A starboard satellite laser terminal turntable pointing zero offset calibration method

Abstract

A starboard laser terminal turntable pointing zero offset calibration method using double star sensors.A kind of starboard laser terminal turntable pointing zero offset calibration method using double star sensors is disclosed.The invention establishes a complete attitude transfer chain model, fuses the inertial attitude data output by the platform star sensor and the terminal star sensor, constructs the measurement relative attitude of the terminal star sensor relative to the satellite platform, aligns the measurement attitude with the pre-established theoretical attitude chain model with high precision, constructs a nonlinear estimation model about the azimuth encoding angle zero offset and the pitch encoding angle zero offset of the turntable, solves the problem, autonomously estimates the azimuth and pitch zero offset values of the turntable with high precision in orbit, and finally realizes the on-orbit autonomous calibration of the turntable pointing zero offset.The whole process does not need ground intervention, effectively improves the autonomy and long-term stability of satellite pointing control.

Description

Technical Field

[0001] This invention relates to the field of spacecraft attitude measurement and pointing control technology, specifically to a zero-bias calibration method for a spaceborne laser terminal turntable using dual-star sensors. Background Technology

[0002] Spaceborne laser communication systems, as a crucial technology for high-speed information transmission in future space, possess core advantages in high bandwidth, strong anti-interference capabilities, and excellent security. However, due to the extremely narrow divergence angle of laser beams used in laser communication, the system demands extremely high pointing accuracy. Spaceborne laser terminals typically employ a "two-axis turntable + optical head" structure to achieve wide-range coarse pointing and fine tracking functions. The turntable undertakes the task of large-angle pointing adjustment, and its angular accuracy directly affects the final pointing accuracy of the optical axis.

[0003] In practical engineering applications, the azimuth and pitch angles output by the turntable encoder are not equivalent to the pointing angle of the actual optical axis in space, and there is usually a non-negligible systematic deviation. The sources of this deviation are complex, mainly including but not limited to the following aspects:

[0004] (1) Zero position error of turntable encoder: The mechanical zero position of the encoder is inconsistent with the structural zero position, or there is a slight offset during the assembly process, resulting in a fixed deviation in the overall encoding angle;

[0005] (2) Assembly error of azimuth axis and pitch axis: During the machining and assembly process, the two-axis turntable mechanism may have geometric errors such as non-orthogonality of the axes and tilt of the axes;

[0006] (3) Installation error of turntable base relative to platform: There is an attitude deviation of the turntable relative to the satellite platform, which causes the coding angle reference datum to be inconsistent with the platform coordinate system;

[0007] (4) Optomechanical installation error and coaxiality deviation: There is a slight angular error between the optical axis of the optical engine and the mechanical axis of the turntable;

[0008] (5) Effect of structural thermal deformation: The thermal expansion and contraction of the structure caused by the change of temperature in orbit leads to a slow change in the attitude chain of the turntable;

[0009] (6) Encoder resolution and nonlinear error: High-resolution encoders may still have systematic nonlinear characteristics.

[0010] The aforementioned errors will directly cause a stable deviation between the laser optical axis and the target direction, affecting the link acquisition time, stability, and link margin. Especially in scenarios such as reacquisition and rapid pointing switching, if the turntable zero offset is not accurately calibrated, the target may exceed the terminal's field of view, reducing system reliability.

[0011] In existing technologies, calibration methods for turntable pointing deviations mainly include the following categories:

[0012] (a) Ground calibration method, which involves zero-offset calibration of the turntable using precision optical measuring equipment or alignment instruments during the final assembly stage. Although this method can obtain initial calibration results, it cannot eliminate the effects of on-orbit thermal deformation and long-term drift, and it is difficult to achieve periodic updates.

[0013] (b) Target scanning method: This method uses the target position deviation to deduce the turntable zero bias by scanning stars or cooperative targets. However, this method relies on external targets, the scanning process is time-consuming, and it consumes valuable on-orbit resources.

