Real-time orbit determination trigger starting method for low-orbit satellite

Abstract

The invention discloses a low-orbit satellite real-time orbit determination trigger starting method, which belongs to the field of satellite positioning time service and is used for ground data processing, and real-time low-orbit satellite satellite-borne GNSS observation updating conditions are detected, low-orbit satellite satellite-borne GNSS observation and real-time completeness and continuity detection calculation is carried out on GNSS products, so that the real-time low-orbit satellite orbit determination trigger starting is realized. Cyclic standard judgment is carried out among different GNSS systems, orbit determination arc lengths and GNSS products, real-time orbit determination is triggered and started only when observation and product quality reach the standard and orbit determination arc section observation is updated, the real-time orbit determination precision can be guaranteed, repeated calculation when observation is not updated is avoided, and the real-time orbit determination efficiency is improved. In addition, invalid / low-quality orbit determination or frequent error reporting when feeding observation and product quality have problems can be avoided, the calculation efficiency can be saved, and repeated problem tracing during operation and maintenance is avoided.

Description

Technical Field

[0001] The invention belongs to the field of satellite positioning and timing, and in particular relates to a low-orbit satellite real-time orbit determination triggering and starting method. 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 a series of advantages such as strong signal strength, short convergence time and whitening of multipath effects, and have received more and more attention in recent years. In order to better utilize low-orbit navigation signals to achieve high-precision real-time positioning and timing on the ground, the high-precision real-time orbit of low-orbit satellites has become an important prerequisite and the key to determining the accuracy of future low-orbit enhanced GNSS ground positioning, navigation and timing.

[0003] At present, single-satellite real-time orbit determination based on low-orbit satellite onboard GNSS observation is the most timely and high-precision low-orbit satellite orbit determination method. To achieve real-time orbit determination, there are usually two methods: 1) On-orbit orbit determination. Based on the satellite-borne GNSS observations, orbit calculation is performed on-orbit. The advantage of this method is that there is no need to transmit the satellite-borne GNSS observations back to the ground in real time. However, the sources and accuracy of high-precision real-time GNSS orbit star clock products obtained on-orbit are limited, and the selection range is not as wide as that of ground processing. In addition, the computing power of the on-board payload is also limited compared to the ground, and sometimes it needs to give way to other tasks, which is not as good as the current situation of ground calculations with high-performance processors.

[0004] 2) Ground solution. The satellite-borne GNSS observations are transmitted back to the ground in real time through the inter-satellite link of low-orbit satellites, and precise orbit determination is performed on the ground. This method can choose to use GNSS real-time high-precision orbit star clock products provided by various institutions, and the computing and processing performance is not limited. However, since the unloading of low-orbit satellite-borne GNSS observations may be delayed, incomplete, discontinuous, and out of sequence, the scheduled start of low-orbit satellite orbit determination and orbit solution based on incomplete and discontinuous satellite-borne GNSS data will affect the accuracy and integrity of the orbit results, and may frequently cause program errors and failure to pass self-test. Summary of the invention

[0005] 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: A low-orbit satellite real-time orbit determination triggering and starting method, used for ground data processing, the method comprising: 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.

[0006] Beneficial effects of the present invention: The solution provided by the embodiment of the present invention detects the update status of real-time 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 during the real-time orbit determination of low-orbit satellites, performs cyclic compliance judgment among different GNSS systems, orbit determination arc lengths, and GNSS products, and triggers the start of real-time orbit determination only when the observation and product quality meet the standards and the orbit determination arc segment observation is updated. This 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 errors when problems occur in the input observations and product quality. This can save computing efficiency and avoid tracing repeated problems during operation and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 A schematic diagram of a flow chart of a method for triggering and starting real-time orbit determination of a low-orbit satellite provided by an embodiment of the present invention; Figure 2 A schematic diagram of the execution process of the low-orbit satellite real-time orbit determination triggering start method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0008] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0009] The present invention is based on the ground solution method, and provides a method for triggering and starting the real-time orbit determination of low-orbit satellites based on the batch least squares method simplified dynamics real-time precise orbit determination after the satellite-borne GNSS observation data is transmitted back to the ground. The orbit determination will be triggered only when some conditions for the orbit determination trigger are met. Figure 1 As shown, the method is used for ground data processing and may include the following steps: 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; The implementation basis of the present invention is that the onboard GNSS observation data of the target low-orbit satellite has been obtained.

