Abstract
The design of the University of California Ten Meter Tele-scope (TMT) calls for a primary mirror composed of 36 hexago-nal segments. An active control system maintains the optical figure of the array in the face of gravitational, thermal, and wind perturbations. Three degrees of freedom of each segment, piston, and tilts about two axes, are controlled. An engineering demonstration of the active control system and the development of segment fabrication techniques are in progress and will be completed this year. We report below the current program status. Major goals include the development of optical testing methods and the evaluation of segment support, control actuators, and sensors, as well as the overall performance of the control system. The engineering demonstration will use a full-sized segment, 1.8m across and 0.075m thick. The fabrication of this very thin and flexible segment presents unusual challenges. The polishing support system has been developed. We have also developed test apparatus and procedures that provide an extremely accurate measurement of the radius of curvature. A circular mirror has been polished to a specified radius of curvature. Any warping that results from cutting the segment from this mirror will be established soon. The passive support of a segment is to be provided by two systems, one to carry axial loads and one to carry radial loads. The design of these systems is described. The TMT active control system is designed to use capacitive sensors to measure the relative orientations of the segments, and torque-motor driven displacement actuators to adjust segment position. The demonstration system uses 4 sensors and 3 actuators to control the tilt and piston of a single segment with respect to a reference mirror. The design of the system prototype is described.