[0014] (c) Empirical compensation or closed-loop parameter tuning method, which involves manually adjusting the compensation amount based on error performance during actual operation. This method lacks a clear geometric model to support it, making it difficult to guarantee convergence and overall attitude consistency. Summary of the Invention

[0015] To address the issues of on-orbit drift, resource dependence, and model deficiencies in existing calibration methods, this invention proposes a zero-bias calibration method for a spaceborne laser terminal turntable utilizing dual star-sensors. By establishing a complete attitude transfer chain model, the inertial attitude outputs of the platform star-sensors and the terminal star-sensors are fused, and the measured attitude of the terminal star-sensors relative to the satellite platform is constructed. Aligned with the theoretical attitude chain model, a nonlinear estimation model for the turntable's azimuth and pitch zero bias is established, thereby achieving autonomous on-orbit calibration of the turntable's pointing zero bias.

[0016] The method includes the following steps:

[0017] S1. Obtain the inertial attitude output by the platform star sensor. and the inertial attitude output by the terminal star sensor ;

[0018] S2, based on Calculate the attitude of the satellite platform ;

[0019] S3, based on and Constructing the measurement attitude of the terminal star-sensor relative to the satellite platform ;

[0020] S4. Obtain the orientation rotation angle of the turntable through the encoder of the turntable. and pitch axis rotation angle and will and Mapped to the attitude quaternion of the turntable ;

[0021] S5, based on Constructing a theoretical attitude chain model ;

[0022] S6, based on and Construction error quaternion and will Convert to a three-dimensional small-angle residual vector ;

[0023] S7, Collection The attitude data of the turntable is for... Construct the least squares objective function;

[0024] S8. Solve the least squares objective function constructed in step S7 by Gauss-Newton iteration to obtain the zero bias value with the smallest residual;

[0025] S9. Add the zero-bias value with the smallest residual to the encoder output of the turntable to complete the zero-bias calibration.

[0026] further, ,in, This refers to quaternion multiplication. Let be the installation quaternion of the platform star sensor relative to the satellite platform, where This is a conjugate operation.

[0027] further, .

[0028] Furthermore, the aforementioned and Mapped to the attitude quaternion of the turntable Specifically: ,in, for Quaternions, for Quaternions.

[0029] Furthermore, the theoretical attitude chain model Specifically:

[0030] ,in, The quaternion for the installation of the terminal star sensor relative to the onboard laser terminal optical head. For the coordinate system of the spaceborne laser terminal optical head, The mounting quaternion for the spaceborne laser terminal optical engine head relative to the turntable. Let be the mounting quaternion of the turntable relative to its base. For the first The true attitude quaternion of the turntable corresponding to each valid data point. For the first The azimuth rotation angle of the turntable corresponding to each valid data point. To achieve zero azimuth of the turntable, For the first The pitch and rotation angle of the turntable corresponding to each valid data point. To achieve zero pitch deviation for the turntable, The mounting quaternion of the turntable base relative to the turntable.

[0031] Furthermore, error quaternions The formula for calculation is: ;

[0032] 3D small-angle residual vector The formula for calculation is: ,in, Extract operators for the vector part of quaternions.

[0033] Furthermore, the least squares objective function is specifically as follows: ,in, For norm operations, the unknowns of the least squares objective function .

[0034] Furthermore, the method is implemented through a zero-bias calibration device, which includes: a spaceborne laser terminal main control unit, a turntable, a terminal star sensor, a turntable base, a platform star sensor, a spaceborne laser terminal optical engine head, and a satellite platform;

[0035] The turntable base is fixed to the satellite platform;

[0036] The turntable is mounted on the turntable base;

[0037] Both the spaceborne laser terminal optical head and the terminal star sensor are mounted on the turntable, which is used to drive the spaceborne laser terminal optical head and the terminal star sensor to rotate synchronously.

[0038] The platform's star sensor is installed on a satellite platform;

[0039] The main control unit of the spaceborne laser terminal is connected to the turntable, platform star sensor and terminal star sensor signals respectively.

[0040] The beneficial effects of the method described in this invention are as follows:

[0041] (1) This invention simultaneously acquires the quaternion of the satellite platform star-sensor output attitude and the quaternion of the terminal star-sensor output attitude. By installing the quaternion on the satellite platform star-sensor, the attitude of the satellite platform relative to the inertial frame is reconstructed, thereby further constructing the relative measurement attitude of the terminal star-sensor relative to the satellite platform. All measurements are formed entirely by the output attitude of the two star-sensors relative to the inertial frame, and are independent of external cooperative targets, ground targets, or orbital target points, thereby achieving autonomous on-orbit calibration of the terminal.

