Thermal Design of an Observatory on a Highly Eccentric Orbit

The upcoming increased launch capacity of larger and more powerful rockets opens doors for the development of large space telescopes that would not require the mechanical deployment of optical structures in space. The University of Arizona is currently working on a space-based telescope concept that would use a 6.5 m monolithic borosilicate primary mirror typically seen in ground telescopes. Borosilicate presents manufacturing advantages but has a higher coefficient of thermal expansion than materials typically used in large space telescopes, thus requiring more precise thermal control. The observatory would be in either a highly elliptical Earth orbit, an Earth-trailing orbit, or on Earth-Moon Lagrange point 2. The telescope will require great thermal stability, so each potential orbit brings a different set of thermal requirements and leads to different modeling constraints. This paper presents preliminary thermal analyses to determine the bounds of the mission requirements, allowing the team to design a telescope that will meet the required thermal stability constraints. We are performing orbital analyses in Ansys, merging STK and thermomechanical models to calculate the heat flux from external sources, such as the sun, and estimate the heat losses to the environment. We will use the model to understand the effects of the thermal environment on the telescope mirrors and check for their survivability and optical stability under the given conditions. We will perform iterations on a mechanical design and evaluate the impacts of different passive and active thermal control systems on the thermal stability of the mirrors.