Proceedings Article | 4 February 2003
S. Willem Esterhuyse, De Wet Strydom, Jian Swiegers, Johan Wannenburg
KEYWORDS: Mirrors, Computer aided design, Telescopes, Temperature metrology, Kinematics, Finite element methods, Tolerancing, Structural design, 3D modeling, Monte Carlo methods
The Southern African Large Telescope (SALT), being erected in Sutherland, South Africa, will be the largest single optical telescope in the southern hemisphere, and the 4th largest telescope in the world, when it is completed in late 2004. The SALT design is based on the Hobby-Eberly Telescope (HET). Deviations from the HET design with respect to the telescope structure, primary mirror truss and tracker beam structure are presented in this paper. Finite element models were generated to perform static, dynamic and thermal analyses on the structures. Despite a significantly heavier payload and increased wind loading requirements, equivalent or improved stiffness characteristics were achieved, without increasing structure mass. Dynamic response analyses were performed to characterize the maximum deflections under dynamic wind loading. Automation of the truss design process, which included the control of the 3-D CAD software, the finite element software, as well as CAM software, with a central computer program, allowed the generation of a full 3-D CAD model, as well as CAM inputs, of a structurally optimized truss, within a few days. Extensive analyses, including Monte Carlo simulations, as well as experimentation, were performed to ensure linear temperature-displacement response of the truss. A methodology was developed, using the complete finite element model, to calculate mirror corrections required to correct for lower order deformations of the primary mirror due to temperature fluctuations in the truss.