[0042] (2) This invention establishes a complete theoretical attitude chain model including installation and kinematic terms, and uses error quaternions to align the "measurement chain" and "model chain" in a closed loop; then it maps them to small-angle residuals to form optimizable geometric consistency constraints. These constraints directly correspond to the physical assembly and turntable zero-bias parameters, and the model has a clear meaning and strong interpretability, avoiding reliance on experience compensation or manual parameter tuning.

[0043] (3) This invention collects different turntable pointing angles and corresponding dual-star sensitive attitude outputs at multiple times, stacks the three-dimensional residuals at each time into the overall residuals, and constructs the Jacobian matrix to form an overdetermined least squares problem. By covering multiple attitudes, the parameter correlation is reduced and the unobservability under a single attitude is weakened, making the estimation results less sensitive to noise and local errors, thereby improving robustness and calibration accuracy.

[0044] (4) This invention unifies the parameters to be estimated in vector form and solves them through a unified framework of error quaternion-small angle residual-least square iteration. Therefore, when it is necessary to further calibrate errors such as base installation error, terminal star sensor / optical-mechanical coaxial deviation, or axis non-orthogonality, it is only necessary to introduce the corresponding parameterized form into the theoretical model and extend it to complete the joint estimation under the same solution process, which has good scalability and engineering adaptability. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method described in this invention;

[0046] Figure 2 This is a schematic diagram of the device described in this invention;

[0047] Among them, 1-the main control unit of the spaceborne laser terminal, 2-the turntable, 3-the terminal star sensor, 4-the turntable base, 5-the platform star sensor, 6-the spaceborne laser terminal optical head, and 7-the satellite platform. Detailed Implementation

[0048] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Example 1

[0050] This embodiment provides a zero-bias calibration method for a spaceborne laser terminal turntable using dual-star sensors.

[0051] Existing methods lack unified geometric closed-loop constraints in the inertial reference frame, making it difficult to achieve consistent calibration under multiple attitudes and operating conditions. They also fail to fully utilize existing dual-star sensitive attitude measurement resources, resulting in unclear coupling between calibration results and actual geometric relationships, insufficient engineering interpretability, strong dependence on external targets, and inadequate real-time performance and autonomy.

[0052] On the other hand, modern spaceborne laser terminals typically possess two sets of attitude measurement units: a platform star-sensor for measuring the attitude of the satellite platform in inertial space, and a terminal coaxial star-sensor for measuring the attitude of the laser terminal's optical head in inertial space. Both sets of star-sensors output attitude quaternions relative to the same inertial coordinate system (J2000 system), thus theoretically forming a natural inertial geometric closed-loop relationship. However, current technology lacks a systematic method that unifies and integrates the "dual-star-sensor attitude output" with the "turntable kinematic model" and directly applies it to turntable zero-bias estimation.

[0053] Therefore, this invention proposes a turntable zero-bias calibration method driven by geometric consistency constraints. By establishing a complete attitude transfer chain model, the measured relative attitude of the terminal star sensor to the satellite platform is constructed in inertial space and aligned with the theoretical model to form a nonlinear least squares estimation problem, thereby enabling on-orbit autonomous and high-precision estimation of the turntable azimuth and pitch coding angle zero bias.

[0054] The flowchart of the method is as follows: Figure 1 As shown, the method includes the following steps:

[0055] S1. Obtain the inertial attitude output by the platform's StarSense 5. and the inertial attitude output by the terminal star sensor 3 ;

[0056] The relevant operations in step S1 will be introduced with specific examples:

[0057] Before performing zero-bias calibration, this embodiment sets the coordinate system and quaternions as follows:

[0058] Define quaternions Indicates from the same vector From the coordinate system To coordinate system The rotation satisfies:

[0059] (1)

[0060] in, This represents a mapping operator from quaternions to rotation matrices, used to transform quaternions... Convert to coordinate system To coordinate system The rotation matrix. Representing vectors In coordinate system The coordinates below, Representing vectors In coordinate system The coordinates below.

[0061] Quaternion composition uses:

[0062] (2)

[0063] When quaternion When it is a unit quaternion, its inverse quaternion It is equal to its conjugate quaternion :

[0064] (3)

[0065] The coordinate system and quaternion settings avoid ambiguity in link direction, left / right multiplication, and sign, enabling attitude transfer between coordinate systems to be directly achieved by quaternion multiplication and providing a consistent mathematical basis for the subsequent construction of error quaternions and small-angle residuals.

