Real-time clock error determination method with simultaneous constraints on predicted orbit and clock errors of low-orbit satellites

Abstract

The present invention provides a method for determining a real-time clock error that simultaneously constrains the predicted orbit and clock error of a low-orbit satellite, including: using observation data for the entire time period to solve and obtain the expected value of the satellite clock error and satellite orbit for the entire time period; using the expected value of the satellite orbit for the entire time period to perform a medium- to short-term orbit forecast to obtain the predicted satellite orbit for the predetermined end time period; using the expected value of the satellite clock error for the entire time period to perform a medium- to short-term satellite clock forecast; using the predicted satellite orbit and the predicted satellite clock to constrain the solution process of the near-real-time satellite clock, and combining the observation data at the forecast time to solve the near-real-time satellite clock, and then forecasting it to obtain the real-time satellite clock. The present invention performs medium- to long-term forecasts of the satellite orbit and satellite clock of a low-orbit satellite, introduces and applies appropriate constraints to the two, and improves the solution strength and robustness of the near-real-time satellite clock of a high-frequency filtered kinematic low-orbit satellite, thereby helping to improve the accuracy of the real-time satellite clock solution of the low-orbit satellite.

Description

Technical Field

[0001] The present invention belongs to the technical field of satellite positioning and timing, and in particular relates to a real-time clock difference determination method that simultaneously constrains the predicted orbit and clock difference of a low-orbit satellite. Background Art

[0002] Thanks to the low orbital altitude, high speed, and relatively low cost of low-Earth Orbit (LEO) satellites, the LEO-enhanced GNSS (Global Navigation Satellite System) has demonstrated a range of advantages, including high signal strength, fast convergence time, and white noise reduction of multipath effects. This has become a hot research topic in recent years. To fully leverage the potential of LEO navigation signals for high-precision, real-time positioning and timing on the ground, the acquisition of high-precision, real-time satellite clocks from LEO satellites is a critical prerequisite and a key factor in determining the accuracy of future ground-based positioning, navigation, and timing.

[0003] Based on onboard GNSS observations of low-orbit satellites and real-time, high-precision GNSS orbit and clock products provided by various institutions, the orbits and clocks of low-orbit satellites can be solved in near real time. This allows for short- to medium-term forecasts based on the lag time caused by data transmission and processing. This can be achieved through four main methods:

[0004] (1) Using batch least squares method to perform long arc segment simplified dynamics orbit determination for low-orbit satellites, and at the same time batch solve near-real-time satellite clocks. (2) Based on high-frequency filtering, solve the low-orbit satellite kinematic orbit and satellite clock epoch by epoch. (3) Using batch least squares method to simplify dynamics to perform long arc segment orbit determination, and perform short- and medium-term orbit prediction, introduce the predicted orbit and apply appropriate constraints to the high-frequency filtering kinematic timing solution, reduce the correlation between orbit and satellite clock parameters by external absolute constraints on orbit parameters, improve the model strength, and to a certain extent improve the solution accuracy of low-orbit satellite clock parameters. (4) Using batch least squares method to simplify dynamics to perform long arc segment orbit determination, and at the same time batch solve near-real-time satellite clocks, and perform short- and medium-term satellite clock prediction, introduce the predicted satellite clock and apply appropriate constraints to the high-frequency filtering kinematic timing solution, reduce the correlation between orbit and satellite clock parameters by external absolute constraints on satellite clock parameters, improve the model strength, and to a certain extent improve the solution accuracy of low-orbit satellite clock parameters.

