Construction and broadcasting method and system of space-based inertial reference frame based on beidou MEO satellite

Abstract

The application discloses a method and system for constructing and broadcasting a space-based inertial reference frame based on Beidou MEO satellites, which first acquires the positions of each satellite in the Beidou MEO satellite constellation in the earth-centered inertial coordinate system, and determines the baseline unit direction vector, then selects several groups of satellite pairs, generates a redundant baseline set, divides it into three groups of direction clusters according to the direction similarity, and selects a main direction representative vector in each group, constructs a reference frame, then determines the reference frame attitude parameters based on the main direction representative vector, and broadcasts the reference frame attitude parameters, time tags, validity periods and satellite pair identifiers in real time at a preset update period, finally, the observations are uniformly transformed into the reference frame, and joint orbit determination is performed. The method solves the frame alignment problem of angle measurement, angle interference and inter-satellite ranging in multi-source fusion, reduces the error accumulation in algebraic transformation, and effectively improves the horizontal accuracy of earth-moon space orbit determination.

Description

Technical Field

[0001] This invention relates to the field of satellite navigation and space geodesy technology, and in particular to a method and system for constructing and broadcasting a space-based inertial reference frame based on the BeiDou MEO satellite. Background Technology

[0002] Lunar orbit determination and deep space tracking missions require high consistency with the reference frame, especially angle measurement and ΔDOR / VLBI angle observation missions, which are extremely sensitive to reference frame errors. Existing technologies typically require multi-level coordinate transformations between the station-centered coordinate system, the geocentric-Earth-fixed coordinate system, and the geocentric-inertial coordinate system, relying on Earth Orientation Parameters (EOP), the time system, and the reference frame alignment model. The precession-nutation model errors, EOP prediction errors, and frame connection residuals involved in these multi-level transformations enter the orbit determination calculation as "reference errors." In angle-based observations, this manifests primarily as a significant amplification of orbit determination errors in the lateral direction, i.e., in directions intersecting the orbit.

[0003] On the other hand, Earth-Moon missions are often accompanied by non-angular observation tasks such as inter-satellite ranging and Doppler observations. If there is no unified inertial reference frame for angular and inter-satellite observations, the geometric inconsistency between the two types of observations will lead to frame alignment errors during observation fusion, making weight configuration difficult, reducing filter convergence speed, and decreasing solution stability.

[0004] In traditional methods, VLBI (Vacuum-Low Biological Interference) technology establishes a celestial reference frame by observing extragalactic radio sources, such as ICRF3, achieving directional accuracy on the microarcsecond scale. However, VLBI networks are sparse and reliant on ground infrastructure, making it impossible to provide real-time reference frame services for spacecraft in orbit. Star sensors can determine attitude reference directions in orbit, but their accuracy is limited by factors such as poor star catalog systems, optical distortion, and thermal deformation. Establishing an inertial direction reference using the ultra-long baselines of satellite navigation constellations is a potential approach that balances coverage, update rate, and directional accuracy. Summary of the Invention

[0005] To address some or all of the problems in existing technologies, and in order to reduce the impact of frame alignment errors on orbit determination calculations and improve the accuracy of orbit determination in Earth-Moon space, the first aspect of this invention provides a method for constructing and broadcasting a space-based inertial reference frame based on BeiDou MEO satellites, comprising: Obtain the position of each satellite in the BeiDou MEO satellite constellation in the geocentric inertial coordinate system and determine the baseline unit direction vector; Several satellite pairs are selected to generate a redundant baseline set. These are then divided into three directional clusters based on directional similarity. In each cluster, a principal directional representative vector is selected to construct a reference frame. The reference frame attitude parameters are determined based on the principal direction representative vector. The reference frame attitude parameters, time stamps, validity period, and satellite pair identifiers are broadcast in real time at a preset update cycle.

[0006] Furthermore, the number of satellite pairs selected is 4 to 6 groups.

[0007] Furthermore, several satellite pairs were selected, including: The objective function is determined with the goal of maximizing the baseline length and minimizing the direction angle uncertainty. Determine constraints to avoid the redundant baseline set from being nearly coplanar or nearly collinear; Satellite pairs are selected based on the objective function.

[0008] Furthermore, the objective function is expressed as: , Where N is the number of selected satellite pairs. Let i be the mass weight of the i-th satellite pair. The position accuracy of the poorly aligned satellites in the i-th group of satellites, and Let be the baseline length of the i-th satellite pair.

