Distributed spacecraft positioning system and method based on iterative estimation method

Abstract

The invention relates to the technical field of spacecraft navigation control, in particular to a distributed spacecraft positioning system and method based on an iterative estimation method. Comprising a master satellite and N slave satellites; wherein the main satellite comprises a navigation calculation unit, an inter-satellite distance measurement module A, a positioning calculation module, an orbit forecast updating module and a photon TOA information updating module; wherein the slave satellite comprises a pulsar detector, a data preprocessing module and an inter-satellite distance measuring module B. According to the method, the observed quantity is iteratively updated by utilizing the state estimation value, and the model uncertainty equivalent noise is estimated by adopting the self-adaptive estimator in the iteration estimation process, so that the observed quantity precision and the model precision can be improved, and the navigation precision is improved.

Description

Technical Field

[0001] The present invention relates to the field of spacecraft navigation control technology, and in particular to a distributed spacecraft positioning system and method based on an iterative estimation method. Background Art

[0002] Pulsar autonomous navigation technology is a new means for spacecraft to achieve autonomous navigation. Since the signals emitted by pulsars in the universe are generally weak, in order to ensure that pulsar detectors collect enough pulsar photon information, in recent years, domestic and foreign scholars and technicians have expanded the single-spacecraft pulsar autonomous navigation method and realized the multi-spacecraft pulsar autonomous navigation method. This method of using multiple spacecraft to jointly achieve pulsar autonomous navigation is called the distributed pulsar autonomous navigation method.

[0003] Distributed pulsar autonomous navigation uses multiple different spacecraft to observe certain specific pulsars to obtain pulse phase observations. Based on the inter-satellite ranging data and communication support provided by the inter-satellite links, different pulsar phase observations are filtered in the navigation data processing unit to achieve autonomous navigation and positioning.

[0004] The existing pulsar autonomous navigation has the following problem: when using the X-ray photon data obtained by the pulsar detector to calculate the pulse arrival time (pulse TOA), it is necessary to use the spacecraft orbit information to process the photons, and this orbit information needs to be predicted and estimated. The current method is to obtain it by presetting the initial orbit estimate and recursively using the orbital dynamics model. Therefore, the focus of the problem is the accuracy of the orbit calculation, which will affect the calculation accuracy of the pulse TOA. The current methods are:

[0005] 1) Using inertial navigation measurement equipment to measure orbits, this method has problems such as cumulative errors and is difficult to apply in the weightless conditions of space;

[0006] 2) Using orbital dynamics model to estimate, this method has similar problems as the above method, and there is a large error in long-term estimation;

[0007] 3) Shorten the navigation filter cycle, so that the observation time is also shortened, and the orbit calculation time required is also shortened, thereby alleviating the divergence of long-term calculation. But this is a more compromised method;

[0008] 4) Use the maximum likelihood method to estimate orbital parameters. This method requires a huge amount of calculation and is difficult to carry out in real time on orbit. Summary of the invention

[0009] The present invention provides a distributed spacecraft positioning system and method based on an iterative estimation method, the purpose of which is to solve the problem of low orbit prediction accuracy in the prior art by adaptively updating the observed quantity and performing multiple iterative updates on the orbit in each navigation cycle, thereby improving the accuracy of observed pulse TOA and ultimately improving the accuracy of pulsar navigation.

[0010] To achieve the above object, the technical solution of the present invention is:

[0011] The present invention provides a distributed spacecraft positioning system and method based on an iterative estimation method, comprising a master satellite and N slave satellites;

[0012] Wherein, the main star includes:

[0013] The navigation calculation unit is used to implement navigation calculations and obtain the absolute position estimate of the main satellite based on the latest pulse TOA. The absolute position estimate obtained is The navigation calculation unit includes a pulse TOA update module, which is used to aggregate the photon data set from the photon TOA information update module, and then process the photon data, and then use the contour folding method to achieve pulse folding, and finally use the cross-correlation method to obtain the latest pulse TOA;

[0014] The inter-satellite distance measurement module A is used to obtain the distance and azimuth information of each slave satellite relative to the master satellite, and send the inter-satellite distance measurement data to the positioning calculation module described below; it is also used to form an inter-satellite link with other spacecraft for interconnection;

