A method for triggering and starting real-time orbit determination of low-orbit satellites

Abstract

The present invention discloses a method for triggering and starting real-time orbit determination of a low-orbit satellite, which belongs to the field of satellite positioning and timing. The method is used for ground data processing, detects the update status of real-time low-orbit satellite-borne GNSS observations, detects and calculates the real-time integrity and continuity of low-orbit satellite-borne GNSS observations and GNSS products, performs cyclic compliance judgment among different GNSS systems, orbit determination arc lengths, and GNSS products, and triggers and starts real-time orbit determination when the observation and product quality meet the standards and the orbit determination arc segment observation is updated. The method can ensure the accuracy of real-time orbit determination, avoid repeated calculation when the observation is not updated, and avoid invalid / low-quality orbit determination or frequent error reporting when problems occur in the input observation and product quality, thereby saving calculation efficiency and avoiding tracing repeated problems during operation and maintenance.

Description

Technical Field

[0001] The present invention belongs to the field of satellite positioning and timing, and in particular relates to a method for triggering and starting real-time orbit determination of a low-orbit satellite. Background Art

[0002] Thanks to the low altitude, high speed, and low cost of low-orbit satellites, low-orbit enhanced GNSS (Global Navigation Satellite System) positioning, navigation, and timing have garnered increasing attention in recent years due to their advantages, including strong signal strength, fast convergence time, and multipath noise reduction. To better utilize low-orbit navigation signals for high-precision, real-time positioning and timing on the ground, the high-precision, real-time orbits of low-orbit satellites are a crucial prerequisite and the key to the accuracy of future low-orbit enhanced GNSS ground positioning, navigation, and timing.

[0003] Currently, single-satellite real-time orbit determination based on onboard GNSS observations of low-orbit satellites is the most timely and high-precision means of determining the orbits of low-orbit satellites. To achieve real-time orbit determination, two methods are generally used:

[0004] 1) On-orbit orbit determination. Based on satellite-borne GNSS observations, orbit calculations are performed on-orbit. This method has the advantage of eliminating the need to transmit satellite-borne GNSS observations back to the ground in real time. However, the sources and accuracy of high-precision, real-time GNSS orbit clock products obtained on-orbit are limited, and the range of options available for ground-based processing is not as wide. Furthermore, the computing power of onboard payloads is also limited compared to that of ground-based systems, and sometimes needs to be prioritized for other tasks, making it less competitive than the high-performance processors available for ground-based solutions.

[0005] 2) Ground solution. The spaceborne GNSS observations are transmitted back to the ground in real time via inter-satellite links between low-orbit satellites for precise orbit determination on the ground. This method can use GNSS real-time high-precision orbit clock products provided by various institutions, and the computing and processing performance is not limited. However, since the unloading of GNSS observations from low-orbit satellites may be delayed, incomplete, discontinuous, and out of sequence, the scheduled start of low-orbit satellite orbit determination and the orbit solution based on incomplete and discontinuous spaceborne GNSS data will affect the accuracy and integrity of the orbit results, and may frequently cause program errors and failure to pass self-tests. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a method for triggering and starting real-time orbit determination of low-orbit satellites. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] A low-orbit satellite real-time orbit determination triggering and starting method, used for ground data processing, the method comprising:

[0008] S1, detects the systems contained in the latest updated arc segment in the onboard GNSS observation of the target low-orbit satellite and obtains the set of existing systems;

[0009] S2, according to the order of the systems in the existing system set, based on the name of the target low-orbit satellite, the orbit determination arc length, and the detection sampling interval, detect the continuity and integrity of the latest updated arc segment in the onboard GNSS observation of the target low-orbit satellite, determine the valid epoch and valid arc segment, and thus obtain the valid arc length, integrity, and longest discontinuity;

[0010] S3, determine whether the current valid arc segment has been processed for orbit determination in the previous round; if so, give up triggering orbit determination; if not, execute S4;

[0011] S4: Based on the current valid arc length, integrity, and longest discontinuity, determine whether the current valid arc segment meets the first requirement for onboard GNSS observation integrity and continuity. If not, shorten the orbit determination arc length, change the target system, and perform another detection of onboard GNSS observations. If the first requirement is still not met, abandon the orbit determination trigger. If the first requirement is met, execute S5.

