The thermal distortion of an optical reflector surface due to the changing sunlight in a space environment will cause shift and spreading of its reflected focus and thereby influence the performance of space-to-ground laser communication links. Based on the characteristics of a low orbit satellite, the normal shift of a plan mirror caused by thermal distortion is analyzed with the software of the ANSYS of finite element analysis. A general expression of the transmitted beam from a distorted reflector surface and a counting formula for the shifts of the focus center before and after thermal distortion are deduced. The result of simulation shows that the magnitude order of the normal shift of the antenna mirror surface can be as high as tens of μrad.The worse the mirror thermal distortion is, the larger the shift of the received focus center is. And the change of the shifts does not obey a linear rule.
