Celestial navigation method based on optical angle measurement of space targets under altitude constraints

Abstract

The present invention discloses an astronomical navigation method based on optical angle measurement of space targets under altitude-constrained conditions. This method utilizes an optical imaging system to simultaneously observe satellites and stars, performs attitude calculations based on star observation information, and utilizes altitude constraints combined with the satellite's directional vector information to complete positioning. This method significantly reduces reliance on multiple observations or multi-star observations through single optical observations and directional measurements of a single satellite, simplifying measurement procedures, improving efficiency and data availability, while lowering equipment accuracy requirements and contributing to cost reductions. The present invention is suitable for shipborne applications and can provide a reliable, economical, and efficient navigation and positioning solution for dynamic platforms in complex electromagnetic environments.

Description

Technical Field

[0001] The present invention relates to a celestial navigation method in the field of navigation and positioning, in particular to a celestial navigation method based on optical angle measurement of space targets under altitude limitation conditions. Background Art

[0002] High-precision navigation and positioning information is essential for platforms such as spacecraft, aircraft, missiles, and ships to perform various missions. Satellite navigation is currently the most efficient means of achieving high-precision navigation. However, in complex electromagnetic environments, satellite navigation systems are susceptible to interference or spoofing. Providing fully autonomous, high-precision positioning information to moving vehicles in satellite-denied conditions is a key technical challenge that urgently needs to be addressed in the navigation field.

[0003] Astronomical navigation achieves positioning by observing the directional information of celestial bodies such as stars and the sun, combined with horizontal reference information. In theory, the error does not diverge over time. It has been successfully applied on various platforms such as aircraft, ships, and missiles, and has become a navigation guarantee method in satellite denial conditions. However, traditional astronomical navigation uses stars as navigation beacons. To achieve positioning, it is necessary to use the horizontal attitude reference information provided by the inertial navigation system to convert the direction vector of the star into altitude information for positioning. Due to the initial error of inertial navigation, the error of inertial devices, and the error of the axis system, the horizontal attitude error will be introduced into the positioning result. Without other external information to assist, it is difficult to suppress this error.

[0004] To overcome celestial navigation's reliance on inertial navigation's horizontal attitude information, existing technologies have proposed an angles-only navigation method. This method uses optical observations of three or more satellites to achieve positioning, significantly improving celestial navigation accuracy. However, this method requires simultaneous observation of multiple satellites, or multiple observations of the same satellite. However, observations from ship platforms are susceptible to cloud and fog interference, resulting in poor satellite visibility. Consequently, the availability and real-time nature of navigation information are limited, limiting its application in low-altitude areas.

[0005] How to reduce the requirements for astronomical target observation, simplify the measurement steps, improve data availability and thus enhance positioning accuracy is a technical issue that technical personnel in this field are concerned about. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and adopt space targets determined by orbits such as satellites, space stations, space debris or rocket debris as navigation beacons, to provide an astronomical navigation method based on optical angle measurement of space targets under altitude-limited conditions, thereby improving navigation positioning accuracy and data availability.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: a celestial navigation method based on optical angle measurement of space targets under altitude constraints, comprising the following steps:

[0008] S1. Calculate the coordinates of the space target and select the space target that meets the observation pitch angle threshold;

[0009] S2. Predict the magnitude of the space target selected in step S1, select a navigation space target based on the magnitude, and if there is a navigation space target that meets the conditions, proceed to step S3; otherwise, return to step S1;

[0010] S3. Adjust the optical axis of the optical imaging system to point to the navigation space target, and trigger the camera to expose the image;

[0011] S4, extracting the navigation space target and all the stars in the field of view from the captured star map, and using the star point image coordinate information to calculate the attitude of the optical imaging system;

[0012] S5. Recalculate the current coordinates of the navigation space target according to the camera triggering moment, complete the positioning solution using the space target coordinates and the camera attitude, and obtain the local position coordinates.