[0009] Furthermore, the direction vector with the largest baseline length and the highest quality weight in each direction cluster is taken as the representative vector of the main direction.

[0010] Further, determining the reference frame attitude parameters based on the principal direction representative vector includes: The main direction representative vector is orthogonalized to obtain the rotation matrix of the reference frame attitude.

[0011] Furthermore, the orthogonalization process includes: Gram-Schmidt orthogonalization, or vector cross product normalization, or least squares orthogonalization under orthogonal constraints.

[0012] Furthermore, the preset update cycle is 1 to 10 minutes.

[0013] Furthermore, the reference frame attitude parameters, time stamps, validity period, and satellite pair identifiers are broadcast in real time via the BeiDou short message communication link.

[0014] Furthermore, the construction and broadcasting method also includes: Abnormal satellite pairs are deleted through a consistency self-check.

[0015] Furthermore, the construction and broadcasting method also includes: Based on the statistical analysis of the included angle residuals using consistency detection, combined with the baseline length and satellite position accuracy, the uncertainty of the reference frame attitude parameters is estimated, and incremental correction sequences and covariance refinement sequences of the attitude parameters are generated.

[0016] Based on the construction and broadcasting method described above, a second aspect of the present invention provides a construction and broadcasting system for a space-based inertial reference frame based on a BeiDou MEO satellite, comprising: The data acquisition module is used to acquire BeiDou MEO satellite orbital status information, time synchronization information, and quality indicators; The satellite pair screening module is used to select satellite pairs to form a redundant baseline set; The direction calculation and grouping module is used to divide the redundant baseline set into three direction clusters according to the direction similarity, and select a main direction representative vector in each group; The orthogonalization and uncertainty estimation module is used to determine the reference frame attitude parameters based on the principal direction representative vector. The broadcast and refinement product module is used to broadcast reference frame attitude parameters, time stamps, expiration dates, and satellite pair identifiers in real time at preset update cycles.

[0017] Furthermore, the orthogonalization and uncertainty estimation module is also used to delete abnormal satellite pairs through consistency self-check, and estimate the uncertainty of the reference frame attitude parameters based on the angle residual statistics of consistency detection, combined with the baseline length and satellite position accuracy.

[0018] Furthermore, the broadcast and refinement product module is also used to generate incremental correction sequences and covariance refinement sequences for attitude parameters.

[0019] This invention discloses a method and system for constructing and broadcasting a space-based inertial reference frame based on BeiDou MEO satellites. The system employs a structure with several redundant directions divided into three groups of direction clusters, enabling the reference frame to isolate single-point faults and eliminating reliance on a single baseline, thus improving system reliability and robustness. The reference frame is constructed based on BeiDou MEO satellites. The ultra-long baseline of 30,000 to 50,000 kilometers generated by the orbital plane difference of BeiDou MEO satellites can convert decimeter-level orbital errors into nanoradian-level directional stability, thereby providing a space-based inertial reference comparable to ICRF3. The method ultimately outputs a strictly orthogonal rotation matrix or quaternion and provides minute-level updates, making it suitable for online real-time calculations for spacecraft. It also provides post-processing refinement products to meet the high-precision requirements of scientific research. The method and system for constructing and broadcasting the space-based inertial reference frame completely solves the frame alignment problem in multi-source fusion of angle measurement, angle interferometry, and inter-satellite ranging, reducing error accumulation in algebraic transformations and effectively improving the lateral accuracy of Earth-Moon orbit determination. Attached Figure Description

[0020] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the various embodiments of the present invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0021] Figure 1 This diagram illustrates a process flow of a method for constructing and broadcasting a space-based inertial reference frame based on a BeiDou MEO satellite, according to an embodiment of the present invention. Figure 2 This diagram illustrates the spatial configuration of a space-based inertial reference frame according to an embodiment of the present invention. Figure 3 This diagram illustrates the structure of a space-based inertial reference frame construction and broadcasting system based on the BeiDou MEO satellite, according to an embodiment of the present invention. Detailed Implementation

[0022] In the following description, the invention is described with reference to various embodiments. However, those skilled in the art will recognize that the embodiments may be practiced without one or more specific details or with other alternatives and / or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail so as not to obscure the inventive points of the invention. Similarly, for illustrative purposes, specific quantities, materials, and configurations are set forth to provide a comprehensive understanding of embodiments of the invention. However, the invention is not limited to these specific details. Furthermore, it should be understood that the embodiments shown in the drawings are illustrative representations and are not necessarily drawn to scale.

