A method for transferring time between low-orbit spacecraft and ground spacecraft taking into account prior space-time information

Abstract

The present invention belongs to the technical field of satellite-to-ground time transfer for low-orbit spacecraft, and discloses a satellite-to-ground time transfer method for low-orbit spacecraft taking into account a priori spacetime information. The method aims at the problems of too many unknown parameters and low observation equation strength in satellite-to-ground time transfer for low-orbit spacecraft, extracts and models the a priori spacetime information of the operating orbit of the low-orbit spacecraft and the onboard atomic clock, constructs a low-orbit spacecraft dynamic carrier phase time transfer solution model taking into account the enhancement of a priori spacetime information, obtains high-precision clock error parameters of the onboard GNSS receiver of the low-orbit spacecraft, and obtains the ground GNSS receiver clock error based on the static GNSS non-difference carrier phase time transfer method according to the GNSS receiver observation data connected to the ground atomic clock at the current moment, and then obtains the satellite-to-ground time transfer amount, thereby effectively improving the solution strength of the onboard GNSS receiver clock error and enhancing the performance of satellite-to-ground time transfer.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-orbit spacecraft satellite-to-ground time transfer, and in particular relates to a low-orbit spacecraft satellite-to-ground time transfer method taking into account a priori space-time information. Background Art

[0002] With the continuous development of space science and technology, high-precision time information, as important information for describing the operation of celestial bodies and spacecraft and their mutual relationships, has become a key element in supporting space scientific research activities.

[0003] In recent years, with the continuous deepening of the construction of low-orbit spacecraft, the strategy of carrying high-performance atomic clocks and clock groups on low-orbit spacecraft to build a space-based time benchmark has gradually become an important support method for near-Earth space scientific exploration.

[0004] In order to maintain the synchronization of the atomic clock group on low-orbit spacecraft with the ground standard time, the global navigation satellite system (GNSS) is used to transfer time between low-orbit spacecraft and the ground. This technology is efficient, has no observation blind spots, good continuity, low cost, and simple maintenance.

[0005] However, in the process of satellite-to-earth time transfer based on this type of technology, the gross error noise in the satellite-borne GNSS observation data is more significant because low-orbit spacecraft are affected by factors such as the perturbations of space celestial bodies and the complex and changeable space environment.

[0006] At the same time, although the traditional satellite-borne GNSS orbit determination technology can also estimate the clock error parameters of the satellite-borne GNSS receiver, its complex fitting and batch processing process leads to low efficiency and accuracy of the parameter estimation algorithm.

[0007] Therefore, how to effectively integrate the effective prior spatiotemporal information of GNSS observations of low-orbit spacecraft in order to efficiently realize high-precision satellite-to-ground time transfer of low-orbit spacecraft is a hot issue in the field of time and frequency. Summary of the invention

[0008] The purpose of the present invention is to propose a method for time transfer between low-orbit spacecraft and the ground taking into account a priori spacetime information. The method extracts the orbital information of the periodic motion of the low-orbit spacecraft and the physical characteristics information of the onboard atomic clock group, and establishes a low-orbit spacecraft dynamic carrier phase time transfer solution model that takes into account the enhancement of prior spacetime information, thereby improving the solution intensity of the receiver clock error parameters and further improving the performance of the dynamic GNSS carrier phase time transfer between the low-orbit spacecraft and the ground.

[0009] In order to achieve the above object, the present invention adopts the following technical scheme:

[0010] A method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information comprises the following steps:

[0011] Step 1. Obtain the orbital sequence data of the low-orbit spacecraft, perform a first epoch difference on the time series of its orbital components, obtain the running speed of the low-orbit spacecraft, and construct the orbital model of the low-orbit spacecraft;

[0012] Step 2. Obtain the clock error data of the atomic clock group of the low-orbit spacecraft and build a prediction model for the onboard atomic clock;

[0013] Step 3. Obtain the pseudorange and carrier phase observations of the onboard GNSS receiver on the low-orbit spacecraft, perform data preprocessing, construct the ionosphere-free combined observations, correct the errors of the onboard GNSS receiver, and establish a function model of carrier phase time transfer based on dynamic GNSS non-difference;

