Design, additive manufacturing, processing, and characterization of metal mirror made of aluminum silicon alloy for space applications

Abstract

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.

Topology optimization and additive manufacturing of an optical housing for space applications

“…This is necessary to provide enough material for the mechanical machining of the functional surfaces during the post processing steps. Using the software "Materialise Magics", the orientation of the CAD model within the building volume of the AM machine is set, supporting structure for the mechanical and thermal connection to the baseplate is defined and finally the slicing of the complete model into thin layers is accomplished [4].…”

“…Spherical aluminium silicon powder (AlSi40) with diameters between 20 µm and 60 µm is processed under protective gas. The used process parameters are feasible to generate volume parts with a low porosity < 0.05 % [4]. Fig.…”

An additive manufactured CubeSat mirror incorporating a novel circular lattice

“…Several international teams have demonstrated the potential of AM substrates to be used directly as a mirror surface either after polishing or diamond turning, [5][6][7][8][9] or, indirectly as a core substrate prior to coating with nickel phosphorous (NiP). [10][11][12] Directly polished or diamond turned AM substrates in aluminium (AlSi10Mg) have demonstrated a surface roughness (root mean square, RMS) between 7.5 nm to 22 nm 5,6 for polishing, and 3 nm to 8 nm 8,9 for diamond turning, leading to suitability for near infrared applications. In addition, innovative AM specific lightweight structures are under investigation, for example: organic cellular structures (Voronoi cells) have been successfully demonstrated for a lightweight mirror core; 11,12 the use of topology optimisation (TO) has been implemented, 5,7 where a given volume is optimised following given constraints on mass and applied force; and further, several teams have investigated theoretically combining organic structures and TO for mirror design.…”

Additively manufactured mirrors for CubeSats

“…AM mirrors is an emerging field with several groups investigating different aspects from mirror fabrication [4][5][6][7] to design optimisation. [8][9][10][11] In regard to mirror fabrication mirror, surface roughness root mean square (Sq; RMS) values of 7.5 nm 7 and 22 nm have been demonstrated on AM aluminium mirrors.…”