[0005] In addition to the satellite clock, the low-orbit satellite clock solved by the GNSS method proposed in method (1) also contains various systematic phenomena that cannot be completely eliminated. This makes the prediction of the low-orbit satellite clock difficult and the loss of accuracy is greater than that of the GNSS clock prediction. Method (2) uses the filter kinematic method to solve the high-frequency satellite clock. However, due to the high correlation between the satellite clock parameters and the orbit parameters, the observation model strength under the filter kinematic solution mode is weak and more sensitive to the quality of the observation data, resulting in a decrease in the accuracy of the satellite clock solution compared to the simplified dynamic solution method based on the batch least squares method. Although method (3) or method (4) combines the respective advantages of method (1) and method (2), by imposing external absolute constraints on the orbit or satellite clock parameters, the correlation between the orbit and satellite clock parameters in the filter kinematic solution is reduced to a certain extent. However, the real-time satellite clock accuracy under this type of method is still directly limited by the accuracy of the predicted orbit or predicted satellite clock, and the overall robustness is poor. Summary of the Invention

[0006] To address the aforementioned issues in the prior art, the present invention provides a method for determining a real-time clock error that simultaneously constrains the predicted orbit and clock error of a low-orbit satellite. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] A method for determining a real-time clock error while simultaneously constraining a low-orbit satellite predicted orbit and clock error includes:

[0008] S100, obtaining observation data of low-orbit satellites for the entire period, and using the observation data for the entire period to solve for the satellite clock error and expected value of the satellite orbit for the entire period;

[0009] S200, performing a short- to medium-term orbit forecast using the expected value of the satellite orbit for the entire period to obtain a predicted satellite orbit for the predetermined end period;

[0010] S300, using the expected value of the satellite clock error for the entire period to perform a short- to medium-term satellite clock forecast, to obtain the satellite clock forecast for the predetermined final period;

[0011] S400, constraining the near-real-time satellite clock solution process using the predicted satellite orbit and the predicted satellite clock, and solving the near-real-time satellite clock in combination with the observation data at the predicted time;

[0012] S500: Predict the near real-time satellite clock to obtain the real-time satellite clock.

[0013] Beneficial effects:

[0014] The present invention provides a method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite, including: obtaining observation data of a low-orbit satellite for an entire period, and using the observation data for the entire period to solve for the satellite clock error and expected value of the satellite orbit for the entire period; using the expected value of the satellite orbit for the entire period to perform a short- to medium-term orbit prediction to obtain a predicted satellite orbit for a predetermined final period; using the expected value of the satellite clock error for the entire period to perform a short- to medium-term satellite clock prediction to obtain a predicted satellite clock for the predetermined final period; using the predicted satellite orbit and the predicted satellite clock to constrain the solution process of the near-real-time satellite clock, and solving the near-real-time satellite clock in combination with the observation data at the prediction time; and predicting the near-real-time satellite clock to obtain a real-time satellite clock. The present invention performs a medium- to long-term prediction of the satellite orbit and satellite clock of a low-orbit satellite, simultaneously introducing and applying appropriate constraints to both, thereby improving the solution strength and robustness of the near-real-time satellite clock of a high-frequency filtered kinematic low-orbit satellite, greatly reducing the correlation between orbit and clock parameters, and facilitating improved accuracy in solving the real-time satellite clock of the low-orbit satellite.

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention provides a flowchart of a method for determining a real-time clock error that simultaneously constrains the predicted orbit and clock error of a low-orbit satellite. DETAILED DESCRIPTION

[0017] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0018] like Figure 1 As shown, the present invention provides a real-time clock error determination method that simultaneously constrains the predicted orbit and clock error of a low-orbit satellite, including:

[0019] S100, obtaining observation data of low-orbit satellites for the entire period, and using the observation data for the entire period to solve for the satellite clock error and expected value of the satellite orbit for the entire period;

[0020] In a specific embodiment of the present invention, S100 includes:

[0021] S110, obtaining observation data obtained by the low-orbit satellite observing the GNSS satellite during the entire period, the observation data including carrier phase observation values ​​and pseudorange observation values ​​of the DF-IF combination;

[0022] S120, using a first expected value of the difference between the carrier phase observation value and the known first model value, and a second expected value of the difference between the pseudorange observation value and the known second model value, to solve the expected value of the satellite clock error for the entire period, the dynamic parameters for the entire period, and the floating-point ambiguity for the entire period; the dynamic parameters include the six Kepler numbers and the solar pressure parameter at the initial time;