[0013] The present invention can realize navigation solution through only one space target measurement, so the requirements for observation conditions are relatively low, which can effectively simplify the measurement steps, improve the measurement efficiency and data availability.

[0014] In step S2, the magnitude of the space target m cs_k The calculation formula is:

[0015]

[0016] Among them, α represents the geometric reflectivity of the space target, R SAT Indicates the radius of the space target, d SS Indicates the distance between the sun and the space target, d PS Represents the distance between the observation point and the space target, ρ ⊙ is the solar phase angle, h SAT is the space target height.

[0017] The specific implementation process of the present invention for selecting navigation space targets according to star magnitude includes: screening out all space targets whose star magnitude is lower than a detection threshold magnitude as candidate navigation space targets, and selecting the space target with the lowest magnitude among the candidate navigation space targets as the navigation space target.

[0018] In step S2, before predicting the magnitude of the space target, the following steps are further included: determining whether the space target is blocked by the earth's shadow; if not, predicting the magnitude of the space target; if so, returning to step S1; wherein, when the direction vector of the space target and the direction vector of the sun meet When , it is considered that the space target is not blocked by the earth's shadow, R is the average radius of the earth, represents the jth space target in the set of space targets that meets the observation pitch angle threshold, A unit vector representing the direction of sunlight incident on the Earth.

[0019] In step S4, if the navigation space target cannot be successfully extracted, the process returns to step S3.

[0020] In step S5, the coordinates of the observation point in the earth-fixed coordinate system e are The calculation is done as follows:

[0021]

[0022] in, l is the space target position vector length, R is the average radius of the Earth, R N is the Earth's equatorial radius, is the direction vector of the sight line of the space target in the geographic coordinate system, f is the focal length of the camera, (u0, v0) is the physical coordinate of the camera's principal point, (u s ,v s ) is the center of mass coordinate of the space target on the image, θ is the position vector of the space target and sight direction The angle between H is the altitude of the observation carrier, is the posture of the optical imaging system.

[0023] As an inventive concept, the present invention also provides a celestial navigation system based on optical angle measurement of space targets under altitude constraints, including a memory, a processor and a computer program stored in the memory; the processor executes the computer program to implement the steps of the above method.

[0024] As an inventive concept, the present invention also provides a celestial navigation system based on optical angle measurement of space targets under altitude constraints, comprising:

[0025] Optical imaging systems for imaging space objects and stars;

[0026] A dual-axis turntable comprises a base, an azimuth rotation mechanism and a pitch rotation mechanism; the pitch rotation mechanism is mounted on the azimuth rotation mechanism, and the azimuth rotation mechanism is mounted on the base; the optical imaging system is mounted on the pitch rotation mechanism;

[0027] Inertial measurement unit, used to provide attitude information of the base;

[0028] Time synchronization equipment is used to provide the UTC time information required for navigation solutions and the time synchronization pulse for data collection of various measurement and control equipment;

[0029] A data processing unit communicates with the optical imaging system, the dual-axis turntable, the inertial measurement unit, and the timing equipment, and implements celestial navigation solutions using the steps of the above method;

[0030] The dual-axis turntable, inertial measurement unit, time system equipment and data processing unit are all installed on the measurement carrier.

[0031] In the present invention, the field of view angle of the optical imaging system ranges from 5° to 30°.

[0032] In the present invention, the verticality error between the azimuth rotation axis and the pitch rotation axis of the dual-axis turntable should be less than 0.1°. When the pitch rotation axis and the azimuth rotation axis of the dual-axis turntable are both at zero position, the parallelism between the optical axis of the optical imaging system and the azimuth rotation axis of the dual-axis turntable is better than 1°.