[0066] In this embodiment, the coordinate system To coordinate system It has no actual physical meaning and refers to the coordinate system that needs to be calculated in this embodiment, such as the coordinate system of platform star sensor 5. Inertial coordinate system and the coordinate system of the terminal star sensor 3 wait.

[0067] and Similarly, in this embodiment, it has no actual physical meaning and is used as a parameter medium to introduce the chain relationship of the rotation matrix.

[0068] In this embodiment, the inertial attitude output by the platform star sensor 5 The data is shown in Table 1:

[0069] Table 1

[0070]

[0071] S2, based on Solving the attitude of the satellite platform (7 positions) ;

[0072] The relevant operations in step S2 will be introduced with specific examples:

[0073] The installation quaternion for platform StarSense 5 relative to satellite platform 7 is:

[0074] ,in, Represents the inertial reference coordinate system (J2000 system). Indicates the coordinate system of satellite platform 7. This indicates the coordinate system of the StarSense 5 platform. The first synchronous output for the platform StarSense 5 and the terminal StarSense 3 One valid data point, For the coordinate system of platform StarSense 5, there is the following rotation matrix chain relationship:

[0075] (4)

[0076] in, Representing an inertial coordinate system To the platform star-sensitive 5 coordinate system The rotation matrix, Indicates coordinate system from satellite platform 7 To the platform star-sensitive 5 coordinate system The rotation matrix, Indicates from the inertial coordinate system To the satellite platform 7 coordinate system The rotation matrix.

[0077] The corresponding quaternion composition relation is:

[0078] (5)

[0079] To restore the platform's coordinate attitude from the star-aware coordinate attitude, it is necessary to multiply both sides of equation (5) by the left. , Represents quaternions To find the conjugate, use the inverse rotation of the quaternion to transform the expression in equation (5). The platform's star-sensor 5 outputs attitude from the star-sensor coordinate system. Restored to the body coordinate system of satellite platform 7 The platform attitude reference is obtained in accordance with the installation relationship of the turntable base 4:

[0080] (6)

[0081] S3, based on and Constructing the measurement attitude of terminal star-sensor 3 relative to satellite platform 7 ;

[0082] The relevant operations in step S3 will be introduced with specific examples:

[0083] Terminal StarSense 3 outputs attitude data As shown in Table 2, among which, The coordinate system representing terminal star sensor 3 is defined by the rotation matrix:

[0084] (7)

[0085] in, Representing an inertial coordinate system To the terminal star-sensitive 3 coordinate system The rotation matrix, Indicates coordinate system from satellite platform 7 to inertial coordinate system The rotation matrix, This indicates the coordinate system of the platform star-aware 5 coordinate system. To the terminal star-sensitive 3 coordinate system The rotation matrix.

[0086] Table 2

[0087]

[0088] From the satellite platform coordinate system 7 to inertial coordinate system rotation matrix With from the inertial coordinate system To the satellite platform 7 coordinate system rotation matrix The following relationship exists:

[0089] = (8)

[0090] in, express The transpose of .

[0091] The corresponding quaternion composition relation is:

[0092] (9)

[0093] in, Quaternions Find the conjugate.

[0094] Therefore, the attitude of terminal star-sensor 3 relative to satellite platform 7 is obtained. for:

[0095] (10)

[0096] S4. Obtain the orientation rotation angle of turntable 2 through the encoder of turntable 2. and pitch axis rotation angle and will and Mapped to the attitude quaternion of turntable 2 ;

[0097] The relevant operations in step S4 will be introduced with specific examples:

[0098] The two-axis turntable 2 adopts a kinematic structure that first azimuth and then pitch, with the azimuth axis rotating around the Z-axis and the pitch axis rotating around the Y-axis.

[0099] When the engineering definition of orientation is positive by clockwise rotation, and maintaining a right-handed coordinate system, the sign of the orientation rotation angle should be: Upward tilt is the norm. .

[0100] Define rotational quaternions about the azimuth axis respectively. and rotational quaternions about the pitch axis for:

[0101] (11)

[0102] in, and These are the selected coordinate systems. shaft and The unit vector of the axis, i.e. , .

[0103] The rotational quaternion of the optical axis of turntable 2 relative to turntable base 4 is:

[0104] (12)

[0105] For the quaternion of the rotation axis angle:

[0106] (13)

[0107] in, The unit vector representing the axis of rotation. , , , These are the three components of the rotation axis in the 4-coordinate system of the turntable base. This represents the angle of rotation around the axis of rotation according to the right-hand rule in the 4-coordinate system of the turntable base.