[0015] A positioning calculation module is connected to the navigation calculation unit and the inter-satellite ranging module A respectively; and is used to calculate the absolute position estimate value given by the navigation calculation unit according to the inter-satellite ranging data given by the inter-satellite ranging module A and the and an orbital dynamics model, updating the absolute position estimate of each of the slave satellites; and sending the updated absolute position estimate of each of the slave satellites to the orbital prediction update module described below;

[0016] An orbit prediction update module is connected to the positioning calculation module; it is used to predict the position and speed of each of the slave satellites within a certain time range based on the current absolute position estimate of each of the slave satellites given by the positioning calculation module and in combination with the orbital dynamics model; and transmit the above-mentioned prediction value to the photon TOA information update module described below;

[0017] A photon TOA information update module, connected to the orbit prediction update module and the data preprocessing module of the slave star; used to collect the pulsar photon sequence transmitted from each slave star, then obtain the latest position corresponding to the photon TOA of each slave star by interpolating the prediction value provided by the orbit prediction update module, and then project it in the direction of the pulsar to form a set of photon sequence TOA and corresponding projection position, recorded as {time, position}, and then summarize the {time, position} set of each slave star into a photon data set and transmit it to the pulse TOA update module inside the navigation calculation unit;

[0018] Wherein, the slave stars include:

[0019] A pulsar detector, used to detect pulsars, obtain pulsar photon sequences, and pass the pulsar photon sequences to the following data preprocessing module;

[0020] A data preprocessing module, connected to the pulsar detector; used to preprocess the pulsar photon sequence and transmit the processed pulsar photon sequence to the primary star photon TOA information updating module;

[0021] The intersatellite ranging module B is used for ranging and forming intersatellite links with other spacecraft for interconnection.

[0022] Furthermore, the master satellite also includes a task scheduling module A, which sends scheduling instructions to each of the slave satellites through an intersatellite link based on a unified time reference to unify the detection and data transmission tasks of the spacecraft system.

[0023] Furthermore, the slave satellite also includes a task scheduling module B, which mainly plans and runs related actions according to the task instructions of the master satellite.

[0024] Furthermore, the navigation calculation method in the navigation calculation unit specifically includes the following steps:

[0025] 1) Set the system initial value:

[0026] 2) Assign an initial value to the state starting at time k;

[0027]

[0028]

[0029] Among them, the superscript i * The marked value is the latest estimated value; the superscript T represents the transposition of the matrix; k represents the filter cycle number, k = 1, 2, ..., K; P k represents the filtering variance at time k; P k / k-1represents the prediction variance from time k-1 to time k; Q k represents the state noise variance;

[0030] 3) Perform filtering iterative calculation, the specific steps include:

[0031] ①Use Get observation updates: Then using the latest observations and Recalculate and

[0032]

[0033]

[0034] in,

[0035] Where i represents the number of iterations in a cycle, i = 0, 1, 2, ..., N max ;d k represents the adaptive factor,

[0036] ②Use Implementing EKF filtering:

[0037]

[0038]

[0039] in,

[0040] ③ Loop through steps ① and ② in step 3); if the current number of iterations i is greater than or equal to the set maximum number of iterations N max , then the current iteration ends and enters step 2) to continue the navigation calculation of the next cycle; if the current iteration number i is less than the set maximum iteration number N max , then continue to judge the threshold as follows:

[0041]

[0042] Among them, V th is the set threshold;

[0043] When formula (11) holds true, the current value of i is n, and the output is: and End this round of iteration and go to step 2) to continue the navigation calculation of the next cycle; when formula (11) is not true, go back to step 3) to continue the iterative calculation of this cycle.

[0044] A distributed spacecraft positioning method based on an iterative estimation method comprises the following steps:

[0045] S1. Set the absolute position estimate of the primary star orbit The initial value of

[0046] S2. In the current cycle k, after the task starts, under the unified time reference and task scheduling, each slave satellite is divided into three groups to detect three different pulsars respectively, and each slave satellite obtains the corresponding pulsar photon sequence; at the same time, the master satellite obtains the intersatellite distance of each slave satellite from the master satellite through the intersatellite link, and obtains the attitude of each slave satellite through a camera or other instrument, that is, the master satellite obtains the distance and azimuth information of each slave satellite;