[0023] In this specification, references to "an embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. The phrase "in one embodiment" appearing throughout this specification does not necessarily refer to the same embodiment in all instances.

[0024] It should be noted that the embodiments of the present invention describe the process steps in a specific order; however, this is only for illustrating the specific embodiment and not for limiting the order of the steps. On the contrary, in different embodiments of the present invention, the order of the steps can be adjusted according to the process.

[0025] The BeiDou MEO satellite constellation consists of 24 medium Earth orbit satellites at an altitude of approximately 21,528 km and an orbital period of approximately 12.9 hours. The baseline length between any two MEO satellites in different orbital planes can reach over 30,000 km, with the longest being approximately 50,000 km. Meanwhile, the uncertainty in the baseline orientation angle... Approximately inversely proportional to the baseline length: ,in This is the root mean square value of the satellite position error. This is the baseline length. When using precise ephemeris, At 40,000 km, It is approximately 0.05m, which is on the order of decimeters. It reaches the nanoradian level (nrad), or submicroarcsecond level, when broadcast ephemeris is used. At 40,000 km, Approximately 1m It can be seen that the accuracy of the BeiDou MEO ultra-long baseline is sufficient to construct a high-precision inertial orientation reference. Based on this, this invention provides a method for constructing and broadcasting a space-based inertial reference frame based on the BeiDou MEO satellite ultra-long baseline. Utilizing the 30,000 to 50,000 km ultra-long baseline generated by the orbital plane difference of the BeiDou MEO satellites, it transforms decimeter-level orbital errors into nanoradian-level directional stability, providing a space-based inertial reference comparable to ICRF3. This solves the frame alignment problem for observations such as angle measurement, angle interferometry, and inter-satellite ranging during multi-source fusion, reduces error accumulation in algebraic transformations, and improves the lateral accuracy of Earth-Moon orbit determination.

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings of the embodiments.

[0027] Figure 1 This diagram illustrates a flowchart of a method for constructing and broadcasting a space-based inertial reference frame based on a BeiDou MEO satellite, according to an embodiment of the present invention. Figure 1 As shown, a method for constructing and broadcasting a space-based inertial reference frame based on BeiDou MEO satellites includes: First, in step 101, space-based data and baseline direction calculation are performed. The orbital status, time synchronization information, and mass identifiers of each satellite in the BeiDou MEO satellite constellation are acquired, and the baseline unit direction vector is determined. In one embodiment of the invention, a designated primary satellite or management satellite acquires the orbital status information and mass identifiers of each MEO satellite via inter-satellite links or ground injection. The orbital status information can be obtained using real-time available broadcast ephemeris, or post-hoc available precise ephemeris with an accuracy better than 5 cm, or an orbital solution obtained by fusing both. Simultaneously, at least one of the following is acquired as time synchronization information: constellation time reference, inter-satellite time transfer information, or ground-injected time correction information.

[0028] For ease of subsequent calculations, the position vectors of each satellite at observation epoch t are uniformly represented in the J2000.0 epoch geocentric inertial coordinate system. For example, the position vectors of satellites A and B in the geocentric inertial system are denoted as follows: , , The baseline vector for satellite pair (A, B) is then: , The baseline length is: , The baseline unit direction vector is: ; Next, in step 102, satellite pairs are selected and grouped. Several groups of satellite pairs are selected to generate a redundant baseline set, which is then divided into three directional clusters based on directional similarity. A principal direction representative vector is selected from each cluster to construct a reference frame. In one embodiment of the invention, the number of selected satellite pairs is 4 to 6. In one embodiment of the invention, the objective function is determined with the goal of maximizing baseline length and minimizing directional uncertainty. Geometric distribution constraints are also set to avoid the redundant baseline set from being nearly coplanar or nearly collinear, ensuring the linear independence of the selected directional set. In one embodiment of the invention, the objective function is expressed as: , Where N is the number of selected satellite pairs. The mass weight of the i-th satellite pair is determined based on the mass identifier. The position accuracy of the poorly aligned satellites in the i-th group of satellites, and Let be the baseline length of the i-th satellite pair. The constraints are as follows: Any two candidate baseline direction vectors and The included angle between them is It should meet or ,in It is a linearly independent threshold, with a value ranging from 15° to 30°.

