A method for constructing a navigation star library of a star tracker based on radial and circumferential directions

Abstract

The present invention discloses a method for constructing a navigation star library based on the radial and circumferential directions, belonging to the field of astronomical navigation. First, navigation stars that meet the detection performance of the star tracker are screened from the 2MASS star catalog and divided into southern and northern hemisphere star libraries according to declination. Secondly, the navigation stars in the northern hemisphere are processed. The celestial sphere is divided into multiple equal-width circular rings, and the number of stars is allocated according to the area. Multiple candidate star groups are generated through sector division, distance and brightness scoring mechanisms, and dynamic sectors. The best star group is selected by combining the uniformity of the circumferential and radial star distributions. Subsequently, the faint stars with an angular distance between stars less than the minimum distance are deleted, and the angular distance threshold is dynamically adjusted to supplement the number of stars, and an optimal star library is generated on the basis of considering the uniformity and brightness of the star distribution. Finally, the stars in the southern hemisphere are processed similarly, and the southern and northern hemisphere star libraries are merged to construct a global celestial sphere navigation star library. The present invention significantly improves the uniformity of the navigation star distribution and is applicable to global star tracking tasks.

Description

Technical Field

[0001] The present invention belongs to the field of celestial navigation, and particularly 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 an inertial navigation system (SINS) and a celestial navigation system (CNS) is of great significance in the fields of aerospace, aviation, navigation, etc., and can provide high-precision, long-endurance, and 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, and 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 drawback: its errors will accumulate over time. Especially during long-term operation, the position and velocity errors will continuously amplify, resulting in a decrease in navigation accuracy.

[0003] The celestial 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 celestial navigation relies on natural celestial bodies, is not affected by electromagnetic interference, and there is no problem of error accumulation over time, it has unique advantages in long-endurance navigation tasks. A star sensor is the most commonly used observation device in celestial navigation. Traditional large-field-of-view star sensors can independently output attitude information, have strong autonomy, and have been widely used in the aerospace field and the technology is relatively mature. However, in near-ground navigation tasks, large-field-of-view star sensors are greatly restricted by weather and observation conditions. For example, they may not be able to work properly under conditions such as cloud cover and strong light interference.

[0004] To solve these problems in near-ground navigation, a star tracker with all-weather observation capabilities is usually adopted. A star tracker is essentially a small astronomical telescope system with a very small field of view. Usually, only one star can be observed at a time, so it cannot independently output attitude information like a large-field-of-view star sensor. Without external reference position and attitude information, the star tracker cannot observe stars independently. 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 the navigation accuracy and system stability. This combined navigation system can provide high-precision attitude and position estimation in an environment without GPS signals, ensuring the autonomy and continuous navigation ability of the aircraft during the mission.

[0005] The design of the navigation star library is the key and foundation for the star tracker 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. A reasonable navigation star library design helps to improve the star map recognition efficiency, attitude determination accuracy, and reduce the data storage and calculation burden. However, the star tracker does not need to perform star map recognition like a large-field-of-view star sensor, and its star library usually contains only dozens to hundreds of navigation stars. Therefore, the key to the design of the star tracker navigation star library lies in ensuring the uniform distribution of navigation stars 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 the uniform distribution of navigation stars, brightness optimization, and near-ground observation conditions, it is urgent to develop a method for constructing a star tracker navigation star library based on radial and circumferential directions, which can effectively solve the above problems, provide an efficient and reliable navigation star library for the star tracker, 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 star tracker navigation star library based on radial and circumferential directions, aiming to solve the problem of uneven distribution of navigation stars in the celestial sphere. This method efficiently constructs a navigation star library by dividing the celestial sphere into multiple equidistant declination rings and further dividing each ring into right ascension sectors. First, the number of navigation stars is allocated according to the area weight of each declination ring, ensuring that more stars are allocated to the rings with larger areas and fewer stars are allocated to the rings with smaller areas. In each right ascension sector, the star closest to the sector center and with higher brightness is selected as a candidate star, ensuring that the selected stars are 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 group of combinations 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, to avoid excessive concentration of stars between adjacent declination rings, the combination with the largest average angular distance between adjacent stars in the outer ring is selected to further improve the global uniformity of the celestial sphere. Finally, the dim stars with an angular distance between stars less than the minimum angular distance are deleted. If the number of stars in the candidate combination is insufficient, stars with the largest angular distance from the neighboring selected stars are selected for supplementation, and the initial angular distance between stars is dynamically adjusted. Based on considering the uniformity and brightness of the star distribution in the candidate star library, an 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, laying a foundation for high-precision position and attitude reference, and can effectively support the all-weather navigation mission requirements worldwide.