[0012] S5. Based on the product order in the GNSS real-time orbit star clock product priority ranking, and according to the currently input valid arc segment, sampling interval, and target system, determine whether the current product meets the second requirement regarding the integrity and continuity of the GNSS real-time orbit star clock product. If not, re-detect by replacing the product, shortening the orbit determination arc length, or replacing the target system. If the second requirement is still not met, abandon triggering orbit determination. If the second requirement is met, use the corresponding product to trigger orbit determination.

[0013] Beneficial effects of the present invention:

[0014] The solution provided by the embodiment of the present invention detects the real-time update status of low-orbit satellite onboard GNSS observations, detects and calculates the real-time integrity and continuity of low-orbit satellite onboard GNSS observations and GNSS products, and performs cyclic compliance judgment among different GNSS systems, orbit determination arc lengths, and GNSS products during the real-time orbit determination of low-orbit satellites. The solution triggers the start of real-time orbit determination only when the observation and product quality meet the standards and the orbit determination arc observation is updated. This can ensure the accuracy of real-time orbit determination, avoid repeated calculations when the observations are not updated, and avoid invalid / low-quality orbit determination or frequent errors when there are problems with the input observations and product quality. This can save computing efficiency and avoid repeated problem tracing during operation and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A flowchart of a method for triggering and starting real-time orbit determination of a low-orbit satellite provided by an embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of the execution process of the low-orbit satellite real-time orbit determination triggering and starting method provided by an embodiment of the present invention. DETAILED DESCRIPTION

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

[0018] The present invention is based on a ground-based solution method and provides a method for triggering and starting real-time orbit determination of low-orbit satellites based on the batch least squares simplified dynamics method after the satellite-borne GNSS observation data is transmitted back to the ground. The orbit determination will be triggered only when certain conditions for orbit determination triggering are met. Figure 1 As shown, the method is used for ground data processing and may include the following steps:

[0019] S1, detects the systems contained in the latest updated arc segment in the onboard GNSS observation of the target low-orbit satellite and obtains the set of existing systems;

[0020] The implementation basis of the present invention is that the onboard GNSS observation data of the target low-orbit satellite has been obtained.

[0021] S1 may include the following steps:

[0022] 1) Detect the last updated epoch of the onboard GNSS observation of the target LEO satellite based on the name of the target LEO satellite, the orbit determination arc length, the detection sampling interval, and the set of GNSS systems to be detected;

[0023] 2) Within the observation arc determined by the last updated epoch of the onboard GNSS observation of the target low-orbit satellite and the orbit determination arc length, each system in the set of GNSS systems to be detected is detected one by one. For a detected system, if an epoch containing dual-frequency observations of at least four satellites is found, the system is determined to exist. After all systems are detected, the set of existing systems is obtained.

[0024] Specifically, the present invention can execute the low-orbit satellite real-time orbit determination triggering and starting method for each target low-orbit satellite to be detected.

[0025] First, enter the name of the target low-orbit satellite {sat}, orbit determination arc length {TALL}, sampling interval of detection {samp} and the set of GNSS systems to be detected {mysys}; the GNSS system set to be detected {mysys} contains multiple GNSS systems, which have been sorted according to predefined rules. Using this information, the last updated epoch of the onboard GNSS observation of the target low-orbit satellite can be detected {TIMEEND}. Represents a variable, such as a refers to the variable a, and {} are brackets.

[0026] Then, in [ {TIMEEND}- {TALL}, {TIMEEND}], for All systems in {mysys} are detected one by one. For the detected system, if the epoch containing at least 4 satellites with dual-frequency observation can be found, the system is determined to exist. After all systems in {mysys} are detected, the existing system set is obtained {allsys} represents the set of GNSS systems within the above observation arc.