[0023] Among them, the first model value refers to the calculated value of the signal delay error term that can be precisely modeled, mainly including the model values ​​calculated by known models for example, ionospheric delay, antenna phase center correction at the GNSS satellite end and the LEO receiver end, antenna phase winding, relativistic effects, etc. The second, third, and fourth model values ​​have the same meaning as the first model value, and the first to fourth are only used to distinguish the calculated values ​​for different signals. For example, the first model value and the third model value are for the carrier phase signal, and the second model value and the fourth model value are for the pseudorange observation signal. Different signals are also divided into time periods, so there are the first model value and the third model value, and the second model value and the fourth model value.

[0024] The present invention is based on the carrier phase and pseudorange observation data of the dual-frequency (DF) ionosphere-free (IF) GNSS onboard low-orbit satellites, combined with the existing dynamic model, and solves some dynamic parameters, floating-point integer ambiguity, and the clock error of the low-orbit satellite through the batch least squares method. The satellite clock error of the low-orbit satellite at each moment in the entire period, the six Kepler numbers at the initial moment, the solar pressure parameter, and a group of random accelerations set every few minutes are obtained.

[0025] The first expected value is expressed as:

[0026] (1);

[0027] Where, express The first expected value of Indicates any moment in the entire period The difference between the pseudorange observation value and the first model value, Indicates time The pseudorange observation pair The partial derivative of represents the kinetic parameters of the entire period, represents the speed of light, Indicates time Satellite clock error;

[0028] The second expected value is expressed as:

[0029] (2);

[0030] Where, express The second expected value of Indicates time The difference between the carrier phase observation value and the second model value, Indicates time The carrier phase observation pair The partial derivative of represents the wavelength after DF-IF combination, Indicates the floating point ambiguity of the DF-IF combination for the entire period, with the subscript Represents a low-orbit satellite, with a superscript Indicates GNSS satellites, with superscript Indicates transpose.

[0031] S130, using the dynamic parameters of the entire time period, solving the expected value of the satellite orbit of the entire time period.

[0032] Finally, this step uses the existing kinetic model and batch least squares method to estimate the kinetic parameters , and solve the satellite orbit of the low-orbit satellite in the Cartesian coordinate system through numerical integration , the specific solution process is as follows:

[0033] a) Construct the dynamic equations of motion of the low-orbit satellite:

[0034] (3);

[0035] Where, represents the sum of all perturbation accelerations on the low-orbit satellite; represents the non-spherical perturbation acceleration of the Earth that affects the low-orbit satellite; represents the acceleration of other non-conservative forces acting on low-orbit satellites; Respectively represent the position and velocity vectors of the satellite in the inertial Cartesian coordinate system; and represents the gravity model parameters and non-conservative force model parameters; 、 、 、 and are all known quantities, Indicates the integration end time;

[0036] b) Arrange the dynamic equations of motion into state space form:

[0037] (4);

[0038] Where, Indicates the current status of the low-orbit satellite;

[0039] Then the dynamic equation of motion can be written as a system of first-order differential equations:

[0040] (5);

[0041] (6);

[0042] c) Use numerical integration to solve the satellite orbit in the Cartesian coordinate system for the entire period:

[0043] Use numerical integration (such as the Collocation method or the Runge-Kutta method) to integrate the above first-order differential equations to obtain the satellite orbits over the entire period:

[0044] (7);

[0045] Where, is the initial state of the low-orbit satellite, arrive is the integration time range, which is 24 hours. represents the initial time of integration, Represents the satellite orbit of the low-orbit satellite in the Cartesian coordinate system during the entire time period.

