Star tracker navigation star library construction method based on radial direction and annular direction

Abstract

The invention discloses a radial and annular star tracker navigation star library construction method, and belongs to the field of celestial navigation. The method comprises the following steps: firstly, screening navigation stars conforming to the detection performance of a star tracker from a 2MASS star catalogue, and dividing the navigation stars into a south hemisphere star library and a northern hemisphere star library according to declination; secondly, northern hemisphere navigation stars are processed, a celestial sphere is divided into a plurality of equal-width circular rings, and the number of the stars is distributed according to the area; a plurality of candidate star groups are generated through sector division, a distance and brightness scoring mechanism and a dynamic sector, and an optimal star group is screened in combination with the uniformity of annular and radial star distribution. And then, deleting dark stars of which the inter-satellite angular distance is smaller than the minimum distance, dynamically adjusting an angular distance threshold to supplement the star number, and generating an optimal star library on the basis of considering the star distribution uniformity and brightness. And finally, performing similar processing on the southern hemisphere star, combining the southern hemisphere star library and the northern hemisphere star library, and constructing an all-celestial-sphere navigation star library. The method obviously improves the distribution uniformity of the navigation stars, and is suitable for global star tracking tasks.

Description

Technical Field

[0001] The invention belongs to the field of celestial navigation, and in particular relates to a method for constructing a navigation star library of a star tracker based on radial and circumferential directions. Background Art

[0002] The combined navigation technology of the inertial navigation system (SINS) and the celestial navigation system (CNS) is of great significance in the fields of aerospace, aviation, navigation, etc., and can provide high-precision, long-duration, fully autonomous navigation information. The inertial navigation system is a completely autonomous navigation method that can output position, velocity and attitude information in real time without an external reference source. It is particularly suitable for environments where GPS signals are limited or external signals cannot be received (such as deep space exploration, underwater navigation or complex electromagnetic environments). However, the inertial navigation system has a significant disadvantage: its errors will accumulate over time, especially when it is running for a long time, the position and velocity errors will continue to amplify, resulting in a decrease in navigation accuracy.

[0003] The astronomical navigation system is a navigation method based on the observation of celestial bodies such as stars and planets, and has the characteristics of high precision and good stability. Since astronomical navigation relies on natural celestial bodies, it is not affected by electromagnetic interference, and there is no problem of error accumulation over time, so it has unique advantages in long-duration navigation missions. Star sensors are the most commonly used observation equipment in astronomical navigation. Traditional large-field-of-view star sensors can independently output attitude information and have strong autonomy. They have been widely used in the aerospace field and the technology is relatively mature. However, in near-ground navigation missions, large-field-of-view star sensors are greatly restricted by weather and observation conditions. For example, they may not work properly in the case of cloud cover or strong light interference.

[0004] In order to solve these problems in near-ground navigation, star trackers with all-day observation capabilities are usually used. A star tracker is essentially a small astronomical telescope system with a very small field of view. It can usually only observe one star at a time, so it cannot output attitude information autonomously like a large-field-of-view star sensor. Without external reference position and attitude information, the star tracker cannot observe the stars autonomously. At this time, the inertial navigation system can provide reference position and attitude information for the star tracker, and the star tracker can effectively correct the attitude error in the inertial navigation system, thereby improving navigation accuracy and system stability. This combined navigation system can provide high-precision attitude and position estimates in an environment without GPS signals, ensuring the autonomy and continuous navigation capability of the aircraft in the mission.

