On-Demand Additive Manufacturing of Astronomical Mirrors

The proposed technology will meet the Air Force’s need for new techniques to allow 3D printing at nanometer scales to produce astronomical mirrors requiring little to no figuring or modification to achieve the form fidelity, surface finish, and reflectance. Astronomical mirrors are traditionally produced via a combined casting, diamond turning, and that is time consuming, expensive, and yields a heavy cumbersome solid mirror structure for large numerical apertures. Phase I demonstrated the feasibility of a two-step on-demand manufacturing approach to directly print 60 mm Al mirror via Additive Manufacturing and non-contact electrochemical polishing to create the mirror surface for astronomical telescopes. In specific, we built a rough AM mirror shape out of 7A77 Al alloy, then demonstrated rapid electropolishing (~8 hours) to achieve an optical surface roughness of ~7 nm (with RMS of ~8 nm) on a sub 100 nm vertical and lateral resolution scale. Additionally, we devised lightweighting strategy to reduce the mass of the additively manufactured mirror by up to 70%. In Phase II, we will scale the mirror manufacturing process to 8-inch (218 mm) mirrors and incorporate lightweighting designs, enabling further process refinement and production/delivery of next generation Newtonian telescopes that contain these astronomical mirrors.