[0014] Step 4. Establish a random model of carrier phase time transfer based on dynamic GNSS non-difference;

[0015] Step 5. Combine the function model and random model of carrier phase time transfer based on dynamic GNSS non-difference with the prior space-time information constructed in step 1 and step 2, respectively, to construct the function model and random model of LEO spacecraft satellite-to-ground time transfer that take into account the prior space-time information;

[0016] Step 6. For the GNSS receiver connected to the ground atomic clock, i.e., the ground GNSS receiver, the receiver clock difference of the ground station is obtained by using the method based on static GNSS non-differenced carrier phase time transfer, and the function model and random model based on static GNSS non-differenced carrier phase time transfer are obtained;

[0017] Step 7. Based on the mathematical model and parameter solution algorithm obtained in Steps 5 and 6, the GNSS observation data at both ends of the satellite-to-ground time transfer link are processed respectively to obtain the receiver clock difference of the current epoch of the two stations. Combined with the inherent delay calibration of the satellite-to-ground time transfer link, a dynamic carrier phase time transfer solution model for low-orbit spacecraft that takes into account the enhancement of prior space-time information is constructed, and the satellite-to-ground time transfer of low-orbit spacecraft that takes into account the prior space-time information is completed.

[0018] In addition, based on the above-mentioned method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information, the present invention further proposes a computer device, which includes a memory and one or more processors;

[0019] The memory stores executable codes, and when the processor executes the executable codes, it is used to implement the steps of the above-mentioned method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information.

[0020] In addition, based on the above-mentioned method for transferring time between a low-orbit spacecraft and the ground taking into account a priori spacetime information, the present invention also proposes a computer-readable storage medium on which a program is stored; when the program is executed by a processor, it is used to implement the steps of the above-mentioned method for transferring time between a low-orbit spacecraft and the ground taking into account a priori spacetime information.

[0021] The present invention has the following advantages:

[0022] As described above, the present invention relates to a method for transferring time between low-orbit spacecraft and the ground, which takes into account a priori spacetime information. The method realizes the effective extraction of a priori spacetime information by the low-orbit spacecraft orbit information and the onboard atomic clock system in the space domain and the time domain; utilizes the correlation of the low-orbit spacecraft's in-orbit operation in the space domain to establish a low-orbit spacecraft orbit model, thereby obtaining the constraints between adjacent epochs of the orbit information, and effectively avoiding the influence of the rapid movement of the low-orbit spacecraft on the solution of the receiver clock error parameters in the traditional dynamic GNSS time transfer model; at the same time, the correlation of the onboard atomic clock of the low-orbit spacecraft in the time domain is extracted, and a onboard atomic clock prediction model is established, which further enhances the solution accuracy of the onboard GNSS receiver clock error parameters. In addition, the method of the present invention also effectively simplifies the dynamic GNSS carrier phase time transfer model, reduces the number of parameters to be estimated, and enhances the strength of target parameter solution; and discards the tropospheric parameters in the traditional model, effectively eliminating the abnormal problem of the mapping function established based on the tropospheric altitude angle in the satellite-borne GNSS carrier phase time transfer, while enhancing the solution strength of the satellite-borne spacecraft position information and the receiver clock error parameters, and further enhancing the satellite-to-ground time transfer performance. The method of the present invention extracts the orbital information of the periodic motion of the low-orbit spacecraft and the physical characteristics information of the satellite-borne atomic clock group, and establishes a low-orbit spacecraft dynamic carrier phase time transfer solution model that takes into account the enhancement of prior space-time information, thereby improving the solution strength of the receiver clock error parameters and further improving the performance of the low-orbit spacecraft satellite-to-ground dynamic GNSS carrier phase time transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a flowchart of a method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information in an embodiment of the present invention.

[0024] Figure 2 Schematic diagram of information exchange between a low-orbit spacecraft and a ground-based GNSS receiver in an embodiment of the present invention.

[0025] Figure 3 The system block diagram of the method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information in an embodiment of the present invention.