[0005] The design of the navigation star library is the key and foundation for star trackers to achieve near-ground star observation. Most of the existing navigation star library designs are based on large-field-of-view star sensors, which contain thousands of navigation stars. Reasonable navigation star library design helps to improve the efficiency of star map recognition, attitude determination accuracy, and reduce data storage and computing burdens. However, star trackers do not need to perform star map recognition like large-field-of-view star sensors, and their star libraries usually contain only dozens to hundreds of navigation stars. Therefore, the key to the design of the star tracker navigation star library is to ensure that the navigation stars are evenly distributed on the celestial sphere, so that the carrier can observe a certain number of navigation stars at any position, thereby ensuring the reliability and accuracy of the navigation system. Considering that the design of the star tracker navigation star library needs to meet the requirements of uniform distribution of navigation stars, optimization of brightness, and near-ground observation conditions, it is urgent to develop a star tracker navigation star library construction method based on radial and circumferential directions, which can effectively solve the above problems, provide an efficient and reliable navigation star library for star trackers, and further improve the performance of the integrated navigation system. Summary of the invention

[0006] The present invention relates to a method for constructing a navigation star library of a star tracker based on radial and circumferential directions, aiming to solve the problem of uneven distribution of navigation stars in the sky. The method divides the celestial sphere into a plurality of equally spaced declination rings, and further divides each ring into right ascension sectors, thereby efficiently constructing a navigation star library. First, the number of navigation stars is allocated according to the area weight of each declination ring, ensuring that the ring with a larger area is allocated with more stars, and the ring with a smaller area is allocated with fewer stars. In each right ascension sector, the star closest to the center of the sector and with a higher brightness is selected as a candidate star, ensuring that the selected star is easy to observe and can provide a high-precision attitude reference. Then, multiple candidate star combinations are generated, the right ascension standard deviation of each combination is calculated, and the combination with the smallest right ascension standard deviation and the largest number of stars is selected as the final candidate combination to ensure uniform distribution in the right ascension direction. At the same time, in order to avoid excessive concentration of stars between adjacent declination rings, the global uniformity of the celestial sphere is further improved by selecting the combination with the largest average angular distance between neighboring stars in the outer ring. Finally, the dark stars with inter-star angular distances less than the minimum angular distance are deleted. If the number of stars in the candidate combination is insufficient, they are supplemented by selecting the stars with the largest angular distances from the nearest selected stars, and the initial inter-star angular distances are adjusted dynamically. Based on the uniformity and brightness of the star distribution in the candidate star library, the optimal star library is generated to ensure the uniformity and integrity of the star library. Through the above systematic construction process, the navigation stars in the navigation star library generated by this method show good spatial distribution uniformity, which lays the foundation for high-precision position and attitude reference, and can effectively support all-weather navigation mission requirements around the world.

[0007] The technical solution of the present invention is as follows: A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, characterized in that it comprises the following steps:

[0008] S110, selecting navigation stars that meet the detection performance of the star tracker, and separating the navigation stars located in the northern hemisphere and the southern hemisphere;

[0009] S120, screens and processes navigation stars in the northern hemisphere;

[0010] S130, select the best candidate star group in each ring in the northern hemisphere;

[0011] S140, Supplement navigation star: delete the satellites with angular distance less than the minimum distance The number of dark stars in the northern hemisphere is counted, and if the total number is less than , then select the remaining northern hemisphere navigation star library to supplement;

[0012] S150, dynamically generate candidate navigation star libraries and select the optimal navigation star library;

[0013] S160, processing the navigation star in the southern hemisphere according to steps S120 to S150, wherein the latitude of the upper boundary of the ring in the southern hemisphere Adjust to a negative value, that is , is the index of the ring, is the number of southern hemisphere rings, and then the northern hemisphere navigation star library and the southern hemisphere navigation star library are merged to form a star tracker navigation star library for the entire celestial sphere.

[0014] The beneficial effects of the present invention are:

[0015] 1. Uniform distribution of navigation stars: Through radial and circumferential division methods, combined with dynamic optimization mechanisms, the navigation stars can be prevented from being too concentrated or sparse in local areas.

[0016] 2. Multi-objective optimization selection mechanism: A multi-objective optimization scoring mechanism including distance, brightness, quantity and distribution uniformity is adopted to comprehensively consider various performance indicators of navigation stars to ensure that the selected navigation stars are optimal in both spatial distribution and brightness, thereby improving the quality of the star library.

[0017] 3. Strong dynamic supplementation and adjustment capabilities: By setting the initial value of the dynamic angular distance and adjusting the minimum distance threshold, the candidate star with the largest angular distance from the nearest neighboring selected navigation star is given priority, and the uniform distribution of the navigation star on the celestial sphere is optimized to meet the mission requirements.

