Low earth orbit satellite orbit determination method and system based on BDS-3 navigation message SISRE accuracy improvement

Abstract

The present application relates to a kind of low-orbit satellite orbit determination method and system based on BDS-3 navigation message SISRE precision promotion.Method includes: according to the broadcast of BDS-3 navigation message broadcast parameter, the broadcast clock difference of current time in 1 hour is calculated;Based on historical 24 hours broadcast clock difference data, using fitting method to correct current time clock speed;Based on the corrected current time clock speed, the initial clock difference of next time is calculated;Clock difference jump is detected, when clock difference jump occurs, 24 hours of BDS-3 navigation message broadcast parameter is accumulated again, repeat the above steps;And using the corrected broadcast clock difference parameter, combined with low-orbit satellite on-board observation data completes autonomous orbit determination.The method proposed in the present application, calculation step is simple, can greatly reduce SISRE error, so that on-board autonomous orbit determination has high precision and timeliness, meet the requirements of occultation detection and satellite measurement and other important scientific tasks.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of satellite navigation and orbit determination, and particularly relates to a low-orbit satellite orbit determination method and system based on BDS-3 navigation message SISRE accuracy improvement. BACKGROUND

[0002] The Beidou-3 satellite navigation system (BDS-3) was officially completed in July 2020 and can provide services to global users. In addition to basic positioning, navigation, and timing services, it also integrates satellite-based augmentation, precise point positioning, international search and rescue services, and short message communication functions [1]. BDS-3 provides real-time continuous navigation and positioning services to global users by broadcasting navigation signals and navigation messages.

[0003] As a space-based monitoring station, low-orbit satellites can receive BDS-3 navigation signals by carrying receivers, thereby realizing low-orbit satellite orbit determination. As an alternative to traditional ground processing, on-board autonomous orbit determination can be considered in combination with BDS-3 navigation signals and navigation messages to further reduce the overall delay in providing accurate low-orbit satellite orbit information. However, the Signal-In-Space Range Error (SISRE) of the BDS-3 satellite navigation message directly affects the accuracy of the low-orbit satellite autonomous orbit determination. Due to factors such as prediction strategy and measurement error, the BDS-3 satellite clock error determination accuracy is poor, which is the main bottleneck limiting the improvement of the SISRE accuracy of the BDS-3 navigation message. So far, there have been few studies on low-orbit satellite orbit determination using BDS-3 navigation messages, and the impact of BDS-3 broadcast clock errors on low-orbit satellite autonomous orbit determination has not been considered. In the existing technology, there are several schemes for low-orbit satellite orbit determination:

[0004] Scheme one, a low-orbit satellite orbit determination method and device are provided. First, the navigation message and observation data of the navigation satellite are obtained, and the positioning information of the navigation satellite is calculated according to the navigation message. Then, the correction information of the positioning information sent by the ground system is received, and the positioning information is corrected to obtain the corrected positioning information. Finally, the low-orbit satellite is determined by using the corrected positioning information and the observation data. This method introduces the correction information of the positioning information, and uses the corrected positioning information to determine the low-orbit satellite, thereby improving the orbit determination accuracy. However, this method requires additional correction information to correct the positioning information of the navigation satellite, and the correction information includes orbit correction numbers and clock correction numbers. The acquisition of the correction information requires real-time precise orbit determination of the navigation satellite using observation data from the ground station, which is already quite complex. Therefore, this method is not easy to implement, and the data transmission cost is large. This method also depends on the navigation satellite and the ground station, and the autonomy is poor.

[0005] In scheme two, a low-orbit satellite constellation autonomous orbit determination method is provided, which comprises obtaining inter-satellite link ranging data and satellite-borne GNSS (Global Navigation Satellite System) receiver observation data; using the observation data to establish an observation model and pre-process the observation data; using the pre-processed observation data to perform on-satellite PPP (Precise Point Positioning) calculation to obtain the on-orbit rough spatial position of each low-orbit satellite; selecting an orbit determination perturbation correction mechanics model to establish a low-orbit satellite dynamics differential equation; establishing an orbit determination function model in combination with the observation model; constructing a random model, fusing the orbit determination function model and the random model to establish a joint adjustment model, and obtaining a low-orbit satellite orbit determination result; using the inter-satellite link ranging data to construct a low-orbit satellite constellation space network, combining the joint adjustment model to obtain a low-orbit satellite constellation autonomous orbit determination result, and directly using the inter-satellite link ranging data and the GNSS receiver observation data to achieve on-satellite high-precision safe autonomous orbit determination of the low-orbit satellite. The problem to be solved by the method is that in the prior art, the number of ground monitoring stations is small, and the geographical position distribution of the ground monitoring stations is uneven, causing inaccurate orbit determination of the low-orbit satellite constellation. The method does not pass through the ground monitoring station, but directly uses the inter-satellite link data and the GNSS receiver observation data to achieve on-satellite high-precision safe autonomous orbit determination of the low-orbit satellite. In the method, the inter-satellite link ranging data is integrated into the low-orbit satellite orbit determination, the geometric configuration of the low-orbit satellite is increased, and the low-orbit satellite orbit determination precision is improved. According to the constellation space network constructed by the inter-satellite link ranging data, the inter-satellite link can determine the mutual position relationship of each satellite, and the positioning reliability and precision are enhanced. However, the method includes multiple key steps, and requires more data types and data quantities. Both the precise point positioning method and the dynamics orbit determination method are needed. The PPP calculation needs to provide high-precision GNSS satellite orbit and clock error information, and the acquisition of this information still cannot completely get rid of the ground station building problem, otherwise the problem of inaccurate space reference of the low-orbit constellation may occur.