[0026] Figure 4The present invention provides a flowchart for establishing a low-orbit spacecraft dynamic carrier phase time transfer solution model that takes into account the enhancement of prior space-time information in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0028] Example 1

[0029] In this embodiment, a method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information is proposed. The general process is as follows: Figure 3 As shown in the figure, it includes the following parts: first, obtain the prior space-time information of the low-orbit spacecraft orbit and clock error and the observation data of the satellite and ground stations, that is, the observation data of the satellite-borne GNSS receiver on the low-orbit spacecraft and the observation data of the ground GNSS receiver, specifically including the GNSS dual-frequency pseudo-range and carrier phase observation data of the two stations of the low-orbit spacecraft satellite-ground time transfer link. Then, the GNSS observation data of the satellite and ground stations are preprocessed separately, including data integrity check, outlier detection, i.e., gross error identification and elimination, cycle slip detection and marking, to obtain clean observation data, i.e., dual-frequency ionosphere-free combined observations. Then, by correcting the ionospheric errors, troposphere, satellite and receiver-related deviations, as well as errors such as earth tides and ocean tides, various preparations before generating the model observation equations are completed. Finally, by establishing a low-orbit spacecraft dynamic carrier phase time transfer solution model that takes into account the enhancement of prior space-time information, various parameters to be estimated in the observation equation are solved, and the GNSS receiver clock difference parameters of the satellite and ground stations are obtained respectively, and the satellite and ground time transfer results are further obtained.

[0030] like Figure 1 As shown, a method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information comprises the following steps:

[0031] Step 1. Obtain the orbital sequence data of the low-orbit spacecraft, perform a first epoch difference on the time series of its orbital components, obtain the operating speed of the low-orbit spacecraft, and construct the orbital model of the low-orbit spacecraft.

[0032] Specifically, the orbital sequence data file of the low-orbit spacecraft for nearly 6 hours is obtained. Considering that the running speed of the low-orbit spacecraft has good stability and regularity, the time series of the three components of its orbit are differentiated between epochs, as shown in formula (1), to obtain the running speed of the low-orbit spacecraft in three directions:

[0033] (1)

[0034] in, , , Respectively represent the running speed of low-orbit spacecraft in three directions, is the epoch marker, , , They are The three orbital components of the LEO spacecraft at the epoch, , , They are The three orbital components of a LEO spacecraft at the epoch.

[0035] Based on the running speed of the low-orbit spacecraft obtained by formula (1), the orbit model of the low-orbit spacecraft is constructed as shown in formula (2): :

[0036] (2)

[0037] in, , and are the coefficients of the quadratic term, the first-order term, and the constant term, respectively; and represents the coefficients of the periodic function, is the period of the periodic function, , n represents the order.

[0038] Step 2. Obtain the clock error data of the atomic clock group of the low-orbit spacecraft and build a prediction model for the onboard atomic clock.

[0039] Specifically, the clock error data file of the atomic clock group of the low-orbit spacecraft in the past hour is obtained, and the prediction model of the onboard atomic clock is constructed as shown in formula (3):

[0040] (3)

[0041] in, for The clock error of the satellite-borne GNSS receiver at time , , Respectively represent the reference time The initial clock error, clock speed, and clock drift, represents the error residual term.

[0042] Step 3. Obtain the pseudorange and carrier phase observations of the onboard GNSS receiver on the low-orbit spacecraft, perform data preprocessing, construct the ionosphere-free combined observations, correct the errors of the onboard GNSS receiver, and establish a function model of carrier phase time transfer based on dynamic GNSS non-difference.

[0043] Specifically, the acquired satellite-borne GNSS pseudorange and carrier phase observations on the low-orbit spacecraft are subjected to data integrity check, gross error identification, cycle slip detection and marking, and a dual-frequency ionosphere-free combined observation is constructed. Considering that the low-orbit spacecraft is located in space more than 300 km from the earth, the troposphere in the atmosphere has little effect on it, so the troposphere parameters are no longer estimated in the mathematical model. However, since errors such as antenna phase center errors and relativistic effects of satellites and satellite-borne GNSS receivers still exist, they need to be corrected.

[0044] The function expression for establishing the dynamic GNSS carrier phase time transfer model is:

[0045] (4)

[0046] in, represents the pseudo-range ionosphere-free combined observation of the satellite-borne GNSS receiver clock, represents the ionospheric-free combined observation of the carrier phase of the satellite-borne GNSS receiver clock, For GNSS satellites With onboard GNSS receiver The distance between is the speed of light, is the satellite-borne GNSS receiver clock error, is the clock error of the GNSS satellite, is the pseudorange noise of the satellite-borne GNSS receiver clock, is the carrier phase ambiguity of the satellite-borne GNSS receiver clock, is the carrier phase noise of the onboard GNSS receiver clock.

