Application of adaptive optical techniques to figure control of large telescopes

Large telescopes in space offer a great advantage to astronomers because their performance is not limited by the atmosphere. The space environment provides a further advantage in that it is free of gravity, but the thermal environment is a distinct disadvantage with respect to the performance of large optics. Weight in a large space system is always a major design problem. With these considerations in mind there has been increasing consideration of large mirrors of light weight, but this results in considerable flexibility. This paper reviews the progress toward systems in which the errors of figure of the mirror in space are measured and corrections made to perfect the figure by the application of controlled mechanical stresses. Several laboratory systems to demonstrate the principles and the design of a system for the Large Space Telescope are described. Some directions for future development are indicated.