STRUCTURAL DESIGN OF A LARGE DEFORMABLE PRIMARY MIRROR FOR A SPACE TELESCOPE.

摘要

A 4-meter aperture deformable primary mirror is designed with the mirror and its supports integrated into a single structure. The 2 cm thick, solid ULE mirror is supported by a high modulus graphite epoxy truss structure. The integrated active mirror system is extremely light-weight, making it desirable for a space telescope, as well as for terrestrial applications. Utilizing displacement actuators, the active controls at the mirror's surface include position control and slope control in both the radial and tangential directions at each of the 40 actuator points. Influence functions for each of the controls are nearly independent, reducing the complexity of the control system. Experiments with breadboard models verify the structural concept and the techniques used in the finite element method of computer structural analysis for a system incorporating a solid mirror. The mechanical design of the servo-mechanisms and the flexures to connect the structural members is provided.; The majority of this paper describes the finite element analysis results for the 4-m system with the solid mirror. However, techniques for modeling a lightweight plate with a sandwich core are compared to analytical results, and selected results are included for a lightweight mirror system. Influence functions for various methods of position and slope control are generated with a simplified model to determine the optimum methods of actuation. To evaluate the diffraction limited performance of the 4-m design the complete model is loaded by gravity, a thermal gradient through the mirror thickness, and a uniform thermal soak. Loads are also applied to defocus the mirror and to cause fourth-order astigmatism. Mirror scallop, instigated by the focus shift, has been virtually eliminated with the 40-actuator design. Stresses throughout the system have adequate safety margins for all loads. The structural concept is so effective that it should be considered for uncontrolled primary mirrors as well as active mirrors. Topics for continuing research provide methods of improving both system performance and analysis methods.