Satellite-borne laser communication terminal on-orbit optical axis rapid calibration method

Abstract

The invention relates to a satellite-borne laser communication terminal in-orbit optical axis rapid calibration method, and aims to improve the pointing precision and stability of a satellite-borne laser communication system. According to the method, the optical axis of the laser communication terminal is quickly and accurately calibrated by comprehensively applying technical means such as coordinate system conversion, an error correction matrix, least square method optimization and a golden section method. According to the method, complex coordinate system conversion and an error correction matrix are comprehensively applied, and high-precision correction of a theoretical pointing vector is achieved; the golden section method is combined with the optimization strategy of the least square method, so that the convergence speed and precision of the calibration process are improved; higher real-time performance and automation degree are achieved, related data can be acquired and processed in real time, and real-time correction of the optical axis pointing error is achieved; the method has wide applicability and expandability, and can be applied to other spacecraft systems needing high-precision pointing control.

Description

Technical Field

[0001] The present invention belongs to the field of laser aerospace communication technology and can be applied to the on-orbit pointing error correction of space laser communication to make up for the problems of large correction error and long on-orbit calibration time in traditional on-orbit calibration methods. Specifically, it is a method for rapid on-orbit optical axis calibration of a satellite-borne laser communication terminal. Background Art

[0002] With the continuous development of satellite communication technology, the application of intersatellite services is becoming more and more extensive, showing an exponential growth trend. Free space optical communication has the advantages of high communication rate, low power consumption, and good confidentiality, making it the preferred method for long-distance intersatellite communication. Compared with traditional microwave communication, free space optical communication uses laser as the carrier of information transmission and has excellent directivity. Therefore, in order to ensure the stability and reliability of the communication link, the communication terminal needs to have high-precision pointing of the transmitted light beam.

[0003] In recent years, the field of satellite Internet has developed rapidly. With limited frequency and orbital resources, many giant Internet constellations have been planned both at home and abroad. Among them, the Starlink system of the United States plans to launch 42,000 satellites, and has launched more than 7,000 satellites so far, initially establishing a satellite communication network covering the world; Europe's OneWeb has also launched more than 600 satellites; my country has also planned multiple constellation plans, mainly including the GW constellation, the Hongyan constellation, the Xingyun Project, and the Galaxy. Among them, the China Satellite Network Group established in 2021 and the G60 Starlink released in 2023 both plan to launch more than 12,000 satellites. Intersatellite laser communication technology has the characteristics of large communication capacity, miniaturization, and low power consumption. Point-to-point on-orbit laser communication is also becoming increasingly mature, providing a new solution for the realization of satellite Internet, that is, building the next generation of satellite optical networks. Judging from the current application situation, intersatellite laser communication networking is already a general trend, and the subsequent problem to be solved is to improve the on-orbit robustness and service capabilities of laser communication links.

[0004] However, low-orbit satellite networking has factors such as long communication distance, limited signal transmission power, certain sensitivity of receiving sensors, and limited receiving aperture. The beam divergence angle is required to be tens of microradians. The small divergence angle makes terminal capture difficult, so it is necessary to accurately align the transmitting terminal with the target terminal. The laser communication terminal captures the process of pointing to the target star through the star sensor, and can calibrate the pointing deviation of the transmitting optical axis on-orbit. Finally, by correcting the terminal installation matrix, the pointing error can be reduced.

[0005] The traditional pointing calibration method uses the traversal search step method, which not only has large calibration errors and long cycles, but also requires multiple iterative calibrations, and is even more powerless when the error deviation is too large. These problems seriously restrict the efficiency of on-orbit link establishment and greatly affect the user experience. Therefore, how to quickly and accurately achieve on-orbit calibration has become a major bottleneck in the development of current satellite-borne laser communication terminal technology. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a method for rapid on-orbit optical axis calibration of a satellite-borne laser communication terminal. The method adopts a convex optimization method, is not limited by the search step length, and can achieve rapid and high-precision on-orbit calibration. It makes up for the problems of large correction error and long on-orbit calibration time in traditional on-orbit calibration methods.