[0033] Compared with the prior art, the present invention has the following beneficial effects: the present invention provides an astronomical navigation solution that does not rely on high-precision horizontal reference information, and positioning can be achieved only through astronomical observation through an optical imaging system; the dual-axis turntable and inertial measurement unit required by the present invention are only used to provide rough measurement and control of the optical axis pointing of the optical imaging system, and have low requirements on the accuracy of the equipment, which is beneficial to reducing the hardware cost of the equipment; the present invention can achieve navigation solution through only one space target measurement, so the requirements for observation conditions are relatively low, which can effectively simplify the measurement steps, improve measurement efficiency and data availability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of a celestial navigation device based on optical angle measurement of space targets according to an embodiment of the present invention;

[0035] Figure 2 This is the coordinate definition of the celestial navigation device and method based on optical angle measurement of space targets in an embodiment of the present invention;

[0036] Figure 3 This is an algorithm flow chart of a celestial navigation method based on optical angle measurement of space targets according to an embodiment of the present invention;

[0037] Figure 4 It is a schematic diagram of the principle of a celestial navigation positioning solution method based on optical angle measurement of space targets according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the following uses a satellite in a space target as a navigation beacon as an example, combined with the accompanying drawings, to clearly and completely illustrate the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] Embodiment 1 of the present invention provides a celestial navigation device, such as Figure 1 As shown, the celestial navigation device includes an optical imaging system 1, a dual-axis turntable 2, an inertial measurement unit 3, a data processing computer 4 and a time synchronization device 5.

[0041] like Figure 2 As shown, the optical imaging system includes a camera 101 and an optical lens 102, which are used to image satellites and stars. A typical optical imaging system can adopt a visible light band optical imaging system or a near-infrared enhanced optical imaging system. The optical system should have an appropriate field of view angle, generally ranging from 5° to 30°. The optical imaging system selected in the embodiment of the present invention is a visible light band optical imaging system, and the field of view angle of the optical imaging system is 14°. The camera can be a scientific-grade or industrial-grade camera. A preferred solution is a scientific-grade camera. The selected camera can use a CMOS image sensor or a CCD image sensor.

[0042] The dual-axis turntable includes a turntable base 201, an azimuth rotation mechanism 202, and a pitch rotation mechanism 203. The pitch rotation mechanism is mounted on the azimuth rotation mechanism, with the azimuth and pitch rotation axes mounted approximately perpendicularly. A general-purpose shelf product can be used for the dual-axis turntable. In this embodiment, it is recommended that the perpendicularity error between the azimuth and pitch rotation axes be less than 0.1°.

[0043] The optical imaging system is fixedly mounted on the pitch rotation mechanism. When both rotation mechanisms of the dual-axis turntable are at their zero positions, the optical axis of the optical imaging system is approximately parallel to the azimuth rotation axis of the dual-axis turntable. The dual-axis turntable is used to control the pointing direction of the optical axis of the optical imaging system, aligning it with the target satellite during astronomical observations. In this embodiment, the optical imaging system preferably has an angular deviation of no more than 1° between the optical axis and the azimuth rotation axis of the dual-axis turntable when both the pitch and azimuth axes are at their zero positions.

[0044] The inertial measurement unit (IMU) is used to provide attitude information for the measurement turntable base. This IMU can be a laser gyro IMU, a fiber optic gyro IMU, or a MEMS IMU. Fiber optic gyro IMUs are preferred for cost and accuracy. In another embodiment, an IMU may not be required, and instead a navigation device on the measurement vehicle may be used to provide attitude and rough position information for the measurement vehicle.

[0045] The timing device is used to provide the UTC time information required for navigation solutions and the second pulse for synchronization of data acquisition by various measurement and control devices. This timing device can be a B-code terminal, an atomic clock, or other timing device. In another embodiment, a timing device is not required, and instead a universal timing device installed on the measurement carrier provides time and second pulse information for the celestial navigation device.

[0046] The data processing computer is used for data acquisition from the optical imaging system, motion control of the dual-axis turntable, data acquisition from the inertial measurement unit, and astronomical navigation solutions. This data processing computer can be a general-purpose computer, an embedded computer, or other data processing device. It requires strong computing power and must be configured with corresponding communication interfaces based on the data interfaces of the optical imaging system and the inertial measurement unit to achieve camera image acquisition and inertial navigation data collection.