[0006] Scheme three, a low earth orbit satellite real-time orbit determination and time-frequency synchronization method based on B2b signal is provided. First, the B2b signal broadcast by Beidou-3 GE0 (Geostationary Earth Orbit) satellite is received, matched with navigation message, and restored to B2b real-time ephemeris with higher accuracy. Second, the real-time orbit determination algorithm of numerical integral prediction-filtering correction is used instead of pseudorange single point positioning method, combined with pseudorange, carrier phase and Doppler observation value and B2b real-time ephemeris, to improve the real-time orbit and clock error accuracy of satellite receiver. Finally, in the case of insufficient Beidou navigation observation value, the low earth orbit satellite orbit is extrapolated through the dynamic model, and the receiver clock error is determined by using single satellite timing method, so as to ensure the continuity of real-time orbit determination and time synchronization. The method uses B2b signal and integral prediction-filtering correction orbit determination method, which can improve the accuracy and continuity of low earth orbit satellite real-time orbit determination and time-frequency synchronization. However, this method needs to introduce B2b signal, which increases the data type and transmission cost. In the B2b signal blind area segment, the orbit and clock correction parameters need to be extrapolated, and the blind area and non-blind area segments are weighted respectively, which increases the algorithm complexity.

[0007] Scheme four, a positioning method, device and terminal based on Beidou-3 satellite satellite-based augmentation is provided. The current satellite clock correction parameters are estimated through the historical satellite clock correction parameters released by Beidou-3 satellite, and the current ephemeris correction parameters are estimated through the historical ephemeris correction parameters. Therefore, the estimated ephemeris correction parameters and satellite clock correction parameters can correct the satellite clock and ephemeris of Beidou-3 satellite, so that the corrected satellite clock and ephemeris are closer to the actual satellite clock and ephemeris at the time of initiating positioning, reducing the error between the corrected satellite clock and ephemeris and the actual satellite clock and ephemeris, thus improving the positioning accuracy of the terminal. This scheme uses historical ephemeris and satellite clock correction parameters, which need to be obtained by additional processing means, the data source is more complex, the availability is reduced, and the transmission cost is increased.

[0008] The scheme fits the historical ephemeris and satellite clock correction parameters and estimates the future ephemeris and satellite clock parameters, and the fitting accuracy and estimation accuracy cannot be guaranteed. Although the weight function is increased, only the time difference factor is considered, and the influence of estimation error is not considered.

[0009] Scheme five provides a satellite positioning method and device based on BDS-3 B2b signal, the method comprising: obtaining original observation data broadcast by BDS-3 satellite and a plurality of correction numbers carried in the broadcast B2b signal; calculating the orbit and clock difference correction numbers at the current time by using the orbit and clock difference correction numbers at a plurality of historical broadcast times; determining the satellite precise orbit and satellite precise clock difference at the current time according to the navigation message and the orbit and clock difference correction numbers at the current time; correcting the pseudo-range observation values of different frequencies according to the code bias correction number; and determining the position of the device to be positioned at the current time according to the satellite precise orbit, the satellite precise clock difference and the corrected pseudo-range observation values. The scheme uses a plurality of historical broadcast time correction data to determine the orbit and clock difference correction numbers at the current time, which weakens the influence of the mismatch between the current time and the broadcast time on the precise orbit and the precise clock difference, and realizes high-precision real-time precise positioning. The scheme relies on external B2b signal correction numbers, and cannot guarantee the accuracy of the correction. The scheme uses polynomial fitting correction numbers, which does not have a theoretical basis, that is, the correction numbers do not necessarily conform to the polynomial characteristics, and there may be a large fitting error.

[0010] The existing low-orbit satellite orbit determination technology scheme has many deficiencies, such as the need for additional correction information, high data transmission cost, poor autonomy, the need for multiple types of data, complex data processing, the introduction of special signals to increase data processing cost and algorithm complexity, etc. Therefore, there is an urgent need for a method that can effectively improve the low-orbit satellite autonomous orbit determination accuracy based on BDS-3 navigation message. SUMMARY

[0011] In view of some or all of the problems in the prior art, the present application provides a low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE accuracy improvement, which comprises the following steps:

[0012] According to the broadcast parameters of the BDS-3 navigation message, the broadcast clock difference at the current time within 1 hour is calculated;

[0013] Based on the historical 24-hour broadcast clock difference data, the current clock rate is corrected using a fitting method;

[0014] Based on the corrected current clock rate, the initial clock difference at the next time is calculated;

[0015] Detecting clock difference jump, when the clock difference jump occurs, 24 hours of BDS-3 navigation message broadcast parameters are re-accumulated, and the above steps are repeated; and

[0016] Using the corrected broadcast clock difference parameters, autonomous orbit determination is completed in combination with low-orbit satellite on-board observation data.

[0017] Further, according to the broadcast parameters of the BDS-3 navigation message, the broadcast clock difference at the current time within 1 hour is calculated, which comprises:

[0018] The satellite navigation message broadcast parameter interval is 1 hour, and 24 groups are broadcast per day;

[0019] The broadcast clock difference at the current time within 1 hour is calculated,

[0020]

[0021] wherein, is the broadcast clock difference at the current time, i.e., at time t, 、 、 is the initial clock difference, the clock speed, and the clock drift at time t, respectively, is the reference time.

