Since 1999, MERSEN BOOSTEC designs, manufactures and sells products made of sintered silicon carbide (SiC) mainly for space applications. Improvement of the state of surface of SiC substrates is essential to reduce scattering losses. In collaboration with CNES, a comparative study of microstructural, mechanical, and optical performances of different ceramic processes has been involved to optimized SiC substrates. Then, the comparative study has been extended to scattering losses in collaboration with the Institut FRESNEL which is expert in light scattering metrology. Comparative measurements on the developed substrates have been performed on Spectrally and Angularly resolved Light Scattering characterisation Apparatus (SALSA). This communication will present the results of this study which are already very promising for the development of the next generation SiC optics.
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.
The performances that are required today for optical components are increasingly demanding, both in terms of the spectral response and the conditions to which the components are subjected. So-called dense deposition techniques for thin film coating currently make it possible to respond in many cases to this ever-increasing requirement. Indeed, conventional evaporation techniques that can address a large number of applications such as metallic coatings, antireflection coatings, mirrors, are no longer sufficient and we currently rely on the dense deposition techniques such as, for instance, magnetron sputtering which allow implementing layers stable and low-ageing behavior. In this paper, we will review the recent achievements at CILAS by magnetron sputtering technique on high-performance silver coatings for space applications.
In our premises in Aubagne, CILAS has implemented a large dimension in-line magnetron sputtering coating machine with which such silver coatings are realized. This equipment with oversized dimensions involving a 6 meters by 3 meters vacuum chamber, 12 turbomolecular pumps and 7 planar magnetrons over 2.50m long will be presented in detail. In particular, the wide range of configurations will also be illustrated with complex coatings achievements with respect to the capability of the machine which is equipped with magnetrons, that may be powered in Radio Frequency, Mid Frequency, Direct Current or pulsed Direct Current modes.
For several years, CILAS has improved its coating processes to produce high quality silver coatings, taking into account spectral performances, environmental conditions and also coating uniformity over 2meter by 2 meter dimensions.
Further developments have been led by CILAS with the support of the French Space Agency as part of Research and Development activities to improve environmental performance; we present here characterization results on samples before and after environmental qualification (temperature, humidity, vacuum heat ...) and on components with dimensions up to 600mm. A multi-year test campaign including stress measurements and adhesion tests on samples and mirror demonstrator will also be presented.
Stray light is an important issue in optical systems and may be responsible for huge limitation of final performances. Use of black coated surfaces is known to be an efficient means to reduce such parasitic light sources and various solutions exist that can be applied to mechanical surfaces such as black paints or black anodization; these coatings are relatively thick and to produce thin, black baffle edges, a thin layer technology is thus needed. In this paper, we show how thin film multilayer coatings can be a solution to answer this problematic as it is possible to design accurate spectral response that present a very low level of reflectance with a zero value of transmittance.
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