[0047] Parameter vector to be estimated for:

[0048] (5)

[0049] in, are the three orbital components of a low-orbit spacecraft.

[0050] Step 4. Establish a random model of carrier phase time transfer based on dynamic GNSS undifference.

[0051] According to the state parameter characteristics of different types of parameters in the estimated parameter vector X obtained by formula (5), the corresponding random model is determined; for the fuzzy parameter When no cycle slip occurs, the process noise variance is set to 0; when a cycle slip occurs, it needs to be reinitialized and the process noise variance is set to 10 10 ; For the satellite GNSS receiver clock error parameters Three orbital component parameters of low-orbit spacecraft White noise process is used for simulation.

[0052] The random model of carrier phase time transfer based on dynamic GNSS non-difference is established as shown in formula (6):

[0053] (6)

[0054] in, represents the covariance matrix of the parameters to be estimated of the spaceborne GNSS receiver, represents the co-factor of the three orbital components of the LEO spacecraft, The co-factor representing the clock error parameters of the onboard GNSS receiver, represents the co-factor of the ambiguity parameters of the onboard GNSS receiver, and m represents the number of ambiguity parameters of the onboard GNSS receiver clock.

[0055] Step 5. Combine the function model and random model of carrier phase time transfer based on dynamic GNSS non-difference with the prior spacetime information obtained from the LEO spacecraft orbit model in step 1 and the satellite-borne atomic clock prediction model in step 2, respectively, to further construct the function model and random model of LEO spacecraft satellite-to-ground time transfer that take into account the prior spacetime information.

[0056] Since the dynamic GNSS carrier phase time transfer model established in step 3 and step 4 specifically includes the function model of carrier phase time transfer based on dynamic GNSS non-difference established in step 3 and the random model of carrier phase time transfer based on dynamic GNSS non-difference established in step 4, there are many parameters to be estimated, especially the low-orbit spacecraft is in a state of high-speed motion, which makes it difficult to accurately obtain high-precision position and onboard GNSS receiver parameters by relying solely on the pseudo-range and carrier phase observations of the onboard GNSS receiver of the low-orbit spacecraft. Therefore, it is necessary to combine the prior space-time information constructed in step 1 and step 2 to further construct a low-orbit spacecraft satellite-to-ground time transfer model that takes into account the prior space-time information, including a function model and a random model of low-orbit spacecraft satellite-to-ground time transfer that takes into account the prior space-time information.

[0057] The function model of low-orbit spacecraft time transfer between satellite and ground taking into account the prior space-time information is expressed as:

[0058] (7)

[0059] in, express Pseudorange ionosphere-free combined observations from epoch spaceborne GNSS receivers, express GNSS satellites in epoch With onboard GNSS receiver The distance between express The onboard GNSS receiver clock error at the epoch, express The clock error of the GNSS satellite at the epoch, express Pseudorange noise of epoch spaceborne GNSS receiver, express The carrier phase ionospheric-free combined observations of the epoch spaceborne GNSS receiver, express Carrier phase noise of epoch spaceborne GNSS receiver, express The three orbital components of the epoch low-orbit spacecraft, express The three orbital components of the epoch low-orbit spacecraft, express The LEO spacecraft orbit model for the epoch, is the time interval of the LEO spacecraft orbit, for The onboard GNSS receiver clock error at the epoch.

[0060] The stochastic model of time transfer between low-orbit spacecraft and ground spacecraft taking into account prior space-time information is further written as:

[0061] (8)

[0062] in, , , They are the weight distribution of the dynamic GNSS carrier phase time transfer model, the low-orbit spacecraft orbit model, and the onboard atomic clock prediction model. , , They are , , The corresponding mean error.

[0063] Step 6. For the GNSS receiver connected to the ground atomic clock, that is, the ground GNSS receiver, the receiver clock difference of the ground station is obtained by using the method based on static GNSS non-difference carrier phase time transfer, and a static GNSS carrier phase time transfer model is obtained, including a function model and a random model based on static GNSS non-difference carrier phase time transfer.