[0007] The technical solution of the present invention is as follows:

[0008] A method for rapid on-orbit optical axis calibration of a satellite-borne laser communication terminal can be applied to on-orbit pointing error correction of space laser communication, making up for the problems of large correction error and long on-orbit calibration time in traditional on-orbit calibration methods, and improving the execution efficiency and success rate of space laser communication tasks. The method for rapid on-orbit optical axis calibration of a satellite-borne laser communication terminal includes the following steps:

[0009] 1) Obtain the actual pointing vector based on the motor angle values ​​of the terminal azimuth and pitch axis;

[0010] 2) Calculate the theoretical pointing vector of the terminal based on the position vectors of the host and target satellites in the J2000.0 inertial coordinate system, the attitude matrix of the host platform, and the theoretical installation matrix;

[0011] 3) Calculate the pointing errors of the azimuth and elevation of the laser communication terminal;

[0012] 4) Use the least squares optimization method to obtain the optimal installation angle correction matrix and complete the on-orbit optical axis rapid pointing calibration.

[0013] In step 1), the actual pointing vector is obtained according to the motor angle value of the terminal azimuth and pitch axis:

[0014]

[0015] Among them, Az a is the azimuth angle value in the laser communication terminal coordinate system, El a It is the pitch angle value in the laser communication terminal coordinate system. Here, it is defined that the X-axis of the terminal coordinate system is the direction of the zero position value of the azimuth and pitch motor encoder calibrated on the ground, the Z-axis is vertically upward, and the Y-axis is determined by the right-hand system direction determined by the Z-axis and the X-axis.

[0016] Step 2) According to the position vectors of the local satellite and the target satellite in the J2000.0 inertial coordinate system, the attitude matrix of the local satellite platform, and the theoretical installation matrix, the theoretical pointing vector of the terminal is calculated as follows:

[0017] 2.1 Position vector set V of the local and target satellites in the J2000.0 inertial coordinate system b and V t :

[0018]

[0019] 2.2 Based on the position vector set V of the local and target satellites in the J2000.0 inertial coordinate system b and V t Calculate the pointing vector set P of the target satellite relative to the local position:

[0020] P=V t -V b

[0021] 2.3 The attitude matrix of the local platform is R J2000_to_satellite , the attitude matrix is ​​the transformation matrix of the J2000.0 inertial coordinate system relative to the satellite body coordinate system, usually expressed in Euler angles. Assuming that the rotation angles around the X-axis, Y-axis, and Z-axis are α, β, and γ respectively, the rotation matrix is

[0022]

[0023] According to the rotation sequence of "ZXY", the attitude matrix R of the local platform is J2000_to_satellite It is expressed as:

[0024]

[0025] 2.4 Theoretical installation matrix R satellite_to_terminal , is the transformation matrix from the satellite system to the laser communication terminal coordinate system, including the transformation matrix R from the satellite system to the laser communication terminal cubic mirror (reference coordinate system) satellite_to_reference , the transformation matrix R from the laser communication terminal cubic mirror to the terminal pointing coordinate system reference_to_terminal , and the installation error correction matrix R caused by thermal deformation, etc. rectification Among them, R reference_to_terminal The calibration method is to calculate the deviation between the motor code disk value and the motor zero position value of the reflected light from the terminal mirror and the cubic mirror into the same angle cone.

[0026] R satellite_to_terminal =R rectification *R reference_to_terminal *R satellite_to_reference

[0027]

[0028] Among them, α, β, and γ are the initial theoretical pointing vector in the terminal coordinate system to the corrected theoretical pointing vector R satellite_to_terminal Rotation angles around the x-axis, y-axis, and z-axis; rot(·) is counterclockwise rotation around the axis. The calibration is completed by multiplying the obtained correction matrix with the initial theoretical installation angle matrix to finally obtain the corrected theoretical installation angle matrix.

[0029] 2.5 According to the position vectors of the local satellite and the target satellite in the J2000.0 inertial coordinate system, the attitude matrix of the local satellite platform, and the theoretical installation matrix, the theoretical pointing vector set P of the laser communication terminal is calculated. cal for

[0030]

[0031] Among them, V x 、V y 、V z It is the x, y, and z coordinate values ​​of the theoretical pointing vector of the laser communication terminal in the J2000.0 inertial coordinate system.

