DEVELOPMENT OF STRUCTURAL COMPOSITE MIRROR TECHNOLOGY FOR SUBMILLIMETER SPACE TELESCOPES

Lightweight, low-cost, high-precision mirrors are needed to support a number of near-term and far-term submillimeter, space-based astronomic al telescopes. These telescopes will range in size from 3 to 20 m, and will possibly be larger. They will utilize mirrors varying from 1 to 2 m in size and from 1 to 3 mum rms in surface precision; they will op erate in an orbital thermal environment somewhere between 100 and 200 K. The Precision Segmented Reflector (PSR) program, sponsored by the N ASA Office of Aeronautics, Exploration and Technology (OAET), was form ulated and implemented specifically to develop the telescope technolog ies associated with future NASA missions. A major element of that prog ram is the development of lightweight structural composite mirrors, wh ich is the subject of this paper. The most significant technology chal lenges associated with the development of these highly specialized mir rors are (a) the processing and manufacturing required to produce high -precision. lightweight mirrors and (b) the determination of materials and structural mirror configurations that produce the thermal stabili ty needed for specific classes of applications. These challenges have been addressed by a joint partnership between the Jet Propulsion Labor atory (JPL) and the Hexcel Corporation during the 4-year PSR program. This paper describes the technical approach used for the design, manuf acturing, testing, and analytical simulation of lightweight graphite/e poxy mirrors. This program has produced (a) 1.0 m graphite/epoxy panel s with areal densities of 7 kg/m2 and as-manufactured surface precisio n near 1 mum rms. (b) 0.5 m panels with figure changes of < 1 mum rms for temperature reductions of 100 K, (c) analytical performance-predic tion capability with submicron accuracy relative to panel thermal dist ortion, and (d) a unique thermal vacuum test facility for structural c omposite mirrors.