High accuracy interferometric star tracker based on diffraction grating

In order to overcome the problems where traditional star trackers’ directional accuracy, field of view, volume, weight and other factors are difficult to balance, we studied a highly accurate interferometric star tracker structure based on a diffraction grating. By using the angular spectrum theory, the mathematical models between the incident angle of starlight, the centroid position of spots, and the relative intensity of spots on the detector were established. Secondly, the methods that estimate a relative coarse position of the target star from a centriod of the spots on the detector, and estimate a relative fine position of the target star from the relative intensity of the spots were determined. Therefore, the relative incident angle of star light was obtained by using successive estimates of the coarse and fine positions. Then, we drew a conclusion that the angle resolution for a single star is affected by the grating period, the distance between the two gratings and the electric subdivision of the intensity signal. Finally, a computer simulation was used to confirm the feasibility of this relative fine positioning technique and this combination technique of coarse positioning and fine positioning. The results show that this measure is praticable, and the angle resolution for a single star can reach 0.1 arc-seconds when the grating period is 50 μm, the distance between two gratings is 50 mm and the intensity signal of each period is subdivided by 1024 times. Compared with traditional star trackers, the accuracy is improved significantly.