[0032] 3. Step 3) Calculate the pointing errors of the azimuth and elevation of the laser communication terminal as follows:

[0033] 3.1 The theoretical pointing vector set P of the laser communication terminal obtained in step 2.5 cal Substitute into the following formula to calculate the theoretical azimuth angle Az of the laser communication terminal c and the theoretical pitch angle El c

[0034]

[0035] 3.2 By changing the theoretical azimuth angle Az of the laser communication terminal c and the actual azimuth Az a The azimuth pointing error e is obtained by difference Az , the theoretical pitch angle El c and the actual pitch angle El a The difference is the pitch angle pointing error e El , and thus calculate the deviation e of azimuth and pitch aft

[0036] e Az =Az c -Az a

[0037] e El =El c -El a

[0038]

[0039] Step 4) Use the optimization method based on the least squares method to obtain the best installation angle correction matrix, and complete the on-orbit optical axis fast pointing calibration. In the calculation of the least squares method, the golden section method is used for iteration to find the optimal installation error correction matrix. This method has the advantages of a wide search range, being unrestricted by the search step size, small calibration error, and fast calibration speed. The specific steps are as follows:

[0040] The first step is to determine the initial interval. For the correction angles α, β, and γ of the installation error correction matrix R rectification in step 2.4, set the initial interval [a, b], where a is the upper boundary of the value range in degrees (°), b is the lower boundary of the value range in degrees (°), set the threshold epsilon, and the boundary values are adjustable without setting the step size.

[0041] The second step is to calculate two division points a 1 and a 2

[0042] a 1 = b - 0.618 * (b - a)

[0043] a 2 = a + 0.618 * (b - a)

[0044] The third step is to calculate the function values f(a 1 ) and f(a 2 ) at these two division points, so that the original interval is divided into three segments, where f(·) is to find the root mean square error of the deviation amounts e aft of N azimuths and pitches, and N is the number of samples in the pointing vector set.

[0045] The fourth step is to use the unimodal property of the function according to the comparison results of the function values, remove the interval segments that do not contain the extreme point, and retain the interval segments that contain the extreme point.

[0046] The fifth step is to repeat the above steps on the retained interval until the threshold condition a N - a M < epsilon is satisfied. Among them, a N and a M are the interval ranges after the i-th iteration, so as to obtain an approximate solution of the optimal correction installation angle.

[0047] Compared with the prior art, the technical effects of the present invention:

[0048] 1) The present invention compares the theoretical values ​​of the azimuth and pitch pointing angles obtained based on the theoretical values ​​of the installation matrix with the measured data to correct the installation matrix parameters. The pointing angle of the laser communication terminal is corrected by compensating for the long-term mechanical thermal deformation and ground installation errors in orbit to ensure that the target satellite is within the effective field of view of the laser communication terminal and as close to the center of the field of view as possible. The convex optimization-based method is used to find the optimal installation error correction matrix. Different from the traditional on-orbit calibration method that searches by step size, it uses a range search method, which shortens the calibration time and improves the calibration accuracy.

[0049] 2) A complex conversion process combining the laser communication terminal coordinate system, J2000.0 inertial coordinate system, satellite body coordinate system and theoretical installation matrix. By calculating the positional relationship between the host satellite and the target satellite in the J2000.0 inertial coordinate system and combining the attitude matrix of the host satellite platform, an accurate conversion from the inertial coordinate system to the satellite body coordinate system and then to the laser communication terminal coordinate system is achieved. At the same time, an installation error correction matrix including the influence of factors such as thermal deformation is introduced to achieve high-precision correction of the theoretical pointing vector and improve the accuracy of optical axis calibration.

[0050] 3) The present invention realizes the rapid calibration of the optical axis on orbit by integrating complex coordinate system conversion and error correction processes. Compared with traditional calibration methods, this method has higher real-time performance and automation. By acquiring the azimuth and pitch axis motor angle values ​​of the laser communication terminal, as well as the position information of the local and target satellites in real time, the deviation between the theoretical pointing vector and the actual pointing vector can be quickly calculated, and the installation error correction matrix can be automatically adjusted to realize real-time correction of the optical axis pointing error. This improvement in real-time performance and automation is of great significance to improving the stability and reliability of satellite-borne laser communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The present invention is a flowchart of a method for rapid on-orbit optical axis calibration of a satellite-borne laser communication terminal.