[0027] Among them, for The dual-frequency observation frequency bands for each GNSS system in {mysys} are predefined. For example, for the GPS (Global Positioning System) system, the dual-frequency observation frequency bands can be defined as L1 at 1575.42 MHz and L2 at 1227.6 MHz. The dual-frequency observation frequency bands for other GNSS systems are not described here.

[0028] S2, according to the order of the systems in the existing system set, based on the name of the target low-orbit satellite, the orbit determination arc length, and the detection sampling interval, detect the continuity and integrity of the latest updated arc segment in the onboard GNSS observation of the target low-orbit satellite, determine the valid epoch and valid arc segment, and thus obtain the valid arc length, integrity, and longest discontinuity;

[0029] This step is to detect the latest valid arc segment and its integrity and continuity of the spaceborne GNSS observations in a given system.

[0030] Each time S2 is executed, the system to be processed is called the target system. When S2 is executed for the first time, the target system is the first system in the set of existing systems. {system} example.

[0031] For the target system, the process of executing S2 includes:

[0032] 1) Detecting the last updated epoch of the onboard GNSS observation of the target LEO satellite based on the name of the target LEO satellite, the input orbit determination arc length, and the detection sampling interval;

[0033] The last updated epoch of the onboard GNSS observation of the target LEO satellite is expressed as {TIMEEND}.

[0034] 2) within the observation arc determined by the last updated epoch of the onboard GNSS observation of the target low-orbit satellite and the orbit determination arc length, searching for all epochs of at least four satellites that contain dual-frequency observations of the target system, and defining the found epochs as valid epochs;

[0035] Specifically, the observation arc of this step is [ {TIMEEND}- {TALL}, {TIMEEND}], and searching for all epochs of at least four satellites in dual-frequency observations containing the target system in the observation arc corresponding to the target system. The method of searching from back to front is adopted. The above two steps can be understood by referring to the relevant steps in S1.

[0036] 3) Define the orbit determination arc segment from the first valid epoch to the last valid epoch as the valid arc segment, determine its arc length as the valid arc length, and output the time of the first valid epoch as the start time of the valid arc segment;

[0037] The effective arc length is {TALL_valid} indicates that the time of the first valid epoch can include {YEAR} (year), {DOY} (Days per Year), {sec} (seconds per day).

[0038] 4) Divide the number of valid epochs in the valid arc by the expected number of epochs to obtain a percentage as the completeness;

[0039] The expected epoch number is obtained based on the input orbit arc length and sampling interval. For example, if the orbit arc length is 24 hours and the sampling interval is 30 seconds, the expected epoch number is (24×60×60)÷30=2880.

[0040] Completeness {ava} means, {ava}=(number of valid epochs in the valid arc segment / number of expected epochs)×100%.

[0041] 5) The longest arc length without a valid epoch within the valid arc is determined as the longest discontinuity.

[0042] Among them, the longest interruption {gap} means.

[0043] The effective arc length, integrity and longest discontinuity are used as detection results of the continuity and integrity of the latest updated arc segment in the onboard GNSS observation of the target low-orbit satellite for the target system.

[0044] S3, determine whether the current valid arc segment has been processed for orbit determination in the previous round; if so, give up triggering orbit determination; if not, execute S4;

[0045] In S3, it is determined whether the current valid arc has been subjected to orbit determination in the previous round, including:

[0046] Based on the name of the target low-orbit satellite, the start time of the current valid arc segment, the valid arc length and the target system, and the log file of the previous round of orbit determination processing, it is determined whether the current valid arc segment has been orbit determined in the previous round.

[0047] Specifically, according to the name of the target low-orbit satellite {sat}, the start time of the current valid arc { {YEAR}, {DOY}, {sec}}, effective arc length {TALL_valid} and the target system {system}, query the log file from the previous orbit determination round to determine whether the current valid arc segment has already been orbit determined in the previous round. It is understood that if no observation updates are made within the valid arc segment between two orbit determination rounds, it may indicate that the arc segment has already been orbit determined in the previous round. If it has been orbit determined, the orbit determination mechanism is not triggered, and no further orbit determination is required, thus saving computing resources. If it has not been orbit determined, then execute S4.

