Abstract
The manufacture of segmented active primary mirrors poses difficult fabrication problems for the component off-axis aspheric mirrors. An effort was conducted to develop and demonstrate the necessary fabrication technology to rapidly manufacture the segments of 10-m-class active mirrors. On this project, a 4-m, pie-shaped, 1.7-cm-thick, off-axis parabolic facesheet was fabricated. The key steps of this operation were shaping the segment (prior to all surfacing steps), generating the back and front surfaces using numerically controlled machining, and computer-controlled optical surfacing (CCOS) for vacuum grinding and polishing the front surface. The CCOS polishing rapidly brought the facesheet to within 0.035 μm rms of the proper parabolic surface and produced a superior surface finish with only 8-A roughness and no visible scratches.
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