Sagem – Reosc has been awarded by ESO a contract for the manufacturing and testing of seven prototype segments of
the E-ELT primary mirror in 2008. The purpose of this contract was to demonstrate the ability to produce aspherical off-axis
hexagonal segments with very little edge effect and very high quality wavefront error and plan the production of the
931 segments needed for the primary mirror and spares.
The manufacturing of the prototype segments is now completed. They have been delivered. Sagem has achieved for the
best segment integrated on its support an overall surface error of 23 nm RMS and 6 nm RMS after removal of the
allowed amount of Focus, Astigmatism and Trefoil. This article will present the process developped by Sagem and its
Sagem has also assessed the performances of an alternate manufacturing process based on the polishing of the segments
under stress conditions (Stress Mirror Polishing). The results obtained by this process will also be presented.
Thanks to its experience in lightweighting ceramic glass mirrors by machining, R.E.O.S.C. won the contract for designing and manufacturing the primary mirror and its lateral fixations of the 2.7 m. SOFIA telescope which will be installed aboard a 747 SP Boeing aircraft to constitute the Stratospheric Observatory for Infrared Astronomy (SOFIA).