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Through the years, Safran Reosc developed and matured state of the art optical manufacturing technologies dedicated to Hi-Tech and large optics. We have unique heritage in glass ceramic mirror substrate lightweighting and fully master the various steps of production of accurate freeform optical surfaces: profile generating, lapping, polishing. An advanced specific expertise in SiC optics has been built more recently.
Safran Reosc has pioneered glassy mirror lightweighting operation by diamond grinding more than 30 years ago with METEOSAT and SPOT first space optics of the company. We deeply improved our process through the years considering the capabilities of the NC machinery, the design and quality control of the specific diamond tools used for the process, the milling cinematics and safety of the operation in order to bring failure risk to nearly zero. Typical lightweighting ratio is > 80%, i.e. less than 20% of the mass of the solid piece remains after the lightweighting operation.
More recently improved technology has been developed to reach > 90% lightweighting ratio thanks to thinner and higher ribs within the glass structure as well as thinner front sheet.
HF Acid etching is conducted in order to remove all micro-racks generated in the glass and thus restore the intrinsic glass strength. Let's highlight that the mirror body strength is also much linked to a carefully optimized opto-mechanical design of the structure with its Mirror Fixing Devices (MFD).
To our knowledge, the world record in glassy lightweight mirror substrate obtained by machining is held by Reosc with the 2.7-m Stratospheric Observatory for IR Astronomy (SOFIA).