[0010] Wherein, S1 may include the following steps: 1) 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; 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 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.

[0011] 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.

[0012] 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 set of GNSS systems 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 observations of the target LEO satellite can be detected. {TIMEEND}. Among them, Represents a variable, such as a refers to the variable a, and {} are brackets.

[0013] 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 from back to front, the system is considered to exist. After all systems in {mysys} are detected, the existing system set is obtained {allsys} represents the set of GNSS systems existing in the above observation arc.

[0014] Among them, for For each GNSS system in {mysys}, the frequency band of dual-frequency observation is pre-defined. For example, for the GPS (Global Positioning System) system, the frequency band of dual-frequency observation can be defined as L1 is 1575.42 MHz and L2 is 1227.6 MHz. The frequency bands of dual-frequency observation of other GNSS systems are not given here as examples.

[0015] 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; This step is to detect the latest valid arc segment and its integrity and continuity of the satellite-borne GNSS observations in a given system.

[0016] Each time S2 is executed, the current 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.

[0017] For the target system, the process of executing S2 includes: 1) 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; The last updated epoch of the onboard GNSS observation of the target LEO satellite is expressed as {TIMEEND}.

[0018] 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 epochs of at least four satellites with dual-frequency observations of all the target systems, and defining the epochs found as valid epochs; Specifically, the observation arc of this step is [ {TIMEEND}- {TALL}, {TIMEEND}], and finding the epochs of at least four satellites in dual-frequency observations of all target systems, in a way of searching from back to front. The above two steps can be understood by referring to the relevant steps in S1.

[0019] 3) 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 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).

[0020] 4) Divide the number of valid epochs in the valid arc by the expected number of epochs to obtain a percentage as the completeness; The expected epoch number is obtained based on the input orbit determination arc length and sampling interval; for example, if the orbit determination arc length is 24 hours and the sampling interval is 30 seconds, then the expected epoch number is (24×60×60)÷30=2880.

[0021] Completeness {ava} means, {ava}=(number of valid epochs in the valid arc / number of expected epochs)×100%.

[0022] 5) The longest arc length without a valid epoch in the valid arc is determined as the longest discontinuity.

[0023] Among them, the longest interruption {gap} means.

[0024] 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.

[0025] 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; 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.

[0026] 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}, perform corresponding query in the log file of the previous round of orbit determination processing to determine whether the current valid arc segment has been processed in the previous round. It is understandable that if there is no observation update in the valid arc segment during two rounds of orbit determination processing, it may appear that the arc segment has been processed in the previous round of orbit determination. If it has been processed, the orbit determination mechanism will not be triggered, and there is no need to process it again, thereby saving computing resources. If it has not been processed, execute S4.

[0027] 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; In S4 of the embodiment of the present invention, judging whether the current valid arc segment meets the first requirement on the integrity and continuity of the space-borne GNSS observation according to the current valid arc length, integrity and longest discontinuity includes: 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.

[0028] Specifically, the current effective arc length {TALL_valid} is compared with the corresponding threshold. If {TALL_valid} is greater than the corresponding threshold, indicating that the parameter {TALL_valid} met the target; The current completeness {ava} is compared with the corresponding threshold. If {ava} is greater than the corresponding threshold, indicating that the parameter {ava} meet the standard; The current longest break {gap} is compared with the corresponding threshold. If {gap} is less than the corresponding threshold, indicating that the parameter {gap} meet the target; In this step, the thresholds corresponding to the three parameters of effective arc length, completeness and longest discontinuity are preset based on empirical values.

[0029] When any of the parameters does not meet the standard, it is determined that the current valid arc segment does not meet the requirements for the integrity and continuity of the onboard GNSS observation. At this time, the onboard GNSS observation is detected again by shortening the orbit determination arc length and replacing the target system. If the first requirement is met during the detection process of S4, S5 is directly executed. If the onboard GNSS observation is detected again by shortening the orbit determination arc length and replacing the target system, the first requirement is still not met in the end, indicating that the requirements for the integrity and continuity of the onboard GNSS observation cannot be met, the triggering of orbit determination is abandoned.