[0029] After filtering, the resulting N baseline unit direction vectors are divided into three direction clusters {C} based on direction similarity. X C Y C Z In one embodiment of the present invention, a threshold criterion is used for grouping; specifically, for direction vectors... , If the angle between the two They are then grouped into the same directional cluster, among which The threshold value is 15° to 45° within the cluster. This method ensures that the three directional clusters approximately correspond to three independent directions in space.

[0030] Then, within each directional cluster, the directional vector with the longest baseline length and the best quality label is selected as the principal directional representative vector, denoted as u. X u Y u Z The remaining direction vectors serve as redundancy check vectors. For example, when selecting 6 satellite pairs, each of the three direction clusters contains 2 direction vectors, with one vector representing the main direction and one serving as a redundancy check vector in each cluster; when selecting 5 satellite pairs, two direction clusters each contain 2 directions, and the other cluster contains 1 direction. The redundancy check vectors are used for subsequent consistency self-checks and fault isolation. Next, in step 103, the reference frame attitude parameters are determined. The reference frame attitude parameters are determined based on the principal direction representative vector. In one embodiment of the invention, the principal direction representative vector u... X u Y u Z Orthogonalization is performed to obtain a strictly right-handed orthogonal basis. This refers to the rotation matrix of the reference frame's attitude. The orthogonalization process can employ Gram-Schmidt orthogonalization, vector cross product normalization, or least-squares orthogonalization under orthogonal constraints. Gram-Schmidt orthogonalization first selects the principal direction with the longest baseline length as the representative vector. Assuming the direction of the first axis for ,but The second principal direction represents the vector. Remove Projection components of direction The second axis direction is obtained by normalization. Finally, the cross product forms the third axis of the right-hand orthogonal basis. Then the rotation matrix of the reference frame attitude It can be seen that It is a 3x3 orthogonal matrix that satisfies and Equivalently, it can be Convert to quaternion representation ,in For the scalar part, satisfying Quaternion representation avoids gimbal lock in numerical computation and has fewer parameters, making it suitable for broadcast transmission. The vector cross product normalization method is similar to Gram-Schmidt orthogonalization; it first selects the principal direction with the longest baseline length as the first axis direction, assuming it is... ,but Then determine the direction of the third axis. Finally, the cross product forms the second axis of the right-hand orthogonal basis. The least-squares orthogonalization method under orthogonal constraints involves simultaneously fitting three representative vectors and minimizing... Make the output as close as possible to all representative vectors.

[0031] To ensure that the generated inertial coordinate system frame is not affected by single-point failures, in one embodiment of the present invention, after orthogonalization is completed, step 104 is performed to remove abnormal satellite pairs.

[0032] In step 104, abnormal satellite pairs are removed. Abnormal satellite pairs are removed through a consistency self-check. In one embodiment of the invention, a redundancy check vector is used for the consistency self-check. For the first... Redundancy check vectors in group direction clusters Calculate its relationship with the corresponding axial direction. The residual angle between them: , when Exceeding the preset residual threshold When determining the redundancy check vector The corresponding satellite pair exhibits anomalies and is therefore isolated. In one embodiment of the present invention, The value ranges from 0.001° to 0.1°, and the specific value can be dynamically adjusted based on the baseline length and satellite position accuracy. When the principal direction representative vector is in the same direction cluster... When an anomaly is detected, switch to the redundant test vector that is not isolated within the same cluster and re-perform orthogonalization.

[0033] In order to provide a precise ephemeris that is usable after the fact and has an accuracy better than 5 cm, in one embodiment of the present invention, step 105 is also performed to determine the uncertainty.

[0034] In step 105, the uncertainty is determined. Based on the angular residual statistics and combined with baseline length and satellite position accuracy information, the uncertainty of the reference frame attitude parameters is estimated. In one embodiment of the present invention, the uncertainty can be expressed as a covariance matrix, a diagonal approximation covariance, or a quality level factor. The covariance matrix form refers to a 3×3 covariance matrix constructed using the direction angle uncertainties of the three axes. diagonal elements Off-diagonal elements are determined by residual cross-statistics. The diagonal approximate covariance form refers to taking only... The diagonal elements, i.e., the uncertainties of the three axial direction angles. , , The quality level factor form converts uncertainty into discrete levels, such as 1-5, to facilitate broadcast transmission under bandwidth-constrained conditions.