[0018] 4. Full celestial sphere coverage: By processing and merging the northern and southern hemispheres separately, a navigation star library for the entire celestial sphere is constructed, which is suitable for star tracking tasks on a global scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The overall flow chart of the method for constructing a navigation star library of a star tracker based on radial and circumferential directions is shown;

[0020] Figure 2 Original star map showing the distribution of navigation stars in the Northern Hemisphere;

[0021] Figure 3 Screened star chart showing the distribution of navigation stars in the Northern Hemisphere;

[0022] Figure 4 Original star map showing the distribution of navigation stars in the southern hemisphere;

[0023] Figure 5 Filtered star chart showing the distribution of navigation stars in the Southern Hemisphere. DETAILED DESCRIPTION

[0024] In the embodiments of the present invention, in order to make the description clearer, only some components or processes may be shown. Under the guidance of the present invention, parameters or methods can be flexibly adjusted according to specific application requirements. For example, the present invention focuses on the construction method of the navigation star library based on radial and circumferential directions, including the uniform distribution of navigation stars through sector division, distance and brightness normalization scoring mechanism and candidate star group optimization selection. However, in practical applications, certain steps or parameters can be adjusted according to specific needs, such as using only distance or brightness as the basis for scoring without considering both at the same time; or adjusting the number and range of sector divisions to adapt to different navigation star distribution densities; or adjusting the weight coefficients of distance and brightness according to scene requirements. In addition, the selection of candidate star groups can also be scored based on only a single indicator of the number of navigation stars or distribution uniformity. These adjusted or simplified embodiments also fall within the scope of disclosure or recording of the present application.

[0025] The present invention is further described in detail below in conjunction with specific embodiments.

[0026] Figure 1 The overall flow chart of the method for constructing a navigation star library for a star tracker based on radial and circumferential directions is shown. Figure 1 As shown, the method comprises the following steps:

[0027] S110, selecting navigation stars that meet the detection performance of the star tracker, and separating the stars located in the northern hemisphere and the southern hemisphere. The specific implementation process is as follows:

[0028] S110-1, selection of original star catalog: 2MASS is used as the original star catalog, which meets the requirement of brighter stars in the infrared band. Navigation stars in the H band with a wavelength of 1.4~1.8μm are selected, and the magnitude threshold is set. , filter out the star magnitude values ​​less than The magnitude threshold is set to ensure that the brightness of the selected navigation star meets the detection performance requirements of the star tracker. .

[0029] S110-2, Division of the Northern and Southern Hemisphere Navigation Star Library: Based on declination ( ) divides the navigation stars into two parts: the northern hemisphere and the southern hemisphere: The navigation star of is used as the navigation star library of the northern hemisphere; The navigation stars are used as the southern hemisphere navigation star library.

[0030] S120, screens and processes the navigation stars in the northern hemisphere. The specific implementation process is as follows:

[0031] S120-1, Division of the celestial sphere: The northern hemisphere is divided into There are rings of the same width, the ring width The calculation formula is expressed as , the latitude of the upper boundary of the ring From outside to inside, it can be expressed as:

[0032] ,

[0033] in, Indicates The latitude of the upper boundary of the ring, is the index of the ring, from 1 to .

[0034] In one embodiment, the ring width , the latitudes of the ring boundaries from outside to inside are .

[0035] S120-2, Allocation of the number of navigation stars: Assume the total number of navigation stars that need to be screened in the northern hemisphere , the number of navigation stars is allocated according to the area of ​​each ring. The number of stars falling into each ring Calculated by the following formula:

[0036] ,

[0037] in, and Respectively represent The latitudes of the upper and lower boundaries of the rings, represents a rounding function. This formula ensures that the number of navigation stars in each ring is proportional to the corresponding celestial sphere surface area, thereby achieving uniform distribution of navigation stars in the radial direction. In one embodiment, Therefore, the number of navigation stars allocated from the outermost ring to the innermost ring is: 8, 8, 7, 6, 6, 4, 3, 2, 1.

