13.1 Overview

A simple two-mirror telescope will be used to demonstrate integrated analysis techniques common in optomechanical systems. Although this design was created for analysis demonstration only, the performance requirements placed on this system are representative of real applications. The level of detail in these models is quite coarse yet consistent with a conceptual-design study model; it also keeps the model files small and readable. The models are available for download from www.sigmadyne.com. The models are in MSC/Nastran and Zemax format because both programs are commonly used to model telescopes. Most FE preprocessors can read Nastran data files and convert to other FE codes. The Readme.txt file explains the filenames used for each analysis described below.

The flow of this chapter represents the flow of some of analyses required to support the design of a telescope.

Section 13.2: The optical model is usually developed first to determine optical performance of the nominal design.

Section 13.3: The structural model is developed to determine on-orbit performance. The model is broken into numbering ranges and files so that multiple engineers can design individual components.

Section 13.4: Because the PM is the long-lead item, it must be designed first. A 3D equivalent model is used during design optimization.

Section 13.5: Once a concept model of the complete telescope is developed, line-of-sight equations are determined.

Section 13.6: Using the LOS equations, an on-orbit jitter analysis is conducted to see if the concept will meet performance requirements.

Section 13.7: The surface RMS under random loads is considered.

Section 13.8: Once the design meets jitter requirements, a detailed design of the PM is conducted with a full shell model. This model can be dropped right into the modular model, replacing the equivalent stiffness model.

Section 13.9: During detailed studies of the PM, the question of bond design and material must be studied. The tradeoff of soft RTV verses stiffer epoxy is analyzed in this section.

Section 13.10: The telescope assembly must be analyzed in various 1-g test configurations. Results are presented as Zernike polynomials. When polynomials do not represent the surface due to high-order quilting, then grid arrays can represent the data for further optical analysis. There is often a requirement to determine the optical performance over a subaperture (or cookie) for off-axis field points.

Section 13.11: Isothermal temperature conditions are always required to be analyzed. After radial correction, these distortions are well represented by Zernike polynomials.

Section 13.12: Polynomial coefficients can be determined by writing MPC equations in the model file, as shown in this section. However, the residual RMS cannot be represented as linear MPC equations.

Section 13.13: All telescopes require assembly conducted in a 1-g environment. Depending on the assembly process, it is possible to create locked-in strain, resulting in distortions at zero gravity.