A navigation method applied to a pulsar autonomous navigation system

Abstract

The present application relates to the technical field of pulsar autonomous navigation of space vehicles, and particularly relates to a navigation unit and method applied to a pulsar autonomous navigation system. The navigation unit is attached to a distributed space vehicle system, and the method is realized based on the navigation unit. Firstly, the pulsar TOA information collected by each space vehicle is subjected to threshold screening, the screened TOA information is not completely eliminated, but is sent to a central navigation filtering calculation module after being replaced by a set threshold, then sequential filtering calculation is performed in the central navigation filtering calculation module, and the calculation process can sequentially filter all the screened information. The central navigation filtering calculation module can also set the pulsar TOA screening threshold of each space vehicle in combination with the motion state information, and can receive the sent pulsar TOA data and screening state information, so as to realize high-precision filtering calculation. In the sequential filtering process, the present application can simultaneously perform measurement screening processing and out-of-order processing.

Description

Technical Field

[0001] This invention relates to the field of pulsar autonomous navigation technology for spacecraft, and specifically to a navigation method applied to pulsar autonomous navigation systems. Background Technology

[0002] Pulsar autonomous navigation technology is a novel approach for spacecraft to achieve autonomous navigation. Because the signals emitted by pulsars in the universe are generally weak, in order to ensure that pulsar detectors collect sufficient pulsar photon information, scholars and technicians both domestically and internationally have, in recent years, expanded the single-spacecraft pulsar autonomous navigation method, realizing a multi-spacecraft pulsar autonomous navigation method. This method of using multiple spacecraft to jointly achieve pulsar autonomous navigation is referred to in this patent as a distributed or distributed cluster pulsar autonomous navigation method.

[0003] Distributed pulsar autonomous navigation utilizes multiple spacecraft to observe specific pulsars, obtaining pulse phase observations. Based on data such as inter-satellite ranging provided by inter-satellite links and communication support, the navigation data processing unit filters the different pulsar phase observations to achieve autonomous navigation and positioning. However, distributed pulsar navigation has the following problems:

[0004] (1) It lacks measurement and filtering processing functions. Since the pulse arrival time requires a complex data processing process, the pulse arrival time (TOA) observed by some spacecraft may deviate significantly from the true value, or the calculated TOA value of some pulses may differ greatly from the mean, affecting subsequent processing. Traditional navigation filters only perform threshold removal on these data, that is, they remove pulse TOA values ​​that exceed the threshold, which results in the loss of certain observation information.

[0005] (2) Lacking sequential processing capabilities, in the vast network of distributed clustered spacecraft systems, information transmission is difficult to synchronize. This means that the actual TOA (Transmission of Availability) pulse measurements from different spacecraft within the same cycle do not arrive at the central navigation processing unit simultaneously. Traditional batch processing methods require waiting for all measurements to arrive before constructing unified measurement equations and performing unified filtering, which undoubtedly wastes waiting time and computational resources. Therefore, it is essential to perform sequential processing on these pulse TOA information according to their arrival order.

[0006] (3) It does not have the function of out-of-order processing. The distributed cluster navigation method greatly reduces the pulsar navigation filtering period. However, due to the resource allocation of inter-satellite links and the spacecraft's spatial position limitations, some spacecraft's pulse TOA observations may not be transmitted to the central navigation processing unit in the current navigation cycle. In order not to waste these pulse TOA observation resources, the navigation algorithm needs to be able to process the delayed observations from the previous cycle in the current cycle. Summary of the Invention