[0108] This step maps the encoder angle (including zero bias) to the turntable 2 attitude quaternions, ensuring that the signs and rotation order are consistent with the mechanism definition. This avoids model deviations caused by inconsistencies between the azimuth angle definition and the right-handed system, ensuring that the calibration residuals originate from the true zero bias.

[0109] S5, based on Constructing a theoretical attitude chain model ;

[0110] The relevant operations in step S5 will be introduced with specific examples:

[0111] This embodiment defines the following installation quaternion:

[0112] The installation quaternion of terminal star sensor 3 relative to the spaceborne laser terminal optical head 6:

[0113] ;

[0114] Mounting quaternion of spaceborne laser terminal optical head 6 relative to turntable 2:

[0115] ;

[0116] Mounting quaternions of turntable base 4 relative to satellite platform 7:

[0117] .

[0118] Mounting quaternion of turntable 2 relative to turntable base 4: , Solve using formula (15), and according to Further solution and .

[0119] Turntable 2 outputs the actual azimuth and pitch angles as follows: and The values ​​are provided by the encoder, as shown in Tables 1 and 2. However, there is a zero offset in the azimuth to be estimated. and pitch zero bias Therefore, the true values ​​of the azimuth and pitch angles output by turntable 2 are expressed as: , The relationship is as follows:

[0120] (14)

[0121] Therefore, the theoretical model of the attitude of terminal star-sensor 3 relative to satellite platform 7 is as follows:

[0122] (15)

[0123] For the first The true attitude quaternion of turntable 2 corresponding to each valid data point.

[0124] Given the turntable 2 angle and zero-bias parameters, predict the attitude of the terminal star sensor 3 relative to the satellite platform 7 for consistent alignment with the measured relative attitude. Explicitly parameterize the complex installation effects and decouple them from the turntable kinematics, giving the zero-bias estimation a clear physical meaning and allowing direct application to engineering compensation.

[0125] S6, based on and Construction error quaternion and will Convert to a three-dimensional small-angle residual vector ;

[0126] The relevant operations in step S6 will be introduced with specific examples:

[0127] Construction error quaternion:

[0128] (16)

[0129] When the model Correct, azimuth zero deviation. and pitch zero bias When correct:

[0130] (17)

[0131] For small rotations Quaternion approximation:

[0132] (18)

[0133] in, , , These are the attitude error vectors. Orbiting in the 7 coordinate system of the satellite platform , and The minute rotational components of the shaft, It is the field of real numbers.

[0134] Therefore, the first The small angle error vector of the attitude corresponding to the set of data for:

[0135] (19)

[0136] in, This represents the quaternion vector part extraction operator, for quaternions , .

[0137] attitude error Convert to a three-dimensional small-angle residual vector Facilitates the construction of least squares optimization. Three-dimensional small-angle residual vector. Represented as:

[0138] (20)

[0139] The unit is radians.

[0140] S7, Collection The attitude data of turntable 2 is for... Construct the least squares objective function;

[0141] The relevant operations in step S7 will be introduced with specific examples:

[0142] This embodiment collects 8 ( ) sets of different pose data, for Construct the least squares objective function;

[0143] (twenty one)

[0144] Among the unknowns:

[0145] (twenty two)

[0146] Given initial values Selecting multiple sets of attitude data helps improve geometric observability and suppress the impact of single-time noise and random errors on zero-bias estimation.

[0147] S8. Solve the least squares objective function constructed in step S7 by Gauss-Newton iteration to obtain the zero bias value with the smallest residual;

[0148] The relevant operations in step S8 will be introduced with specific examples:

[0149] The residual function (least square objective function) is used in the current estimate Perform a first-order Taylor expansion at this point:

[0150] (twenty three)

[0151] in, The current iteration point The residual at the location, Given the current Jacobian matrix, The first-order change in residuals caused by parameter variations. For the first Parameter estimates at the next iteration for Compared to The parameter increment satisfies .

[0152] Among them, the Jacobian matrix For partial derivatives:

[0153] (twenty four)

[0154] Substituting into least squares, we obtain the normal equation:

[0155] (25)

[0156] To enhance numerical stability, damping is added:

[0157] (26)

[0158] in, Let be the damping coefficient, and take . , It is the identity matrix, used to improve solution stability and suppress parameter update step size when the nonlinearity is strong.