[0048] S4: Based on the current valid arc length, integrity, and longest discontinuity, determine whether the current valid arc segment meets the first requirement for onboard GNSS observation integrity and continuity. If not, shorten the orbit determination arc length, change the target system, and perform another detection of onboard GNSS observations. If the first requirement is still not met, abandon the orbit determination trigger. If the first requirement is met, execute S5.

[0049] In S4 of the embodiment of the present invention, judging whether the current valid arc segment meets the first requirement of integrity and continuity of spaceborne GNSS observations based on the current valid arc length, integrity, and longest discontinuity includes:

[0050] The three parameters of the current effective arc length, completeness and longest interruption are compared with the corresponding thresholds to determine whether the corresponding parameters meet the standards. When any of the parameters does not meet the standards, it is determined that the current effective arc segment does not meet the first requirement. When all parameters meet the standards, it is determined that the current effective arc segment meets the first requirement.

[0051] Specifically, the current effective arc length {TALL_valid} is compared with the corresponding threshold value. If {TALL_valid} is greater than the corresponding threshold, indicating that the parameter {TALL_valid} met the standard;

[0052] The current completeness {ava} is compared with the corresponding threshold value. If {ava} is greater than the corresponding threshold, indicating that the parameter {ava} meet the standards;

[0053] The current longest pause {gap} is compared with the corresponding threshold. If {gap} is less than the corresponding threshold, indicating that the parameter {gap}meet the target;

[0054] In this step, the thresholds corresponding to the three parameters of effective arc length, integrity and longest discontinuity are preset based on empirical values.

[0055] If any of these parameters do not meet the requirements, the current valid arc segment is determined to have failed to meet the requirements for onboard GNSS observation integrity and continuity. In this case, the onboard GNSS observations are re-detected by shortening the orbit determination arc length and changing the target system. If the first requirement is met during the detection process in S4, S5 is directly executed. If the first requirement is still not met after shortening the orbit determination arc length and changing the target system, the onboard GNSS observations are still not met, indicating that the requirements for onboard GNSS observation integrity and continuity cannot be met, and the orbit determination trigger is abandoned.

[0056] In S4, the orbit determination arc length was shortened and the target system was replaced to detect the spaceborne GNSS observations again, including:

[0057] 1) According to predefined rules, the input orbit arc length is shortened step by step, and the system returns to S2 to start detecting again;

[0058] It can be understood that after shortening the input orbit determination arc length and returning to S2, the orbit determination arc length used in S2 is the newly input orbit determination arc length, thereby obtaining the effective arc length, integrity and longest discontinuity again. Then, in S3, it is determined whether the effective arc segment at this time has been orbit determined in the previous round. If no orbit determination has been performed, S4 is executed again. If the effective arc segment at this time still cannot meet the first requirement of integrity and continuity of spaceborne GNSS observations, the input orbit determination arc length is shortened again and the above process is repeated.

[0059] 2) If the orbit arc length has been shortened to the minimum value and still cannot meet the first requirement, return to S2 to execute the next target system, and the orbit arc length uses the original value before shortening;

[0060] If the orbit determination arc length has been shortened to the minimum value, but the first requirement regarding the integrity and continuity of the onboard GNSS observations is still not met during this period, then the process returns to S2 and the target system is replaced with the next system in the set of existing systems. However, for the new target system, the orbit determination arc length at this time uses the original value before shortening. Then, S3 and S4 are executed in sequence.

[0061] 3) If all target systems fail to meet the first requirement after detection, it is determined that the first requirement cannot be met in the end.

[0062] If all target systems in the existing system set cannot meet the first requirement of onboard GNSS observation integrity and continuity after detection, the triggering of orbit determination is abandoned.