[0022] Further, based on historical 24-hour broadcast clock difference data, the current time clock speed is corrected using a fitting method, including:

[0023] The 24-hour broadcast clock difference data is fitted using a quadratic polynomial fitting model to correct the current time clock speed ;

[0024] The quadratic polynomial fitting model is,

[0025]

[0026] wherein, is the broadcast clock difference at time t, and the broadcast clock difference formula is combined to solve the clock difference deviation , the clock speed , and the clock drift based on the least squares method; ; The clock speed correction value is used instead of the original clock speed value of the 24th hour.

[0027] Further, based on the corrected current time clock speed, the initial clock difference at the next time is calculated, including:

[0028] Based on the corrected current time clock speed , the initial clock difference at the next time is calculated,

[0029]

[0030]

[0031] wherein, is the initial clock difference at the start time, is the initial clock difference at the corrected time t, is the clock speed at the corrected time t.

[0032] ​​Further, the absolute median difference method is used to detect the clock jump, which comprises the following steps:

[0033] Calculate the median of the clock difference sequence ;

[0034] Calculate the absolute deviation of the clock difference at time i from the median,

[0035]

[0036] wherein, is the clock difference at time i;

[0037] Calculate the median of the absolute deviation M AD,

[0038] ;

[0039] If the clock difference is outside the set threshold range, it is determined that a clock jump has occurred,

[0040] The set threshold range is,

[0041]

[0042] wherein n is 3.

[0043] Further, the low-orbit satellite on-board observation data is calculated by the pseudo-range and phase observation equation of the dual-frequency ionosphere-free combination,

[0044]

[0045] wherein C, L, and i respectively represent the BDS-3 satellite, the low-orbit satellite, and the frequency, is the geometric distance between the BDS-3 satellite and the low-orbit satellite, and are the low-orbit satellite on-board receiver clock difference and the BDS-3 satellite clock difference, respectively, and c represents the speed of light in vacuum, , respectively represent the pseudo-range hardware delay of the low-orbit receiver and the GNSS satellite under the IF combination, , respectively represent the phase bias of the LEO receiver and the GNSS satellite under the IF combination, , respectively represent the phase wavelength and the phase ambiguity under the IF combination, , respectively represent the pseudo-range and phase IF combination observation value measurement noise.

[0046] Further, the spatial signal ranging error SISRE is used to evaluate the autonomous orbit determination accuracy,

[0047]

[0048] wherein, 、 、 are the radial, tangential and normal orbital errors in the satellite orbit reference frame respectively, is the clock error, 、 are the radial and tangential-normal plane error projection coefficients of the BDS-3 satellite orbit respectively.

[0049] The application further provides a system for the low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement, which comprises:

[0050] a broadcast clock error calculation module configured to calculate the broadcast clock error at the current time within one hour according to the BDS-3 navigation message broadcast parameters;

[0051] a clock rate fitting module configured to correct the clock rate at the current time by using a fitting method based on the historical 24-hour broadcast clock error data;

[0052] an initial clock error calculation module configured to calculate the initial clock error at the next time based on the corrected clock rate at the current time;

[0053] a clock error jump detection module configured to detect the clock error jump and re-accumulate the 24-hour BDS-3 navigation message broadcast parameters when the clock error jump occurs, and repeat the above steps; and

[0054] an autonomous orbit determination module configured to complete autonomous orbit determination by using the corrected broadcast clock error parameters in combination with the low-orbit satellite on-board observation data.

[0055] The application further provides an electronic device, which comprises:

[0056] a processor configured to execute machine readable instructions;

[0057] a graphics card with an artificial intelligence chip configured to train the low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement; and

[0058] a memory configured to store machine readable instructions, wherein the machine readable instructions perform the steps of the low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement when executed by the processor and / or the graphics card.

[0059] The application further provides a computer readable storage medium having machine readable instructions stored thereon, wherein the machine readable instructions perform the steps of the low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement when executed by the processor.

[0060] The technical scheme provided by the application has the following advantages:

[0061] 1. The low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement provided by the application has simple calculation steps, can greatly reduce SISRE error, enables on-board autonomous orbit determination to have high precision and timeliness, and meets the requirements of important scientific tasks such as occultation detection and satellite measurement.

[0062] 2. The low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement provided by the application only uses satellite-borne GNSS observation data and navigation messages as data sources, does not need additional data input, only needs to perform correction operation on the navigation messages, uses less types and amounts of data, and therefore reduces the cost.

[0063] 3. The low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement provided by the application can correct clock speed through simple polynomial fitting, and correct initial clock difference according to first-order polynomial recursion, has low realization difficulty of correction algorithm, has no obvious difference in workload compared with conventional on-board autonomous orbit determination, does not need to use additional auxiliary information, does not depend on a ground system, and effectively improves orbit determination precision, thereby improving the autonomy and reliability of autonomous orbit determination. BRIEF DESCRIPTION OF DRAWINGS

[0064] To further clarify the above and other advantages and features of the embodiments of the present application, a more particular description of the embodiments of the present application will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the application and are therefore not to be considered limiting of its scope. In the drawings, the same or corresponding elements are denoted by the same or similar reference signs.