[0046] S200, performing a short- to medium-term orbit forecast using the expected value of the satellite orbit for the entire period to obtain a predicted satellite orbit for the predetermined end period;

[0047] In a specific embodiment of the present invention, S200 includes:

[0048] S210, selecting an expected value of the satellite orbit in a predetermined end time period from the expected values ​​of the satellite orbit in the entire time period;

[0049] This implementation can select the satellite orbits of the last few hours Fit the dynamic parameters and make orbit predictions. The expected value of the satellite orbit can be obtained by fitting. The fitting method can be found in the fitting process described in the prior art and will not be described in detail here. The fitted dynamic parameters usually include the six Kepler elements at the initial moment of the predetermined end period. and solar pressure parameters The expected value of the satellite orbit at the end of the predetermined period is expressed as follows:

[0050] (8);

[0051] in, express The expected value, Indicates the time at the end of the scheduled period satellite orbits; Indicates time Satellite orbit pairs in Cartesian coordinate system The partial derivative, Indicates time Satellite orbit pairs in Cartesian coordinate system The partial derivative, The six Kepler numbers representing the initial moment of the predetermined end period, Represents the solar pressure parameter.

[0052] S220 , performing a short- to medium-term orbit forecast on the expected value of the satellite orbit at the end of the scheduled period, to obtain a predicted satellite orbit at the end of the scheduled period.

[0053] S300, using the expected value of the satellite clock error for the entire period to perform a short- to medium-term satellite clock forecast, to obtain the satellite clock forecast for the predetermined final period;

[0054] In a specific embodiment of the present invention, S300 includes:

[0055] S310, selecting an expected value of the satellite clock error for a predetermined end time period from the expected values ​​of the satellite clock error for the entire time period;

[0056] S320, performing polynomial parameter fitting on the expected value of the satellite clock error in the predetermined end period to obtain polynomial satellite clock parameters;

[0057] S330, performing a short- to medium-term satellite clock forecast on the polynomial satellite clock parameters to obtain a satellite forecast satellite clock for a predetermined end period;

[0058] This implementation selects the last few hours of low-orbit satellite clock errors from the satellite clock errors for the entire period calculated using the least squares method. Taking into account the periodic effects contained in the clock errors of low-orbit satellites, model parameters are fitted based on existing models. Medium- to short-term satellite clock predictions are then made based on the fitted model parameters, resulting in a series of predicted satellite clocks for future moments. The predicted satellite clocks are expressed as follows:

[0059] (9);

[0060] Where, Indicates the satellite forecast clock for the end of the scheduled period. Indicates the forecast time within the scheduled end period. Indicates the initial time of the scheduled end period, represents the fitting coefficient of the polynomial, , represents the order of the polynomial, represents the number of periodic terms, 、 and denote the period, amplitude and phase of the periodic term respectively, Indicates the sequence number of the period item.

[0061] S400, constraining the near-real-time satellite clock solution process using the predicted satellite orbit and the predicted satellite clock, and solving the near-real-time satellite clock in combination with the observation data at the predicted time;

[0062] In a specific embodiment of the present invention, S400 includes:

[0063] S410, obtain epoch The observation data of the low-orbit satellite is collected, and the solution equations containing the near-real-time satellite clock and the near-real-time satellite orbit to be solved are constructed using the observation data.

[0064] The present invention constructs a spaceborne GNSS DF IF combined pseudorange and carrier phase observation equation based on near-real-time space-based feedback, that is, solves the equation. The solution equation is expressed as:

[0065] (10);

[0066] (11);

[0067] Where, express The third expected value of Represents any epoch The difference between the pseudorange observation value and the third model value, Represents epoch The pseudorange observation pair The partial derivative of Represents the epoch of the low-orbit satellite in the Cartesian coordinate system The three-dimensional orbit correction value, Represents epoch The near-real-time satellite clock to be solved; express The fourth expected value of Represents epoch The difference between the carrier phase observation value and the fourth model value, Represents epoch The carrier phase observation pair The partial derivative of Represents epoch The floating point ambiguity of the DF-IF combination.