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

[0008] S110. Select navigation stars that meet the detection performance of the star tracker and separate the navigation stars located in the northern and southern hemispheres;

[0009] S120. Screen and process the navigation stars in the northern hemisphere;

[0010] S130. Select the optimal candidate star group in each ring in the northern hemisphere;

[0011] S140. Supplement navigation stars: Delete the faint stars with the inter-star angular distance less than the minimum distance , count the number of candidate stars screened in the northern hemisphere. If the total number is less than , then supplement from the remaining navigation star library in the northern hemisphere;

[0012] S150. Dynamically generate a candidate navigation star library and select the optimal navigation star library;

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

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

[0015] 1. Uniform distribution of navigation stars: Through the radial and circumferential division methods, combined with the dynamic optimization mechanism, it is avoided that the navigation stars are too concentrated or sparse in local areas.

[0016] 2. Multi-objective optimization selection mechanism: Adopt a multi-objective optimization scoring mechanism such as distance, brightness, quantity, and distribution uniformity, comprehensively consider various performance indicators of the navigation stars, and ensure that the selected navigation stars reach the optimal in terms of spatial distribution and brightness, improving the quality of the star library.

[0017] 3. Strong dynamic supplement and adjustment ability: By setting the initial value of the dynamic angular distance and adjusting the minimum distance threshold, preferentially select the candidate star with the largest angular distance from the nearest selected navigation star, optimize the uniform distribution of the navigation stars on the celestial sphere, and meet the task requirements.

[0018] 4. Full celestial sphere coverage: By separately processing and merging the northern and southern hemispheres, the construction of a navigation star library for the entire celestial sphere is realized, which is applicable to star tracking tasks worldwide. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shows the overall flowchart of the method for constructing a star tracker navigation star library based on radial and circumferential directions;

[0020] Figure 2 The original star chart showing the distribution of navigational stars in the Northern Hemisphere;

[0021] Figure 3 The screened star chart showing the distribution of navigational stars in the Northern Hemisphere;

[0022] Figure 4 The original star chart showing the distribution of navigational stars in the Southern Hemisphere;

[0023] Figure 5 The screened star chart showing the distribution of navigational stars in the Southern Hemisphere. Detailed implementation manners

[0024] In the embodiments of the present invention, for clearer illustration, 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 method for constructing a navigational star library based on radial and circumferential directions, including achieving uniform distribution of navigational stars through sector division, distance and brightness normalization scoring mechanisms, and optimized selection of candidate star groups. However, in actual applications, certain steps or parameters can be adjusted according to specific requirements. For example, only distance or brightness can be used as the scoring basis without considering both simultaneously; or the number and range of sector divisions can be adjusted to adapt to different navigational star distribution densities; or the weight coefficients of distance and brightness can be adjusted according to scenario requirements. In addition, the selection of candidate star groups can also be scored based on a single index such as the number of navigational stars or distribution uniformity. These adjusted or simplified embodiments also fall within the scope of disclosure or the scope of recordation of this application.

[0025] The following further describes the present invention in detail with specific embodiments.

