Design and test of pointing mirror assembly for spaceborne remote sensing camera

In order to ensure the surface figure of the pointing mirror (460 mm long, 290 mm wide) in spaceborne remote sensing camera, Silicon Carbide was selected as the mirror material. The form of composite triangular and rectangular and the combination of open and closed back was explored in the lightweight design. A new kinematic mount and flexible structure in axis is used to hold the mirror around the lateral surface. The structure can minimize distortions induced by coefficient of thermal expansion mismatch among the materials. This eliminates the bending of the integral mount under the weight of the mirror. Optical performance of the mirror was analyzed under gravity load and temperature load using finite element method. Predicted surface figure error based on the removal of bias, tilt and power was calculated using an in-house Matlab script for mirrors. The pointing mirror assembly was tested using open loop servo control. And the surface figure was checked using interferometer. Surface figure accuracy is better than 1/30 λ ( λ =632.8 nm,rms). The results show that the kinematic mount induces minimal figure error on the optical surface.