[0007] This invention provides a navigation method for pulsar autonomous navigation systems, aiming to solve the problems existing in the prior art and further improve the navigation efficiency of pulsars.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a navigation method for a pulsar autonomous navigation system, wherein the navigation unit is attached to a distributed spacecraft system, and the method is implemented based on the navigation unit; the navigation unit includes: The pulse TOA filtering module filters the pulse TOA signals acquired by each spacecraft according to the pulse TOA threshold set by the threshold setting module below. When the observed pulse TOA signal exceeds the threshold, it is reassigned a specified value, and the filtered pulse TOA observation and related flag parameters are passed to the misorder determination module below for further processing. Here, pulse TOA refers to the pulse arrival time. The threshold setting module exchanges data bidirectionally with the central navigation filter calculation module; and uses a pre-set pulsar database, combined with the orbital parameters of each spacecraft, to determine the confidence range of the pulse TOA observations of each spacecraft, thereby determining the TOA threshold. The out-of-order determination module determines the navigation filtering period corresponding to the obtained pulse TOA information and informs the central navigation filtering calculation module through the corresponding flag bits. The central navigation filtering calculation module uses the filtered pulse TOA data from each spacecraft and combines it with relevant information from the out-of-order determination module to complete the navigation and positioning calculation. The method includes the following steps: Step 1: The main star initiates the mission, assigning initial position and velocity estimates. and initial state estimation variance , ( )

[0009] Step 2, during initial execution Use the following formula to perform Calculation of the state and initial covariance values ​​at time 1: ( )

[0010] ( )

[0011] ( )

[0012] ( )

[0013] Step 3, Initial Preparing to receive the first Each observation is processed; Step 4: Determine if it is an out-of-order measurement; if yes, proceed to step 6; if no, proceed to step 5. Step 5: Enter the sequential processing flow and process the following formula... Individual observation:

[0014] ( )

[0015] ( )

[0016] ( )

[0017] Then proceed to step 7; Step 6: Enter the out-of-order processing flow and process the following formula: Individual observation, Utilize the current Based on existing observations of the filtering period, construct the system equations: ( )

[0018] ( )

[0019] State estimation backward deduction: ( )

[0020] ( )

[0021] Tracing the state covariance: ( )

[0022] ( )

[0023] ( )

[0024] Measurement traceability covariance: ( )

[0025] ( )

[0026] Update the state estimate and its covariance: ( )

[0027] ( )

[0028] Step 7: Determine if all observations for the current period have been processed; if yes, proceed to step 8; otherwise, Then proceed to step 3; Step 8: Enter the navigation output calculation module and use the following formulas (12) and (13) to calculate the navigation position and velocity; output the position and velocity calculation results and pass the results to step 9; finally, let... Proceed to step 2 to begin a new round of navigation calculation; ( )

[0029] ( )

[0030] Step 9: Receive the position and velocity calculation results from Step 8, perform a new threshold calculation and measurement screening process, and incorporate the screened observations into the new round of navigation solution process.

[0031] Furthermore, the new threshold calculation and measurement screening process described in step 9 includes the following steps: Step 91: Perform threshold calculation; Step 92: The primary satellite distributes the threshold to the secondary satellites via inter-satellite links; Step 93: Observe, process, and threshold-filter the star-to-star pulsar. The threshold selection uses the following formula: ( ).

[0032] The beneficial effects achieved by this invention are as follows: (1) A new pulsar navigation sequential filtering unit with measurement screening and out-of-order processing functions is provided, along with its implementation method. During the sequential filtering process, measurement screening and out-of-order processing can be performed simultaneously.

[0033] (2) A pulse TOA threshold setting and filtering module is specially set up to dynamically set the pulse TOA measurement values ​​obtained by pulsar detection of each spacecraft, and to filter the pulse TOA measurement values ​​using the set threshold. A filtering method for the filtered measurement is provided, and pulsar navigation filtering calculation under the pulse TOA measurement value filtering condition is realized.

[0034] (3) Due to inter-satellite transmission delay and other reasons, the current filtering cycle may receive the pulse TOA measurement value of the previous filtering cycle. To address the problem of such measurement values ​​arriving out of order across cycles, a pulse TOA measurement value misorder determination module is specially set up to determine the filtering cycle corresponding to the current measurement value and provides a misorder measurement processing method to enable the processing of misorder measurements.