[0026] Figure 1 The overall flowchart showing the method for constructing a navigational star library of a star tracker based on radial and circumferential directions. As Figure 1 shown, the method includes the following steps:

[0027] S110, select navigational stars that meet the detection performance of the star tracker, and separate the stars located in the Northern Hemisphere and the Southern Hemisphere. The specific implementation process is as follows:

[0028] S110-1, selection of the original star catalog: Use 2MASS as the original star catalog. This star catalog meets the requirement that stars are brighter in the infrared band. Select navigational stars in the H band with wavelengths of 1.4 - 1.8 μm, and set a magnitude threshold , and screen out navigational stars with magnitude values less than to ensure that the brightness of the selected navigational stars meets the detection performance requirements of the star tracker. In one embodiment, set the magnitude threshold .

[0029] S110 - 2, Division of the navigation star library in the northern and southern hemispheres: According to the declination ( ), the navigation stars are divided into two parts, the northern hemisphere and the southern hemisphere: The navigation stars with declination are used as the navigation star library in the northern hemisphere; the navigation stars with declination are used as the navigation star library in the southern hemisphere.

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

[0031] S120 - 1, Division of the celestial sphere rings: Divide the celestial sphere in the northern hemisphere into rings with the same width. The width of the ring is calculated by the formula . The latitude of the upper boundary of the ring can be successively expressed from the outside to the inside as:

[0032] ,

[0033] where, represents the latitude of the upper boundary of the th ring, is the index of the ring, ranging from 1 to .

[0034] In an implementation manner, the width of the ring , and the latitudes of the ring boundaries from the outside to the inside are successively .

[0035] S120 - 2, Allocation of the number of navigation stars: Let the total number of navigation stars to be screened in the northern hemisphere be . Allocate the number of navigation stars according to the area of each ring. The number of stars falling into each ring is calculated by the following formula:

[0036] ,

[0037] where, and respectively represent the latitudes of the upper boundary and the lower boundary of the th ring, represents the rounding function. This formula ensures that the number of navigation stars in each ring is proportional to its corresponding celestial sphere surface area, thus realizing the uniform distribution of navigation stars in the radial direction. In an implementation manner, . Therefore, the number of navigation stars allocated from the outermost ring to the innermost ring is successively: 8, 8, 7, 6, 6, 4, 3, 2, 1.

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

[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] is the longitude of the center of the th sector in the th ring, in degrees (°). For example, for the outermost ring , the longitude of the sector center is , and the same applies to other rings.

[0042] S120-5, Generating candidate star groups for each ring: Select one best navigation star for each sector of the ring, and the best navigation stars of each sector form a candidate star group. The principle for selecting the best navigation star is based on the distance between the navigation star and the sector center longitude and the brightness weight. The specific implementation process is as follows:

[0043] S120-51, Distance normalization: Calculate the distance between the navigation stars in each sector within each ring and the sector center, and normalize this distance. The formula for distance normalization is:

[0044] ,

[0045] where is the right ascension of the navigation star in the current sector, in degrees (°), is the normalized distance value, with a range of .

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

[0047] ,

[0048] where is the magnitude of the navigation star; and are the minimum and maximum magnitudes of the navigation stars in the current sector respectively; is the normalized brightness value, with a range of .

[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 the distance and brightness of the navigation star and , calculate the navigation star score according to the following formula and determine the optimal navigation star based on this score:

[0050] .

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

[0052] S120 - 54, sector center movement: determine a sector center movement interval , the sector center movement interval is , where is the number of movements. Recalculate the navigation star score within the sector after each movement to ensure the diversity of the candidate star group. The total distance of the sector movement is . For example, in ring 1 , then the total distance of the sector movement is .