[0052] Figure 2 The invention provides a definition of the azimuth and elevation angles of a laser communication terminal in the J2000.0 inertial coordinate system of the on-orbit optical axis rapid calibration method of a satellite-borne laser communication terminal. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with implementation cases and drawings, but this should not limit the protection scope of the present invention.

[0054] See also Figure 1 , Figure 1 The present invention is a schematic flow chart of a method for rapid calibration of an optical axis of a satellite-borne laser communication terminal on-orbit. As shown in the figure, a method for rapid calibration of an optical axis of a satellite-borne laser communication terminal on-orbit comprises the following steps:

[0055] Step 1. Obtaining the actual pointing vector:

[0056] According to the motor angle values ​​of the azimuth and pitch axes of the laser communication terminal, the actual pointing vector of the terminal optical axis in the current state is calculated. The formula is as follows:

[0057]

[0058] In the formula, Az a is the azimuth angle value in the laser communication terminal coordinate system, El a It is the pitch angle value in the laser communication terminal coordinate system.

[0059] Define the terminal coordinate system to describe the azimuth, pitch, and direction of the optical axis of the terminal. In the terminal coordinate system, the X-axis is the direction in which the zero position value of the motor encoder for the azimuth and pitch calibrated on the ground points. The Z-axis is vertically upward, opposite to the direction of gravity of the earth, representing the vertical direction of the terminal. The Y-axis is determined by the Z-axis and the X-axis through the right-hand system direction.

[0060] Step 2. Calculation of theoretical pointing vector:

[0061] Calculate the theoretical pointing vector of the terminal based on the position vectors of the own satellite and the target satellite in the J2000.0 inertial coordinate system, the attitude matrix of the own satellite platform, and the theoretical installation matrix;

[0062] 2.1 Calculate the position vector set V of the local and target satellites in the J2000.0 inertial coordinate system b and V t :

[0063]

[0064] 2.2 Calculate the pointing vector set P of the target satellite relative to the local position:

[0065] P=V t -V b

[0066] 2.3 The attitude matrix of the local platform is R J2000_to_satellite , the attitude matrix is ​​the transformation matrix of the J2000.0 inertial coordinate system relative to the satellite body coordinate system, usually expressed in Euler angles. Assuming that the rotation angles around the X-axis, Y-axis, and Z-axis are α, β, and γ respectively, the rotation matrix is

[0067]

[0068] According to the rotation sequence of "ZXY", the attitude matrix R of the local platform is J2000_to_satellite It is expressed as:

[0069]

[0070] 2.4 Theoretical installation matrix R satellite_to_terminal , is the transformation matrix from the satellite system to the laser communication terminal coordinate system, including the transformation matrix R from the satellite system to the laser communication terminal cubic mirror (reference coordinate system) satellite_to_reterence , the transformation matrix R from the laser communication terminal cubic mirror to the terminal pointing coordinate system reference_to_terminal , and the installation error correction matrix R caused by thermal deformation, etc. rectification Among them, R reference_to_terminal The calibration method is to calculate the deviation between the motor code disk value and the motor zero position value of the reflected light from the terminal mirror and the cubic mirror into the same angle cone.

[0071] R satellite_to_terminal =R rectification *R reference_to_terminal *R satellite_to_reference

[0072]

[0073] Among them, α, β, and γ are the initial theoretical pointing vector in the terminal coordinate system to the corrected theoretical pointing vector R satellite_t_oterminal Rotation angles around the x-axis, y-axis, and z-axis; rot(·) is counterclockwise rotation around the axis. The calibration is completed by multiplying the obtained correction matrix with the initial theoretical installation angle matrix to finally obtain the corrected theoretical installation angle matrix.

[0074] 2.5 Calculation of the theoretical pointing vector set P of the laser communication terminal cal :

[0075]

[0076] Among them, V x 、V y 、V z It is the x, y, and z coordinate values ​​of the theoretical pointing vector of the laser communication terminal in the J2000.0 inertial coordinate system.

