Optimized Asphere Fabrication and Finishing, for Future Optical Windows

The ORCLE program is a hybrid high-bandwith communication design based on laser, infrared and radio transmissions between aircraft and other communication points. The communications terminals that protrude into the air stream around the aircraft require a protective cover that can reduce drag and minimize damage from heat, dust, and rain. Technical requirements for suitable windows/domes include Laser/IR/RF transmission at all temperatures, resistance to erosion and heat damage, and strength, within an acceptable cost target. Magnesium aluminate spinel offers a low-cost option to fabricate the necessary components, which are potentially less costly to operate than competitive transparent ceramics, sapphire and ALON. Spinel is optically superior in the infrared particularly from 3 to 5.5 microns. Its cubic crystal structure is optically isotropic, unlike sapphire, which exhibits birefringence. This Phase II development effort will focus on improving the manufacturability of high-transmission spinel and the material’s engineering properties. Large flat spinel windows will be hot pressed and HIPed and large spinel domes will be pressureless sintered and HIPed. Both processes have been proven by TA&T for smaller windows and domes. The two process routes offer different opportunities for improvement of spinel’s engineering properties.