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1 January 1987 Active Forces For Figure Control On A 1.8-Meter Mirror
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The surface accuracy of the primary mirror of a large telescope can be compromised by polishing errors, thermal distortions, material inhomogeneities, stress relaxation and errors in support forces. One method of correcting the mirror figure is to apply forces to the mirror to introduce deformations that cancel out these errors. The image quality goals of the National New Technology Telescope (NNTT) will require highly accurate surfaces on 8-meter diameter primary mirrors, and it is anticipated that an active force system will be necessary to maintain the required accuracy. An active support system has been built and tested on a 1.8-meter prototype of the primary mirrors for the NNTT. The existing astatic counterweight support system was modified to allow computer-controlled variation of the forces exerted . Tests of the system have been conducted in two different modes; it has been used to compensate measured optical surface distortions, as well as to correct the thermal distortion predicted by computer modeling based on measured mirror temperatures. Test results show that distortions corresponding to astigmatism, coma, spherical aberration, trefoil and quatrefoil can be effectively countered.
© (1987) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
E. Pearson, L. Stepp, and J. Fox "Active Forces For Figure Control On A 1.8-Meter Mirror", Proc. SPIE 0817, Optomechanical Systems Engineering, (1 January 1987);


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