[0047] The dual-axis turntable and inertial measurement unit are both fixedly mounted on the measurement carrier 6. The time tracking equipment and data processing computer are preferably mounted on the measurement carrier using shock absorbers. The measurement carrier can be a ship, vehicle, aircraft, or other vehicle. In this embodiment, a ship is used as the measurement carrier.

[0048] Figure 2 Define the coordinate system of the dual-axis turntable base as b system O b -X b Y b Z b , define the coordinate system of the optical imaging system as s system O s -X s Y s Z s , define the coordinate system of the turntable surface as t system O t -X t Y t Z t , the Earth-centered Earth-fixed coordinate system (ECEF) is the e system O e -X e Y e Z e , local horizontal coordinate system n system O n -X n Y nZ n (Using the Northeast Celestial coordinate system), the inertial measurement unit coordinate system is rigidly connected to the turntable base.

[0049] The method of the embodiment of the present invention is now further introduced based on a specific embodiment. Figure 3 The overall flow chart of the measurement method of the present invention is as follows:

[0050] Step 1: Calculate the current coordinates of all satellites in the navigation satellite database based on their orbital parameters and time information. Filter out satellites that are above the horizontal plane of the observation carrier and whose pitch angles are greater than the observation pitch angle threshold based on the satellite's spatial coordinates and the rough position information of the measurement carrier.

[0051] 1.1 According to the orbital parameters and time information of the satellites in the navigation satellite database, calculate the current time t k The coordinates of all satellites in the star library in the Earth-fixed coordinate system The navigation satellite star library consists of navigation satellite orbital parameters pre-stored in a data processing computer. A preferred satellite orbital parameter format is the Two-Line Element (TLE) format published by the North American Aerospace Defense Command (NORAD). The navigation satellite star library can be downloaded from the US Space-Track website. The real-time satellite position can be calculated using the Simplified General Perturbations 4 (SGP4) model. David A. Vallado's 2006 paper, "Revisiting Spacetrack Report #3," outlines the specific implementation of this algorithm.

[0052] 1.2 According to the satellite's spatial coordinates and the rough longitude of the measurement carrier latitude and height information (with error), filter out satellites that are above the horizontal plane of the measurement carrier and whose pitch angle is higher than the observation pitch angle threshold. The specific calculation method is:

[0053] First calculate the direction of the satellite relative to the observer's line of sight k=1,2,…,N, where N is the total number of satellites in the navigation satellite database, and the unit vector of the line of sight is further calculated: To measure the coordinates of the rough position of the carrier in the e system (i.e. the position coordinates with errors), we can use The conversion calculation is performed using the WGS-84 coordinate system standard method. are the rough longitude, latitude and elevation of the observation point respectively.

[0054] From this, we can calculate the vector n in the local horizontal coordinate system in It is obtained by local calculation, and the calculation method is as follows:

[0055]

[0056] Satellite elevation angle is greater than the critical value γ min , the observation line of sight requirement can be met:

[0057]

[0058] Wherein, the subscript z represents the vector In n series Z n Axis projection.

[0059] Satellites that meet the above observation requirements are denoted as

[0060] Step 2: Predict the magnitudes of the satellites selected in step 1, arrange the satellite magnitudes from low to high, and select satellites with magnitudes above the magnitude threshold as candidate navigation stars for observation. If there are no satellites that meet the magnitude threshold requirements, return to step 1:

[0061] 2.1 First, determine whether the satellite selected in step 1 is in the Earth's shadow. The determination method is as follows:

[0062] The unit vector of the incident direction of sunlight hitting the earth is denoted by This calculation can be performed using the method published in Andreas A.'s 2003 paper, "Solar Position Algorithm for Solar Radiation Application." When the satellite's direction vector and the sun's direction vector satisfy the following relationship, the satellite is considered unobstructed by the Earth's shadow. Otherwise, it is obstructed by the Earth's shadow.

