The navigation star library of star sensors plays a crucial role in star sensor star map recognition and attitude determination R&D systems. It is not only the foundation of star map simulation, but also the basis for achieving star map recognition, and is the soul of attitude determination after successful star map recognition. The relationship between the tables of the navigation star library and various functional modules is shown in Figure 3.12.
How to select navigation stars from basic data will have an impact on the establishment of navigation star databases, star map recognition algorithms, and satellite attitude determination.
The navigation star library mainly consists of a basic navigation star catalog, a navigation star catalog for star map recognition, a navigation star catalog for attitude determination, and a star diagonal distance table. Among them, the basic navigation catalog is composed of 8870 Epoch J1991.25 Hipparcos navigation stars with magnitudes brighter than 6.5; The navigation star catalog and attitude determination star catalog used for star map recognition also have 8870 stars. Different star identifiers are used to determine which processing processes to participate in. The epoch is the satellite observation time, updated in days. The navigation star catalog used for star map recognition stores the Cartesian coordinates of the right ascension system; The star diagonal distance data table is determined by the star map recognition algorithm used in this study, which stores information such as the angular distance, star number, and star offset between all two stars that may appear in the same field of view.
The establishment of a navigation star library is highly dependent on the performance of the star sensor optical system and the accuracy of satellite attitude determination, as well as the star image recognition algorithm. The main content of the navigation star database based on the ground application system is shown in Figure 3.7,
The main content of the navigation star library – navigation star catalog
(1) Basic navigation catalog: Epoch J1991.25 Hipparcos navigation catalog. The catalog mainly includes: stellar HIP number, magnitude, right ascension, declination, right ascension motion, right ascension motion, parallax, apparent velocity, standard deviation and correlation coefficients of six astronomical parameters. Used to establish a navigation catalog for star map recognition through precise epoch conversion.
(2) Navigation star catalog for star map recognition: Its epoch is the satellite epoch time, updated daily. Used to calculate the instantaneous position of stars. The catalog mainly includes: star number, HIP number, magnitude, equatorial coordinates (X, Y, Z) of stars, mid year sky count, and star identification. Star map recognition uses a navigation catalog to sort by magnitude, with bright stars in the first place. Using the storage of equatorial Cartesian coordinates instead of non spherical coordinates can save time in generating star diagonal distance tables and avoid trigonometric function operations during angular distance calculations.
(3) Navigation star catalog for attitude determination: its epoch is the satellite epoch time, updated daily. The content of the star catalog mainly includes: star number, HIP number, magnitude, right ascension, right ascension, right ascension motion, right ascension motion, and star identification. It is used to solve the satellite’s instantaneous attitude after successful star map recognition.
Star diagonal distance table: The storage of recognition features in the navigation star library is based on the star diagonal distance between two stars. It stores all the angular distances between two stars that may appear in the same field of view and the serial numbers of the two stars in the basic navigation star table. It is arranged in ascending order according to the size of the star diagonal distance, and the order of the two stars corresponding to the angular distance is bright stars first. The content of the star diagonal distance table mainly includes: star diagonal distance number, star diagonal distance star 1 number, star diagonal distance star 2 number (bright star in front), and the star difference between the two stars. Arrange in ascending order of angular distance size for quick search during star map recognition.
Based on the navigation star selection method, a customized application software for navigation star library has been developed. This application software can extract navigation stars from the basic navigation star catalog based on configuration parameters such as field of view size, star magnitude threshold, position accuracy threshold, and sky range, and generate real-time navigation star libraries suitable for different sensors. The launch of the FY-4 geostationary meteorological satellite was carried out after 2012, and the distribution of navigation stars in the 2012 epoch for the visible light channel CCD star sensitivity of the FY-4 star sensor and radiometer is presented here.
The field of view of the imager determines that it is impossible for the imager to observe the entire celestial sphere of stars. The declination of stars determines the height at which stars appear in the field of view of the scanning imager, and the right ascension of stars determines the time at which stars appear in the field of view [95]. The field of view of the scanning imager is 23 ° east-west × The north and south are 22 degrees, and the Earth accounts for 17.4 degrees in the field of view. The field of view where stars can be observed is divided into two parts: ① Two rectangular areas that are not obstructed by the Earth: each rectangular field of view is 23 degrees east west × 2.3 ° north-south, 8.7 ° 
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