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Topological design of lightweight additively manufactured mirrors for space

DOI: 10.1117/12.2313353 DOI Help

Authors: Carolyn Atkins (UK Astronomy Technology Centre) , Charlotte Feldman (University of Leicester) , David Brooks (Univiversity College London) , Stephen Watson (UK Astronomy Technology Centre) , William Cochrane (UK Astronomy Technology Centre) , Mélanie Roulet (UK Astronomy Technology Centre; Aix Marseille University) , Emmanuel Hugot (Aix Marseille University) , Mat Beardsley (RAL Space) , Christopher Spindloe (Central Laser Facility) , Simon Alcock (Diamond Light Source) , Ioana-theodora Nistea (Diamond Light Source) , Christian Morawe (ESRF - The European Synchrotron) , Francois Perrin (ESRF - The European Synchrotron) , Michael Harris (STFC Rutherford Appleton Laboratory)
Co-authored by industrial partner: No

Type: Conference Paper
Conference: SPIE Astronomical Telescopes + Instrumentation 2018
Peer Reviewed: No

State: Published (Approved)
Published: July 2018

Abstract: Additive manufacturing (AM), more commonly known as 3D printing, is a commercially established technology for rapid prototyping and fabrication of bespoke intricate parts. To date, research quality mirror prototypes are being trialled using additive manufacturing, where a high quality reflective surface is created in a post-processing step. One advantage of additive manufacturing for mirror fabrication is the ease to lightweight the structure: the design is no longer confined by traditional machining (mill, drill and lathe) and optimised/innovative structures can be used. The end applications of lightweight AM mirrors are broad; the motivation behind this research is low mass mirrors for space-based astronomical or Earth Observation imaging. An example of a potential application could be within nano-satellites, where volume and mass limits are critical. The research presented in this paper highlights the early stage experimental development in AM mirrors and the future innovative designs which could be applied using AM. The surface roughness on a diamond-turned AM aluminium (AlSi10Mg) mirror is presented which demonstrates the ability to achieve an average roughness of ~3.6nm root mean square (RMS) measured over a 3 x 3 grid. A Fourier transform of the roughness data is shown which deconvolves the roughness into contributions from the diamond-turning tooling and the AM build layers. In addition, two nickel phosphorus (NiP) coated AlSi10Mg AM mirrors are compared in terms of surface form error; one mirror has a generic sandwich lightweight design at 44% the mass of a solid equivalent, prior to coating and the second mirror was lightweighted further using the finite element analysis tool topology optimisation. The surface form error indicates an improvement in peak-to-valley (PV) from 323nm to 204nm and in RMS from 83nm to 31nm for the generic and optimised lightweighting respectively while demonstrating a weight reduction between the samples of 18%. The paper concludes with a discussion of the breadth of AM design that could be applied to mirror lightweighting in the future, in particular, topology optimisation, tessellating polyhedrons and Voronoi cells are presented.

Subject Areas: Materials

Technical Areas: Metrology , Optics