Research On High Accuracy Interferometric Star Tracker Based On Diffraction Grating

Star tracker has the advantages of safety,high reliability,high precision and strong anti-interference,and it has been widely used in earth remote sensing,earth surveying mapping,intercontinental missile and planetary surveying mapping,etc.With the development of aerospace and the specialization of application field,it is required that star tracker with the performances of higher precision,larger field of view,lighter weight and smaller size.The measurement accuracy of traditional star tracker is restricted by the performances of field of view,volume and mass.At present,high-precision star tracker with small field of view,large size and heavy weight,while the micro star tracker with large field of view,low measurement accuracy,and the accuracy level is one order of magnitude lower than that of the large size star tracker.Based on the image spot centroid positioning of traditional star tracker,the interferometric star tracker uses the intensity information of the image spots of the target star to further subdivide and obtains the starlight incident angle.Therefore,the interferometric star tracker break down that the measurement accuracy is limited by centroid extraction,and higher angle measurement accuracy can be obtained under the same field of view and array number of detectors.In this background,we developed the research of high accuracy interferometric star tracker based on diffraction grating.Firstly,the mathematical model of the transmission process of the star light field in the interferometric star tracker was established.And the changes of the star pattern on interferometric star tracker with the starlinght incident angle was simulated,and the theoretical feasibilities of this relative fine positioning technique and this combination technique of coarse positioning and fine positioning were analyzed.Then the structure of interferometric star tracker based on diffraction grating was designed.Lastly,designed experiment,and the practical feasibility of this combination technique of coarse positioning and fine positioning was confirmed.The main works of this paper are as follows:Firstly,by the angular spectrum theory,the mathematical model of the transmission process of the star light field in the interferometric star tracker was established.The methods were determined that estimate a relative coarse position of the star from a centroid of the spots on the detector and estimate a relative fine position of the star from relative intensity of the spots,and obtained the starlight incident angle by the combination of coarse and fine positioning.The conclusion that the angle resolution for single star is affected by the grating period,the distance between the two gratings and the electric subdivision times of intensity signal was drawn.And the relationship between the light intensity of each spot on the detector and starlight incident angle was simulated,and the theoretical feasibilities of this relative fine positioning technique and this combination technique of coarse positioning and fine positioning were analyzed.Secondly,an interferometric star tracker based on diffraction grating was designed by ZEMAX.The effective FOV of the designed system is 20 degree,the F number is 1.77,the effective focal length is 70.89 mm.And from the spot diagram,we can see each star point correspond to four image spots,and the four spots form a compact square area,and the RMS radius of four spots in different FOV is small enough,and the energy distribution of each spot is uniform and concentrated.Lastly,designed the experiment,and the practical feasibility of this combination technique of coarse positioning and fine positioning was confirmed.