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

[0054] S120 - 55, candidate star group scoring: retain the unique candidate star group for candidate star groups containing the same navigation stars, and then score each candidate star group. The scoring formula is:

[0055] ,

[0056] Among them, is the score of the th candidate star group; is the number of navigation stars in the th candidate star group; and are the minimum and maximum values of the number of navigation stars in all candidate star groups within the current ring respectively; is the standard deviation of the right ascension of the navigation stars in the th candidate star group; and are respectively the minimum and maximum values of the right ascension standard deviation among all candidate star groups within the current ring; and are respectively the weight coefficients of the number of navigation stars and the distribution uniformity, satisfying ; In one embodiment, ;

[0057] S120 - 56, select the top candidate star groups with the highest scores in each ring. The value of can be adjusted according to the total number of navigation stars in the ring and the requirement of distribution uniformity. If the number of candidate star groups in the ring is less than

[0058] S130, select the optimal candidate star groups in each ring in the northern hemisphere, including the following steps:

[0059] S130 - 1, directly select the candidate star group with the maximum score according to the score calculated by S120 - 55 for the outermost ring.

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

[0061] S130 - 21, for each group of navigation stars in the current ring (where 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 minimum inter - star angular distance from all navigation stars in the previous ring (where is the number of navigation stars in the previous ring):

[0062] ,

[0063] where the inter - star angular distance is calculated by the formula:

[0064] ,

[0065] where, and are respectively and 's declinations; is the right ascension difference, and are respectively and right ascension.

[0066] S130-22, calculate the average value of the minimum inter-star angular distances for each group of navigation stars within the current ring: take the average value of the minimum inter-star angular distances for each group of navigation stars within the current ring:

[0067] .

[0068] S130-23, select the optimal candidate star group within the current ring according to the maximum principle:

[0069] .

[0070] S140, supplement navigation stars: delete the faint stars with inter-star angular distances less than the minimum distance , count the number of candidate stars screened in the northern hemisphere. If the total number is less than the expected quantity , then supplement from the remaining northern hemisphere navigation star library after screening. When supplementing, calculate the minimum inter-star angular distance between each candidate star and the selected navigation stars, and select the star with the largest angular distance from the selected navigation stars and add it to the navigation star library. In one embodiment, , . Include the following steps:

[0071] S140-1, calculate the minimum inter-star angular distances between all stars in the screened 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 faint star among them. The calculation formula for the minimum inter-star angular distance is:

[0072] ,

[0073] where and respectively represent the th selected star and the th selected star's declination, and , the th selected star and the th selected star's right ascension difference, and the calculation formula is:

[0074] ,

[0075] and respectively represent the th selected star and the th selected star's right ascension.

[0076] S140-2, Determine if the quantity is insufficient: If the number of selected navigation stars is less than , then enter the replenishment 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 among the candidate stars from the navigation stars, and add it to the northern hemisphere navigation star library.

[0078] S140-4, Dynamically adjust the minimum angular distance threshold: If no navigation star that meets the comprehensive gap requirement can be found under the current minimum angular distance threshold, gradually decrease the minimum angular distance threshold , and continue the search. In one embodiment, the decreasing 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 a candidate navigation star library 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 a scoring function. The specific steps are as follows:

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

[0082] S150-11, Initialize parameters: Set the initial value of the minimum angular distance threshold to , the decreasing step size of the angular distance initial value is , and the angular distance termination value is . In one embodiment, the value can be , where is the number of navigation stars allocated to the outermost ring, take , then ; Set the decreasing step size of the angular distance initial value to ; Set the angular distance termination value to .

[0083] S150-12, Generate a candidate navigation star library: Each time the angular distance initial value is decreased by , a candidate navigation star library is generated.

[0084] S150-13, Repeat the above steps until the angular distance initial value is decreased to , and a total of candidate navigation star libraries are generated.

[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 score The largest candidate navigation star library is used as the optimal navigation star library. The calculation formula of is:

[0086] ,

[0087] Among them, is the standard deviation of the angular distance between stars in the th candidate navigation star library; is the maximum value of the standard deviation of the angular distance between stars in all candidate navigation star libraries; is the minimum value of the standard deviation of the angular distance between stars in all candidate navigation star libraries; is the average brightness (magnitude) of the stars in the th candidate navigation star library; is the maximum value of the average brightness in all candidate star libraries; is the minimum value of the average brightness in all candidate star libraries; and are the weight coefficients of the standard deviation and average brightness of the navigation star library respectively, satisfying , in this embodiment, take , .