[0063]

[0064] Where R is the average radius of the Earth.

[0065] 2.2 For satellites not obscured by the Earth's shadow, the following method is used to calculate the satellite magnitude:

[0066]

[0067] The second term is related to the physical properties of the satellite itself, α represents the geometric reflectivity of the satellite, and R SAT Indicates the radius of the satellite; d in the third term SSrepresents the distance between the sun and the satellite, d PS represents the distance between the observation point and the satellite, ρ ⊙ is the solar phase angle (the angle between the sun and the satellite line of sight), h SAT is the satellite height. Typically for Starlink satellites, α can be 0.2, R SAT It is approximately taken as 1m.

[0068] The apparent magnitude of the satellite's brightness obscured by the Earth's shadow is set to m cs_k =20.0 or greater.

[0069] 2.3 All satellites whose magnitude is lower than the detection threshold are selected as candidate navigation stars. The candidate navigation stars are arranged in order from low to high magnitude, and the satellite with the lowest magnitude is selected as the target navigation star.

[0070] Determine whether the satellite meets m cs_k <m TH , m TH is the detection threshold magnitude. The satellite that meets the threshold condition is selected as the navigation target star. The coordinates of the navigation target star are marked as Its magnitude is recorded as m ns . m TH It is generally selected based on the magnitude of the detection instrument of the optical imaging system and combined with the observation conditions. Typically, the threshold magnitude can be selected as 6th magnitude.

[0071] 2.4 If there is no navigation target star that meets the conditions, return to step 1.

[0072] Step 3: Calculate the direction vector of the satellite in the turntable base coordinate system based on the coordinates of the target navigation star selected in step 2, the attitude information of the measurement carrier, and the rough position information. Control the azimuth rotation mechanism and pitch rotation mechanism of the dual-axis turntable to point the optical axis of the optical imaging system toward the target satellite. Trigger the camera to capture images of the target satellite and the stars in the field of view, and record the camera triggering moment.

[0073] 3.1 According to the target navigation star coordinates selected in step 2 Measuring carrier's posture information and coarse location information Calculate the direction vector of the satellite in the turntable base coordinate system. The specific calculation method is as follows:

[0074]

[0075] where x b ,y b ,z b for Components in three directions.

[0076] 3.2 Control the azimuth and elevation rotation mechanisms of the dual-axis turntable so that the optical axis of the optical imaging system points toward the target satellite. The rotation angles of the azimuth and elevation rotation mechanisms of the dual-axis turntable are calculated as follows:

[0077]

[0078] 3.3 After the azimuth and elevation rotation mechanisms of the dual-axis turntable are rotated to the target angles, the data processing computer controls the camera to trigger the exposure and image the navigation target star. This can be triggered once or multiple times continuously. The image captured by each camera trigger is acquired and the exposure trigger time is recorded as t trig .

[0079] Step 4: Extract the target satellite and all stars in the field of view from the captured star map. Use the extracted star point image coordinates to calculate the optical imaging system's attitude. If the target satellite cannot be successfully extracted, return to Step 3 and track the next satellite with a higher magnitude. If the target satellite is successfully extracted, proceed to Step 5.

[0080] 4.1 First, process the captured star image to obtain the attitude matrix of the optical imaging system The data processing process can be implemented using the common data processing methods in star sensor technology. For specific data processing methods, please refer to the monograph "APS CMOS Star Sensor System Principle and Implementation Method" published by the National Defense Industry Press in 2017. trig Recalculate T=t trig +t expo / 2 The coordinates of the navigation target star in the Earth coordinate system at this moment t expo is the camera exposure time. The calculation method is the same as described in step 1.1.