[0035] (4) Within the same filtering period, a sequential processing method is provided to address the issue of asynchronous arrival times of pulsed TOA measurements detected by various spacecraft at the host satellite. This method can directly process asynchronous pulsed TOA measurements in real time, exhibiting excellent timeliness and rationally allocating computational resources, without having to wait for all pulsed TOA measurements to be available before unified processing. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the system architecture of the present invention.

[0038] Figure 2 This is a flowchart of the method of the present invention.

[0039] Figure 3 This is a schematic diagram of the main satellite payload system architecture of the present invention.

[0040] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0043] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, if the word "and / or" appears throughout the text, it means including three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0044] This invention provides a navigation method for pulsar autonomous navigation systems, addressing the shortcomings of existing technologies in measurement and filtering processes, including the lack of sequential and out-of-order processing capabilities. The navigation unit is attached to a distributed spacecraft system, and the method is implemented based on this unit. First, the pulse TOA information collected by each spacecraft undergoes threshold filtering. This filtered TOA information is not completely rejected but replaced with a predefined threshold before being sent to a central navigation filtering calculation module. Then, sequential filtering calculations are performed in the central navigation filtering calculation module, which sequentially filters all the filtered information. The central navigation filtering calculation module can also set the pulse TOA filtering threshold for each spacecraft based on motion state information and can receive the pulse TOA data and filtering status information transmitted by the spacecraft, thereby achieving high-precision filtering calculations. Furthermore, by incorporating an out-of-order processing process, the central navigation filtering calculation module can effectively process out-of-order arrival observation data.

[0045] The navigation unit described above is based on a distributed spacecraft system, and the system architecture is as follows: Figure 1As shown in the diagram. Photon detection and TOA calculation 1-N represent the detection of pulsars and the calculation of pulse TOA by spacecraft 1-N, respectively. Filtering modules 1-N are used to perform threshold filtering on the pulse TOA measurement and calculation results of each spacecraft. They can be distributed and embedded into the data processing units of each spacecraft's detectors. Their filtering thresholds are determined by the threshold setting module in the navigation master satellite (the spacecraft primarily responsible for navigation filtering calculations). The threshold setting module calculates reasonable thresholds based on the navigation and positioning data of each slave satellite (the spacecraft that distributes pulsar detection and TOA filtering processing) and sets the thresholds for each filtering module. Since the slave satellites transmit data asynchronously via inter-satellite links, and due to transmission delays, slave satellite observation data from the current navigation cycle may arrive at the master satellite in the next navigation cycle, a misorder determination module is set in the navigation master satellite to judge all currently received pulse TOA measurements to determine whether a pulse TOA observation is a delayed arrival from a previous navigation cycle. Navigation calculation software is embedded in the central navigation filter calculation module. This software performs sequential processing on the filtered pulse TOA observations through the calculation process and implements the function of handling out-of-order errors.

[0046] Specifically, such as Figure 1 As shown, the navigation unit includes: The pulse TOA filtering module filters the pulse TOA signals acquired by each spacecraft according to the pulse TOA threshold set by the threshold setting module below. When the observed pulse TOA signal exceeds the threshold, it is reassigned a specified value and the filtered pulse TOA observation and related flag parameters are passed to the disorder judgment module below for further processing. The specific filtering logic is referenced in the following formula (1).

[0047] The threshold setting module utilizes a pre-set pulsar database and, in conjunction with the orbital parameters of each spacecraft, determines the confidence range of the pulse TOA observations for each spacecraft, thereby determining the TOA threshold. Its orbital parameters are calculated using navigation and positioning data from the previous moment. This module engages in bidirectional data exchange with the central navigation filtering calculation module via a specific interface. It receives orbital information from the central navigation filtering calculation module, combines it with the dynamics information of each spacecraft to calculate the pulse TOA threshold for each spacecraft, and sends the calculated threshold information back to the central navigation filtering calculation module for subsequent calculations. Simultaneously, it replaces the original thresholds for each spacecraft with the calculated threshold information, thus completing the dynamic setting of the pulse TOA threshold for each spacecraft.

