Additively manufactured mirrors for CubeSats

Additive manufacturing (AM; 3D printing) is a fabrication process that builds an object layer-upon-layer and promotes the use of structures that would not be possible via subtractive machining. Prototype AM metal mirrors are increasingly being studied in order to exploit the advantage of the broad AM design-space to develop intricate lightweight structures that are more optimised for function than traditional open-back mirror lightweighting. This paper describes a UK Space Agency funded project to design and manufacture a series of lightweighted AM mirrors to fit within a 3U CubeSat chassis. Six AM mirrors of identical design will be presented: two in aluminium (AlSi10Mg), two in nickel phosphorous (NiP) coated AlSi10Mg, and two in titanium (Ti64). For each material mirror pair, one is hand-polished and the other is diamond turned. Metrology data, surface form error and surface roughness, will be presented to compare and contrast the different materials and post-processing methods. To assess the presence of porosity, a frequent concern for AM materials, X-ray computed tomography measurements will be presented to highlight the location and density of pores within the mirror substrates; methods to mitigate the distribution of pores near the optical surface will be described. As a metric for success the AlSi10Mg + NiP and AlSi10Mg mirrors should be suitable for visible and infrared applications respectively.