[0038] S120-3, Filling of navigation stars: Fill the ring with navigation stars that meet the latitudes of the upper and lower boundaries of the ring in order from the outermost ring to the innermost ring. For example, fill the outermost ring with declination navigation star.

[0039] S120-4, Division of right ascension sectors of the ring: according to the number of pre-allocated navigation stars in each ring , divide each ring into sectors. The longitude of the center of each sector can be expressed as:

[0040] ,

[0041] For the The first The central longitude of the sector, in degrees. For example, the outermost ring , then the longitude of the sector center is , and so on for other rings.

[0042] S120-5, generate candidate star groups for each ring: select an optimal navigation star for each sector of the ring, and the optimal navigation star group of each sector forms a candidate star group. The optimal navigation star selection principle is based on the distance between the navigation star and the longitude of the sector center and the brightness weight. The specific implementation process is as follows:

[0043] S120-51, distance normalization: Calculate the distance between the navigation star and the center of each sector in each ring and normalize the distance. The distance normalization formula is:

[0044] ,

[0045] in, is the right ascension of the navigation star in the current sector, in degrees (°), is the normalized distance value, ranging from .

[0046] S120-52, brightness normalization: Calculate the brightness of the navigation star in each sector of each ring and normalize it. The brightness normalization formula can be expressed as:

[0047] ,

[0048] in, is the magnitude of the navigation star; and They are the minimum and maximum magnitudes of the navigation star in the current sector respectively; is the normalized brightness value, ranging from .

[0049] S120-53, assign an optimal navigation star to each sector. The process of obtaining the optimal navigation star includes: assigning a weight coefficient to each of the distance and brightness of the navigation star and , calculate the navigation star score according to the following formula and determine the best navigation star based on the score:

[0050] .

[0051] in, is the score of the navigation star, and are the weight coefficients of distance and brightness, respectively, satisfying , weight coefficient and It can be adjusted according to actual application requirements, usually determined by experiments or optimization algorithms to meet the requirements of uniformity and brightness of navigation star distribution. and .

[0052] S120-54, Sector center movement: Determine a sector center movement interval , the sector center moving interval is ,in is the number of moves. After each move, the navigation star score in the sector is recalculated to ensure the diversity of the candidate star group. The total distance of sector movement is For example, in ring 1 , then the total distance the sector moves is .

[0053] In this way, each sector obtains multiple optimal navigation stars, and the best navigation stars of each sector are combined in a customized manner to form multiple candidate star groups.

[0054] S120-55, Candidate star group scoring: For candidate star groups that contain the same navigation star, retain the only candidate star group, and then score each candidate star group. The scoring formula is:

[0055] ,

[0056] in, For the The scores of the candidate star groups; For the The number of navigation stars in the candidate star group; and are the minimum and maximum number of navigation stars in all candidate star groups in the current ring respectively; For the The standard deviation of the right ascension of the navigation stars in the candidate star group; and are the minimum and maximum values ​​of the standard deviation of right ascension among all candidate star groups in the current ring, respectively; and are the weight coefficients of the number of navigation stars and the uniformity of distribution, respectively, satisfying In one embodiment, ;

[0057] S120-56, select the top one with the highest score in each ring Candidate star groups. The value of can be adjusted according to the total number of navigation stars in the ring and the uniformity of distribution. If the number of candidate star groups in the ring is less than , then all are selected. In one embodiment, m=5.

[0058] S130, selecting the best candidate star group in each ring in the northern hemisphere, including the following steps:

[0059] S130-1, the outermost ring directly selects the candidate star group with the largest score according to the score calculated in S120-55.

[0060] S130-2, for the inner ring, according to the principle of maximizing the average value of the minimum inter-satellite angular distance between the navigation star in the current ring and the navigation star in the previous ring, select an optimal candidate star group for each ring, including the following steps:

[0061] S130-21, for each set of navigation stars in the current ring (in represents the candidate star group index in the current ring, and ), is the actual number of each group of navigation stars in the current ring, ), calculate its distance from all navigation stars in the previous ring (in is the number of navigation stars in the previous ring) is the minimum inter-satellite angular distance:

[0062] ,

[0063] Among them, the inter-satellite angular distance The calculation formula is:

[0064] ,

[0065] in, and They are and declination; is the right ascension difference, and They are and Right ascension.

