Metal mirrors are used for spaceborne optical systems, such as telescopes and spectrometers. In addition to the optical performance, the mechanical needs and the mass restrictions are important aspects during the design and manufacturing process. Using the additive manufacturing process, optimized internal lightweight structures are realized to reduce the weight of the system while keeping the mechanical stability. A mass reduction of ≈60.5 % is achieved. Using the aluminum silicon alloy AlSi40, the thermal mismatch of the mirror base body to a necessary electroless nickel-polishing layer is minimized. Based on an exemplary mirror design, the optimization of the interior lightweight structure is described, followed by the manufacturing process from additive manufacturing to diamond turning, plating, and polishing. Finally, the results of surface metrology and light scattering measurements are presented. A final form deviation below 80 nm p . − v . and a roughness of ∼1 nm rms could be demonstrated.
Additive manufacturing enables enhanced designs for metal mirrors and housings of optical systems like telescopes. Internal lightweight structures are used for the mirror modules to reduce the weight of the system while keeping the mechanical stability. Internal structures can be produced by selective laser melting, which cannot be realized by conventional machining. Using an aluminum silicon alloy, the thermal mismatch of the mirror base body to the necessary polishing layer is minimized. Resulting thermal induced deformations are greatly reduced. The additive manufacturing of a mirror module with two optical surfaces is described in detail. Using a adapted process chain for the application in the visible range, first results of the additive manufacturing as well as subsequent machining steps like diamond turning of the optical surfaces are presented.