NASA 1996 SBIR Phase I

PROPOSAL NUMBER : 96-1 11.01-0204

PROJECT TITLE : Ultra-Lightweight Continuous Fiber Reinforced Ceramic (CFRC) Silicon Carbide Mirror Substrates for Large Aperture, Space-Based Telescope Systems


New technologies are required for fabrication of ultralightweight mirror substrates for application to the Next Generation Space Telescope (NGST) and other large aperture telescope systems. The NGST 8 m deployable primary mirror needs to be produced with an areal density of 15 kg/m2 while providing visible quality performance. One suggested approach is to utilize thin membranes of silicon carbide (SiC) as an actively controlled mirror substrate. These membranes would be optically finished using ion beam figuring or optical replication. The significant gravity release associated with these thin mirror substrates will be managed by application of metrology mounts and with active mirror control on orbit. We propose the application of an innovative Continuous Fiber Reinforced Ceramic (CFRC) SiC mirror substrate as an ultra-lightweight, composite mirror substrate for application to the NGST problem. The excellent bulk material properties of the CFRC SiC material and the ultralightweight fabrication geometries possible will allow the fabrication of large, lightweight optical substrates which can meet the NGST weight requirements while eliminating the gravity release issues associated with the thin membrane mirror approach; e.g., a 2 mm thick, 1 m diam. Chemical Vapor Deposition (CVD) SiC substrate will have a gravity release term of >550 waves p-v (@ visible), whereas the ultralightweight CFRC SiC mirror substrate proposed here will have a gravity release term of 2 waves p-v while maintaining a weight comparable to the 2 mm membrane mirror. Alternatively the CFRC SiC mirror substrate can be fabricated to have a gravity release term equal to the membrane mirror while weighing >5X less than the thin SiC membrane. The innovative composite mirror substrate proposed here will greatly simplify the current NGST deployable mirror configuration thereby significantly impacting the cost and complexity of the NGST system. During Phase I the viability of the proposed CFRC SiC mirror substrate will be demonstrated by fabricating and cryogenically testing an an ultra-lightweight 0.25 m diam. SiC mirror substrate. The proof-of-concept piece will be fabricated to meet the performance and weight requirements of the NGST mission while using low-cost processes which are scalable to the aperture sizes required for the NGST mission.
Applications for the proposed mirror substrate include several space-based optical systems. NASA, DoD and commercial remote sensing missions are all being driven to utilize significantly lighter and cheaper optical systems. The approach proposed here will provide >100X weight savings vs. conventional space-based mirror substrates, and have a strong impact on production and launch costs associated with next-generation space-based remote sensing missions.
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