[0081] 4.3 Using the Posture Matrix of the Optical Imaging System and the coordinates of the navigation target satellite in the Earth coordinate system Estimate the coordinates of the navigation satellite in the image coordinate system, and record the estimated coordinates of the navigation satellite in the image coordinate system as The specific estimation method is as follows:

[0082] First, calculate the direction vector of the navigation satellite's line of sight at the moment the camera is triggered in the coordinate system of the optical imaging system:

[0083] Then the camera imaging model is used to estimate the coordinates of the navigation satellite in the image coordinate system:

[0084]

[0085] Where (u0, v0) is the physical coordinate of the camera principal point, and f is the focal length of the camera. These parameters can be provided by the optical imaging system manufacturer or calibrated in advance.

[0086] 4.4 Estimated coordinates of navigation satellite in image coordinate system As the center, a small extraction window is selected, and the method described in the patent "A star point extraction algorithm adapted to stray light interference" (application number CN202310656893.4) ​​is used to extract the position deviation (δu s ,δv s ). Finally, calculate the centroid coordinates of the satellite in the entire image (u s ,v s ):

[0087]

[0088] If the target satellite cannot be successfully extracted, return to step 1; if the target satellite is successfully extracted, go to step 5.

[0089] Step 5: Use satellite coordinates and camera attitude to complete positioning solution and obtain local position coordinates. The calculation principle is as follows Figure 4 The specific calculation method is as follows:

[0090] First, the distance from the water level corresponding to the observation point to the center of the earth is calculated based on the rough latitude information of the observation carrier. The calculation method is:

[0091]

[0092] Where R is the average radius of the Earth, R N is the equatorial radius of the Earth.

[0093] Then obtain the altitude information H of the observation carrier. For an observer at sea level, H≈0. For other land or aircraft carriers, the altitude can be measured by an absolute barometric altimeter. The distance from the observer to the center of the earth is R e +H.

[0094] Calculate the direction vector of the satellite line of sight in the geographic coordinate system

[0095]

[0096] Where f is the focal length of the camera, (u0, v0) is the physical coordinate of the camera's principal point, (u s ,v s ) is the centroid coordinate of the satellite on the image.

[0097] Satellite position vector and sight direction It is known that the angle θ between the two vectors is determined as follows:

[0098]

[0099] Where l is length.

[0100] Solve the d between the satellite and the observation point by the following method PS :

[0101]

[0102] In the earth-fixed coordinate system e, the earth-fixed coordinate system coordinate expression of the observation point is:

[0103]

[0104] Step 6: Determine whether the command to end measurement is received. If so, end navigation; otherwise, jump to step 1.

[0105] Example 2

[0106] Embodiment 2 of the present invention provides a terminal device corresponding to the above-mentioned embodiment 1. The terminal device can be a processing device for a client, such as an embedded computing device, a laptop computer, a mobile phone, a desktop computer, etc., to execute the method of the above-mentioned embodiment.

[0107] The terminal device of this embodiment includes a memory, a processor, and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method in the above-mentioned embodiment 1.

[0108] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk storage.

[0109] In other implementations, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors, which are not limited herein.

[0110] Example 3

[0111] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to the above-mentioned embodiment 1, on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method of the above-mentioned embodiment 1 are implemented.

[0112] Computer readable storage media can be tangible devices that hold and store instructions used by instruction execution devices. Computer readable storage media can be, for example, but not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any combination thereof.

[0113] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiment of the present application can be implemented in various computer languages, for example, object-oriented programming language C++ and literal translation scripting language JavaScript, etc.