[0065] Figure 1 Fig. 1 shows a flowchart of the low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement of one embodiment of the application;

[0066] Figure 2 Fig. 2 shows a comparison diagram of clock speed random errors before and after correction of one embodiment of the application;

[0067] Figure 3 Fig. 3 shows a comparison diagram of clock difference standard deviations before and after correction of one embodiment of the application;

[0068] Figure 4 Fig. 4 shows a comparison diagram of clock difference Allan variances before and after correction of one embodiment of the application;

[0069] Figure 5 Fig. 5 shows a comparison diagram of broadcast message SISRE before and after clock speed correction of one embodiment of the application;

[0070] Figure 6 A clock correction before and after the broadcast message of four satellites of an embodiment of the application is shown in the orbit determination accuracy comparison diagram; and

[0071] Figure 7 A low-orbit satellite orbit determination system based on BDS-3 navigation message SISRE accuracy improvement of an embodiment of the application is shown in the schematic diagram. DETAILED DESCRIPTION

[0072] In the following description, reference is made to specific embodiments of the application. Those skilled in the art will recognize that the application can be practiced with one or more of the specific details set forth herein. In other instances, well-known structures or operations are not shown or described in order to not obscure the application. Similarly, for the purpose of explanation, specific numbers and configurations are set forth in order to provide a thorough understanding of the embodiments of the application. Nevertheless, the application is not limited to the disclosed embodiments.

[0073] In this specification, reference to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0074] It should be noted that the embodiments of the present application describe the method steps in a particular order, however this is only for the purpose of illustrating the specific embodiment, and does not limit the order of the steps. Conversely, in different embodiments of the present application, the order of the steps can be adjusted according to the actual needs of the adjustment.

[0075] High-precision GNSS orbit and clock products have been widely used in traditional ground systems for post-processing low-orbit satellite precise orbit determination. However, in addition to the orbit determination accuracy, the timeliness of the low-orbit satellite orbit is more critical for important scientific tasks such as occultation detection and satellite measurement. As an alternative to traditional ground processing, on-board autonomous orbit determination can be considered in combination with BDS-3 navigation signals and navigation messages to further reduce the overall delay of providing accurate low-orbit satellite orbit information.

[0076] The existing research on the implementation of low-orbit satellites based on BDS-3 navigation messages can only achieve limited accuracy, which is mainly limited by the BDS-3 navigation message error. The navigation message error is usually represented by the space signal accuracy SISRE, which includes two parts of broadcast orbit error and clock difference parameter error. Therefore, the SISRE level of the BDS-3 satellite navigation message directly affects the on-board autonomous orbit determination accuracy of the low-orbit satellite. Due to the influence of factors such as prediction strategy and measurement error, the BDS-3 satellite clock difference determination accuracy is poor. Therefore, the SISRE accuracy of the BDS-3 satellite is poor, which is mainly attributed to the broadcast clock difference error.

[0077] Currently, the research on the accuracy improvement of GNSS navigation messages mainly focuses on the positioning service verification of ground stations, and is less applied to the field of on-board autonomous orbit determination of low-orbit satellites based on navigation messages. The influence of the accuracy improvement of the navigation message SISRE on the on-board autonomous orbit determination accuracy of the low-orbit satellite is unknown.

[0078] The present application proposes a low-orbit satellite orbit determination method based on the SISRE accuracy improvement of the BDS-3 navigation message, which mainly includes the following steps: for the error of the BDS-3 navigation message, the broadcast clock difference error which accounts for the main part is corrected, the BDS-3 broadcast clock difference parameter is composed of the initial clock difference and the clock speed , wherein the clock speed sequence contains random errors, and the historical clock speed information is used to correct the clock speed information at the current time; based on the correction result of the clock speed at the current time, the initial clock difference at the next time is derived in combination with the initial clock difference at the current time, so as to replace the original initial clock difference; for the case that the clock difference jumps, the algorithm is restarted at the time when the jump occurs, that is, the above steps are repeated, so as to improve the compatibility of the correction algorithm; the broadcast clock difference error and the SISRE error change before and after the correction are analyzed, and the corrected broadcast clock difference is used for the on-board autonomous orbit determination of the low-orbit satellite, and the effect is verified.

[0079] Figure 1 The present application proposes a low-orbit satellite orbit determination method based on the SISRE accuracy improvement of the BDS-3 navigation message, which mainly includes the following steps: for the error of the BDS-3 navigation message, the broadcast clock difference error which accounts for the main part is corrected, the BDS-3 broadcast clock difference parameter is composed of the initial clock difference Figure 1 , the present application proposes a low-orbit satellite orbit determination method based on the SISRE accuracy improvement of the BDS-3 navigation message. In an embodiment of the present application, the low-orbit satellite orbit determination method based on the SISRE accuracy improvement of the BDS-3 navigation message can be executed by a computer. As shown in Figure 1 , the low-orbit satellite orbit determination method based on the SISRE accuracy improvement of the BDS-3 navigation message includes the following steps:

[0080] Firstly, according to the BDS-3 navigation message broadcast parameters, the broadcast clock difference of the current time within 1 hour is calculated. The broadcast interval of the BDS-3 navigation message is 1 hour, and 24 groups are broadcast every day. According to the parameters broadcast every hour, the broadcast clock difference of the current time within 1 hour can be calculated by the following formula,

[0081]

[0082] wherein, is the broadcast clock difference at the current time t, , , is the initial clock difference, clock speed and clock drift at t, is the reference time.

[0083] At intervals of 30s, the broadcast clock difference at multiple times within the past 24 hours is calculated according to the above formula.

[0084] Next, based on the historical 24-hour broadcast clock difference data, the current time clock speed is corrected using a fitting method.