[0064] Specifically, for a GNSS receiver connected to a ground-based atomic clock, pseudorange and carrier phase observations of the ground-based GNSS receiver are obtained, and data preprocessing is performed to construct ionosphere-free combined observations of the ground-based GNSS receiver.

[0065] Among them, data preprocessing includes data integrity check, gross error identification, cycle slip detection and marking.

[0066] Correct the errors of ground GNSS receivers, including ionospheric errors, antenna phase center errors, tropospheric errors, tides and relativistic effects.

[0067] Based on the static GNSS non-differential carrier phase time transfer method, the ground station receiver clock error is obtained. The function model of static GNSS carrier phase time transfer is obtained as shown in formula (9):

[0068] (9)

[0069] in, is the pseudo-range ionosphere-free combined observation of the ground GNSS receiver, is the carrier phase ionospheric-free combined observation of the ground GNSS receiver, is the distance between the GNSS satellite and the ground GNSS receiver, is the clock error parameter of the ground GNSS receiver, represents the tropospheric delay parameter, is the pseudorange noise of the ground GNSS receiver, is the carrier phase ambiguity of the ground GNSS receiver, is the carrier phase noise of the ground GNSS receiver.

[0070] The stochastic model of static GNSS carrier phase time transfer is expressed as:

[0071] (10)

[0072] in, represents the covariance matrix of the parameters to be estimated of the ground GNSS receiver, The cofactor representing the three-dimensional coordinates of the ground GNSS receiver, The co-factor representing the ground GNSS receiver clock error parameter, is the cofactor representing the tropospheric parameters, represents the cofactor of the ambiguity parameters of the ground GNSS receiver, and n represents the number of ambiguity parameters of the ground GNSS receiver.

[0073] Considering that the ground GNSS receiver is in a relatively static state, in the random model based on static GNSS undifferenced carrier phase time transfer, the coordinate parameters are fixed based on the prior position information.

[0074] Step 7. Based on the mathematical model and parameter solution algorithm obtained in Steps 5 and 6, the GNSS observation data at both ends of the satellite-to-ground time transfer link are processed respectively to obtain the receiver clock difference of the current epoch of the two stations. Combined with the inherent delay calibration of the satellite-to-ground time transfer link, a dynamic carrier phase time transfer solution model for low-orbit spacecraft that takes into account the enhancement of prior space-time information is constructed, and the satellite-to-ground time transfer of low-orbit spacecraft that takes into account the prior space-time information is completed.

[0075] The mathematical models and parameter calculation algorithms (e.g., the least squares principle and method) of steps 5 and 6 are used to process the GNSS observation data at both ends of the satellite-to-ground time transfer link respectively, and the receiver clock difference of the two stations at the low-orbit spacecraft and the ground GNSS receiver at the current epoch is obtained. That is, the satellite-to-ground time transfer model of the low-orbit spacecraft taking into account the prior spacetime information in step 5 (i.e., formulas (7) and (8)) is combined, and the GNSS observation data at the low-orbit spacecraft are processed using the least squares principle and method to obtain the satellite receiver clock difference parameter at the current moment. , combined with the static GNSS carrier phase time transfer model in step 6 (i.e., formula (9) and formula (10)), the GNSS observation data at the ground GNSS receiver is processed using the least squares principle and method to obtain the ground GNSS receiver clock error parameter at the current moment , and combined with the inherent delay calibration of the satellite-to-ground time transfer link, the dynamic carrier phase time transfer solution model for low-orbit spacecraft taking into account the enhancement of prior space-time information is obtained:

[0076] (11)

[0077] in, is the amount of time passed, A calibrated amount of inherent delay in a time transfer link.

[0078] The LEO spacecraft dynamic carrier phase time transfer solution model taking into account the prior spacetime information enhancement shown in formula (11) is used to complete the LEO spacecraft satellite-to-ground time transfer taking into account the prior spacetime information.