[0066] S130-22, calculate the average value of the minimum inter-satellite angular distance of each group of navigation stars in the current ring: take the average value of the minimum inter-satellite angular distance of each group of navigation stars in the current ring:

[0067] .

[0068] S130-23, in accordance with The biggest principle is to select the best candidate star group in the current ring:

[0069] .

[0070] S140, Supplement navigation star: delete the satellites with angular distance less than the minimum distance The number of dark stars in the northern hemisphere is counted, and if the total number is less than the expected number , then the remaining northern hemisphere navigation star library is supplemented. When supplementing, the minimum inter-star angular distance between each candidate star and the selected navigation star is calculated, and the star with the largest angular distance from the selected navigation star is selected and added to the navigation star library. In one embodiment, , . The following steps are included:

[0071] S140-1, calculate the minimum inter-star angular distance between all the stars in the filtered northern hemisphere navigation star library. If the minimum inter-star angular distance between two stars is less than the minimum angular distance threshold , then delete the dark stars. The calculation formula for the minimum inter-star angular distance is:

[0072] ,

[0073] in, and Respectively represent Selected stars and The declination of the selected star, and , No. Selected stars and The right ascension difference of the selected stars is calculated as follows:

[0074] ,

[0075] and Respectively represent Selected stars and The right ascension of the selected star.

[0076] S140-2, determine whether the number is insufficient: If the number of selected navigation stars is less than , then enter the supplementary process.

[0077] S140-3, from the remaining northern hemisphere navigation star library, calculate the angular distance between each candidate star and the closest selected navigation star, select the star with the largest angular distance from the navigation star among the candidate stars, and add it to the northern hemisphere navigation star library.

[0078] S140-4, Dynamically adjust the minimum angular distance threshold: If a navigation star that meets the comprehensive gap requirement cannot be found under the current minimum angular distance threshold, gradually reduce the minimum angular distance threshold , continue searching. In one implementation, the decrementing step size is set to 1.

[0079] S140-5, loop replenishment process: repeat steps S140-2 to S140-4 until the number of selected navigation stars reaches .

[0080] S150, dynamically generate candidate navigation star libraries and select the optimal navigation star library: by dynamically adjusting the initial value of the minimum angular distance threshold, repeat S140-2 to S140-4 to generate multiple candidate navigation star libraries, and select the optimal navigation star library through the scoring function. The specific steps are as follows:

[0081] S150-1, dynamically generating a candidate navigation star library, including the following steps:

[0082] S150-11, initialization parameters: Set the minimum angular distance threshold to , the initial value of the angular distance decreases in steps of , the angular distance end value is In one embodiment, the value can be ,in The number of navigation stars allocated to the outermost ring is ,but ; Assume that the initial value of the angular distance decreases by the step length ; Assume the end value of the angular distance is .

[0083] S150-12, generate candidate navigation star library: each time the initial value of the angular distance Decreasing Finally, a candidate navigation star library is generated.

[0084] S150-13, repeat the above steps until the initial value of the angular distance decreases to , co-generate A candidate navigation star library.

[0085] S150-2, Navigation star library scoring and optimal selection: To evaluate the quality of each navigation star library, set a scoring function , finally select the rating The largest candidate navigation star library is used as the optimal navigation star library. The calculation formula is:

[0086] ,

[0087] in, It is The standard deviation of the angular distances between the stars in the candidate navigation star library; It is the maximum value of the standard deviation of the inter-satellite angular distances in all candidate navigation star libraries; It is the minimum value of the standard deviation of the inter-satellite angular distances in all candidate navigation star libraries; It is The average brightness (magnitude) of stars in the candidate navigation star library; is the maximum value of the average brightness of all candidate star libraries; is the minimum value of the average brightness of all candidate star libraries; and are the weight coefficients of the standard deviation and average brightness of the navigation star library, satisfying In this embodiment, , .