[0085] The satellite clock difference conforms to the polynomial characteristics, and a quadratic polynomial fitting model is used to fit the broadcast clock difference data within 24 hours to correct the clock speed at the current time If the clock speed at the next time is to be corrected, the broadcast clock difference of the next time within 24 hours needs to be fitted. With a 24-hour window for sliding processing, the subsequent broadcast clock speed can be corrected. The historical clock speed data of the present invention is based on the current time, and the 24 clock speed values in the sliding window are the clock speeds at the historical time, and the 24th clock speed value is the original clock speed at the current time. When sliding to the next time, the first clock speed is discarded and the original clock speed at the next time is added, and thus a new clock speed is fitted by sliding.

[0086] The quadratic polynomial fitting model is,

[0087]

[0088] wherein, is the broadcast clock difference at the current time t, is the broadcast clock difference at the current time t, and the broadcast clock difference formula is combined to solve the clock difference deviation , clock speed and clock drift ; as the clock speed correction value instead of the original clock speed value at the 24th hour.

[0089] Next, based on the corrected clock speed at the current time, the initial clock difference at the next time is calculated.

[0090] Based on the corrected clock speed at the current time Calculate the initial clock difference for the next time step.

[0091]

[0092]

[0093] in, The initial clock difference at the start time, For the revised The initial clock difference of the time, For the revised The speed of time.

[0094] It's important to note that the start time here is not necessarily related to the current time mentioned earlier. For example, if the algorithm is first started in the 24th hour, then this 24th hour is the algorithm's start time. The algorithm here is the broadcast clock error correction algorithm. The current time is the 24th hour; the clock rate value can be corrected by fitting the clock error calculated from the 1st to the 24th hour. However, the initial clock difference at the 24th hour cannot be directly corrected; the initial clock difference at this moment... Keep the original broadcast values. (Right now However, for the clock rate at the 25th hour, the current time is the 25th hour, but the 25th hour is already a non-starting time. Therefore, the clock rate is corrected by fitting the clock difference calculated from the 2nd to the 25th hour. The initial clock difference at the 25th hour Using the 24th hour and the 25th hour Calculations are performed to obtain (i.e.) ).

[0095] One hour is the broadcast interval for clock bias parameters, i.e., the validity period (this set of parameters can be used within one hour). Each broadcast clock bias has a reference time. To calculate the satellite clock bias at the current time, it can be calculated based on the time difference between the current time and the reference time, combined with the broadcast clock bias parameters. Initial clock bias recursion does not lead to error accumulation because the initial clock bias is based on the corrected clock rate, which is corrected every hour. The initial clock bias can then be corrected based on the corrected clock rate, preventing error accumulation. Regarding quantifying long-term stability, the accuracy of the clock bias after algorithm correction can be evaluated using historically known clock bias data.

[0096] Figure 2 This diagram illustrates a comparison of the random clock speed errors of four satellites before and after correction according to an embodiment of the present invention. Figure 2 In the diagram, blue dots represent the area before correction, and red dots represent the area after correction. For example... Figure 2 As shown, the corrected clock speed random error is significantly reduced compared to the original error.

[0097] Figure 3 The clock error standard deviation before and after correction of one embodiment of the application is shown in the comparative schematic diagram. Figure 3 In the figure, the light blue column is before correction, and the red column is after correction. After correction, the clock error standard deviation (STD) is lower than before correction for most satellites. It should be noted that the method provided in the application significantly improves the clock error accuracy as a whole, and since the entire BDS-3 constellation of satellites is used for orbit determination rather than a single satellite, the orbit determination accuracy is also improved.

[0098] Figure 4 The clock error Allan variance before and after correction of one embodiment of the application is shown in the comparative schematic diagram. Figure 4 In the figure, the left graph is before correction, and the right graph is after correction. It can be seen that Figure 4 After broadcast clock error correction, the clock error frequency stability is significantly improved. Before correction, the 1,000-second stability is 3.54 10 -13 to 8.37 10 -13 , and the 10,000-second stability is 1.08 10 -13 to 2.15 10 -13 . After correction, the 1,000-second stability is 1.71 10 -14 to 3.68 10 -14 , and the 10,000-second stability is 1.74 10 -14 to 3.49 10 -14 . Comparing the two, the 1,000-second stability and the 10,000-second stability are both improved by an order of magnitude after correction. It should be noted that in the application, all represent multiplication.

[0099] Next, the clock error jump is detected, and when the clock error jump occurs, 24 hours of BDS-3 navigation message broadcast parameters are re-accumulated, and the above steps are repeated. The clock error jump detection is to prevent the clock error jump from affecting the fitting, so when the clock error jump is detected, the algorithm is restarted at the time when the clock error jump occurs, and 24 hours of BDS-3 navigation message broadcast data need to be accumulated again to continue the correction process. The re-accumulation of historical data corrects the clock speed and the initial clock error to prevent the fitting window from containing jump data. This strategy increases the compatibility of the algorithm to meet the continuous broadcast clock error correction under complex long-arc conditions.

[0100] The absolute median deviation (MAD) method is used to detect the clock jump, which comprises the following steps:

[0101] The median of the clock error sequence is calculated ;

[0102] The absolute deviation of the clock error at time i from the median is calculated,

[0103]

[0104] wherein, is the clock error at time i;

[0105] The median of the absolute deviation, MAD, is calculated

[0106] ;

[0107] If the clock error is outside the set threshold range, it is determined that a clock jump has occurred,

[0108] The set threshold range is,

[0109]

[0110] wherein n is usually 3, and the coefficient 1.4826 is used to normalize to a scale similar to the standard deviation of the normal distribution.

