Effect analysis of thermal deformations on image quality for low-orbit space telescope

To achieve diffraction-limited imagery with a space telescope, a basic problem to be soluted is to avoid image degradation due to the thermal deformation of the optical surfaces. Thermal effects can be divided into thermal soaks and thermal gradients. Generally speaking, the only result of thermal soaks is a net change in focal length, which can usually be tolerated, while the thermal gradients are the most difficult to control. The effect of the axial thermal gradient through the primary mirror is analyzed. Some numerical results is presented.