[0077] Step 3. Calculate the azimuth and elevation pointing errors of the laser communication terminal;

[0078] 3.1 The theoretical pointing vector set P of the laser communication terminal obtained in step 2.5 cal Substitute into the following formula to calculate the theoretical azimuth angle Az of the laser communication terminal c and the theoretical pitch angle El c

[0079]

[0080] 3.2 By changing the theoretical azimuth angle Az of the laser communication terminalc and the actual azimuth Az a The azimuth pointing error e is obtained by difference Az , the theoretical pitch angle El c and the actual pitch angle El a The difference is the pitch angle pointing error e El , thus obtaining the deviation e of azimuth and elevation aft

[0081] e Az =Az c -Az a

[0082] e El =El c -El a

[0083]

[0084] Step 4. Use the least squares optimization method to obtain the best installation angle correction matrix and complete the on-orbit optical axis rapid pointing calibration;

[0085] The golden section method is used in the calculation of the least square method to iteratively search for the optimal installation error correction matrix. This method has the advantages of a wide search range, no restrictions on the search step length, small errors after calibration, and fast calibration speed. The specific steps are as follows:

[0086] The first step is to determine the initial interval. For the installation error correction matrix R in step 2.4 rectification The correction angles α, β, and γ are used to set the initial interval [a, b], where a is the upper boundary of the value range in degrees (°), and b is the lower boundary of the value range in degrees (°). The threshold epsilon is set, and the boundary value is adjustable without setting the step size.

[0087] The second step is to calculate two segmentation points a in the interval [a, b] according to the golden ratio (0.618 and 0.382). 1 and a 2

[0088] a 1 = b-0.618*(ba)

[0089] a 2 =a+0.618*(ba)

[0090] The third step is to calculate the function value f(a) at these two split points. 1 ) and f(a 2 ) divides the original interval into three segments, where f(·) is the deviation e of N azimuths and elevations. aftThe root mean square error is , where N is the number of samples in the pointing vector set.

[0091] The fourth step is to use the unimodal property of the function to remove the interval segments that do not contain extreme points based on the comparison results of the function values, and retain the interval segments that contain extreme points.

[0092] Step 5: Repeat the above steps on the retained interval to reduce the interval infinitely until the threshold condition a is met. N -a M <epsilon. Among them, a N and a M is the interval range after the i-th iteration, thereby obtaining an approximate solution for the optimal modified installation angle.

[0093] This embodiment firstly comprehensively applies complex coordinate system transformation and error correction matrix to achieve high-precision correction of theoretical pointing vector; secondly, it adopts the optimization strategy of golden section method combined with least square method to improve the convergence speed and accuracy of calibration process; thirdly, it has higher real-time and automation level, can obtain and process relevant data in real time, and realize real-time correction of optical axis pointing error; fourthly, it has wide applicability and scalability, and can be applied to other spacecraft systems that require high-precision pointing control. The present invention provides an efficient and accurate on-orbit optical axis calibration method for satellite-borne laser communication terminals, which is of great significance for improving the performance and stability of satellite-borne laser communication systems.

Claims

1. A method for rapid on-orbit optical axis calibration of a satellite-borne laser communication terminal, characterized in that: The method comprises the following steps: Step 1. Obtaining the actual pointing vector: According to the azimuth axis motor angle value and the pitch axis motor angle value of the laser communication terminal, the actual pointing vector is calculated in the laser communication terminal coordinate system, wherein the X-axis of the laser communication terminal coordinate system is defined as the direction of the zero position value of the azimuth and pitch motor code disk calibrated on the ground, the Z-axis is vertically upward, and the Y-axis is determined by the right-hand system direction determined by the Z-axis and the X-axis; Step 2. Calculation of theoretical pointing vector: According to the position vectors of the own satellite and the target satellite in the J2000.0 inertial coordinate system, the attitude matrix of the own satellite platform and the theoretical installation matrix, the theoretical pointing vector of the laser communication terminal is calculated, including: 2.1) Obtain the position vector set of the local and target satellites in the J2000.0 inertial coordinate system; 2.2) Calculating the pointing vector set of the target satellite relative to the local position based on the position vector set; 2.3) According to the attitude matrix of the satellite platform, the position vector in the J2000.0 inertial coordinate system is converted into the position vector in the satellite body coordinate system; 2.4) Using the theoretical installation matrix, the position vector in the satellite body coordinate system is converted into the theoretical pointing vector in the laser communication terminal coordinate system; Step 3. Calculate the pointing error between the actual pointing vector of the laser communication terminal and the theoretical pointing vector, specifically including: 3.1) Convert the calculated theoretical pointing vector into a theoretical azimuth angle and a theoretical elevation angle; 3.2) Compare the theoretical azimuth angle and the theoretical elevation angle with the actual azimuth angle and the actual elevation angle of the laser communication terminal, respectively, and calculate the azimuth pointing error and the elevation pointing error; Step 4. Use the least squares optimization method to iteratively find the optimal installation error correction matrix within the set initial correction angle interval through the golden section method to minimize the pointing errors of azimuth and elevation and complete the on-orbit optical axis rapid pointing calibration, including: 4.1) Setting the initial interval and threshold of the correction angle of the installation error correction matrix; 4.2) In the initial interval, calculate two segmentation points according to the golden ratio; 4.3) Calculate the function values ​​at these two segmentation points, i.e., the root mean square errors of the N azimuth and elevation deviations; 4.4) According to the comparison result of the function value, remove the interval segments that do not contain the extreme value points, and keep the interval segments that contain the extreme value points; 4.5) Repeat the above steps on the retained interval until the threshold condition is met and an approximate solution for the optimal modified installation angle is obtained.