[0048] The out-of-order detection module accurately records the navigation cycle and determines the timing information accompanying the received pulse TOA observations from each spacecraft. It then determines the navigation filtering cycle corresponding to the obtained pulse TOA information and informs the central navigation filtering calculation module via appropriate flags.

[0049] The central navigation filtering calculation module uses the filtered pulse TOA data from each spacecraft and combines it with relevant information from the out-of-order determination module to complete the navigation and positioning calculation. It mainly includes filtering after pulse TOA filtering, sequential filtering calculation, measurement out-of-order processing, navigation calculation, and pulse TOA threshold calculation for each spacecraft.

[0050] Data processing and navigation filtering methods include the following parts: I. Pulse TOA Screening

[0051] From the star, The filtered pulse TOA observations are shown on the right side of the following equation, which represents the filtering logic. The pulsed TOA observations are calculated from the detected pulsar photon sequence. and All of these are the filtering thresholds provided by the threshold setting module; ( )

[0052] II. Sequential Processing Navigation Filter Calculation

[0053] Using the screening rule in (1), three Bernoulli random variables are introduced ( , , To model it, the system equations can be constructed as follows: ( )

[0054] ( )

[0055] in, for The state variables are the navigation position and velocity information that need to be filtered and calculated. Here is the state transition matrix. For the observation matrix, and Modeled as Gaussian white noise with a mean of 0, and variances respectively and subscript This represents the filter cycle number.

[0056] The sequential processing method is as follows: Input: Initial position, velocity state estimate and initial state estimation variance ; Output: Current time State estimation and its variance ; The filtering estimation process is as follows: ( )

[0057] For ,do

[0058] ( )

[0059] ( )

[0060] ( )

[0061] ( )

[0062] For ,do

[0063] ( )

[0064] ( )

[0065] ( )

[0066] end

[0067] ( )

[0068] ( )

[0069] end

[0070] in, Represents filter gain. Representative seeking expectations, Represents the sequence number of the observations obtained in sequence, superscript T and T represent matrix inversion and transpose, respectively. Some variables are calculated as follows:

[0071] ①

[0072] ②

[0073]

[0074] ③

[0075] ④

[0076] in, , These are intermediate quantities in the calculation process, and their specific meanings are not explained. It is a normal probability density function; This is the normal cumulative distribution function; it is involved in the calculation. The most recently updated estimate is used instead in the calculation, and the same applies below.

[0077] III. Navigation Filtering Method for Out-of-Order Processing

[0078] 1) The above sequential filtering operates normally based on the measurement arrival order. If the filter is currently at time... At this moment, the sequence is sequentially updated to sequence number . Then there are the observations. and They are based on Before the time (including) The posterior state estimates and variances of all existing measurements at time ( ). Also... and They are based on Before the time (including) The prior state estimates and variances of all measurements at time ( ).

[0079] 2) If a measurement is received (dimensionality is) ),in Then the state estimate and covariance can be updated as follows: and The steps are as follows: (1) System Restructuring: Utilizing Observations that are already in place Reconstruct the system equations: ( )

[0080] ( )

[0081] in, Dimension is , For a moment The measurement matrix reconstructed from the existing measurements is shown below, with commas used to distinguish out-of-order moments.

[0082] (2) Estimating the state from time t Working backwards to the time ,have to

[0083] ( )

[0084] ( )

[0085] in: The calculation of any quantity in the above is performed according to ④, and the result is a separate calculation for each observation. *1 matrix; The calculation is performed according to ②, and each observation is calculated separately to form the result. * Diagonal array; The calculation is performed according to ③, and each observation is calculated separately to form the result. * Diagonal array; (3) Calculate the traceability state covariance: ( )

[0086] ( )

[0087] Conditional covariance for state tracing: ( )

[0088] (4) Calculation time Measurement traceability covariance: ( )

[0089] in, For a moment The out-of-order measurement observation matrix; The calculation is performed according to ③, and each observation is calculated separately to form the result. * Diagonal array; The calculation is performed according to ②, and each observation is calculated separately to form the result. * Diagonal array; (5) Calculation time state and moment Retrospective measurement covariance