[0079] The method for satellite-to-ground time transfer of low-orbit spacecraft taking into account a priori spacetime information described in the present invention aims to solve the problems of too many unknown parameters and low observation equation strength in satellite-to-ground time transfer of low-orbit spacecraft. It utilizes pseudo-range and carrier phase observations of the low-orbit spacecraft and ground GNSS receivers, as well as precise GNSS satellite orbit and clock error data, extracts and models the priori spacetime information of the low-orbit spacecraft's operating orbit and onboard atomic clock, and constructs a low-orbit spacecraft dynamic carrier phase time transfer solution model taking into account the enhancement of prior spacetime information, obtains high-precision clock error parameters of the onboard GNSS receiver of the low-orbit spacecraft, obtains the ground GNSS receiver clock error based on the GNSS receiver observation data connected to the ground atomic clock at the current moment and the function model and random model of carrier phase time transfer based on static GNSS non-difference, and further obtains the satellite-to-ground time transfer amount. This method improves the calculation strength of the satellite-borne GNSS receiver clock error by extracting prior spatiotemporal information and constructing an enhanced model, and further enhances the performance of satellite-to-ground time transfer. It has the characteristics of advanced algorithm and strong stability, and can effectively support the establishment and maintenance of space-based time standards.

[0080] Example 2

[0081] This embodiment 2 describes a computer device, which includes a memory and one or more processors.

[0082] An executable code is stored in the memory. When the processor executes the executable code, it is used to implement the steps of the low-orbit spacecraft satellite-to-ground time transfer method taking into account a priori space-time information in the above-mentioned embodiment 1.

[0083] In this embodiment, the computer device is any device or apparatus with data processing capability, which will not be described in detail here.

[0084] Example 3

[0085] This embodiment 3 describes a computer-readable storage medium having a program stored thereon, which, when executed by a processor, is used to perform steps of a method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information.

[0086] The computer-readable storage medium may be an internal storage unit of any device or apparatus with data processing capabilities, such as a hard disk or memory, or an external storage device of any device with data processing capabilities, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc., equipped on the device.

[0087] Of course, the above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It should be noted that all equivalent substitutions and obvious deformation forms made by any technician familiar with the field under the guidance of this specification fall within the essential scope of this specification and should be protected by the present invention.

Claims

1. A method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information, characterized in that: The steps include: Step 1. Obtain the orbital sequence data of the low-orbit spacecraft, perform a first epoch difference on the time series of its orbital components, obtain the running speed of the low-orbit spacecraft, and construct the orbital model of the low-orbit spacecraft; Step 2. Obtain the clock error data of the atomic clock group of the low-orbit spacecraft and build a prediction model for the onboard atomic clock; Step 3. Obtain the pseudorange and carrier phase observations of the onboard GNSS receiver on the low-orbit spacecraft, perform data preprocessing, construct the ionosphere-free combined observations, correct the errors of the onboard GNSS receiver, and establish a function model of carrier phase time transfer based on dynamic GNSS non-difference; Step 4. Establish a random model of carrier phase time transfer based on dynamic GNSS non-difference; Step 5. Combine the function model and random model of carrier phase time transfer based on dynamic GNSS non-difference with the prior space-time information constructed in step 1 and step 2, respectively, to construct the function model and random model of LEO spacecraft satellite-to-ground time transfer that take into account the prior space-time information; Step 6. For the GNSS receiver connected to the ground atomic clock, i.e., the ground GNSS receiver, the receiver clock difference of the ground station is obtained by using the method based on static GNSS non-differenced carrier phase time transfer, and the function model and random model based on static GNSS non-differenced carrier phase time transfer are obtained; Step 7. Based on the mathematical model and parameter solution algorithm obtained in Steps 5 and 6, the GNSS observation data at both ends of the satellite-to-ground time transfer link are processed respectively to obtain the receiver clock difference of the current epoch of the two stations. Combined with the inherent delay calibration of the satellite-to-ground time transfer link, a dynamic carrier phase time transfer solution model for low-orbit spacecraft that takes into account the enhancement of prior space-time information is constructed, and the satellite-to-ground time transfer of low-orbit spacecraft that takes into account the prior space-time information is completed.

