| Star sensor is a kind of high-precision attitude measuring instrument, which refers to stars on the celestial sphere. Star sensors measure attitudes very fast in any position of space without any supplementary instrument. Compared with other attitude measuring instruments, Star sensors has many advantages, which include better autonomy, stronger anti-interference ability, higher precision and measurement error is not accumulated over time. Star identification is one of the key technologies of star sensor, and directly determines the success rate and output rate of star sensor. In this paper as a starting point to study in order to find a way that ensure the success rate of star sensor attitude output, how to through the rapid star identification improve star sensor attitude update rate.Main study in this paper is follow:With data from the Smithsonian observatory catalog(SAO) under epoch J2000, the establishment of the guide star catalog has been accomplished. Firstly, base on the limit magnitude guide stars are selected from about 250 000 stars of the SAO, and then the conversion of star apparent position is carried out by astronomical correction algorithm. Secondly, in terms of navigation star selection, this paper proposes a method based on navigation star pairs for screening, ensures that the quantity of the navigation star pair uniform. Finally, using K vector storage method is used to store the navigation star pair in the navigation star database, which can improve the efficiency of navigation information retrieval.The analysis of star coordinates transformation from the celestial coordinate system to the image plane coordinate system is carried out. And the projection transformation and nonlinear imaging model are also discussed in this dissertation. After the gray conversion the simulation star map is generated. Finally star map simulation software is completed, which is necessary for the simulation experiments for following algorithms.For all-sky autonomous star identification, to improve the existing triangle star identification algorithm, an improved method of triangle star map identification is proposed. The algorithm stores the angular distances information instead of storing the characteristic information of the navigation star triangles, and instead of triangle identification with angular distance recognition, by adding a test star eliminate the redundancy of the triangle matching. The algorithm solves the position error and magnitude error and pseudo observed stars problems in a certain extent, and has high recognition accuracy.For the identification of local area star with the prior information, this paper proposes a local sky star identification method which based on the QTM navigation star database partition. The algorithm divides and encoding of celestial navigation star database using the Quaternary Triangular Mesh, utilizing the bore sight direction of last update, the angular distance search scope is reduced to 2% than all-sky star identification method, and shorten the time of the star identification.Aiming at the problem of tracking mode of star identification, a star tracking algorithm for star sensor using star angular distance matching between adjacent frames was proposed. Through maintains a small real-time star database in memory, the range of angular search is narrowed, so as to further improve the efficiency of star identification. The result of the simulation experiment indicates that the tracking algorithm has the ability to track stars steadily under a large angular speed condition. |
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