[0090] ( )

[0091] (6) Using delay measurement Update the state estimate and its covariance: ( )

[0092] ( )

[0093] in, The calculation of any quantity in the above is performed according to ④, and the result is a separate calculation for each observation. *1 matrix; IV. Threshold Calculation

[0094] After the position and velocity information is calculated by the central navigation filter, it is combined with the orbital dynamics model of each spacecraft to predict the position and velocity information of each spacecraft within a certain time. In addition, combined with the pulsar timing model, the position and velocity information is further converted into the predicted value of pulse TOA. The predicted value of pulse TOA is used as the new pulse TOA observation reference threshold for each spacecraft, and the pulse TOA observation is screened for threshold.

[0095] Implementation process

[0096] The navigation filtering unit and method described above are illustrated in the following diagram. The main components include: A: Sequential filtering process

[0097] B: Out-of-order processing flow

[0098] C: Threshold Calculation and Measurement Screening Process

[0099] The overall implementation process includes the three main processes mentioned above.

[0100] like Figure 2 As shown, the method includes the following steps: Step 1: The main star initiates the mission, assigning initial position and velocity estimates. and initial state estimation variance , ( )

[0101] Step 2, during initial execution Use the following formula to perform Calculation of the state and initial covariance values ​​at time 1: ( )

[0102] ( )

[0103] ( )

[0104] ( )

[0105] Step 3, Initial Preparing to receive the first Each observation is processed; Step 4: Determine if it is an out-of-order measurement; if yes, proceed to step 6; if no, proceed to step 5. Step 5: Proceed to the sequential processing flow and process the following formula... Individual observations: ( )

[0106] ( )

[0107] ( )

[0108] Then proceed to step 7; Step 6: Enter the out-of-order processing flow and process the following formula: Individual observation, Utilize the current Based on existing observations of the filtering period, construct the system equations: ( )

[0109] ( )

[0110] State estimation backward deduction: ( )

[0111] ( )

[0112] Tracing the state covariance: ( )

[0113] ( )

[0114] ( )

[0115] Measurement traceability covariance: ( )

[0116] ( )

[0117] Update the state estimate and its covariance: ( )

[0118] ( )

[0119] Step 7: Determine whether all observations for the current period have been processed (i.e., when...). At that time, among them (The total number of observations received in this period); Yes, proceed to step 8; No, Then proceed to step 3; Step 8: Enter the navigation output calculation module and use the following formulas (12) and (13) to calculate the navigation position and velocity; output the position and velocity calculation results and pass the results to step 9; finally, let... Proceed to step 2 to begin a new round of navigation calculation; ( )

[0120] ( )

[0121] Step 9: Receive the position and velocity calculation results from Step 8, perform a new threshold calculation and measurement screening process, and incorporate the screened observations into the new round of navigation solution process.

[0122] Specifically, the new threshold calculation and measurement screening process described in step 9 includes the following steps: Step 91: Perform threshold calculation; Step 92: The primary satellite distributes the threshold to the secondary satellites via inter-satellite links; Step 93: Observe, process, and threshold-filter the star-to-star pulsar. The threshold selection utilizes the following formula: ( ).

[0123] The construction of a navigation system using the navigation unit and method disclosed in this application includes the following parts: 1. Establishment of Distributed Spacecraft Systems

[0124] (1) Construct a distributed spacecraft system in Earth's space, with each spacecraft carrying a pulsar detection payload, which can detect and process data from specific pulsars. The spacecraft are interconnected through inter-satellite links and can complete observation and navigation tasks under unified scheduling.

[0125] (2) In a distributed spacecraft system, at least one spacecraft serves as the carrier for navigation filtering calculations, and is called the navigation master satellite. The master satellite and several other spacecraft (slave satellites) carry pulsar detection payloads to achieve pulsar detection and data preprocessing. The preprocessing process includes the arrival time of the detected photon data, pulse arrival time (TOA) estimation, and pulse TOA estimation screening.