[0035] It should be understood that, in some specific embodiments, steps 104 and 105 may be omitted, and only a broadcast ephemeris that can be used in real time may be generated.

[0036] Finally, in step 106, broadcasting is performed. The reference frame attitude parameters, timestamps, validity periods, and satellite pair identifiers are broadcast in real-time at a preset update cycle. In one embodiment of the invention, the broadcast is performed at a minute-level update cycle, for example, any cycle from 1 to 10 minutes. The reference frame attitude parameters include a rotation matrix R or a quaternion q, the timestamp refers to the reference epoch timestamp, and the satellite pair identifier refers to the PRN number pair. In one embodiment of the invention, when consistency checks and uncertainty calculations are performed, the broadcast content further includes uncertainty and redundancy verification information. In one embodiment of the invention, broadcasting is achieved through a BeiDou short message communication link.

[0037] In one embodiment of the invention, a post-processing refinement correction product is further generated based on the uncertainty, including an incremental correction sequence for the real-time attitude parameters. or and covariance refinement sequence Post-processing refinement has lower real-time performance but higher accuracy. It utilizes more precise ephemeris data, longer data arcs over longer time spans, and more refined force models to recalculate baseline orientation, thereby achieving reference frame accuracy superior to real-time products. In one embodiment of the invention, the post-processing refinement correction product is published via SMS broadcast and / or ground product documentation; After receiving the aforementioned broadcast reference frame attitude parameters R or q and uncertainty information, the ground control center and / or the Earth-Moon probe transform all types of observations to the inertial reference frame for expression. In one embodiment of the present invention, the observations mainly include angular measurements, ΔDOR / VLBI angular measurements, inter-satellite ranging, and Doppler observations. The angular measurements mainly include azimuth A and elevation E, and their transformation includes: obtaining the direction vector in the inertial frame from the angular measurements in the station-centered coordinate system through a conventional transformation chain from the station-centered system to the Earth-fixed system, and then to the geocentric inertial system; then transforming it to the reference frame using R, eliminating the influence of reference errors such as EOP prediction errors in the traditional transformation chain. The transformation of the ΔDOR / VLBI angular measurements includes: expressing the VLBI baseline under the reference frame, directly calculating the two angular components of the target direction, avoiding additional rotation between the celestial reference frame (ICRF) and the ground reference frame. The transformation of inter-satellite ranging and Doppler observation includes: inter-satellite observation is essentially modeled in an inertial frame, and the state of the target and navigation satellite is uniformly expressed using R and then directly participates in the construction of orbit determination equations, eliminating the systematic deviations introduced by inconsistencies in the reference frame.

[0038] After the unified transformation is completed, joint orbit determination is performed within the framework of Kalman filtering or least squares adjustment. The general form of the observation equation is: , in, For the first One observation value, Represents the observation function, The state vector to be estimated contains the target orbit parameters and related estimates. To observe noise.

[0039] In one embodiment of the present invention, the uncertainty of the reference frame is involved in weighting in two ways, one of which is to use the covariance matrix of the reference frame attitude parameters. The additional covariance matrix is ​​obtained by propagating the Jacobian matrix of the observation function to the observation domain. This is superimposed on the observation noise covariance. superior: and with It participates in weighted least squares or filtering updates. Another approach is to use the reference frame quality level factor. Scaling the variance of the observations: ,in The lower the quality grade, the better. The larger.

[0040] Through the above unified expression and weighted joint orbit determination, angle-type observations and inter-satellite observations have geometric consistency under the same reference frame, which can reduce the impact of frame alignment error on orbit determination solution, which is conducive to filter convergence and improves the orbit determination accuracy of Earth-Moon space targets.