2. According to claim 1, the on-orbit optical axis rapid calibration method of a satellite-borne laser communication terminal is characterized in that: In step 1, the actual pointing vector is obtained based on the terminal azimuth and the motor angle value of the pitch axis: Among them, Az a is the azimuth angle value in the laser communication terminal coordinate system, El a It is the pitch angle value in the laser communication terminal coordinate system.

3. According to claim 1, the on-orbit optical axis rapid calibration method of a satellite-borne laser communication terminal is characterized in that: Step 2. The attitude matrix of the satellite platform is the transformation matrix of the J2000.0 inertial coordinate system relative to the satellite body coordinate system, expressed by Euler angles and calculated based on the rotation angles around the X-axis, Y-axis and Z-axis.

4. The on-orbit optical axis rapid calibration method of a satellite-borne laser communication terminal according to claim 1 is characterized in that: Step 2. The theoretical installation matrix includes the conversion matrix R from the satellite system to the laser communication terminal cubic mirror satellite_to_reference , the transformation matrix R from the laser communication terminal cubic mirror to the terminal pointing coordinate system reference_to_terminal , and the installation error correction matrix R caused by thermal deformation, etc. rectificacion The correction matrix is ​​obtained by calculating the deviation between the motor code disk value and the motor zero position value of the reflected light of the terminal mirror and the cubic mirror in the same angle cone, and multiplying it with the initial theoretical installation angle matrix to obtain the corrected theoretical installation angle matrix.

5. According to claim 4, the on-orbit optical axis rapid calibration method of a satellite-borne laser communication terminal is characterized in that: The corrected theoretical installation angle matrix R satellite_to_terminal Obtained through: R satellite_to_terminal =R rectification *R reference_to_terminal *R satellite_to_reference Among them, α, β, and γ are the initial theoretical pointing vector in the terminal coordinate system to the corrected theoretical pointing vector R satellite_to_terminal Rotation angles around the x-axis, y-axis, and z-axis; rot(·) is counterclockwise rotation around the axis; the calibration is completed by multiplying the correction matrix with the initial theoretical installation angle matrix to obtain the corrected theoretical installation angle matrix.

6. The on-orbit optical axis rapid calibration method of a satellite-borne laser communication terminal according to claim 1 is characterized in that: 3.1) Convert the calculated theoretical pointing vector into a theoretical azimuth angle Az c and the theoretical pitch angle El c , the formula is as follows: Where V x 、V y 、V z It is the x, y, and z coordinate values ​​of the theoretical pointing vector of the laser communication terminal in the J2000.0 inertial coordinate system.

7. The on-orbit optical axis rapid calibration method of a satellite-borne laser communication terminal according to claim 6 is characterized in that: 3.2) The theoretical azimuth angle and the theoretical elevation angle are compared with the actual azimuth angle and the actual elevation angle of the laser communication terminal, respectively, and the azimuth pointing error e is calculated. Az and the pitch angle pointing error e El , the formula is as follows: yes Az =Az c -Az a and El =The c -He a In the formula, Az c , Az a are the theoretical azimuth and actual azimuth of the laser communication terminal.

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