[0088] Through the systematic screening process from step S110 to step S150, the optimization of the northern hemisphere navigation stars is completed. Figure 2 As shown in the figure, the screening star map of the distribution of navigation stars in the northern hemisphere is as follows Figure 3 As shown. The parameters determined in the process of selecting stars in the northern hemisphere: The initial value of the optimal minimum angular distance threshold is , the number of stars selected by radial and circumferential directions is 30, the number of supplementary stars is 15, and some of the selected northern hemisphere navigation stars are shown in Table 1:

[0089] Table 1 Some selected northern hemisphere navigation stars

[0090] S160, construction of the southern hemisphere navigation star library: the southern hemisphere navigation stars are processed according to steps S120 to S150. The latitude of the upper boundary of the southern hemisphere ring It needs to be adjusted to a negative value to ensure the symmetry of the ring division, that is:

[0091] , in, is the index of the ring, is the number of rings in the southern hemisphere.

[0092] Then the screened northern hemisphere navigation star library and southern hemisphere navigation star library are merged to form a star tracking navigation star library for the entire celestial sphere.

[0093] The original star map of the distribution of navigation stars in the southern hemisphere is as follows: Figure 4 As shown in the figure, the screening star map of the distribution of southern navigation stars is as follows Figure 5 As shown. The parameters determined in the southern hemisphere star selection process: The initial value of the optimal minimum angular distance threshold is , the number of stars selected by radial and circumferential directions is 31, the number of supplementary stars is 14, and some of the selected southern hemisphere navigation stars are shown in Table 2:

[0094] Table 2 Some selected southern hemisphere navigation stars

[0095] Through the above steps, a full-celestial navigation star library containing 90 navigation stars was successfully constructed, including 45 navigation stars in the northern hemisphere and 45 in the southern hemisphere. The navigation stars are evenly distributed in the radial direction, and the number and distribution uniformity of the navigation stars in each ring meet the design requirements. The standard deviation of the inter-star angular distance and the average brightness (measured by the average magnitude value) of the original star library and the screened navigation star library in the southern and northern hemispheres are now counted. The screened star library can be called the navigation star library. The calculation rule for the inter-star angular distance in the original star library in the southern and northern hemispheres is: select the selected star in the original star library, calculate its angular distance with the nearest neighbor star, and then calculate the standard deviation of these angular distance values. The standard deviation and average brightness of the angular distance of the original and navigation star libraries in the southern and northern hemispheres are shown in Table 3:

[0096] Table 3 Standard deviation and average brightness of the original and navigation star library angular distances in the southern and northern hemispheres

[0097] It can be seen from Table 3 that the standard deviation of the angular distance of the southern and northern hemisphere navigation star libraries is significantly lower than that of the original star library, indicating that the inter-satellite distribution of the navigation star library is more uniform. At the same time, the average brightness of the navigation star library is higher, indicating that the selected navigation stars are brighter and more suitable for navigation tasks.

[0098] It should be noted that the above description of the preferred embodiment is relatively detailed, but it cannot be regarded as limiting the scope of protection of the present invention. Under the guidance of the present invention, ordinary technicians in this field can make several improvements and modifications without departing from the scope of protection of the claims of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention. The scope of protection requested by the present invention should be based on the attached claims.

Claims

1. A method for constructing a navigation star library for a star tracker based on radial and circumferential directions, characterized in that: The following steps are involved: S110, selecting navigation stars that meet the detection performance of the star tracker, and separating the navigation stars located in the northern hemisphere and the southern hemisphere; S120, screens and processes navigation stars in the northern hemisphere; S130, select the best candidate star group in each ring in the northern hemisphere; S140, Supplement navigation star: delete the satellites with angular distance less than the minimum angular distance The number of dark stars in the northern hemisphere is counted, and if the total number is less than the expected number , then supplement it by screening the remaining northern hemisphere navigation star library; S150, dynamically generating candidate navigation star libraries and selecting the optimal navigation star library; S160, processing the navigation star in the southern hemisphere according to steps S120 to S150, wherein the latitude of the upper boundary of the ring in the southern hemisphere Adjust to a negative value, i.e. , is the index of the ring, is the number of southern hemisphere rings, and then the northern hemisphere navigation star library and the southern hemisphere navigation star library are merged to form a star tracker navigation star library for the entire celestial sphere.