[0068] S420: constrain the solution equation using the predicted satellite orbit and the predicted satellite clock, and solve the constrained solution equation to obtain the near-real-time satellite orbit and the near-real-time satellite clock.

[0069] In a specific embodiment of the present invention, S420 includes:

[0070] S421, using satellite predicted orbits to construct epochs The constraint equations for near-real-time satellite orbits and their corresponding first variance-covariance matrices, as well as the constraint equations for constructing near-real-time satellite clocks using satellite prediction clocks and their corresponding second variance-covariance matrices;

[0071] The parameters of the near-real-time satellite clock are estimated using Kalman filtering or sequential least squares, while simultaneously constraining the predicted orbit and the predicted clock. The specific process of sequential least squares estimation is given below:

[0072] When using the sequential least squares method to solve the near-real-time satellite clock of a low-orbit satellite, although the floating-point ambiguity is solved at each epoch, a time constraint (constrained to a constant) should be imposed between epochs to achieve the solution of the filtering mode. The inter-epoch constraint equations and their corresponding variance-covariance matrices are:

[0073] (12);

[0074] (13);

[0075] Where, Indicates the last epoch The floating point blurriness, Indicates the last epoch The variance-covariance matrix corresponding to the constraint equation.

[0076] Among them, the ambiguity parameters to be solved in this epoch are Constrained to the previous epoch ambiguity solution value , the variance-covariance matrix of the constraint equations for this epoch Equivalent to the variance-covariance matrix of the ambiguity parameters of the previous epoch .

[0077] In addition to the time constraints of the ambiguity parameters, the present invention also introduces the satellite prediction orbit and satellite prediction clock of the low-orbit satellite and performs appropriate constraints. First, within the last prediction orbit and satellite clock time period, find and Matching time, while introducing the satellite prediction orbit in the Cartesian coordinate system and satellite prediction clock , and make the following absolute constraints:

[0078] (14);

[0079] (15);

[0080] The variance-covariance matrix of constraint equations (14) and (15) is and It is necessary to calculate the satellite orbit and satellite clock of the low-orbit satellite. For satellite orbits, first calculate the predicted time To the initial time of forecast duration, i.e. forecast duration Based on low-orbit satellite forecasts The accuracy in the RSW direction is expanded accordingly based on experience and the standard deviation of the orbit constraint equation is set 、 and , calculate the variance-covariance matrix of the near-real-time satellite orbit in the Cartesian coordinate system :

[0081] (16);

[0082] (17);

[0083] in, is the variance-covariance matrix of the satellite orbit in the RSW direction (ignoring the correlation between directions), For the coordinate transformation matrix from the orbital RSW coordinate system to the Cartesian coordinate system, The accuracy is expanded accordingly based on experience and the standard deviation of the clock error constraint equation is set , get the variance-covariance matrix of the near-real-time satellite clock .

[0084] S422, using the predicted satellite orbit, the predicted satellite clock, the first variance-covariance matrix, and the second variance-covariance matrix, to solve the near-real-time satellite orbit and the near-real-time satellite clock;

[0085] In this step, the satellite prediction orbit, satellite prediction clock, first variance-covariance matrix and second variance-covariance matrix are substituted into the following formula:

[0086] (18);

[0087] Solve the near-real-time satellite orbit and near-real-time satellite clock;

[0088] in, ; , , ;

[0089] Where, are the parameters to be solved, including near-real-time satellite orbits, near-real-time satellite clocks, and floating-point ambiguities; represents the identity matrix, represents a matrix with zero elements, represents the zero element; represents the first variance-covariance matrix, represents the second variance-covariance matrix, represents the cofactor matrix corresponding to the pseudorange observation value, represents the cofactor matrix corresponding to the carrier phase value, The cofactor matrix corresponding to the ambiguity of the carrier phase value is represented by Represents epoch The predicted satellite orbits of Represents epoch Satellite prediction clock.

[0090] S500: Predict the near real-time satellite clock to obtain the real-time satellite clock.