[0111] Finally, the corrected broadcast clock error parameters are used to complete autonomous orbit determination in combination with the low-orbit satellite on-board observation data.

[0112] The BDS-3 broadcast orbit, and the broadcast clock error before and after correction are respectively used for low-orbit satellite autonomous orbit determination on board. The precise ephemeris of the low-orbit satellite is used as a reference orbit to evaluate the improvement effect of the autonomous orbit determination accuracy.

[0113] The low-orbit satellite receives the BDS-3 satellite signal through the on-board receiver carried, and adopts the dynamic orbit determination method to solve the precise orbit and dynamic parameters of the low-orbit satellite based on the on-board BDS-3 pseudo-range and phase observation data.

[0114] Generally, the BDS-3 dual-frequency data is combined, such as the combination of signals of B1I and B3I frequency points, which can eliminate the influence of ionospheric delay. The on-board observation data of the low-orbit satellite is calculated by the pseudo-range and phase observation equation of the dual-frequency ionosphere-free combination (IF). The pseudo-range and phase observation equation of the dual-frequency ionosphere-free combination (IF) can be expressed as:

[0115]

[0116] where C, L, i represent BDS-3 satellite, LEO satellite and frequency, respectively, is the geometric distance between BDS-3 satellite and LEO satellite, and are the clock bias of LEO satellite and BDS-3 satellite, respectively, c represents the speed of light in vacuum, 、 and 、 are the phase bias of LEO receiver and GNSS satellite under IF combination, respectively, 、 are the phase wavelength and phase ambiguity under IF combination, respectively, 、 are the measurement noise of pseudorange and phase under IF combination, respectively.

[0117] According to the dynamic model of LEO satellite, the satellite acceleration is mainly related to the satellite position, velocity and dynamic parameters, so the satellite motion equation can be expressed as:

[0118]

[0119] where, is the state of satellite at time t, is the satellite position, is the satellite velocity, is the satellite acceleration, is the dynamic parameter.

[0120] Based on the above formula, the satellite position and velocity at any time can be obtained by numerical integration given the initial state of satellite. The essence of precise orbit determination of LEO satellite is to solve the initial state of satellite and dynamic parameters by using observation data. Combined with the motion equation and observation equation, the initial state of satellite and dynamic parameters can be solved by batch least squares processing, and then the satellite state and corresponding dynamic parameters of the whole arc segment can be obtained by numerical integration.

[0121] SISRE is an important indicator to evaluate the accuracy of GNSS service, which can be represented by the broadcast navigation message and the satellite broadcast message error and clock bias parameter error calculated by precise product[2]. The calculation formula of SISRE is,

[0122]

[0123] where, 、 、 are the radial, tangential and normal orbit errors in the satellite orbit reference system, respectively, is the clock error; , respectively are the radial and tangential plane error projection coefficients of BDS-3 satellite orbits proposed by Montenbruck et al. [3], is 0.981, is 0.136.

[0124] Figure 5 shows a broadcast message SISRE comparison schematic diagram before and after clock speed correction of an embodiment of the application. Figure 5 In the figure, the light blue column is before correction, and the red column is after correction. Figure 5 It can be seen that after the clock speed correction, the SISRE of most BDS-3 satellites is reduced. The average SISRE of 23 satellites is reduced from 27.73 cm to 20.49 cm, and the average precision improvement rate is 25.49%.

[0125] The satellite orbit obtained by broadcast message orbit determination is subtracted from the centimeter-level reference orbit, and the RMS values of RTN and 3D direction orbit errors are counted, as shown in Figure 6 . Figure 6 shows a broadcast message orbit determination precision comparison schematic diagram of four satellites before and after clock speed correction of an embodiment of the application. Figure 6 In the figure, the light blue column is before correction, and the red column is after correction. Figure 6 It can be seen that the three-dimensional precision of the broadcast message orbit determination after the clock speed correction is better than that of the clock speed uncorrected result, and the precision of SATA at the annual accumulated day 294 is most obviously improved, and the three-dimensional error is reduced from 32.19 cm to 11.37 cm.

[0126] The present application aims at the problem of poor precision of low-orbit satellite autonomous orbit determination based on BDS-3 navigation message, and proposes a low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement. According to the theory that the broadcast clock error accounts for the main part of the BDS-3 satellite SISRE error, it is proposed to mainly correct the broadcast clock error. In view of the problem that the broadcast clock rate sequence has random error, a polynomial fitting method is proposed to weaken the random error. First, based on the historical broadcast clock rate and the initial clock error, the high-resolution broadcast clock error in the historical arc segment is calculated. Second, the clock rate is obtained by fitting the calculated historical broadcast clock error. The strategy is used to continuously correct the clock rate at future time, and the initial clock error at next time is calculated based on the clock rate at current time and the initial clock error, so as to realize the initial clock error. Based on the corrected initial clock error and clock rate, the corrected broadcast clock error is calculated, and the result is applied to the low-orbit satellite autonomous orbit determination based on BDS-3 navigation message. Through a series of correction algorithms, the precision of broadcast clock error and SISRE is improved. Finally, the precision of low-orbit satellite autonomous orbit determination based on BDS-3 navigation message is effectively improved, which provides a valuable reference for the research in this field.

