Designing Mirrors for the Next Decadal NASA Telescope

Dr. Steve Turley
Brigham Young University
Department of Physics and Astronomy

NASA’s decadal plans for their next space-based telescope include the possibility of a large-aperture telescope capable of reflecting a wide range of wavelengths from the infrared to the vacuum ultraviolet. I will discuss the work we have been doing at Brigham Young University on conceptual optical designs, research on mirror materials, and calculations of the effects of roughness on the reflection from the mirror. With these enhancements, we should be able to extend the effective energy range of the mirror from 0-10 eV to a range of 0-50 eV. The proposed mirror consists of a thin bare aluminum layer with broadband reflectance from about 85 nm into the infrared. Since aluminum oxidizes readily in air, I will describe several ideas for preparing a large bare aluminum surface in space. Assessing the effectiveness of these methods involves measuring the oxidation rate of aluminum under various partial pressures of oxygen. Some of the techniques may roughen the surface of the mirror, decreasing the reflectance at the shortest wavelengths. I will describe our computation of the effects of this roughness and compare these calculations to earlier work. To extend the mirrors reflectance beyond 85 nm, where aluminum becomes transparent we have used a genetic algorithm to design an undercoating on the mirror which can extend its reflectance into bands with wavelengths as short as 25 nm.