[0159] renew:

[0160] (27)

[0161] Output after iterative convergence:

[0162] (28)

[0163] A total of 12 iterations were performed before convergence. The final estimation result (the zero-bias value with the smallest residual) is as follows: Azimuth zero-bias estimation result. Pitch zero bias estimation results Iterative outputs allow calibration results to be updated periodically according to task requirements, adapting to structural thermal deformation and long-term drift.

[0164] S9. Add the zero-bias value with the smallest residual to the encoder output of turntable 2 to complete the zero-bias calibration.

[0165] The relevant operations in step S9 will be introduced with specific examples:

[0166] The zero offset output from the calibration is used to correct the encoder of turntable 2. The corrected azimuth and pitch angles are as follows:

[0167] (29)

[0168] (30)

[0169] This is the azimuth rotation angle after zero-offset calibration. The pitch and rotation angle after zero-bias calibration.

[0170] In this embodiment, both the platform star-sensor 5 coordinate system and the terminal star-sensor 3 coordinate system are right-handed rectangular coordinate systems fixed to the star-sensor body. The origin is the center of the equivalent entrance pupil of the star-sensor optical system, the direction of the star-sensor optical axis is the +Z axis of the platform star-sensor 5 coordinate system, and the other two axes are determined in the image plane of the star-sensor detector according to the right-hand rule, thus forming a right-handed coordinate system.

[0171] The coordinate system of satellite platform 7 is a right-handed rectangular coordinate system fixed to the structure of satellite platform 7. Its origin is the centroid of satellite platform 7, the +X axis points to the direction of satellite flight, and the +Y axis points to the right. The coordinate system P of satellite platform 7 serves as the common installation reference coordinate system for all payloads and turntable base equipment in this application.

[0172] Example 2

[0173] This embodiment further defines Embodiment 1. This embodiment provides a zero-bias calibration device for implementing the method described in Embodiment 1, such as... Figure 2 As shown, the device includes: a spaceborne laser terminal main control unit 1, a turntable 2, a terminal star sensor 3, a turntable base 4, a platform star sensor 5, a spaceborne laser terminal optical head 6, and a satellite platform 7.

[0174] The turntable base 4 is fixed on the satellite platform 7;

[0175] Turntable 2 is mounted on turntable base 4;

[0176] The spaceborne laser terminal optical head 6 and the terminal star sensor 3 are both mounted on the turntable 2, and the turntable 2 is used to drive the spaceborne laser terminal optical head 6 and the terminal star sensor 3 to rotate synchronously.

[0177] Platform StarSense 5 is installed on satellite platform 7;

[0178] The main control unit 1 of the spaceborne laser terminal is connected to the turntable 2, the platform star sensor 5 and the terminal star sensor 3 respectively.

[0179] The main control unit 1 of the spaceborne laser terminal is used to collect the actual azimuth and pitch angle of the turntable 2, the output data of the platform star sensor 5, and the output data of the terminal star sensor 3, and to calculate the zero deviation calibration of the turntable (steps S1-9 in Example 1 are all completed on the main control unit 1 of the spaceborne laser terminal).

[0180] Turntable 2 is used to drive the rotation of the onboard laser terminal optical head 6 and the terminal star sensor 3.

[0181] Terminal Star 3 is used to output the attitude quaternion data of Terminal Star 3 relative to the J2000 series.

[0182] The turntable base 4 is used to fix the turntable 2 and the satellite platform 7.

[0183] Platform Star 5 is used to output the attitude quaternion of Platform Star 5 relative to the J2000 series.

[0184] The spaceborne laser terminal optical head 6 is used to receive laser signals.

[0185] Satellite platform 7 is used to carry and install turntable 2, onboard laser terminal, and platform star sensor 5.

[0186] The operating parameters of the device shown are as follows:

[0187] The data acquisition frequency of the main control unit 1 of the spaceborne laser terminal is 10Hz, and the calculation frequency is 4Hz.

[0188] The azimuth axis of the turntable rotates from 0 degrees to 180 degrees, and the pitch axis rotates from -20 degrees to 20 degrees.

[0189] The terminal star sensor 3 has a solar avoidance angle of 35 degrees, an earth-atmosphere-light avoidance angle of 35 degrees, and a three-axis attitude measurement accuracy of 3 arcseconds, 3 arcseconds, and 25 arcseconds.