[0041] To better illustrate the technical effects of the method described above Figure 2 A schematic diagram of the spatial configuration of a space-based inertial reference frame according to an embodiment of the present invention is shown. Figure 2 As shown, the BeiDou MEO constellation comprises three orbital planes surrounding the Earth: orbital plane A, orbital plane B, and orbital plane C, with eight satellites in each plane. The difference in right ascension between the ascending nodes of the orbital planes is approximately 120°. Taking one satellite each from orbital plane A and orbital plane B to form a satellite pair, when the two satellites are at their farthest points on opposite sides of the orbital plane, the baseline length is approximately: , By taking distant satellite pairs between orbital planes A and C, and between orbital planes B and C, the baseline length can be approximated as approximately 37,000 to 42,000 km. Selecting six satellite pairs (two pairs between every two orbital planes) forms three direction clusters: direction cluster 1, direction cluster 2, and direction cluster 3. Each cluster contains two directions, and the angle between the principal direction vector and the redundancy check vector is defined. Not greater than the intra-cluster threshold This constitutes a highly robust spatial geometric topology, forming a reference frame.

[0042] Under precise ephemeris conditions, i.e. The estimation of the uncertainty of each baseline direction angle is as follows: For baseline length ; For baseline length .

[0043] Under broadcast ephemeris conditions, i.e. The estimation of the uncertainty of each baseline direction angle is as follows: For baseline length ; For baseline length .

[0044] It can be seen that under precise ephemeris conditions, the reference frame orientation accuracy can reach the sub-microarcsecond level, approaching the axis stability measure of ICRF3. Under broadcast ephemeris conditions, the reference frame orientation accuracy is approximately 5 μas, still superior to the absolute pointing accuracy of most on-orbit star sensors. The introduction of redundant directions, such as at least one redundancy per direction cluster, enables the reference frame to isolate single-point faults. When a satellite pair experiences an anomaly, the consistency self-check can detect the anomaly, isolate the faulty pair, and switch to the redundant direction within the same cluster in the next update cycle, ensuring the continuous availability of the reference frame.

[0045] Meanwhile, the minute-level update cycle is extremely short compared to the orbital period of the BeiDou MEO satellite (12.9 hours). The satellite's displacement within one update cycle is approximately 370 km (orbital velocity approximately 3.07 km / s × 300 s), accounting for about 1% of the baseline length. Therefore, the attitude change of the reference frame between adjacent epochs is approximately on the order of milliarcseconds, exhibiting good short-term stability. Post-processing refinement products can further utilize higher-precision orbits and longer arc smoothing to improve the reference frame accuracy to an even higher level.

[0046] Based on the construction and broadcasting methods described above Figure 3 This diagram illustrates the structure of a space-based inertial reference frame construction and broadcasting system based on the BeiDou MEO satellite, according to one embodiment of the present invention. Figure 3As shown, a space-based inertial reference frame construction and broadcasting system based on BeiDou MEO satellites includes a data acquisition module 301, a satellite pair screening module 302, a direction calculation and grouping module 303, an orthogonalization and uncertainty estimation module 304, and a broadcasting and refinement product module 305. The data acquisition module 301 acquires BeiDou MEO satellite orbital status information, time synchronization information, and quality identifiers. The satellite pair screening module 302 selects satellite pairs to form a redundant baseline set. The direction calculation and grouping module 303 divides the redundant baseline set into three direction clusters based on directional similarity, and selects a principal direction representative vector in each cluster. The orthogonalization and uncertainty estimation module 304 determines the reference frame attitude parameters based on the principal direction representative vectors. The broadcasting and refinement product module 305 broadcasts the reference frame attitude parameters, time stamps, validity period, and satellite pair identifiers in real time at a preset update cycle. The ground-based user terminal processing module 001 receives the reference frame parameters, uniformly expresses the observations under the reference frame, and performs joint orbit determination. In one embodiment of the present invention, the orthogonalization and uncertainty estimation module 304 is further configured to delete abnormal satellite pairs through a consistency self-check, and estimate the uncertainty of the reference frame attitude parameters based on the angle residual statistics of the consistency check, combined with the baseline length and satellite position accuracy. In one embodiment of the present invention, the broadcasting and refinement product module 305 is further configured to generate an incremental correction sequence and a covariance refinement sequence for the attitude parameters.

[0047] The system is used to perform the steps of the method as described above. Since the functions of each module in the system correspond to the steps in the method as described above, they can be understood by referring to the method steps, and will not be repeated here.

