Effect of gimbal point displacement on optical axis pointing precision in an image seeker

A concentric glass spherical dome was usually chosen as the transparent window mounted in front of the optical lens in an image seeker. However, optical ray had to change its direction when propagating through the dome due to refraction unless passing through the center of the dome, which demanded gimbal point coincide with the center of the dome exactly. In fact, gimbal point displacement could not be eliminating due to fabrication, assembly and vibration, therefore the optical axis pointing error generated. In this paper, the effect of gimbal point displacement on optical axis pointing precision in an image seeker was analyzed, and the theoretical expression of the optical axis pointing error was derived based on geometric optics, and the error dynamics was explored by numerical. Take a visible light image seeker as a case, the thickness of concentric glass spherical dome was 8mm and the inner radius was 72mm, and the optical axis pointing errors varying dynamically with the look angle and the gimbal point displacement were shown in graph. When the gimbal displacement was 0.11mm, the maximum optical axis pointing error was 0.054mrad that is equal to the instantaneous field of view (IFOV) corresponding to the camera system whose focal length was 120mm and pixel size was 6.5μm. Furthermore, with the gimbal displacement increasing, the optical axis pointing error increased linearly. The analyzed results provided a theoretical basis for the displacement range, which had to be limited strictly in the gimbal design process.