[0063] This embodiment of the present invention performs cyclic detection between predefined different orbit determination arc lengths and different GNSS systems to determine whether the first requirement for onboard GNSS observation integrity and continuity is met. If the first requirement is met during the detection process in S4, the requirements for onboard GNSS observation integrity and continuity have been met, but this is not sufficient for triggering orbit determination, and S5 detection of the GNSS real-time orbit satellite clock product must still be performed.

[0064] S5. Based on the product order in the GNSS real-time orbit star clock product priority ranking, and according to the currently input valid arc segment, sampling interval, and target system, determine whether the current product meets the second requirement regarding the integrity and continuity of the GNSS real-time orbit star clock product. If not, re-detect by replacing the product, shortening the orbit determination arc length, or replacing the target system. If the second requirement is still not met, abandon triggering orbit determination. If the second requirement is met, use the corresponding product to trigger orbit determination.

[0065] This step is to optimize, complete and detect the continuity of the real-time GNSS orbit clock products of a given system within the valid arc.

[0066] In this embodiment of the present invention, the GNSS real-time orbit clock product priority ranking is based on the orbit clock combined product accuracy (SISRE) priority ranking generated by the post-accuracy evaluation of the GNSS real-time orbit clock products. During product detection, the products are selected starting from the first product in the order of the products in the priority ranking.

[0067] Specifically, for the selected current product, based on the valid arc segment, sampling interval, and target system provided during the current step, determine whether the current product meets the second requirement for the integrity and continuity of the GNSS real-time orbit satellite clock product. The judgment process includes:

[0068] 1) For the current target system, calculate the integrity and longest interruption of the real-time GNSS satellite clock of the current product within the current valid arc segment;

[0069] The calculation method of the completeness and the longest interruption in this step can be understood by referring to the calculation method of the completeness and the longest interruption in S2 above.

[0070] 2) Compare the integrity and longest interruption parameters of the real-time GNSS satellite clock of the current product within the currently given valid arc segment with the corresponding thresholds to determine whether the corresponding parameters meet the standards. If any of the parameters does not meet the standards, the current product is determined to have failed to meet the second requirement. If all parameters meet the standards, the current product is determined to have met the second requirement.

[0071] Specifically, the integrity of the product's real-time GNSS star clock within the currently input valid arc segment is compared with the corresponding threshold. If it is greater than the corresponding threshold, it means that it meets the standard;

[0072] Compare the current longest interruption of the real-time GNSS star clock of the product with the corresponding threshold. If it is less than the corresponding threshold, it means that it meets the standard;

[0073] In this step, the thresholds corresponding to the two parameters of integrity and longest interruption are preset based on empirical values, and are different from the thresholds corresponding to the two parameters of integrity and longest interruption in the previous S4.

[0074] The above is product detection, that is, detecting whether the current product meets the requirements for the integrity and continuity of the GNSS real-time orbit star clock product. If not, the detection is repeated by replacing the product, shortening the orbit determination arc length, and replacing the target system. If the second requirement is still not met in the end, the triggering of orbit determination is abandoned. If the second requirement is met during the above detection process, the corresponding product is used to trigger orbit determination.

[0075] In S5, the detection was repeated by replacing the product, shortening the orbit arc length, and replacing the target system, including:

[0076] Detect whether the next product in the priority ranking of the GNSS real-time orbit star clock products meets the second requirement on the integrity and continuity of the GNSS real-time orbit star clock products. If the second requirement is met, the corresponding product is used to trigger orbit determination. If all products do not meet the second requirement, the onboard GNSS observation is detected again by shortening the orbit determination arc length and replacing the target system. If the detection passes, continue to detect the product.

[0077] Specifically, if the first product does not meet the second requirement on the integrity and continuity of the GNSS real-time orbit star clock product, the next product will be postponed for product detection. If there is a product that meets the second requirement, the corresponding product will be used to trigger orbit determination. That is, at this time, the requirements on the integrity and continuity of on-board GNSS observations and the integrity and continuity of the GNSS real-time orbit star clock product are met, and the product mechanism can be selected to trigger orbit determination. The orbit determination method is still the batch least squares method simplified dynamics real-time precise orbit determination.

