Long term durability of protected silver coating for the mirrors of Ariel mission telescope

Paolo Chioetto; Daniele Brienza; Rodolfo Canestrari; Paul Eccleston; Elisa Guerriero; Giuseppe Malaguti; Giuseppina Micela; Emanuele Pace; Enzo Pascale; Raffaele Piazzolla; Giampaolo Preti; Mario Salatti; Giovanna Tinetti; Elisabetta Tommasi; Andrea Tozzi; Paola Zuppella

doi:10.1117/12.2691351

21 July 2023 Long term durability of protected silver coating for the mirrors of Ariel mission telescope

Paolo Chioetto, Daniele Brienza, Rodolfo Canestrari, Paul Eccleston, Elisa Guerriero, Giuseppe Malaguti, Giuseppina Micela, Emanuele Pace, Enzo Pascale, Raffaele Piazzolla, Giampaolo Preti, Mario Salatti, Giovanna Tinetti, Elisabetta Tommasi, Andrea Tozzi, Paola Zuppella

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Proceedings Volume 12777, International Conference on Space Optics — ICSO 2022; 127776P (2023) https://doi.org/10.1117/12.2691351
Event: International Conference on Space Optics — ICSO 2022, 2022, Dubrovnik, Croatia

Abstract

Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large survey) is the fourth medium-size mission in ESA “Cosmic Vision” program. It is scheduled to launch in 2029. Ariel will conduct spectroscopic and photometric observations of a large sample of known exoplanets to survey their atmospheres with the transit method. Ariel is based on a 1 m class telescope designed for the visible and near infrared spectrum, but optimized specifically for spectroscopy in the waveband between 1.95 and 7.8 μm. Telescope and instruments will be operating in cryogenic conditions in the range 40–50 K. The telescope mirrors will be manufactured in aluminum 6061, with a protected silver coating deposited onto the optical surface to enhance reflectivity and prevent oxidation and corrosion. During the preliminary definition phase of the development work, leading to mission adoption, a silver coating with space heritage was selected and underwent a qualification process on disc-shaped samples of the mirrors substrate material. The samples were deposited through magnetron sputtering and then subjected to a battery of tests, including environmental durability tests, accelerated aging, cryogenic tests and mechanical resistance tests. Further to the qualification, the samples have been stored in cleanroom conditions and periodically re-examined and measured to detect any sign of coating degradation. The test program, still ongoing at the time of writing this article, consists of visual inspection with a high intensity lamp, spectral reflectance measurements and Atomic Force Microscopy (AFM) evaluation of nanometric surface features. The goal is to ensure stability of the optical performance, in terms of coating reflectance, during a time span comparable to the period that the actual mirrors of the telescope will spend in average cleanroom conditions. This study presents the interim results after three years of storage.

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Paolo Chioetto, Daniele Brienza, Rodolfo Canestrari, Paul Eccleston, Elisa Guerriero, Giuseppe Malaguti, Giuseppina Micela, Emanuele Pace, Enzo Pascale, Raffaele Piazzolla, Giampaolo Preti, Mario Salatti, Giovanna Tinetti, Elisabetta Tommasi, Andrea Tozzi, and Paola Zuppella "Long term durability of protected silver coating for the mirrors of Ariel mission telescope", Proc. SPIE 12777, International Conference on Space Optics — ICSO 2022, 127776P (21 July 2023); https://doi.org/10.1117/12.2691351

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