[0190] The platform's StarSense 5 has a solar avoidance angle of 35 degrees, an terrestrial-atmosphere avoidance angle of 35 degrees, and a three-axis attitude measurement accuracy of 3 arcseconds, 3 arcseconds, and 25 arcseconds.

Claims

1. A method for zero-bias calibration of a spaceborne laser terminal turntable using dual-star sensors, characterized in that, The method includes the following steps: S1. Obtain the inertial attitude output by the platform star sensor (5). and the inertial attitude output by the terminal star sensor (3) ; S2, based on Calculate the attitude of the satellite platform (7) ; S3, based on and Construct the measurement attitude of the terminal star sensor (3) relative to the satellite platform (7) ; S4. Obtain the orientation rotation angle of the turntable (2) through the encoder of the turntable (2). and pitch axis rotation angle and will and Mapped to the attitude quaternion of the turntable (2) ; S5, based on Constructing a theoretical attitude chain model ; S6, based on and Construction error quaternion and will Convert to a three-dimensional small-angle residual vector ; S7, Collection The attitude data of the turntable (2) is for Construct the least squares objective function; S8. Solve the least squares objective function constructed in step S7 by Gauss-Newton iteration to obtain the zero bias value with the smallest residual; S9. Add the zero bias value with the smallest residual to the encoder output of the turntable (2) to complete the zero bias calibration.

2. The zero-offset calibration method for a spaceborne laser terminal turntable using dual-star sensors according to claim 1, characterized in that, ,in, This refers to quaternion multiplication. The installation quaternion of the platform star sensor (5) relative to the satellite platform (7), where, This is a conjugate operation.

3. The zero-offset calibration method for a spaceborne laser terminal turntable using dual-star sensors according to claim 2, characterized in that, 。 4. The zero-offset calibration method for a spaceborne laser terminal turntable using dual-star sensors according to claim 3, characterized in that, The and Mapped to the attitude quaternion of the turntable (2) Specifically: ,in, for Quaternions, for Quaternions.

5. The zero-offset calibration method for a spaceborne laser terminal turntable using dual-star sensors according to claim 4, characterized in that, The theoretical attitude chain model Specifically: ,in, The installation quaternion of the terminal star sensor (3) relative to the onboard laser terminal optical head (6) is given. Let be the coordinate system of the spaceborne laser terminal optical head (6). The mounting quaternion for the spaceborne laser terminal optical head (6) relative to the turntable (2) is given. The mounting quaternion of the turntable (2) relative to the turntable base (4), For the first The true attitude quaternion of the turntable (2) corresponding to each valid data point, For the first The azimuth rotation angle of the turntable (2) corresponding to each valid data point. For the azimuth zero offset of turntable (2), For the first The pitch and rotation angle of the turntable (2) corresponding to each valid data point. For the pitch zero bias of the turntable (2), The mounting quaternion of the turntable base (4) relative to the turntable (2).

6. The zero-offset calibration method for a spaceborne laser terminal turntable using dual-star sensors according to claim 5, characterized in that, Error Quaternion The formula for calculation is: ; 3D small-angle residual vector The formula for calculation is: ,in, Extract operators for the vector part of quaternions.

7. The zero-offset calibration method for a spaceborne laser terminal turntable using dual-star sensors according to claim 6, characterized in that, The least squares objective function is specifically as follows: ,in, For norm operations, the unknowns of the least squares objective function .

8. The zero-offset calibration method for a spaceborne laser terminal turntable using dual-star sensors according to claim 7, characterized in that, The method is implemented by a zero-bias calibration device, which includes: a spaceborne laser terminal main control unit (1), a turntable (2), a terminal star sensor (3), a turntable base (4), a platform star sensor (5), a spaceborne laser terminal optical head (6), and a satellite platform (7). The turntable base (4) is fixed on the satellite platform (7); The turntable (2) is mounted on the turntable base (4); The spaceborne laser terminal optical head (6) and the terminal star sensor (3) are both mounted on the turntable (2), and the turntable (2) is used to drive the spaceborne laser terminal optical head (6) and the terminal star sensor (3) to rotate synchronously. The platform star sensor (5) is installed on the satellite platform (7); The main control unit (1) of the spaceborne laser terminal is connected to the turntable (2), the platform star sensor (5) and the terminal star sensor (3) respectively.

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