[0091] The present invention performs polynomial fitting on a near-real-time satellite clock and performs ultra-short-term prediction, thereby obtaining a real-time satellite clock of a low-orbit satellite that is simultaneously introduced with a predicted orbit and a constrained satellite clock.

[0092] The present invention provides a method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite, including: obtaining observation data of a low-orbit satellite for an entire period, and using the observation data for the entire period to solve for the satellite clock error and expected value of the satellite orbit for the entire period; using the expected value of the satellite orbit for the entire period to perform a short- to medium-term orbit prediction to obtain a predicted satellite orbit for a predetermined final period; using the expected value of the satellite clock error for the entire period to perform a short- to medium-term satellite clock prediction to obtain a predicted satellite clock for the predetermined final period; using the predicted satellite orbit and the predicted satellite clock to constrain the solution process of the near-real-time satellite clock, and solving the near-real-time satellite clock in combination with the observation data at the prediction time; and predicting the near-real-time satellite clock to obtain a real-time satellite clock. The present invention performs a medium- to long-term prediction of the satellite orbit and satellite clock of a low-orbit satellite, simultaneously introducing and applying appropriate constraints to both, thereby improving the solution strength and robustness of the near-real-time satellite clock of a high-frequency filtered kinematic low-orbit satellite, greatly reducing the correlation between orbit and clock parameters, and facilitating improved accuracy in solving the real-time satellite clock of the low-orbit satellite.

[0093] It is worth noting that the terms "first" and "second" in this disclosure are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of this disclosure, "plurality" means two or more, unless otherwise specifically defined.

[0094] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite, characterized in that: include: S100, obtaining observation data of low-orbit satellites for the entire period, and using the observation data for the entire period to solve for satellite clock errors and expected values ​​of satellite orbits for the entire period; S200, performing a short- to medium-term orbit forecast using the expected value of the satellite orbit for the entire period to obtain a predicted satellite orbit for the predetermined end period; S300, using the expected value of the satellite clock error for the entire period to perform a short- to medium-term satellite clock forecast, to obtain the satellite clock forecast for the predetermined final period; S400, using the predicted satellite orbit and the predicted satellite clock to constrain the near-real-time satellite clock solution process, and combining the observation data at the predicted time to solve the near-real-time satellite clock; S500: Predict the near real-time satellite clock to obtain a real-time satellite clock.

2. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 1, wherein: S100 includes: S110, obtaining observation data obtained by the low-orbit satellite observing the GNSS satellite during the entire period, wherein the observation data includes carrier phase observation values ​​and pseudorange observation values ​​of the DF-IF combination; S120, using a first expected value of the difference between the carrier phase observation value and the known first model value, and a second expected value of the difference between the pseudorange observation value and the known second model value, to solve the expected value of the satellite clock error for the entire period, the dynamic parameters for the entire period, and the floating-point ambiguity for the entire period; the dynamic parameters include the six Kepler numbers and the solar pressure parameter at the initial time; S130, using the dynamic parameters of the entire time period, solving the expected value of the satellite orbit of the entire time period.

3. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 2, wherein: The first expected value is expressed as: ； Where, express The first expected value of Indicates any moment within the entire period The difference between the pseudorange observation value and the first model value, Indicates time The pseudorange observation pair The partial derivative of represents the kinetic parameters of the entire period, represents the speed of light, Indicates time Satellite clock error; The second expected value is expressed as: ； Where, express The second expected value of Indicates time The difference between the carrier phase observation value and the second model value, Indicates time The carrier phase observation pair The partial derivative of represents the wavelength after DF-IF combination, Indicates the floating point ambiguity of the DF-IF combination for the entire period, with the subscript Represents a low-orbit satellite, with a superscript Indicates GNSS satellites, with superscript Indicates transpose.

4. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 3, wherein: S200 includes: S210, selecting an expected value of the satellite orbit in a predetermined end time period from the expected values ​​of the satellite orbit in the entire time period; S220 , performing a short- to medium-term orbit forecast on the expected value of the satellite orbit at the end of the scheduled period, to obtain a predicted satellite orbit at the end of the scheduled period.

5. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 4, characterized in that: The expected value of the satellite orbit at the end of the predetermined period is expressed as follows: ； in, express The expected value, Indicates the time at the end of the scheduled period satellite orbits; Indicates time Satellite orbit pairs in Cartesian coordinate system The partial derivative, Indicates time Satellite orbit pairs in Cartesian coordinate system The partial derivative, The six Kepler numbers representing the initial moment of the predetermined end period, Represents the solar pressure parameter.

6. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 5, characterized in that: S300 includes: S310, selecting an expected value of the satellite clock error for a predetermined end time period from the expected values ​​of the satellite clock error for the entire time period; S320, performing polynomial parameter fitting on the expected value of the satellite clock error in the predetermined end period to obtain polynomial satellite clock parameters; S330, performing a short- to medium-term satellite clock forecast on the polynomial satellite clock parameters to obtain a satellite forecast star clock for a predetermined end period; the satellite forecast star clock is expressed by the formula: ； Where, Indicates the satellite forecast clock for the scheduled end period. Indicates the forecast time within the scheduled end period. Indicates the initial time of the scheduled end period, Represents a polynomial from 0 to The fitting coefficient of the term, represents the order of the polynomial, represents the number of periodic terms, 、 and denote the period, amplitude and phase of the periodic term respectively, Indicates the sequence number of the period item.

7. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 6, wherein: S400 includes: S410, obtain epoch The observation data of the low-orbit satellite is collected and the solution equations containing the near-real-time satellite clock and the near-real-time satellite orbit are constructed using the observation data. S420: Constrain the solution equation using the predicted satellite orbit and the predicted satellite clock, and solve the constrained solution equation to obtain the near-real-time satellite orbit and the near-real-time satellite clock.

8. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 7, wherein: The equation to be solved is expressed as: ； ； Where, express The third expected value of Represents any epoch The difference between the pseudorange observation value and the third model value, Represents epoch The pseudorange observation pair The partial derivative of Represents the epoch of the low-orbit satellite in the Cartesian coordinate system The three-dimensional orbit correction value, Represents epoch The near-real-time satellite clock to be solved; express The fourth expected value of Represents epoch The difference between the carrier phase observation value and the fourth model value, Represents epoch The carrier phase observation pair The partial derivative of Represents epoch The floating point ambiguity of the DF-IF combination.

9. The method for determining a real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 8, wherein: The S420 includes: S421, constructing epochs respectively using the satellite prediction orbits Constraint equations for near-real-time satellite orbits and their corresponding first variance-covariance matrices, and constraint equations for constructing near-real-time satellite clocks using the satellite prediction clock and their corresponding second variance-covariance matrices; S422: Calculate a near-real-time satellite orbit and a near-real-time satellite clock using the predicted satellite orbit, the predicted satellite clock, the first variance-covariance matrix, and the second variance-covariance matrix.

10. The method for determining the real-time clock error by simultaneously constraining the predicted orbit and clock error of a low-orbit satellite according to claim 9, characterized in that: S422 includes: Substitute the satellite prediction orbit, the satellite prediction star clock, the first variance-covariance matrix and the second variance-covariance matrix into the following formula: ； Solve the corresponding near-real-time satellite orbit and near-real-time satellite clock; in, ; , , ; Where, are the parameters to be solved, including near-real-time satellite orbits, near-real-time satellite clocks, and floating-point ambiguities; represents the identity matrix, represents a matrix with zero elements, represents the zero element; represents the first variance-covariance matrix, represents the second variance-covariance matrix, represents the cofactor matrix corresponding to the pseudorange observation value, represents the cofactor matrix corresponding to the carrier phase value, The cofactor matrix corresponding to the ambiguity of the carrier phase value is represented by Represents epoch The predicted satellite orbits of Represents epoch Satellite prediction clock.

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