[0078] If all products fail to meet the second requirement, the onboard GNSS observations are detected again by shortening the orbit determination arc length and changing the target system in the manner of S4. If the first requirement is still not met, the orbit determination is abandoned. If the first requirement is met, that is, the onboard GNSS observation integrity and continuity detection are passed, the product detection is continued from the first product. If the product detection passes, the orbit determination is triggered using the corresponding product. If the product detection fails, the next product is postponed. This is repeated until all orbit determination arc lengths, target systems, and products are traversed. If the orbit determination cannot be triggered, the orbit determination is abandoned.

[0079] The execution process of the low-orbit satellite real-time orbit determination triggering start method according to the embodiment of the present invention can be found in Figure 2 gesture.

[0080] The solution provided by the embodiment of the present invention detects the real-time update status of low-orbit satellite onboard GNSS observations, detects and calculates the real-time integrity and continuity of low-orbit satellite onboard GNSS observations and GNSS products, and performs cyclic compliance judgment among different GNSS systems, orbit determination arc lengths, and GNSS products during the real-time orbit determination of low-orbit satellites. The solution triggers the start of real-time orbit determination only when the observation and product quality meet the standards and the orbit determination arc observation is updated. This can ensure the accuracy of real-time orbit determination, avoid repeated calculations when the observations are not updated, and avoid invalid / low-quality orbit determination or frequent errors when there are problems with the input observations and product quality. This can save computing efficiency and avoid repeated problem tracing during operation and maintenance.

[0081] It should be noted that, in the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0082] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A method for triggering and starting real-time orbit determination of a low-orbit satellite, characterized in that: For ground data processing, the method comprises: S1, detect the systems contained in the latest updated arc segment in the onboard GNSS observation of the target low-orbit satellite, and obtain the existing system set; S2, according to the order of the systems in the existing system set, for the target system to be processed currently, based on the name of the target low-orbit satellite, the orbit determination arc length, and the detection sampling interval, detect the continuity and integrity of the latest updated arc segment in the onboard GNSS observation of the target low-orbit satellite, determine the valid epoch and the valid arc segment, and thus obtain the valid arc length, integrity and longest discontinuity; S3, determine whether the current valid arc segment has been processed for orbit determination in the previous round; if so, give up triggering orbit determination; if not, execute S4; S4, judging whether the current valid arc segment meets the first requirement of integrity and continuity of onboard GNSS observation according to the current valid arc length, integrity and longest discontinuity; if not, shortening the orbit determination arc length, replacing the target system and detecting the onboard GNSS observation again; if the first requirement is still not met, giving up the triggering of orbit determination; if the first requirement is met, executing S5; S5. According to the product order in the priority sorting of GNSS real-time orbit star clock products, and based on the currently input valid arc segment, sampling interval, and target system, determine whether the current product meets the second requirement on the integrity and continuity of the GNSS real-time orbit star clock product. If not, detect again by replacing the product, shortening the orbit determination arc length, and replacing the target system. If the second requirement cannot be met in the end, give up triggering orbit determination; if the second requirement is met, use the corresponding product to trigger orbit determination.

2. The low-orbit satellite real-time orbit determination triggering and starting method according to claim 1, characterized in that: S1, including: Detect the last updated epoch of the onboard GNSS observation of the target low-orbit satellite according to the name of the target low-orbit satellite to be detected, the orbit determination arc length, the detection sampling interval, and the set of GNSS systems to be detected; Within the observation arc determined by the last updated epoch of the onboard GNSS observation of the target low-orbit satellite and the orbit determination arc length, each system in the GNSS system set to be detected is detected one by one. For the detected system, if an epoch containing dual-frequency observation of at least 4 satellites is found, the system is determined to exist, so that after all systems are detected, a set of existing systems is obtained.

