Thales SESO silver coatings for space programs

Abstract

Silver protected is one of the most required coating for space observation telescopes covering the wavelength range from 430 nm to infra-red. Many challenges have to be addressed in such coatings including high efficiency over the wide spectrum, high durability with behavior in AIT conditions and during flight. Thales SESO has already produced more than 166 total space mirrors from which 87 are flying successfully since many years. Most of them are coated with protected silver coatings. For over the past 20 years, Thales SESO has enhanced the characteristics of our coating related to its durability in acceptance test conditions, its mechanical stability when going to vacuum and its behavior toward space aggressions such as ATOX or radiations. A lot of the corresponding developments were substantially sustained by CNES, together with Thales Alenia Space through different French programs. Previous realizations include Pléiades, French national program, MTG mirrors both for sounders (IRS instrument) and imagers (FCI instrument), Sentinel 3 with Na and Ob mirrors and different other export programs. The last improvements were made in the frame of TANGO program for Thales Alenia Space/CNES, with improved adhesion during acceptance tests, with ability to apply the full coating process on sub-assemblies including glued parts, and with reduction in the stress induced on the substrate. The performance and uniformity were demonstrated on 1700 mm diameter in Thales SESO STEP large coating chamber. Through these different developments Thales SESO has gained maturity in the contribution of the coating on stress induced in the mirror as well as its stability when going to vacuum. We now perfectly anticipate this effect in the polishing process. Here after, you find an overview of the Thales SESO realizations starting from Pléiades first results to the status achieved with the last improvements on TANGO program and future prospective developments.