2. The method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information according to claim 1, characterized in that: The step 1 is specifically as follows: Obtain the orbital sequence data of the low-orbit spacecraft, make a time difference between the epochs of the three components of its orbit, and obtain the running speed of the low-orbit spacecraft in three directions as shown in formula (1): (1) in, , , Respectively represent the running speed of low-orbit spacecraft in three directions, is the epoch marker, , , They are The three orbital components of the LEO spacecraft at the epoch, , , They are The three orbital components of the LEO spacecraft at the epoch; Based on the running speed of the low-orbit spacecraft obtained by formula (1), the orbit model of the low-orbit spacecraft is constructed as shown in formula (2): : (2) in, , and are the coefficients of the quadratic term, the first-order term, and the constant term, respectively; and represents the coefficients of the periodic function, is the period of the periodic function, , n represents the order.

3. The method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information according to claim 2, characterized in that: The step 2 is specifically as follows: The clock error data of the atomic clock group of the low-orbit spacecraft are obtained, and the prediction model of the onboard atomic clock is constructed as follows: (3) in, for The clock error of the satellite-borne GNSS receiver at the time, , , Respectively represent the reference time The initial clock error, clock speed, and clock drift, represents the error residual term.

4. The method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information according to claim 3, characterized in that: The step 3 is specifically as follows: Data preprocessing is performed on the pseudorange and carrier phase observations obtained from the onboard GNSS receiver on the low-orbit spacecraft to construct dual-frequency ionosphere-free combined observations; Among them, data preprocessing includes data integrity check, gross error identification, cycle slip detection and marking; The errors of the onboard GNSS receiver, including the ionospheric errors of the GNSS satellite and the onboard GNSS receiver, the antenna phase center errors, and the relativistic effects are corrected, and the tropospheric parameters are no longer estimated; The function model of carrier phase time transfer based on dynamic GNSS non-difference is established as shown in formula (4): (4) in, represents the pseudo-range ionosphere-free combined observation of the satellite-borne GNSS receiver clock, represents the carrier phase ionospheric-free combined observation of the satellite-borne GNSS receiver clock, For GNSS satellites With onboard GNSS receiver The distance between is the speed of light, is the satellite-borne GNSS receiver clock error, is the clock error of the GNSS satellite, is the pseudorange noise of the satellite-borne GNSS receiver clock, is the carrier phase ambiguity of the onboard GNSS receiver clock, is the carrier phase noise of the onboard GNSS receiver clock; Parameter vector to be estimated for: (5) in, are the three orbital components of a low-orbit spacecraft.

5. The method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information according to claim 4, characterized in that: The step 4 is specifically as follows: According to the state parameter characteristics of different types of parameters in the estimated parameter vector X obtained by formula (5), the corresponding random model is determined; for the fuzzy parameter When no cycle slip occurs, the process noise variance is set to 0; when a cycle slip occurs, it needs to be reinitialized and the process noise variance is set to 10 10 ; For the satellite GNSS receiver clock error parameters And the three orbital component parameters of low-orbit spacecraft All simulations were performed using white noise processes; The random model of carrier phase time transfer based on dynamic GNSS non-difference is established as shown in formula (6): (6) in, represents the covariance matrix of the parameters to be estimated for the spaceborne GNSS receiver, represents the co-factor of the three orbital components of the LEO spacecraft, The co-factor representing the clock error parameters of the onboard GNSS receiver, represents the co-factor of the ambiguity parameters of the onboard GNSS receiver, and m represents the number of ambiguity parameters of the onboard GNSS receiver clock.

6. The method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information according to claim 5, characterized in that: The step 5 is specifically as follows: The established dynamic GNSS carrier phase time transfer model, i.e., the function model of the carrier phase time transfer based on the dynamic GNSS non-difference in step 3 and the random model of the carrier phase time transfer based on the dynamic GNSS non-difference in step 4, are respectively combined with the prior space-time information constructed in step 1 and step 2, to further construct the function model and random model of the low-orbit spacecraft satellite-to-ground time transfer taking into account the prior space-time information; Among them, the function model of low-orbit spacecraft satellite-ground time transfer taking into account the prior space-time information is shown in formula (7): (7) in, express Pseudorange ionosphere-free combined observations from epoch spaceborne GNSS receivers, express GNSS satellites in epoch With onboard GNSS receiver The distance between express The onboard GNSS receiver clock error at the epoch, express The clock error of the GNSS satellite at the epoch, express Pseudorange noise of epoch spaceborne GNSS receiver, express The carrier phase ionospheric-free combined observations of the epoch spaceborne GNSS receiver, express Carrier phase noise of epoch spaceborne GNSS receiver, express The three orbital components of the epoch low-orbit spacecraft, express The three orbital components of the epoch low-orbit spacecraft, express The LEO spacecraft orbit model for the epoch, is the time interval of the LEO spacecraft orbit, for The onboard GNSS receiver clock error of the epoch; The random model of time transfer between low-orbit spacecraft and the ground taking into account the prior space-time information is shown in formula (8): (8) in, , , They are the weight distribution of the dynamic GNSS carrier phase time transfer model, the low-orbit spacecraft orbit model, and the onboard atomic clock prediction model. , , They are , , The corresponding mean error.