[0127] The low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement provided by the present application has simple calculation steps, can greatly reduce SISRE error, make the on-board autonomous orbit determination have high precision and timeliness, meet the requirements of important scientific tasks such as occultation detection and satellite measurement; the data source is only the on-board GNSS observation data and navigation message, no additional data input is needed, only the navigation message is corrected, the data type and data amount used are less, so the cost is reduced; only through simple polynomial fitting, the clock rate can be corrected, and according to the first-order polynomial recursion, the initial clock error can be corrected, the correction algorithm has low implementation difficulty, there is no obvious difference in workload compared with the conventional on-board autonomous orbit determination, no additional auxiliary information is needed, it is not dependent on the ground system, and the orbit determination precision is effectively improved, the autonomy and reliability of autonomous orbit determination are improved.

[0128] In an embodiment of the present application, the present application also provides a system for the low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement, as shown in Figure 7 The system comprises:

[0129] A broadcast clock error calculation module configured to calculate the broadcast clock error at the current time within 1 hour according to the BDS-3 navigation message broadcast parameter;

[0130] A clock rate fitting module configured to correct the clock rate at the current time using a fitting method based on historical 24-hour broadcast clock error data;

[0131] An initial clock difference calculation module is configured to calculate an initial clock difference at a next time based on the corrected current time clock rate;

[0132] A clock difference jump detection module is configured to detect a clock difference jump, re-accumulate 24 hours of BDS-3 navigation message broadcast parameters when the clock difference jump occurs, and repeat the above steps; and

[0133] An autonomous orbit determination module is configured to use the corrected broadcast clock difference parameters to complete autonomous orbit determination in combination with low-orbit satellite on-board observation data.

[0134] In an embodiment of the present application, the present application also provides an electronic device, comprising a processor, a graphics card with an artificial intelligence chip, and a memory, the memory being configured to store machine-readable instructions, the graphics card being configured to train the low-orbit satellite orbit determination method based on BDS-3 navigation message SISRE precision improvement, and the processor being configured to execute the machine-readable instructions. The processor and / or the graphics card implement the following processing steps when executing the machine-readable instructions: calculating a broadcast clock difference at a current time within 1 hour according to BDS-3 navigation message broadcast parameters; correcting a current time clock rate based on historical 24-hour broadcast clock difference data using a fitting method; calculating an initial clock difference at a next time based on the corrected current time clock rate; detecting a clock difference jump, re-accumulating 24 hours of BDS-3 navigation message broadcast parameters when the clock difference jump occurs, and repeating the above steps; and using the corrected broadcast clock difference parameters to complete autonomous orbit determination in combination with low-orbit satellite on-board observation data.

[0135] The graphics card can preferably be a GPU algorithm power higher than 5.0 model. Since the amount of data required for training is large, providing a graphics card configuration can significantly improve the training speed.

[0136] The memory includes various media that can store machine-readable instructions, such as a U disk, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk, or an optical disk.

[0137] It can be understood that the above computer system includes other software and hardware components not listed in the present specification in addition to the above-mentioned memory and processor. The specific data processing equipment model can be determined according to different application scenarios, and the present specification will not be listed in detail.

[0138] In one embodiment of the present application, the present application also provides a computer readable storage medium having stored thereon machine readable instructions which, when executed by a processor, implement the following processing steps: calculating a broadcast clock difference at a current time within 1 hour according to a BDS-3 navigation message broadcast parameter; correcting a current time clock rate using a fitting method based on historical 24-hour broadcast clock difference data; calculating an initial clock difference at a next time based on the corrected current time clock rate; detecting a clock difference jump, and when a clock difference jump occurs, re-accumulating 24 hours of BDS-3 navigation message broadcast parameters, repeating the above steps; and using the corrected broadcast clock difference parameter, combined with low-orbit satellite on-board observation data to complete autonomous orbit determination.

[0139] Although the above describes various embodiments of the present application, it should be understood that they are presented only as examples, not as limitations. It is obvious to those skilled in the related art that various combinations, modifications and changes can be made without departing from the spirit and scope of the present application. Therefore, the breadth and scope of the present application disclosed herein should not be limited by the above disclosed exemplary embodiments, but should be defined according to the technical solutions of the present application and their equivalent replacements.

[0140] The references cited in the present application are as follows:

[0141] [1] Cai, H., Meng, Y., Geng, C., et al. Beidou Navigation Satellite System BDS-3 Service Performance Assessment: Positioning, Navigation, Timing, Satellite-Based Augmentation, Precise Point Positioning, Short Message Communication and International Search and Rescue[J]. Acta Geodaetica et Cartographica Sinica, 2021, 50(04): 427-435.

[0142] [2] Chen, G., Hu, Z., Wang, G., Chen, G., Liu, Z., Zhao, Q., 2015. Assessment of BDS Signal-in-Space Accuracy and Standard Positioning Performance During 2013 and 2014. In: Sun, J., Liu, J., Fan, S., Lu, X., (Eds.). In: China Satellite Navigation Conference (CSNC) 2015.

[0143] [3] Montenbruck, O., Steigenberger, P., Hauschild, A., 2018. Multi-GNSS signal-in-space range error assessment - Methodology and results. Advances in Space Research 61, 3020-38. https: / / doi.org / https: / / doi.org / 10.1016 / j.asr.2018.03.041.

