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Due to more and more stringent requirements for observation missions, diameter of primary mirrors for space telescopes is increasing. Difficulty is then to have a design stiff enough to be able to withstand launch loads and keep a reasonable mass while providing high opto-mechanical performance. Among the possible solutions, Thalès Alenia Space France has investigated optimization of ZERODUR® mirrors. Indeed this material, although fragile, is very well mastered and its characteristics well known. Moreover, its thermo-elastic properties (almost null CTE) is unequalled yet, in particular at ambient temperature. Finally, this material can be polished down to very low roughness without any coating. Light-weighting can be achieved by two different means : either optimizing manufacturing parameters or optimizing design (or both). Manufacturing parameters such as walls and optical face thickness have been improved and tested on representative breadboards defined on the basis of SAGEM-REOSC and Thales Alenia Space France expertise and realized by SAGEM-REOSC. In the frame of CNES Research and Technology activities, specific mass has been decreased down to 36 kg/m². Moreover SNAP study dealt with a 2 m diameter primary mirror. Design has been optimized by Thales Alenia Space France while using classical manufacturing parameters -thus ensuring feasibility and costs. Mass was decreased down to 60 kg/m² for a gravity effect of 52 nm. It is thus demonstrated that high opto-mechanical performance can be guaranteed with large highly lightweighted ZERODUR® mirrors.

Abstract-Thales-Alenia-Space has identified the ceramic Si3N4 as an interesting material for the manufacturing of stiff , stable and lightweight truss structure for future large telescopes. Si3N4 ceramic made by FCT has been selected for its own intrinsic properties ( high specific Young modulus , low CTE, very high intrinsic strength for a ceramics ) and its cost effective beams manufacturing capabilities.In order to qualify beam and beams end fittings for future large and thermo-elastical stable truss structure for space telescope, full development and tests activities have been performed. Manufacturing process has been optimised in order to obtain a very high reliable strength. Beams end fittings made also in Si3N4 and its direct bolting capabilities have been also space qualified by tests.Beside this qualification for current space telescope, developments are continuing thank to CNES R&T to develop high loaded brazed junction between Si3N4 parts, enhanced thermal conductivity and mechanical strength through Si3N4 formulation and manufacturing process tuning.