[0088] Through the systematic screening process from step S110 to step S150 above, the optimization work of the northern hemisphere navigation stars is completed. The original star chart of the northern hemisphere navigation star distribution is as Figure 2 shown, and the screened star chart of the northern hemisphere navigation star distribution is as Figure 3 shown. The determined parameters in the process of selecting stars in the northern hemisphere: the initial value of the best minimum angular distance threshold is , the number of selected stars through radial and circumferential directions is 30, the number of supplementary stars is 15, and part of the selected northern hemisphere navigation stars are shown in Table 1:

[0089] Table 1 Part of the selected northern hemisphere navigation stars

[0090]

[0091] S160, Construction of the southern hemisphere navigation star library: Process the navigation stars in the southern hemisphere according to steps S120 to S150. The upper boundary latitude of the southern hemisphere's ring needs to be adjusted to a negative value to ensure the symmetry of the ring division, that is:

[0092] ,

[0093] Among them, is the index of the ring, is the number of rings in the southern hemisphere.

[0094] Then, the completed navigational star library of the Northern Hemisphere and the navigational star library of the Southern Hemisphere are merged to form a celestial sphere star-tracking navigational star library.

[0095] The original star chart of the navigational star distribution in the Southern Hemisphere is as Figure 4 shown, and the screened star chart of the navigational star distribution in the Southern Hemisphere is as Figure 5 shown. The determined parameters in the process of selecting stars in the Southern Hemisphere: The initial value of the optimal minimum angular distance threshold is , the number of selected stars through radial and circumferential selection is 31, the number of supplementary stars is 14, and the partially screened navigational stars in the Southern Hemisphere are shown in Table 2:

[0096] Table 2 Partially Screened Navigational Stars in the Southern Hemisphere

[0097]

[0098] Through the above steps, a celestial sphere navigational star library containing 90 navigational stars has been successfully constructed, with 45 navigational stars in each of the Northern Hemisphere and the Southern Hemisphere. The navigational stars are evenly distributed radially, and the number and distribution uniformity of the navigational stars within each ring meet the design requirements. Now, the standard deviation of the angular distance between stars and the average brightness (measured by the average magnitude value) of the original star libraries in the Northern and Southern Hemispheres and the screened navigational star library are statistically analyzed. The screened star library can be called the navigational star library. The calculation rule for the angular distance between stars in the original star libraries of the Northern and Southern Hemispheres is: Select the selected stars in the original star library, calculate the angular distance between it and the nearest neighbor star, and then calculate the standard deviation of these angular distance values. The standard deviation of the angular distance and the average brightness of the original and navigational star libraries in the Northern and Southern Hemispheres are shown in Table 3:

[0099] Table 3 Standard Deviation of Angular Distance and Average Brightness of Original and Navigational Star Libraries in the Northern and Southern Hemispheres

[0100]

[0101] As can be seen from Table 3, the standard deviation of the angular distance of the navigational star libraries in the Northern and Southern Hemispheres is significantly lower than that of the original star libraries, indicating that the inter-star distribution of the navigational star libraries is more uniform. At the same time, the average brightness of the navigational star libraries is higher, indicating that the screened navigational stars are brighter and more suitable for the navigation task.

[0102] It should be noted that the above description of the preferred embodiment is relatively detailed, and it should not be considered as a limitation to the protection scope of the present invention. Under the inspiration of the present invention, those of ordinary skill in the art can also make several improvements and refinements without departing from the scope protected by the claims of the present invention. These improvements and refinements should also be regarded as the protection scope of the present invention. The scope of protection requested by the present invention shall be subject to the appended claims.

