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Proceedings Paper

Dimensional stability concerns in the manufacture of graphite/epoxy beam-steering mirrors
Author(s): John A. Sultana; Steven E. Forman
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Paper Abstract

A lightweight graphite/epoxy sandwich mirror design has been developed with an aim toward reducing the traditional sources of dimensional instability throughout the mirror structure. The mirror manufacturing process attempts to neutralize the hygroscopic behavior of the epoxy matrix and also minimize the tendency for micro-cracking at the fiber-matrix interface. The process was used to fabricate several mirrors as part of a program to develop a spacebased laser radar beam steering flat for use at 10. 6 rim. The mirror construction consists of two facesheets of ulira-high modulus (UHM) graphite/epoxy prepreg bonded to a triangular-cell core of UHM graphite/epoxy ribs. Aluminum cladding is utilized on each facesheet surface to: a) prevent mairix dimensional changes due to hygroscopic effects such as moisture absorption and outgassing b) tailor the in-plane laminate coefficient of thermal expansion (CTh) yielding a facesheet with near-zero CTh and c) provide a surface suitable for diamond-turning. The core is also clad with a moisture barrier which additionally tailors the CTE to match the facesheets. This paper describes the design analysis fabrication and testing of graphite/epoxy mirrors from the viewpoint of enhancing dimensional stability. Testing and evaluation of mirrors ranging in size from 14 cm square to 65cm in diameter were performed. The evolution of the fabrication process is described in detail. Surface figure data after temperature cycling are presented for several mirrors illustrating the ability to achieve and maintain figures

Paper Details

Date Published: 1 November 1990
PDF: 11 pages
Proc. SPIE 1335, Dimensional Stability, (1 November 1990); doi: 10.1117/12.22886
Show Author Affiliations
John A. Sultana, Lincoln Lab./MIT (United States)
Steven E. Forman, Lincoln Lab./MIT (United States)

Published in SPIE Proceedings Vol. 1335:
Dimensional Stability
Roger A. Paquin, Editor(s)

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