[0126] (3) The main satellite is interconnected with other spacecraft through inter-satellite links, enabling functions such as inter-satellite ranging, communication and time synchronization.

[0127] (4) Using the inter-satellite synchronization timing system, each spacecraft keeps time synchronized. A certain spacecraft plans the observation mission of the entire system based on the orbit estimates of each spacecraft, pulsar parameter database, etc., to realize the observation of pulsars in a certain period (set as the kth period) and record the inter-satellite position and other parameters in that period.

[0128] (5) The main star uses pulsar observations from various spacecraft to construct a navigation filter based on the proposed method to achieve navigation and positioning functions.

[0129] 2 Spacecraft Payload Design

[0130] For the primary satellite implementing navigation filtering calculations, the spacecraft payload system and data processing unit are designed as follows: Figure 3 As shown, the primary satellite, through this payload configuration, conducts pulsar navigation missions based on synchronized timing using the distributed spacecraft system clock. The onboard pulsar detector performs pulsar detection, photon data preprocessing, and calculates pulse TOA observations. Furthermore, pulse TOA observations are filtered according to thresholds. Pulse TOA observations from other spacecraft are also processed using their respective thresholds. The out-of-order identification module primarily identifies each collected pulse TOA observation and determines its corresponding filtering period. The central navigation filtering calculation module performs corresponding sequential or out-of-order filtering calculations based on the identified pulse TOA observation period number, outputting navigation and positioning information. This navigation and positioning information is simultaneously fed back to the threshold calculation and distribution module, where it combines information such as the pulsar database and Earth ephemeris to perform dynamic threshold calculations and broadcasts them to each spacecraft via inter-satellite links. In the distributed spacecraft system, the payload configuration of the slave satellites is consistent with that of the primary satellite.

[0131] The following describes the payloads carried on distributed spacecraft: (1) Pulsar probe payload

[0132] The payload consists of a photon probe, a signal amplification and acquisition unit, a photon sequence encoding unit, and a data processing unit. The photon probe, signal amplification and acquisition unit, and photon sequence encoding unit primarily acquire and preprocess pulsar photon data to generate photon Time of Arrival (TOA) information. The data processing unit mainly estimates the pulse TOA observations. A threshold filtering module is embedded in the data processing unit to filter the pulse TOA observations. The payload establishes communication with the primary satellite via an inter-satellite link and can receive pulse TOA threshold information transmitted by the primary satellite. Considering practical situations such as inter-satellite transmission delays and out-of-order delivery, the threshold filtering module is located on the slave satellite, allowing the slave satellite to perform threshold filtering of pulse TOA data in real time, which helps reduce the storage and computational burden on the primary satellite.

[0133] (2) Star sensor

[0134] This payload is used to determine the spacecraft's attitude and assist in the pulsar detection function.

[0135] (3) Inter-satellite link payload

[0136] Inter-satellite link payloads enable communication and precise ranging between spacecraft. Information necessary for navigation by each spacecraft is transmitted and shared via inter-satellite links. Furthermore, inter-satellite links facilitate spacecraft clock synchronization and precise determination of relative positions.

[0137] (4) Time synchronization timing system

[0138] It consists of an onboard clock, inter-satellite links, embedded systems, and clock synchronization algorithm software. It ensures the accuracy and synchronization of timing for each spacecraft.

[0139] (5) Data processing and navigation computing unit

[0140] This unit expands upon the standard navigation and positioning calculation functions by adding a misordering identification module, a threshold calculation and distribution module, and a misordering and filtering sequential processing module. The misordering identification module primarily determines the order of received pulse TOA observations from each satellite, identifying whether the data predates the current filtering time based on the timestamp. The threshold calculation and distribution module determines the pulse TOA threshold for each spacecraft based on navigation, positioning, and orbit estimation results, calculates it periodically, and transmits it to each spacecraft in real-time or near real-time. The misordering and filtering sequential processing module performs sequential processing of misordered measurement data; the specific process is described in the following flowchart.