Claims

1. A low earth orbit satellite autonomous orbit determination method based on BDS-3 navigation message SISRE accuracy improvement, characterized in that, Under the condition of not relying on the correction information provided by the ground system, comprising the following steps: According to the BDS-3 navigation message broadcast parameter, the broadcast clock difference at the current time within 1 hour is calculated; Based on the historical 24-hour broadcast clock difference data, the current clock rate is corrected using a fitting method; Based on the corrected current clock rate, the initial clock difference at the next time is calculated by recursion; Detecting clock difference jump, when the clock difference jump occurs, re-accumulate 24 hours of BDS-3 navigation message broadcast parameters, repeat the above steps; And Using the corrected broadcast clock difference parameter, combined with the low-orbit satellite on-board observation data to complete the on-board autonomous orbit determination.

2. The low earth orbit satellite autonomous on-board orbit determination method based on BDS-3 navigation message SISRE accuracy improvement of claim 1, wherein, According to the BDS-3 navigation message broadcast parameter, the broadcast clock difference at the current time within 1 hour is calculated, including: The satellite navigation message broadcast parameter interval is 1 hour, and 24 groups are broadcast every day; The broadcast clock difference at the current time within 1 hour is calculated, wherein, is the broadcast clock difference at the current time, i.e. at time t, , , are the initial clock difference, clock rate, and clock drift at time t, respectively, is the reference time.

3. The low earth orbit satellite autonomous on-board orbit determination method based on BDS-3 navigation message SISRE accuracy improvement according to claim 1 or 2, characterized in that, Based on the historical 24-hour broadcast clock difference data, the current clock rate is corrected using a fitting method, including: The broadcast clock difference data within 24 hours is fitted using a quadratic polynomial fitting model to correct the current time clock rate ; The quadratic polynomial fitting model is, Wherein, For The broadcast clock difference corresponding to the moment, combined with the broadcast clock difference formula, the clock deviation is solved based on the least square method , clock speed , clock drift ; As a clock speed correction value instead of the original clock speed value of the 24th hour.

4. The low earth orbit satellite autonomous on-board orbit determination method based on BDS-3 navigation message SISRE accuracy improvement of claim 1, wherein, Based on the corrected current clock rate, the initial clock difference at the next time is calculated by recursion, including: calculating an initial clock difference for the next time based on the corrected current time clock speed , wherein, is the initial clock difference at the start time, is the corrected is the initial clock difference at the start time, is the corrected is the clock rate at the start time.

5. The low earth orbit satellite autonomous on-board orbit determination method based on BDS-3 navigation message SISRE accuracy improvement of claim 1, wherein, The absolute median deviation method is used to detect the clock difference jump, which includes the following steps: calculating a median of the clock error sequence ; Calculate the absolute deviation of the clock difference at time i from the median, wherein, is the clock difference at time i; Calculate the median MAD of the absolute deviation, ； If the clock difference is outside the set threshold range, it is determined that the clock difference jump occurs, The set threshold range is, Where n is 3.

6. The low earth orbit satellite autonomous on-board orbit determination method based on BDS-3 navigation message SISRE accuracy improvement of claim 1, wherein, The low-orbit satellite on-board observation data is calculated by the dual-frequency ionosphere-free combined pseudo-range and phase observation equation, where C, L, i represent BDS-3 satellite, low earth orbit satellite and frequency, respectively, is the geometric distance between BDS-3 satellite and low earth orbit satellite, and are the clock bias of low earth orbit satellite and BDS-3 satellite, respectively, and c is the speed of light in vacuum, , are the pseudorange hardware delays of low earth orbit receiver and GNSS satellite under IF combination, respectively, , are the phase biases of low earth orbit receiver and GNSS satellite under IF combination, respectively, , are the phase wavelength and phase ambiguity under IF combination, respectively, , are the measurement noises of pseudorange and phase under IF combination, respectively.

7. The low earth orbit satellite autonomous on-board orbit determination method based on BDS-3 navigation message SISRE accuracy improvement of claim 1, wherein, The SISRE is used to evaluate the autonomous orbit determination accuracy, where, , , are the radial, tangential and normal orbit errors in the satellite orbit reference frame, respectively, is the clock error, , are the radial and tangential-normal plane error projection coefficients of the BDS-3 satellite orbit, respectively.

8. A system for the on-board autonomous orbit determination method of low earth orbit satellites based on BDS-3 navigation message SISRE accuracy improvement according to any one of claims 1-7, characterized in that, Including: The broadcast clock difference calculation module is configured to calculate the broadcast clock difference at the current time within 1 hour according to the BDS-3 navigation message broadcast parameter; The clock rate fitting module is configured to correct the current clock rate using a fitting method based on the historical 24-hour broadcast clock difference data; The initial clock difference calculation module is configured to calculate the initial clock difference at the next time by recursion based on the corrected current clock rate; The clock difference jump detection module is configured to detect the clock difference jump, and when the clock difference jump occurs, re-accumulate 24 hours of BDS-3 navigation message broadcast parameters, repeat the above steps; and The autonomous orbit determination module is configured to use the corrected broadcast clock difference parameter to complete the on-board autonomous orbit determination combined with the low-orbit satellite on-board observation data.

9. An electronic device, comprising: Including: A processor configured to execute machine-readable instructions; A graphics card with an artificial intelligence chip configured to train a low-orbit satellite on-board autonomous orbit determination method based on the BDS-3 navigation message SISRE accuracy improvement; And A memory configured to store machine-readable instructions, the machine-readable instructions being executed by the processor and / or the graphics card to perform the steps of the method according to any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, Having machine-readable instructions stored thereon, the machine-readable instructions being executed by the processor to perform the steps of the method according to any one of claims 1-7.

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