[0030] In S4, the onboard GNSS observations were detected again by shortening the orbit determination arc length and replacing the target system, including: 1) 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; 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, so as to obtain the effective arc length, integrity and longest discontinuity again, and then determine in S3 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 satellite-borne GNSS observations, the input orbit determination arc length is shortened again to repeat the above process.

[0031] 2) 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 the orbit determination arc length has been shortened to the minimum value, and the first requirement on the integrity and continuity of the onboard GNSS observations cannot be met during this period, then the process returns to S2, and the target system is replaced with the next system in the existing system set, but for the new target system, the orbit determination arc length at this time adopts the original value that has not been shortened. Then, S3 and S4 are executed in sequence.

[0032] 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.

[0033] If all target systems in the existing system set cannot meet the first requirement on the integrity and continuity of onboard GNSS observations after detection, the triggering of orbit determination is abandoned.

[0034] The embodiment of the present invention performs cyclic detection between different orbit determination arc lengths and different GNSS systems defined in advance to determine whether the first requirement on the integrity and continuity of onboard GNSS observations is met. If the first requirement is met during the above detection process of S4, it means that the requirements on the integrity and continuity of onboard GNSS observations have been met, but it is not enough to trigger orbit determination at this time, and S5 detection of GNSS real-time orbit star clock products still needs to be performed.

[0035] 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.

[0036] This step is to optimize, complete and detect the continuity of the real-time GNSS orbit star clock products of a given system within the valid arc.

[0037] In the embodiment of the present invention, the priority ranking of GNSS real-time orbit satellite clock products is based on the priority ranking of orbit satellite clock combined product accuracy (SISRE) generated by the post-accuracy evaluation of GNSS real-time orbit satellite clock products. When detecting products, the products are selected starting from the first product according to the product order in the priority ranking.

[0038] Specifically, for the selected current product, according to the valid arc segment, sampling interval, and target system given during the current step, 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. The determination process includes: 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; 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.

[0039] 2) Compare the integrity and longest interruption of the real-time GNSS star clock of the current product within the currently input valid arc segment 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.

[0040] Specifically, the integrity of the real-time GNSS star clock of the product in 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; Compare the longest interruption of the real-time GNSS star clock of the product with the corresponding threshold value at present. If it is less than the corresponding threshold value, it means that it meets the standard. In this step, the thresholds corresponding to the two parameters of completeness and longest interruption are preset based on empirical values, and are different from the thresholds corresponding to the two parameters of completeness and longest interruption in the previous S4.

[0041] 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, then detect again by replacing the product, shortening the orbit determination arc length, and replacing the target system. If the second requirement still cannot be met in the end, then give up triggering orbit determination; if the second requirement is met during the above detection process, the corresponding product is used to trigger orbit determination.

[0042] In S5, the detection was repeated by replacing the product, shortening the orbit 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.

[0043] 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 GNSS real-time orbit star clock products are met. This product mechanism can be selected to trigger orbit determination, and the means of orbit determination is still the batch least squares simplified dynamics real-time precise orbit determination.

[0044] If all products cannot meet the second requirement, then according to the method in S4, the onboard GNSS observation is detected again by shortening the orbit determination arc length and replacing the target system. If the first requirement is still not met in the end, the triggering of orbit determination is abandoned. If there is a product that meets the first requirement, 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 corresponding product is used to trigger orbit determination. 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 triggering of orbit determination is abandoned.

[0045] 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 referred to Figure 2 Hint.

[0046] The solution provided by the embodiment of the present invention detects the update status of real-time 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 during the real-time orbit determination of low-orbit satellites, performs cyclic compliance judgment among different GNSS systems, orbit determination arc lengths, and GNSS products, and triggers the start of real-time orbit determination only when the observation and product quality meet the standards and the orbit determination arc segment observation is updated. This 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 errors when problems occur in the input observations and product quality. This can save computing efficiency and avoid tracing repeated problems during operation and maintenance.

[0047] It should be noted that, in the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0048] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means 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 may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope 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 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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