BOOSTEC has pioneered, since its creation in 1999, the market of space optics made of ceramics (silicon carbide). BOOSTEC has recently delivered the Herschel space telescope, which is, with its 3.5 m diameter mirror, the largest space telescope ever made in the world. The following paper will review the current status of high performing silicon carbide components for space optics. It will then focus on the new possibilities under development, like focal planes and complex systems. It will finally highlight new areas of development for material, process, and applications.
The following is an overview on sintered silicon carbide (SSiC) material properties and processing requirements for the manufacturing of components for advanced technology optical systems. The overview will compare SSiC material properties to typical materials used for optics and optical structures. In addition, it will review manufacturing processes required to produce optical components in detail by process step. The process overview will illustrate current manufacturing process and concepts to expand the process size capability. The overview will include information on the substantial capital equipment employed in the manufacturing of SSIC.
This paper will also review common in-process inspection methodology and design rules. The design rules are used to improve production yield, minimize cost, and maximize the inherent benefits of SSiC for optical systems. Optimizing optical system designs for a SSiC manufacturing process will allow systems designers to utilize SSiC as a low risk, cost competitive, and fast cycle time technology for next generation optical systems.
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.
Beside the baseline glass-ceramics, the sintered silicon carbide (SSiC) technology appears as a valid and very attractive alternative for the mass production of the next generation extremely large mirror segments. The specific stiffness of SSiC ceramic is about four times better than the one of glass-ceramics. Furthermore, the SSiC manufacturing process allows lightweighing the blanks at very cost effective condition. The spectacular expected gain in mass will dramatically relax the requirements of the moving structure, which supports the mirror segments. Boostec team has got two different and very useful experiences in SSiC components that are serial production of low cost parts and the manufacturing of the largest space telescopes particularly through Herschel ESA program. A paper study has clearly shown that the thousands of OWL segments could be made of SSiC at competitive costs. The needed investments are easily affordable and they do not require any technological development. On the other hand, four hexagonal segments have been designed (1 m flat to flat, only 44 kg/m2) and successfully manufactured in order to qualify this technology.
Since ten years ASTRIUM has developed sintered Silicon Carbide (SiC) technology for space applications. Its unique thermo-mechanical properties, associated with its polishing capability, make SiC an ideal material for building ultra-stable lightweight space based telescopes or mirrors. SiC is a cost effective alternative to Beryllium and the ultra-lighweighted ULE. In Complememt to the material manufacturing process, ASTRIUM has developed several assembly techniques (bolting, brazing, bonding) for manufacturing large and complex SiC assemblies. This technology is now perfectly mature and mastered. SiC is baselined for most of the telescopes that are developed by ASTRIUM. SiC has been identified as the most suitable material for manufacturing very large crygenic telescopes. In this paper we present the development of Φ 3.5 m telescope for Herschel Mission. Herschel main goal is to study how the first stars and galaxies were formed and evolved. The Herschel Space telescope, using silicon carbide technology will be the largest space imagery telescope ever launched. The Herschel telescope will weight 300 kg rather than the 1.5 tons required with standard technology. The Herschel telescope is to be delivered in 2005 for a launch planned for 2007.