Topology optimization of a single point diamond turning fixture for a deployable primary mirror telescope

The aperture size of a space telescope faces constraints dictated by the dimensions of the launch vehicle, resulting in a limited aperture size. This reduction, in turn, imposes limitations on optical resolution and the signal-tonoise ratio of the space telescope. To address this challenge, deployable optical payloads equipped with segmented primary mirrors that unfold, enable larger synthetic apertures and enhanced spatial resolution while benefiting from a smaller, cheaper launch vehicle. This paper investigates the potential of leveraging Additive Manufacturing (AM) and Topology Optimization (TO) for ultra-precision machining applications, with a specific focus on single-point diamond machining. The primary objective is twofold: to concurrently diminish fixture weight and increase stiffness. This dual approach aims to mitigate deformations induced by rotational and cutting forces, two effects known for their influence on the mirror surface form error and consequently on the optical performance. Using Finite Element Analysis (FEA), the study systematically compares fixtures produced through conventional machining (CM) with those employing AM and TO techniques. The results underscore a remarkable 68% reduction in weight for fixtures designed through TO. This substantial weight reduction renders the assembly of a machining fixture with four deployable segments of diameter 600mm when deployed, manageable by a single operator without the necessity for specialised lifting equipment. Additionally, these designs contribute to significant reductions of up to 87% and 37% in deformation caused by rotational and cutting forces, respectively. Overall, these advantages offer a promising perspective for overcoming limitations in space astronomical or Earth Observation telescope apertures.