3. The low-orbit satellite real-time orbit determination triggering and starting method according to claim 1, characterized in that: S2, including: Detecting the last updated epoch of the onboard GNSS observation of the target low-orbit satellite according to the name of the target low-orbit satellite, the input orbit determination arc length, and the detected sampling interval; In the observation arc determined by the last updated epoch of the onboard GNSS observation of the target low-orbit satellite and the orbit determination arc length, searching for epochs of at least four satellites in dual-frequency observations of all satellites containing the target system, and defining the epochs found as valid epochs; The orbit determination arc segment from the first valid epoch to the last valid epoch is defined as a valid arc segment, its arc length is determined as the valid arc length, and the time of the first valid epoch is output as the start time of the valid arc segment; The number of valid epochs in the valid arc segment is divided by the expected number of epochs to obtain a percentage as the completeness; wherein the expected number of epochs is obtained according to the orbit determination arc length and the sampling interval; The longest arc length of the valid arc segment without a valid epoch is determined as the longest discontinuity.

4. The method for triggering and starting real-time orbit determination of a low-orbit satellite according to claim 1, characterized in that: In S3, it is determined whether the current valid arc segment has been subjected to orbit determination processing in the previous round, including: Based on the name of the target low-orbit satellite, the start time of the current valid arc segment, the valid arc length and the target system, and the log file of the previous round of orbit determination processing, it is determined whether the current valid arc segment has been orbit determined in the previous round.

5. The method for triggering and starting real-time orbit determination of a low-orbit satellite according to claim 1, characterized in that: In S4, based on the current effective arc length, integrity and longest discontinuity, it is determined whether the current effective arc segment meets the first requirement of integrity and continuity of spaceborne GNSS observations, including: The three parameters of the current effective arc length, completeness and longest interruption are compared with the corresponding thresholds respectively to determine whether the corresponding parameters meet the standards. When any of the parameters does not meet the standards, it is determined that the current effective arc segment does not meet the first requirement. When all parameters meet the standards, it is determined that the current effective arc segment meets the first requirement.

6. The method for triggering and starting real-time orbit determination of a low-orbit satellite according to claim 1, characterized in that: In S4, the spaceborne GNSS observations were re-detected by shortening the orbit determination arc length and replacing the target system, including: According to the predefined rules, the input orbit determination arc length is shortened step by step, and the system returns to S2 to start detecting again. If the orbit determination arc length has been shortened to the minimum value and still cannot meet the first requirement, then return to S2 to execute the next target system, and the orbit determination arc length adopts the original value that has not been shortened; If all target systems fail to meet the first requirement after detection, it is determined that the first requirement still cannot be met in the end.

7. The method for triggering and starting real-time orbit determination of a low-orbit satellite according to any one of claims 1 to 6, characterized in that: In S5, it is determined whether the current product meets the second requirement on the integrity and continuity of the GNSS real-time orbit star clock product, including: For the current target system, calculate the integrity and longest interruption of the real-time GNSS satellite clock of the current product within the currently input valid arc segment; The two parameters of the integrity and the longest interruption of the real-time GNSS star clock of the current product in the currently given valid arc segment are compared with the corresponding thresholds to determine whether the corresponding parameters meet the standards. When any of the parameters does not meet the standards, it is determined that the current product does not meet the second requirement. When all parameters meet the standards, it is determined that the current product meets the second requirement.

8. The method for triggering and starting real-time orbit determination of a low-orbit satellite according to claim 7, characterized in that: In S5, the detection was repeated by replacing the product, shortening the orbit determination arc length, and replacing the target system, including: Detect whether the next product in the priority ranking of the GNSS real-time orbit star clock products meets the second requirement on the integrity and continuity of the GNSS real-time orbit star clock products. If the second requirement is met, the corresponding product is used to trigger orbit determination. If all products do not meet the second requirement, the on-board GNSS observation is detected again by shortening the orbit determination arc length and replacing the target system, and continue to detect the product when the detection passes.

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