18 December 2002 Athermal lightweight aluminum mirrors and structures
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Aluminum foam core optics can be lightweight, cryo-stable, and low cost. The optimal design of a lightweight mirror is a sandwich with very thin, closely spaced support ribs. Open cell foams, used in sandwich mirrors, approach this optimum design. The availability of high quality aluminum foam and a bare aluminum polishing process have allowed high performance foam core optics made entirely of aluminum to be produced. The long history of aluminum space structures makes all aluminum optical systems attractive for many applications. We report on fabrication and testing of foam core and solid aluminum mirrors. Mirrors with integral mounts were designed for minimum surface error induced by self-weight deflection, thermal gradients, and mounting stresses. Previous work demonstrated the superiority of foam sandwich mirror construction over isogrid lightweighting, and finite element modeling to optimize the mirror design. Recent progress includes: (1) delivery of a lightweight aluminum foam core scan mirror for the Compact Visible-Infrared Radiometer, (2) cryo-stability tests on lightweight foam core spherical mirrors, and (3) an interferometric test of the 'align warm, use cold' concept using a simulated instrument, the Offner Relay. The 'align warm, use cold' concept eliminates the iterative process of misalignment compensation for CTE mismatch as well as figure changing due to CTE mismatch.
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Theo Hadjimichael, Theo Hadjimichael, David A. Content, David A. Content, Charles Frohlich, Charles Frohlich, } "Athermal lightweight aluminum mirrors and structures", Proc. SPIE 4849, Highly Innovative Space Telescope Concepts, (18 December 2002); doi: 10.1117/12.476892; https://doi.org/10.1117/12.476892

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