[0141] 3. Data Processing Flow Implementation Plan

[0142] (1) Under the scheduling of the primary star, the pulsar detection mission is initiated from time t0 and lasts until time t1. N During this period, the pulsar detector continuously detects the photon arrival time series ph of the pulsar radiation; the spacecraft constellation system uses the inter-satellite link payload to measure and calculate the inter-satellite distance L, and the star sensor measures and calculates the spacecraft attitude C.

[0143] (2) Each spacecraft will perform contour folding on the detected photon data, calculate the pulse TOA, and filter and correct the pulse TOA using a set filtering threshold. That is, when the pulse TOA is within the threshold, the pulse TOA value remains unchanged; when the pulse TOA is outside the threshold, the pulse TOA is replaced by the threshold, which is the new pulse TOA value. After the pulse TOA is filtered and corrected, it is combined with other spacecraft parameters to form a data packet (including: time, observation period, pulse TOA value, filtering occurrence status marker, attitude data, inter-satellite distance information, health status parameters, etc.), and transmitted from the slave satellite to the master satellite through the inter-satellite link.

[0144] (3) The primary satellite judges the received data packets from the secondary satellites. If the data packet is within the current filtering period, it enters the central navigation filtering calculation module for sequential filtering. If the current data packet is within a previous filtering period, it is processed out of order, and the data packet is used to update the past state, thereby updating the current state. The specific algorithm implementation process is as follows: Figure 2 As shown.

[0145] (4) The central navigation filtering calculation module runs a sequential filtering algorithm to obtain navigation information. This information includes the position and velocity information of the primary satellite. On the one hand, it serves as the output of the navigation system, providing information to the primary and secondary satellites. On the other hand, it combines spacecraft dynamics to predict the orbits of each spacecraft, sets new filtering thresholds, and sends them to each spacecraft via inter-satellite links.