[0114] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0115] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0116] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0117] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A celestial navigation method based on optical angle measurement of space targets under altitude constraints, characterized in that: The following steps are involved: S1. Calculate the coordinates of the space target and select the space target that meets the observation pitch angle threshold; S2. Predict the magnitude of the space target selected in step S1, select a navigation space target based on the magnitude, and if there is a navigation space target that meets the conditions, proceed to step S3; otherwise, return to step S1; S3. Adjust the optical axis of the optical imaging system to point to the navigation space target, and trigger the camera to expose the image; S4, extracting the navigation space target and all the stars in the field of view from the captured star map, and using the star point image coordinate information to calculate the attitude of the optical imaging system; S5. Recalculate the current coordinates of the navigation space target according to the camera triggering moment, complete the positioning solution using the space target coordinates and the camera attitude, and obtain the local position coordinates; Coordinates of the observation point in the earth-fixed coordinate system e The calculation is done as follows: ； in, , l is the length of the space target position vector, , R is the average radius of the Earth, R N is the Earth's equatorial radius, is the direction vector of the sight line of the space target in the geographic coordinate system, , f is the camera focal length, is the physical coordinate of the camera principal point, is the center of mass coordinate of the space target on the image, is the space target position vector and sight direction The angle between , H is the altitude of the observation carrier, is the posture of the optical imaging system, is the distance from the level surface corresponding to the observation point to the center of the earth, Latitude information.

2. The celestial navigation method based on optical angle measurement of space targets under altitude constraints according to claim 1, characterized in that: In step S2, the magnitude of the space target The calculation formula is: ； in, represents the geometric reflectivity of the space target, represents the radius of the space target, represents the distance between the sun and the space target, Represents the distance between the observation point and the space target, is the solar phase angle, is the space target height.

3. The celestial navigation method based on optical angle measurement of space targets under altitude constraints according to claim 1 or 2, characterized in that: The specific implementation process of selecting navigation space targets according to star magnitude includes: screening out all space targets whose star magnitude is lower than the detection threshold magnitude as candidate navigation space targets, and selecting the space target with the lowest star magnitude among the candidate navigation space targets as the navigation space target.

4. The celestial navigation method based on optical angle measurement of space targets under altitude constraints according to claim 1, characterized in that: In step S2, before predicting the magnitude of the space target, the following steps are further included: determining whether the space target is blocked by the earth's shadow; if not, predicting the magnitude of the space target; if so, returning to step S1; wherein, when the direction vector of the space target and the direction vector of the sun meet When , it is considered that the space target is not blocked by the earth's shadow, R is the average radius of the earth, represents the jth space target in the set of space targets that meets the observation pitch angle threshold, A unit vector representing the direction of sunlight incident on the Earth.

5. The celestial navigation method based on optical angle measurement of space targets under altitude constraints according to claim 1, characterized in that: In step S4, if the navigation space target cannot be successfully extracted, the process returns to step S3.

6. A celestial navigation system based on optical angle measurement of space targets under altitude constraints, comprising a memory, a processor, and a computer program stored in the memory; characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 5.

7. A celestial navigation system based on optical angle measurement of space targets under altitude constraints, characterized in that: include: Optical imaging systems for imaging space objects and stars; A dual-axis turntable, comprising a base, an azimuth rotation mechanism, and a pitch rotation mechanism; The pitch rotation mechanism is mounted on the azimuth rotation mechanism, and the azimuth rotation mechanism is mounted on the base; The optical imaging system is installed on the pitch rotation mechanism; Inertial measurement unit, used to provide attitude information of the base; Time synchronization equipment is used to provide the UTC time information required for navigation solutions and the time synchronization pulse for data collection of various measurement and control equipment; a data processing unit, communicating with the optical imaging system, the dual-axis turntable, the inertial measurement unit, and the timing equipment, and implementing celestial navigation solution by using the steps of the method according to any one of claims 1 to 5; The dual-axis turntable, inertial measurement unit, time system equipment and data processing unit are all installed on the measurement carrier.

8. The system according to claim 7, characterized in that The field of view angle of the optical imaging system ranges from 5° to 30°.

9. The system according to claim 7, wherein: The verticality error between the azimuth rotation axis and the pitch rotation axis of the dual-axis turntable is less than 0.1°. When the pitch rotation axis and the azimuth rotation axis of the dual-axis turntable are both at zero position, the angular deviation between the optical axis of the optical imaging system and the azimuth rotation axis of the dual-axis turntable is no more than 1°.

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