A new generation of large SIC telescopes for space applications

Large Space based IR are presently under development. These telescopes are placed on the L2 Lagrangian point and will operate in far infrared range. EADS-ASTRIUM is manugacturing HERSCHEL telescope and will extend its technology to the SPICA Telescope. HERSCHEL operates in the spectral range between 80 and 670 μm wavelength and is devoted to astronomical investigations in the far-infrared, sub-millimetre and millimetre wavelength range. ASTRIUM has been awarded by ESA to manufacture tgeh 3,5m all SiC telescope. The concept for the HERSCEL telescope is based on an axisymetric, 3,5-m-diameter Cassegrain design. The driving requirements are the large diameter (3,5m) especially for the manufacturing aspects, the WFE which has to be kept below 6μrms, the operational temperatuer (70k) which brings distortionas wrt ambient environment, and finally the mass to keep below 300kg. This Development is part of the ESA HERSCHEL PLANK program. SPICA Telescope driving requirements are also the large diameter (3,5m) especially critical for the manufacturing aspects, the WFE which has to be kept below 350nmrms, and the operational temperature (4,5K) which requires to master the distortions wrt ambient environment. Telescope will operate in the 5 to 200 μm wavelength range. ASTRIUM has been awarded by Sumitomo and ISAS to study the faisability of teh 3,5m all SiC telescope. The main features developed in this paper are: The final design and the recent manufacturing developments of the HERSHEL telescope and the expected performances of such a telescope in space environment The preliminary design of the SPICA telescope and teh predicted performances which are taking advantage from the Silicone Carbide properties developed for HERSCHEL telescope, especially considering the homogeneity inside the structure its stability from abient to the operational temperature range (4,5K). The study shows that the Silicone Carbide Telescope design can fulfil the mechanical and optical requirements, in a passive way without actuators.