Non-deterministic design and analysis of parameterized optical structures during conceptual design

Abstract

The next generation of space observatories will use larger mirrors while meeting tighter optical performance requirements than current space telescopes. The spacecraft designs must satisfy the drive for low-mass, low-cost systems, and be robust to uncertainty since design validation will be based on analysis instead of pre-launch tests. Analytical techniques will be required to identify which technologies or structural architectures are most appropriate to meet conflicting system requirements, but traditionally, model-based dynamic analysis would only take place after a single point design is chosen. The challenges facing future space telescopes require a new approach to conceptual design, and motivate the creation of design tools to identify superior, robust designs earlier in the design lifecycle using model-based analysis methods. A conceptual design methodology is proposed, in which both nominal performance as well as robustness to uncertainty are evaluated across multiple design realizations. A modeling environment is created so that for any set of design variables, such as mirror architecture or dimensions of the spacecraft, a finite element model is automatically generate and analyzed.

(cont.) A frequency-based dynamic analysis is performed for each design realization using integrated disturbance-to-performance models that include control systems and vibration isolators. Next, the uncertainty in early stages of design is considered and Design of Experiments tools such as the analysis of variance are used to identify critical uncertainty parameters. Lastly, parametric uncertainties are propagated through the model to bound the outputs. Aspects of this methodology are applied to several telescopes in order to demonstrate the practicality of this approach in real-life design studies. Critical uncertainty parameter identification and uncertainty analysis tools are applied to the Terrestrial Planet Finder interferometer. A parameterized model is prepared and a trade-space analysis performed for the ground-based Thirty Meter Telescope. Finally, the methodology as a whole is applied to a new space telescope design employing lightweight mirrors and a segmented aperture. An exploration of the design space is followed by uncertainty evaluation of the optimal designs. Over 1200 unique design realizations are evaluated, and the architecture families that provide the best performance and robustness to uncertainty are identified.