2. The method for constructing a navigation star library for a radial and circumferential star tracker according to claim 1, characterized in that: Step S110 includes: S110-1, Selection of original star catalog: Use 2MASS as the original star catalog, select the navigation star in the H band with a wavelength of 1.4~1.8μm, and set the magnitude threshold , filter out the star magnitude values ​​less than The navigation star; S110-2, divides navigation stars into northern and southern hemisphere parts according to declination: The navigation stars of are selected as the northern hemisphere navigation star library, and the declination The navigation stars are used as the navigation star library for the southern hemisphere.

3. The method for constructing a navigation star library for a star tracker based on radial and circumferential directions according to claim 1, characterized in that: Step S120 includes: S120-1, divides the northern hemisphere into There are rings of the same width, the ring width , the latitude of the upper boundary of the ring ,in ,in Indicates The latitude of the upper boundary of the ring, is the index of the ring, is the number of rings; S120-2, allocate the number of navigation stars according to the area of ​​each ring, and the number of stars falling into each ring , calculated by the following formula: ， in, and Respectively represent The latitudes of the upper and lower boundaries of the rings, For the The number of navigation stars that fall into the ring, is the total number of navigation stars that need to be screened in the northern hemisphere, Represents the rounding function; S120-3, in order from the outermost ring to the innermost ring, Fill the circle with the navigation stars one by one; S120-4, divide each ring into sectors, the longitude of the center of each sector ,in ; S120-5, generating a candidate star group for each circular ring: selecting an optimal navigation star for each sector of the circular ring, and combining the optimal navigation stars of each sector into a candidate star group.

4. The method for constructing a navigation star library for a radial and circumferential star tracker according to claim 3, characterized in that: Step S120-5 includes: S120-51, calculate the distance between the navigation star in each sector of each ring and the center of the sector and normalize the distance. The distance normalization formula is: ， in, is the right ascension of the navigation star in the current sector, in degrees (°), For the The first The central longitude of a sector, in degrees, is the normalized distance value; S120-52, calculate the brightness of the navigation star in each sector of each ring in turn and normalize it. The brightness normalization formula is: ， in, is the magnitude of the navigation star, and are the minimum and maximum magnitudes of the navigation star in the current sector, is the normalized brightness value; S120-53, each sector is assigned an optimal navigation star. The process of obtaining the optimal navigation star includes: assigning a weight coefficient to each of the distance and brightness of the navigation star , calculate the navigation star score according to the following formula and determine the best navigation star based on the score: ， in, is the score of the navigation star, and are the weight coefficients of distance and brightness, respectively, satisfying ; S120-54, determine the sector center movement interval , where is the number of moves, and the navigation star score in the sector is recalculated after each move; S120-55, score the candidate star groups, the scoring formula is: ， in, For the The scores of the candidate star groups; For the The number of navigation stars in the candidate star group; and are the minimum and maximum number of navigation stars in all candidate star groups in the current ring respectively; For the The standard deviation of the right ascension of the navigation stars in the candidate star group; and are the minimum and maximum values ​​of the standard deviation of right ascension among all candidate star groups in the current ring, respectively; and are the weight coefficients of the number of navigation stars and the uniformity of distribution, respectively, satisfying ; S120-56, select the top one with the highest score in each ring Candidate star groups.

5. The method for constructing a navigation star library for a radial and circumferential star tracker according to claim 4, characterized in that: and , m=5.

6. The method for constructing a navigation star library for a radial and circumferential star tracker according to claim 4, characterized in that: The step S130 includes the following steps: S130-1, the outermost ring directly selects the candidate star group with the largest score according to the score calculated in S120-55; S130-2, for the inner rings, according to the principle of maximizing the average value of the minimum inter-satellite angular distance between the navigation stars in the current ring and the navigation stars in the previous ring, select an optimal candidate star group for each ring.