[0048] Although various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitations. It will be apparent to those skilled in the art that various combinations, modifications, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. A method for constructing and broadcasting a space-based inertial reference frame based on BeiDou MEO satellites, characterized in that, include: Obtain the position of each satellite in the BeiDou MEO satellite constellation in the geocentric inertial coordinate system and determine the baseline unit direction vector; Several satellite pairs are selected to generate a redundant baseline set. These are then divided into three directional clusters based on directional similarity. In each cluster, a principal directional representative vector is selected to construct a reference frame. The reference frame attitude parameters are determined based on the principal direction representative vector. The reference frame attitude parameters, time stamps, validity period, and satellite pair identifiers are broadcast in real time at a preset update cycle.

2. The construction and broadcasting method as described in claim 1, characterized in that, Several satellite pairs were selected, including: The objective function is determined with the goal of maximizing the baseline length and minimizing the direction angle uncertainty. Determine constraints to avoid the redundant baseline set from being nearly coplanar or nearly collinear; Based on the objective function and constraints, satellite pairs are selected.

3. The construction and broadcasting method as described in claim 2, characterized in that, The objective function is expressed as: ， Where N is the number of selected satellite pairs. Let i be the mass weight of the i-th satellite pair. The position accuracy of the poorly aligned satellites in the i-th group of satellites, and Let be the baseline length of the i-th satellite pair.

4. The construction and broadcasting method as described in claim 1, characterized in that, The redundant baseline set is divided into three directional clusters based on directional similarity using the included angle threshold criterion: For direction vector , If the angle between the two They are then grouped into the same directional cluster, among which This is the intra-cluster threshold, ranging from 15° to 45°.

5. The construction and broadcasting method as described in claim 1, characterized in that, In each directional cluster, the directional vector with the longest baseline length and the highest quality weight is taken as the representative vector of the principal direction.

6. The construction and broadcasting method as described in claim 1, characterized in that, Determining the reference frame attitude parameters based on the principal direction representative vector includes: The representative vector of the main direction is orthogonalized to obtain the rotation matrix of the reference frame attitude. The orthogonalization process includes Gram-Schmidt orthogonalization, vector cross product normalization, or least squares orthogonalization under orthogonal constraints.

7. The construction and broadcasting method as described in claim 1, characterized in that, The reference frame attitude parameters, time stamps, validity period, and satellite pair identifiers are broadcast in real time via the BeiDou short message communication link.

8. The construction and broadcasting method as described in claim 1, characterized in that, Also includes: Satellite pairs in each directional cluster whose absolute value of the angular residual between the directional cluster and the corresponding axis is greater than a preset residual threshold are removed. The angular residual is determined according to the following formula: For the Redundancy check vectors in group direction clusters Calculate its relationship with the corresponding axial direction. The residual angle between them: ， in, For the included angle residual, For the first Redundant test vectors in the group of orientation clusters For the first In a family of directions, the principal direction represents a vector. For the corresponding axial direction; The value of the preset residual threshold is dynamically determined based on the baseline length and satellite position accuracy.

9. The construction and broadcasting method as described in claim 1, characterized in that, Also includes: Based on the statistical analysis of the included angle residuals from consistency detection, combined with the baseline length and satellite position accuracy, the uncertainty of the reference frame attitude parameters is estimated, and incremental correction sequences and covariance refinement sequences for the attitude parameters are generated. The uncertainty of the reference frame attitude parameters is configured to participate in the orbit determination weighting process at the application end. The covariance matrix of the attitude parameters of the reference frame The additional covariance matrix is ​​obtained by propagating the Jacobian matrix of the observation function to the observation domain. This is superimposed on the observation noise covariance. superior: and with Participate in weighted least squares or filter updates; or Reference frame quality level factor Scaling the variance of the observations: ,in The lower the quality grade, the better. The larger.

10. A system for constructing and broadcasting a space-based inertial reference frame based on BeiDou MEO satellites, characterized in that, include: The data acquisition module is configured to acquire BeiDou MEO satellite orbital status information, time synchronization information, and quality indicators; The satellite pair screening module is configured to select satellite pairs to form a redundant baseline set; The direction calculation and grouping module is configured to divide the redundant baseline set into three direction clusters according to direction similarity, and select a main direction representative vector in each group; An orthogonalization and uncertainty estimation module is configured to determine the reference frame attitude parameters based on the principal direction representative vector; The broadcast and refinement product module is configured to broadcast reference frame attitude parameters, timestamps, expiration dates, and satellite pair identifiers in real time at a preset update cycle.

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