The Active Optics System on the Vera C. Rubin Observatory: Optimal Control of Degeneracy among the Large Number of Degrees of Freedom

The Vera C. Rubin Observatory is a unique facility for survey astronomy that will soon be commissioned and begin operations. Crucial to many of its scientific goals is the achievement of sustained high image quality, limited only by the seeing at the site. This will be maintained through an active o...

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Bibliographic Details
Published in:The Astrophysical journal 2024-10, Vol.974 (1), p.108
Main Authors: Megias Homar, Guillem, Kahn, Steven M., Meyers, Joshua M., Crenshaw, John Franklin, Thomas, Sandrine J.
Format: Article
Language:English
Subjects:
Active mirrors
Astronomical instrumentation
Astronomical optics
Astronomy
ASTRONOMY AND ASTROPHYSICS
Degrees of freedom
Error analysis
Error correction
Gravitational effects
Gravity effects
Image quality
Noise levels
Noise measurement
Observational astronomy
Observatories
Optical aberration
Optical components
Optics
Optimal control
Optimization
Singular value decomposition
Telescopes
Wave fronts
Wide-field telescopes
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Summary:The Vera C. Rubin Observatory is a unique facility for survey astronomy that will soon be commissioned and begin operations. Crucial to many of its scientific goals is the achievement of sustained high image quality, limited only by the seeing at the site. This will be maintained through an active optics system that controls optical element misalignments and corrects mirror figure error to minimize aberrations caused by both thermal and gravitational effects. However, the large number of adjustment degrees of freedom available on the Rubin Observatory introduces a range of degeneracies, including many that are induced by noise due to imperfect measurement of the wave-front errors. We present a structured methodology for identifying these degeneracies through an analysis of image noise level. We also present a novel scaling strategy based on truncated singular value decomposition that mitigates the degeneracy and optimally distributes the adjustment over the available degrees of freedom. Our approach ensures the attainment of optimal image quality, while avoiding excursions around the noise-induced subspace of degeneracies, marking a significant improvement over the previous techniques adopted for Rubin, which were based on an optimal integral controller. This new approach is likely to also yield significant benefits for all telescopes that incorporate large numbers of degrees of freedom of adjustment.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ad6cdc