Fiber composite mirror yields ultralight substrate for space applications
Engineers at Composite Mirror Applications (CMA; Tucson, AZ) combined optical-replication techniques and composite-materials technology to produce a 24-in., f/1 substrate weighing just 2 lb. To produce a composite substrate, engineers cover a glass mold polished to the desired figure and finish with 12-in.-wide sheets of prepreg?an uncured composite of fiber in a resin matrix. With the application of heat and pressure, the prepreg cures and hardens, and the
substrate maintains the figure and finish of the mold after release. This technique can produce small optics with surface finishes of 600 to 900 ? rms, but in optics with diameters larger than 12 in., print-through from the overlapped sheets of prepreg causes unacceptable levels of
surface roughness. Robert Romeo at CMA has developed a method of processing graphite fiber cyanate ester resin material (EX1515/M55J; Bryte Technologies Inc.; Milpitas, CA) so that a 20- to 50-?m-thick layer of resin coats the optical surface, eliminating print-through. The 24-in. substrate showed no fiber bond lines and good fidelity to the mold. Only a small amount of low-order aberration was present, which could be controlled by a few low-speed actuators. This type of mirror would be suitable for lunar or space-based applications.