Modeling thermal stability of 1.5-m AMTD ULE® mirror using ‘as-built’ CTE data

Stephen Cheney; jaganathan ranganathan; Thomas Brooks; H. Philip Stahl

doi:10.1117/12.2680789

28 September 2023 Modeling thermal stability of 1.5-m AMTD ULE® mirror using ‘as-built’ CTE data

Stephen Cheney, jaganathan ranganathan, Thomas Brooks, H. Philip Stahl

Proceedings Volume 12664, Optical Modeling and Performance Predictions XIII; 126640A (2023) https://doi.org/10.1117/12.2680789
Event: SPIE Optical Engineering + Applications, 2023, San Diego, California, United States

Abstract

Thermal wavefront stability of primary mirror segments may limit the ability of a potential Habitable Worlds Observatory to accomplish its science goals. To help bound the problem, we revisit the measured cryo-deformation of the 1.5-meter ULE® mirror manufactured by L3Harris under the AMTD-2 (Advanced Mirror Technology Development Phase 2) study. The AMTD-2 mirror’s measured thermal sensitivities (astigmatism and mid-spatial error) may bound the thermal stability needed to perform exo-Earth coronagraphy. But power sensitivity is currently unknown. Two different ‘as-built’ STOP (structural thermal optical performance) models were unable to correlate with the mirror’s measured cryo-performance. Measured performance is 50X larger than the 2018 uncorrelated model’s predicted performance. Measured performance is 2.5X larger than the 2023 ‘as-built’ uncorrelated model’s predicted performance. Correlation requires increasing the mirror’s facesheet CTE by 25 to 30 ppb/K above the boule CTE values provided by Corning. We have no physical explanation for why the facesheet CTE values might have changed as a function of fabrication processing. But the implication casts doubt on the ability of models to accurately predict actual mirror thermal stability performance. Or, maybe to produce an accurate prediction requires a model with many more than 11 CTE layers.

Conference Presentation

(2023) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Stephen Cheney, jaganathan ranganathan, Thomas Brooks, and H. Philip Stahl "Modeling thermal stability of 1.5-m AMTD ULE® mirror using ‘as-built’ CTE data", Proc. SPIE 12664, Optical Modeling and Performance Predictions XIII, 126640A (28 September 2023); https://doi.org/10.1117/12.2680789

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