches. The net deformed surface is validated and compared with a best fit near spherical surface. Additionally the reversibility of the technique is also proved with-in required Surface accuracies. It is felt necessary that these preliminary simulations should form the basis in understanding the warping process and their locations, so that full SMP fixture can be designed which is capable of warping the mirrors.

Keywords: Stressed Mirror Polishing, Segmented Primary Mirror, Aspheric Segment Fabrication, Bending Fixture

DOI: https://doi.org/10.15623/ijret.2016.0504022