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Contrast-based tolerancing of space telescopes for exoEarth imaging

Abstract : The question about the existence of life elsewhere in the universe than on Earth has engaged mankind for centuries and has now become a central question in astronomy. Assuming that life needs is a planet like Earth to exist, we want to use the direct imaging method to gain access to the light reflected by the atmospheres of such "exoEarths", potentially showing signs of biomarkers. These kinds of observations require large, space-based observatories with dedicated high-contrast instruments that allow us to detect and characterize small, rocky exoplanets at 1e-10 brightness ratios and angular separations of 0.1 arcsec. These instruments are very sensitive to any wavefront aberrations which can easily lead to false detections. My PhD thesis treats the impact of wavefront errors on the imaging performance of high-contrast instruments. It presents the development of a statistical forward model for the coronagraphic contrast, and its inversion for the analytical tolerancing of wavefront errors. Focusing on the case of segment-level aberrations and their impact on contrast, the application to a LUVOIR configuration shows that not all segments are subject to the same WFE constraints. A major part of my thesis consisted of the development of the HiCAT testbed, dedicated to system-level laboratory demonstrations for exoEarth-imaging instruments. Using the statistical tolerancing method, I performed experimental demonstrations on HiCAT to validate the model, and to derive contrast sensitivities to aberrations on a real segmented mirror. As part of this thesis, I developed the numerical tools necessary for the simulation and tolerancing of large space telescopes. This enabled the generalization of the theoretical model to other modal bases across a wide range of spatial frequencies, attributed to various physical aberration sources. A central question in the conception of large telescopes is their allowable wavefront error drift over time. I show how to address this temporal aspect of wavefront error stability with the analytical tolerancing model at the core of this work. This allowed me to make connections with other studies going on in parallel with my PhD and obtain concrete results for the required wavefront error limits for segment-level thermal stability on a large, segmented telescope.
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Submitted on : Wednesday, March 9, 2022 - 3:55:46 PM
Last modification on : Tuesday, May 17, 2022 - 5:32:30 PM

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  • HAL Id : tel-03546315, version 2

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Iva Laginja. Contrast-based tolerancing of space telescopes for exoEarth imaging. Astrophysics [astro-ph]. Observatoire de Paris, Université Paris Sciences et Lettres (PSL); Office National d'Études et de Recherches Aérospatiales (ONERA); Space Telescope Science Institute (STScI); Laboratoire d'Astrophysique de Marseille (LAM), 2021. English. ⟨tel-03546315v2⟩

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