7. The method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information according to claim 6, characterized in that: The step 6 is specifically as follows: For the GNSS receiver connected to the ground atomic clock, the pseudorange and carrier phase observations of the ground GNSS receiver are obtained, and data preprocessing is performed to construct the ionosphere-free combined observations of the ground GNSS receiver; Among them, data preprocessing includes data integrity check, gross error identification, cycle slip detection and marking; Correct the errors of ground GNSS receivers, including ionospheric errors, antenna phase center errors, tropospheric errors, tides, and relativistic effects; Based on the method of static GNSS non-difference carrier phase time transfer, the clock error of the ground GNSS receiver is obtained, and the function model of static GNSS non-difference carrier phase time transfer is obtained as shown in formula (9): (9) in, is the pseudo-range ionosphere-free combined observation of the ground GNSS receiver, is the carrier phase ionospheric-free combined observation of the ground GNSS receiver, is the distance between the GNSS satellite and the ground GNSS receiver, is the clock error parameter of the ground GNSS receiver, represents the tropospheric delay parameter, is the pseudorange noise of the ground GNSS receiver, is the carrier phase ambiguity of the ground GNSS receiver, is the carrier phase noise of the ground GNSS receiver; The random model of carrier phase time transfer based on static GNSS non-difference is obtained as shown in formula (10): (10) in, represents the covariance matrix of the parameters to be estimated of the ground GNSS receiver, The cofactor representing the three-dimensional coordinates of the ground GNSS receiver, The co-factor representing the ground GNSS receiver clock error parameter, is the cofactor representing the tropospheric parameters, represents the cofactor of the ambiguity parameters of the ground GNSS receiver, and n represents the number of ambiguity parameters of the ground GNSS receiver.

8. The method for transferring time from a low-orbit spacecraft to the ground taking into account a priori space-time information according to claim 7, characterized in that: The step 7 is specifically as follows: The mathematical model and parameter calculation algorithm of step 5 and step 6 are used to process the GNSS observation data at both ends of the satellite-to-ground time transfer link respectively, and the receiver clock error of the two stations at the low-orbit spacecraft and the ground GNSS receiver at the current epoch is obtained. That is, by combining formulas (7) and (8), the least squares principle and method are used to obtain the satellite receiver clock error parameter at the current time: , combined with formula (9) and formula (10), using the least squares principle and method, that is, to obtain the ground GNSS receiver clock error parameters at the current moment ; Combined with the inherent delay calibration of the satellite-to-ground time transfer link, the dynamic carrier phase time transfer solution model for low-orbit spacecraft taking into account the enhancement of prior space-time information is obtained: (11) in, is the amount of time passed, Calibrate the inherent delay of the satellite-to-ground time transfer link; The LEO spacecraft dynamic carrier phase time transfer solution model taking into account the prior spacetime information enhancement shown in formula (11) is used to complete the LEO spacecraft satellite-to-ground time transfer taking into account the prior spacetime information.

9. A computer device comprising a memory and one or more processors, wherein the memory stores executable code, characterized in that: When the processor executes the executable code, the steps of the method for low-orbit spacecraft-to-ground time transfer taking into account a priori space-time information as described in any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a program stored thereon, characterized in that: When the program is executed by the processor, the steps of the method for transferring time between a low-orbit spacecraft and the ground taking into account a priori space-time information as described in any one of claims 1 to 8 are implemented.

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