[0146] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A navigation method applied to a pulsar autonomous navigation system, wherein the method is implemented based on a navigation unit; characterized in that, The navigation unit includes: The pulse TOA filtering module filters the pulse TOA signals acquired by each spacecraft according to the pulse TOA threshold set by the threshold setting module below. When the observed pulse TOA signal exceeds the threshold, it is reassigned a specified value and the filtered pulse TOA observation and related flag parameters are passed to the misorder determination module below for further processing. The threshold setting module exchanges data bidirectionally with the central navigation filter calculation module; and uses a pre-set pulsar database, combined with the orbital parameters of each spacecraft, to determine the confidence range of the pulse TOA observations of each spacecraft, thereby determining the TOA threshold. The out-of-order determination module determines the navigation filtering period corresponding to the obtained pulse TOA information and informs the central navigation filtering calculation module through the corresponding flag bits. The central navigation filtering calculation module uses the filtered pulse TOA data from each spacecraft and combines it with relevant information from the out-of-order determination module to complete the navigation and positioning calculation. The method includes the following steps: Step 1: The main star initiates the mission, assigning initial position and velocity estimates. and initial state estimation variance , ( ) in, This is the initial position and velocity state estimation vector, which is calculated and updated in subsequent iterations. Its initial value is set to the specific estimated value. ; The covariance matrix is ​​estimated for the initial state and is calculated and updated in subsequent iterations, with its initial value set as the specific estimated variance. ; Step 2, during initial execution Use the following formula to perform Calculation of the state and initial covariance values ​​at time 1: ( ) ( ) ( ) ( ) Among them, the bottom right corner mark The time number. represent Time's up The shift of time, The representative has been transferred This agreement is made throughout the entire text; represent Time's up Predicting the state at any given time. for The system equations and state transition matrix at time t. represent State estimate at time 10:00 for Time's up The predicted state estimate covariance at time 1. for Time-state estimation covariance for A Gaussian white noise variance matrix with a mean of 0 at any given time. for The state estimation at time 1 is marked as 0 in the upper right corner since no observational information has been used at this point. Subsequent estimations will utilize the data from the time step 1. If an observation is updated and estimated, then the upper right corner is... Similarly, for The state estimate covariance at time t is set to 0 since no observational information has been used at this point. This covariance will be used later when the state covariance is... If an observation is updated and estimated, then the upper right corner is... The superscript "T" indicates transpose. Step 3, Initial Preparing to receive the first Each observation is processed; Step 4: Determine if it is an out-of-order measurement; if yes, proceed to step 6; if no, proceed to step 5. Step 5: Proceed to the sequential processing flow and process the following formula... Individual observations: ( ) ( ) ( ) Among them, the upper right corner mark Representing the Each observation sequence number For the first At time, corresponding to the State estimation for each observation For the first At time, corresponding to the Gain matrix for each observation For the first At that moment, the Individual observation (i.e., pulse TOA). This represents the expected value of the quantity within the parentheses; For the first At time, corresponding to the State estimation covariance for each observation It is an m x m identity matrix, where m equals the state estimator. dimensionality Let it be a Bernoulli random variable, as defined in equation (15) below. For the first At time, corresponding to the Individual observations Seeking expectations; For the first At time, corresponding to the The observation matrix for each observation; the superscript -1 indicates matrix inversion; For the first At time, corresponding to the For each observation, the cross-covariance matrix between the Kalman filter error and the state is... For the first At time, corresponding to the For each observation, the inverse of the Kalman filter error variance matrix; Then proceed to step 7; Step 6: Enter the out-of-order processing flow and process the following formula: Individual observation, Utilize the current Based on existing observations of the filtering period, construct the system equations: ( ) ( ) in, The position and velocity state vectors, For the observation of the impulse TOA; using Bernoulli random variables ( , , Modeling observations, The high threshold representing the observation, The low threshold of the representative observation, as mentioned earlier, is state noise. and observation noise Modeled as Gaussian white noise with a mean of 0, and variances respectively and , This represents the observation matrix constructed from existing observations; State estimation backward deduction: ( ) ( ) Wherein, the time of the previous order misordering is denoted as subscript represent Time's up The process of working backward from time, That is Time's up Working backward from the state at any given moment, represent arrive State cumulative noise covariance at time step for and The system state transition matrix between time points. This refers to the actual observed measurements after the current screening, i.e., the actual observed filtered pulse TOA. Tracing the state covariance: ( ) ( ) ( ) in, That is Time's up Time-traveling state covariance Measurement traceability covariance: ( ) ( ) Update the state estimate and its covariance: ( ) ( ) in, Based on the current number Individual measurements and Out-of-order observations at different times, and the calculated update state. Its corresponding covariance; for Disordered observations at time, It is to calculate the conditional expectation of it; Step 7: Determine if all observations for the current period have been processed; if yes, proceed to step 8; otherwise, Then proceed to step 3; Step 8: Enter the navigation output calculation module and use the following formulas (12) and (13) to calculate the navigation position and velocity; output the position and velocity calculation results and pass the results to step 9; finally, let... Proceed to step 2 to begin a new round of navigation calculation; ( ) ( ) Among them, superscript This represents the latest state and the update of the covariance matrix. These are the estimated positions and velocities for this round (time k). This is the covariance estimate for this round (time k); Step 9: Receive the position and velocity calculation results from Step 8, perform a new threshold calculation and measurement screening process, and incorporate the screened observations into the new round of navigation solution process.

2. The navigation method for a pulsar autonomous navigation system according to claim 1, characterized in that, The new threshold calculation and measurement screening process described in step 9 includes the following steps: Step 91: Perform threshold calculation; Step 92: The primary satellite distributes the threshold to the secondary satellites via inter-satellite links; Step 93: Observe, process, and threshold-filter the star-to-star pulsar. The threshold selection utilizes the following formula: ( ) in, yes Time-based observations, which pass through a threshold and After filtering, assign values ​​to That is, the actual observations involved in the filtering calculation.

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