Claims

1. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, characterized in that It includes the following steps: S110, select navigation stars that meet the detection performance of the star tracker, and separate the navigation stars located in the northern hemisphere and the southern hemisphere; S120, screen and process the navigation stars in the northern hemisphere; S130, select the optimal candidate star group in each ring in the northern hemisphere; S140, Supplementary navigation stars: Delete the dim stars with the inter-star angular distance less than the minimum angular distance and count the number of candidate stars screened in the Northern Hemisphere. If the total number is less than the expected quantity , then supplement from the remaining Northern Hemisphere navigation star library after screening; S150, dynamically generate a candidate navigation star library and select the optimal navigation star library; S160, process the navigational stars in the southern hemisphere according to steps S120 to S150, where the upper boundary latitude of the circle in the southern hemisphere is adjusted to a negative value, that is , is the index of the circle, is the number of circles in the southern hemisphere, and then merge the navigational star library in the northern hemisphere and the navigational star library in the southern hemisphere to form the navigational star library of the star tracker for the entire celestial sphere. Among them, step S120 includes: S120-1, divide the northern hemisphere celestial sphere into rings with the same width, the width of the ring , the latitude of the upper boundary of the ring , where , where represents the latitude of the upper boundary of the th 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: ， Among them, and respectively represent the upper and lower boundary latitudes of the th ring, is the number of navigation stars falling in the th ring, is the total number of navigation stars to be screened in the northern hemisphere, represents the rounding function; S120-3, fill the navigation stars whose latitudes satisfy into the ring in sequence from the outermost ring to the innermost ring; S120-4, divide each ring into sectors, and the longitude at the center of each sector , where ; S120-5, generate a candidate star group for each ring: select one best navigation star for each sector of the ring, and the best navigation stars of each sector are combined into a candidate star group.

2. The method for constructing a navigation star library of a star tracker based on the radial and circumferential directions according to claim 1, wherein, Step S110 includes: S110-1, Selection of the original star catalog: Use 2MASS as the original star catalog, select the navigation stars in the H band with wavelengths of 1.4 - 1.8 μm, and set the magnitude threshold , and filter out the navigation stars with magnitude values less than ; S110-2, divide the navigation stars into two parts, the northern hemisphere and the southern hemisphere, according to the declination: the navigation stars with declination of 0 are selected as the navigation star library for the northern hemisphere, while the navigation stars with declination of 0 are used as the navigation star library for the southern hemisphere.

3. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, characterized in that, Step S120-5 includes: S120-51, calculate the distance between the navigation star in each sector within each ring and the sector center and normalize this distance. The distance normalization formula is: ， Among them, is the right ascension of the navigation star in the current sector, in degrees (°), is the th central longitude of the th sector in the normalized distance value; S120-52, calculate and normalize the brightness of the navigation stars in each sector within each ring in turn. The brightness normalization formula is: ， Among them, is the magnitude of the navigation star, and are respectively the minimum and maximum magnitudes of the navigation stars in the current sector, is the normalized brightness value; For S120-53, one optimal navigation star is assigned to each sector. The process of obtaining the optimal navigation star includes: assigning a weight coefficient to the distance and brightness of the navigation star , calculating the navigation star score according to the following formula and determining the optimal navigation star based on this score: ， Among them, 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 movements, and the navigation star scores within the sector are recalculated after each movement; S120-55, score the candidate star group. The scoring formula is: ， Among them, is the score of the th group of candidate star groups; is the number of navigation stars in the th group of candidate star groups; and are respectively the minimum and maximum values of the number of navigation stars in all candidate star groups within the current ring; is the standard deviation of the right ascension of the navigation stars in the th group of candidate star groups; and are respectively the minimum and maximum values of the standard deviation of the right ascension in all candidate star groups within the current ring; and are respectively the weight coefficients of the number of navigation stars and the distribution uniformity, satisfying ; S120-56, select the top candidate star groups with the highest scores in each ring.

4. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, as claimed in claim 3, wherein and , m = 5.

5. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions according to claim 3, characterized in that The said step S130 includes the following steps: S130-1, directly select the candidate star group with the largest score according to the score calculated by S120-55 for the outermost ring; S130-2, for the inner ring, select an optimal candidate star group for each ring according to the principle that the average value of the minimum inter-star angular distances between the navigation stars in the current ring and the navigation stars in the previous ring is the largest.

6. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, characterized in that, Step S130-2 includes the following steps: S130-21, for each group of navigation stars within the current ring , where represents the candidate star group index within the current ring, and , is the actual number of each group of navigation stars within the current ring, ), calculate the minimum inter-star angular distance between it and all navigation stars in the previous ring , where is the number of navigation stars in the previous ring: ， Among them, the inter-satellite angular distance is calculated by the following formula: ， wherein, and are respectively and declinations; is the right ascension difference, and are respectively and right ascensions; S130-22, calculate the average value of the minimum inter-star angular distances of each group of navigation stars in the current ring: take the average value of the minimum inter-star angular distances of each group of navigation stars in the current ring; ， S130-23, select the optimal candidate star group within the current ring according to the maximum principle: 。 7. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, characterized in that, Step S140 includes: S140-1. Calculate the minimum angular separation between all stars in the filtered northern hemisphere navigation star library. If the minimum angular separation between two stars is less than the minimum angular separation threshold , then delete the dim star among them. The calculation formula for the minimum angular separation is as follows: ， Among them, and respectively represent the declinations of the th and th selected stars, and , represents the difference in right ascension between the th and th selected stars. The calculation formula is: ， and respectively represent the right ascension of the th selected star and the th selected star; S140-2, Determine whether the quantity is insufficient: If the number of selected navigation stars is less than the expected number , then enter the replenishment 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 candidate stars to the navigation star, and add it to the northern hemisphere navigation star library; S140-4, Dynamically adjust the minimum angular distance threshold: If no star that meets the comprehensive gap requirement can be found under the current minimum angular distance threshold , gradually decrease the minimum angular distance threshold and continue the search. S140-5, Loop replenishment process: Repeat steps S140-2 to S140-4 until the number of selected navigation stars reaches .

8. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, characterized in that, The said step S150 includes dynamically adjusting the initial value of the minimum angular distance threshold, repeating S140-2 to S140-4 to generate multiple candidate navigation star libraries, and selecting the optimal navigation star library through a scoring function, including the following steps: S150-1, dynamically generate a candidate navigation star library, including the following steps: S150-11, Initialize parameters: Set the initial value of the minimum angular distance threshold to , and the decreasing step size of the initial value of the minimum angular distance threshold to , and the termination value of the angular distance to ; S150-12, generate a candidate navigation star library: Each time, initialize the minimum angular distance threshold decrease and then generate a candidate navigation star library; S150-13, repeat the above steps until the initial angular distance decreases to , and a total of candidate navigation star libraries are generated; S150-2, Navigation Star Library Scoring and Optimal Selection: Set the Scoring Function , and finally select the scored candidate navigation star library with the highest score as the optimal navigation star library, and its calculation formula is: ， Among them, is the standard deviation of the angular separation between stars in the th candidate navigation star library; is the maximum value of the standard deviation of the angular separation between stars in all candidate navigation star libraries; is the minimum value of the standard deviation of the angular separation between stars in all candidate navigation star libraries; is the average brightness of the stars in the th candidate navigation star library; is the maximum value of the average brightness in all candidate star libraries; is the minimum value of the average brightness in all candidate star libraries; and are the weight coefficients of the standard deviation and the average brightness of the navigation star library respectively, satisfying .

9. A method for constructing a navigation star library of a star tracker based on radial and circumferential directions, characterized in that, During the process of screening navigational stars in the Northern Hemisphere, the initial value of the minimum angular separation threshold is ; during the process of screening navigational stars in the Southern Hemisphere, the initial value of the minimum angular separation threshold is .

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