ATLAST-8 is an 8-meter monolithic UV/optical/NIR space observatory to be placed in orbit at Sun-Earth L2 by
NASA's planned Ares V cargo launch vehicle. ATLAST-8 will yield fundamental astronomical breakthroughs. A one
year mission concept study has developed a detailed point design for the optical telescope assembly and spacecraft. The
mission concept assumes two enabling technologies: NASA's planned Ares-V launch vehicle (scheduled for 2019) and
autonomous rendezvous and docking (AR&D). The unprecedented Ares-V payload and mass capacity enables the use
of a massive, monolithic, thin-meniscus primary mirror - similar to a VLT or Subaru. Furthermore, it enables simple
robust design rules to mitigate cost, schedule and performance risk. AR&D enables on-orbit servicing, extending
mission life and enhancing science return.
Thermal requirements for the Jet Propulsion Laboratory (JPL) Technology Demonstration Mirror (TDM) to support the Terrestrial Planet Finder (TPF) Mission push the state-of-the-art for lightweight mirror design. A detailed evaluation by Brasher LP during the TPF TDM Mirror Study shows that Corning ULE glass is the best choice to meet these requirements. Even using ULE,
careful selection of the grade and individual boule stacking are required to optimize the design and achieve the desired operational performance. The grade of ULE varies from premium to tooling and is determined by the distribution of Coefficient of Thermal Expansion (CTE) variation about a mean value, both radially and axially. The total range of CTE throughout the mirror must be carefully evaluated to determine operational performance. To support this evaluation, a specialized Finite Element Method (FEM) model generator was modified to assign CTE values to each element based upon its position within the boule and the specified mean CTE, radial and axial gradients for each run. The user can specify different CTE mean and radial gradients for front and back face sheets and for two levels of core to match the expected two boule stack for the TDM mirror blank. The program (model generator) can select random values for each of these inputs within the range of a given grade and generate a new model within minutes. This permits statistical studies of ranges as well as worst-case evaluations with ease. This paper describes the evolution of this type of modeler and some of the results obtained from recent studies of small variations in the CTE affecting mirror performance.
The Starlab telescope's design approach used extensive nonlinear FEM analyses of the suspension systems and primary mirror/bonded assemblies in order to achieve the requisite optical sensitivity to attachment system-induced forces, in combination with the distribution of launch loads through thin sections from concentrated attachment points. A test program verified all aspects of the design. Attention is presently given to the design principle used, involving the splitting of the suspension system's functionality.