Opto-Mechanical Design and Stray Light Analysis for Unobscured off-Axis Telescope using BRDF Data of Black Paints

Abstract

Space telescopes are an extension of the human eye into distant galaxies that allow forthe observation and imaging of phenomena light years away from Earth. There are many variants of space telescopes; a widely cherished design is the three mirror anastigmat (TMA). The TMA is coveted because of its ability to correct for aberrations over a wide field of view. A variation of a typical TMA is an off-axis system that removes the central obscuration of the telescope’s primary mirror (M1). However, the benefits of an off-axis TMA come at the cost of complex mechanical housing of the optical components and stray light correction. Professor Daewook Kim has optically designed an off-axis TMA. This thesis will give an overview of the optical design of the TMA, give an in-depth description of the mechanical design of the baffles, vanes, and apertures of the telescope, describe the collection process of real scatter data of black paints applied to the housing, and outline the stray light analysis performed on this system. The TMA is an f/14 system with a clear aperture of 3000 mm that is essentially diffraction limited. The system has an approximated FOV of +/-0.27◦ by +/-.08◦ and is designed for a semicircle detector plane. In addition to the three curved mirrors, there is also a fourth, folding mirror at the end of the system before the detector. Baffles, vanes, apertures were designed for stray light control of the TMA system. The design was constrained to be less than 9 m by 5 m, and as compact as possible. Real BRDF data was collected and processed for stray light analysis. Different black paints have varied scattering characteristics. Thus, it is essential to measure and apply real BRDF data of various black paints to the mechanical system to ensure accurate stray light analysis. Stray light analysis was performed with the target of less than 10−5 of light was incident on the detector relative to the in-science field for far out-of-science fields.