7. The method for constructing a navigation star library for a radial and circumferential star tracker according to claim 6, characterized in that: Step S130-2 includes the following steps: S130-21, for each set of navigation stars in the current ring ,in represents the index of the candidate star group in the current ring, and , is the actual number of each group of navigation stars in the current ring, ), calculate its distance from all navigation stars in the previous ring The minimum inter-satellite angular distance between is the number of navigation stars in the previous ring: ， Among them, the inter-satellite angular distance The calculation formula is: ， in, and They are and declination; is the right ascension difference, and They are and Right ascension; S130-22, calculate the average value of the minimum inter-satellite angular distance of each group of navigation stars in the current ring: take the average value of the minimum inter-satellite angular distance of each group of navigation stars in the current ring: ， S130-23, in accordance with The biggest principle is to select the best candidate star group in the current ring: 。 8. The method for constructing a navigation star library for a radial and circumferential star tracker according to claim 7, characterized in that: Step S140 includes: S140-1, calculate the minimum inter-star angular distance between all stars in the filtered northern hemisphere navigation star library. If the minimum inter-star angular distance between two stars is less than the minimum angular distance threshold , then delete the dark stars, and the calculation formula for the minimum inter-star angular distance is: ， in, and Respectively represent Selected stars and the declination of the selected star, and , Indicates Selected stars and The right ascension difference of the selected stars is calculated as follows: ， and Respectively represent Selected stars and The right ascension of the selected star; S140-2, determine whether the number is insufficient: If the number of selected navigation stars is less than the expected number , then enter the supplementary process; S140-3, from the remaining northern hemisphere navigation star library, calculate the angular distance between each candidate star and the closest selected navigation star, select the star with the largest angular distance from the navigation star among the candidate stars, and add it to the northern hemisphere navigation star library; S140-4, dynamically adjust the minimum angular distance threshold: If the current minimum angular distance threshold If no star that meets the comprehensive gap requirement can be found, the minimum angular distance threshold is gradually reduced. , continue searching; S140-5, loop replenishment process: repeat steps S140-2 to S140-4 until the number of selected navigation stars reaches .

9. The method for constructing a navigation star library for a radial and circumferential star tracker according to claim 8, characterized in that: The step S150 includes dynamically adjusting the initial value of the minimum angular distance threshold, repeating S140-2 to S140-4, generating multiple candidate navigation star libraries, and selecting the optimal navigation star library through a scoring function, including the following steps: S150-1, dynamically generating a candidate navigation star library, including the following steps: S150-11, initialization parameters: Set the minimum angular distance threshold to , the minimum angular distance threshold initial value decreases in steps of , the angular distance end value is ; S150-12, generate candidate navigation star library: each time the minimum angular distance threshold initial value Decreasing After that, a candidate navigation star library is generated; S150-13, repeat the above steps until the initial value of the angular distance decreases to , co-generate A candidate navigation star library; S150-2, Navigation star library scoring and optimal selection: Setting the scoring function , finally select the rating The largest candidate navigation star library is used as the optimal navigation star library. The calculation formula is: ， in, It is The standard deviation of the angular distances between the stars in the candidate navigation star library; It is the maximum value of the standard deviation of the inter-satellite angular distances in all candidate navigation star libraries; It is the minimum value of the standard deviation of the inter-satellite angular distances in all candidate navigation star libraries; It is The average brightness of stars in the candidate navigation star library; is the maximum value of the average brightness of all candidate star libraries; is the minimum value of the average brightness of all candidate star libraries; and are the weight coefficients of the standard deviation and average brightness of the navigation star library, satisfying .

10. The method for constructing a navigation star library of a star tracker based on radial and circumferential directions according to claim 9, characterized in that: In the process of selecting navigation stars in the northern hemisphere, the initial value of the minimum angular distance threshold is ; In the process of selecting navigation stars in the southern hemisphere, the initial value of the minimum angular distance threshold is .

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