Graphite Fiber Reinforced Magnesium as a Beryllium Replacement Material for EKV Seeker Mirrors and Substructures

Graphite fiber reinforced Mg alloys with quasi-isotropic architecture has nearly the same specific stiffness (Young's modulus/density) as beryllium and 12 x the thermal stability (thermal conductivity/coef. thermal expansion). Compared to beryllium, Sicoated and polished Mg-Gr mirrors will be lighter, less expensive, and will not be encumbered with toxicity and environmental liabilities associated with manufacturing and processing beryllium components. In addition Mg/Gr composites will always beavailable whereas the future availability of beryllium is doubtful due to toxicity and litigation concerns. Thermal seasoning experiments will result in heat treatments designed to produce dimensional stability after thermal cycling associated with theapplication. The proposed research will result in an optimized architecture that results in a rigid mirror that weighs less and cost less than beryllium and can be quickly manufactured. Feasibility will be demonstrated by manufacturing a prototype mirrorbody with the desired thermal stability, stiffness, mass and potential cost reduction to replace beryllium. The data generated will enable the design of optical benches and other substructures now manufactured from beryllium. A 5-10 kg/m2 areal densityspace mirror material will become readily available to the space and missile defense community with short lead times. Cost of fabricating mirrors will be a fraction of that of beryllium or other competitive materials. Innovative control of fiberarchitecture will result in low thermal expansion, high thermal conductivity and high stiffness, and hence, in a highly stable mirror with high vibration dampening capacity. Economic benefits will be measured in launch weight reductions and increasedsystem performance as well as system procurement savings. Immediate applications will be for EKV, CEKV, LEAP, directed energy applications, ABL as well as a number of AF NRO and NASA applications. Alternative applications in electronic thermalmanagement markets will also benefit from the concurrent development of the preforming technology developed for mirror substrates. Gr/Al materials are non-toxic.