The dynamical behavior of opto-mechanical systems is crucial for ensuring the performance in noisy environments. In particular, vibration mitigation is one of the design drivers for pointing and wavefront error requirements. During the initial development stages, the typical design process is based on nominal material properties, geometries, and interface behaviors, resulting in a unique set of frequency response functions. However, this approach lacks robustness and often necessitates extensive redesigns following initial testing or the use of significant margin factors. Conversely, incorporating deviations from the baseline in a statistical manner is computationally heavy and often constrained by confidentiality issues. We give an overview of the most common techniques that can be used in large projects to account for the uncertainty in material properties. We also present a computationally light method aimed at deriving a robust family of system responses via a simple relationship between uncertainties in material properties and system responses. The proposed method is also applicable to models in a modal space representation. We compare a few parametric methodologies that account for material property uncertainties in a rigorous way, showcasing their use with real opto-mechanical systems for both ground and space telescopes. We show that the simplified method yields results comparable to more complex algorithms, offering a practical solution for early-stage design considerations.
The Natural Guide Star Adapter (NGSA), a circular structure that is part of the Extremely Large Telescope (ELT) Pre-Focal Station (PFS) [6], defines with its rotation axis one of the reference coordinate systems of the entire telescope and has a key role in the performance of all the instruments. The PFS NGSA hosts three sensor arms (SA), which are free to move in a roughly annulus area to support to support closing control loops on natural guide stars when the light beam is controlled by the telescope[2]. The actuation of these SA’s causes a deformation of the mechanical structure and consequently uncertainty on the position and orientation of the reference coordinate system. Starting from the Finite Element Analysis (FEA) of the PFS, we develop a model that reconstructs the behavior of the structure for all the possible combinations of SA positions, and we conceive strategies for a robust definition of the reference coordinate system, as described in this paper.
Structural, thermal, and optical performance (STOP) analysis is gradually becoming a crucial tool in the development of optical systems in general and astronomical telescopes and instruments in particular. We describe the approach of the European Southern Observatory to STOP analysis at the examples of the phasing and diagnostic station and of the pre-focal station of the European Extremely Large Telescope under construction. Further, we discuss the fundamentals of the estimation of thermal effects on optical performance and how to carry it out with the in-house developed software tool Sensitizer.
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