[0047] S3. The positioning calculation module uses the distance and azimuth information of each slave star obtained in S2 to first calculate the relative position of each slave star in the constellation, and then combines it with the absolute position estimate of the master star orbit Determine the absolute position estimate of each slave star; at the same time, each slave star records the pulsar photon sequence detected and transmits it to the master star;

[0048] S4. Based on the estimated absolute positions of the satellites, the orbit prediction update module performs orbit prediction for a certain time range and sends these prediction data to the photon TOA information update module;

[0049] S5. The master satellite uses the prediction data provided by the orbit prediction update module to update the photon data of each slave satellite in the photon TOA information update module;

[0050] S6. The pulse TOA update module in the navigation calculation unit calculates the pulse TOA based on the latest photon data provided in S5; then uses the navigation calculation method to perform navigation positioning calculation to obtain the latest absolute position estimate of the primary star. Then, S2 to S6 are executed in a loop.

[0051] The beneficial effects achieved by the present invention are:

[0052] (1) The present invention provides a new distributed pulsar navigation method. The method iteratively updates the observation quantity by using the state estimation value, and in the iterative estimation process, uses an adaptive estimator to estimate the model uncertainty equivalent noise, thereby improving the observation quantity accuracy and model accuracy, thereby improving the navigation accuracy.

[0053] (2) The present invention provides a new distributed pulsar navigation system, which is equipped with a positioning calculation module, an orbit prediction update module, a photon TOA information update module, a navigation calculation unit, etc. These modules constitute the main iterative loop, specifically implementing the method in (1) to achieve high-precision navigation.

[0054] (3) The traditional constellation based on intersatellite links can only give the relative position of the spacecraft by using the intersatellite links combined with the dynamic model. However, the application of this method and system in the spacecraft constellation system not only introduces pulsar observations to achieve absolute positioning, but also can further improve the absolute positioning accuracy through the iterative method proposed in this system. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0056] Figure 1 It is a schematic diagram of the system architecture of the present invention.

[0057] Figure 2 It is a flow chart of the method implementation of the present invention.

[0058] Figure 3 It is a scheme diagram of the distributed navigation and positioning system of the present invention. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0061] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if the meaning of "and / or" appearing in the full text is to include three parallel schemes, taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0062] The present invention provides a distributed spacecraft positioning system and navigation method based on an iterative estimation method, which can adaptively perform iterative orbit estimation. In each navigation cycle, the orbit is iteratively updated multiple times, which not only improves the orbit prediction accuracy, but also improves the accuracy of observed pulse TOA, which is very beneficial to the accuracy improvement of pulsar navigation and realizes the improvement of distributed pulsar navigation accuracy.

[0063] To achieve the above goals, we must first establish a distributed spacecraft system that meets the following requirements:

[0064] (1) Construct a distributed spacecraft system in Earth space, with each spacecraft carrying a pulsar detection payload that can detect and process data for a specific pulsar. Spacecraft are interconnected through intersatellite links and can complete observation and navigation tasks under unified scheduling.

[0065] (2) In a distributed spacecraft system, at least one spacecraft is used as a carrier for implementing navigation filtering calculations, which is called the navigation master. The master and other spacecraft (slave) carrying pulsar detection payloads realize pulsar detection and data preprocessing. The preprocessing process includes preliminary screening of detection photon data, etc.

[0066] (3) The main satellite is interconnected with other spacecraft through intersatellite links, which can realize functions such as intersatellite ranging, communication and time synchronization.

[0067] (4) Using the intersatellite synchronization timing system, each spacecraft maintains time synchronization. The master satellite plans the observation mission of the entire system based on the orbital estimates of each spacecraft and the pulsar parameter database, realizes the pulsar observation of a certain period (set as the kth period), and records the intersatellite position and other parameters of this period.

[0068] (5) The master satellite uses the pulsar observations of each slave satellite to construct a navigation filter according to the proposed method to achieve the navigation and positioning function.

[0069] Specifically, Figure 1 As shown, the distributed pulsar navigation system includes a master star and N slave stars; the configurations of the master star and the slave stars can be exactly the same, and both can be reduced accordingly according to demand to save costs; when the configurations of the master star and the slave stars are exactly the same, the master star can be specified arbitrarily.

[0070] Wherein, the main star includes:

[0071] The navigation calculation unit is used to realize navigation calculation, and the absolute position estimate of the main star is obtained by performing navigation filtering calculation based on the pulse TOA obtained by the latest pulsar detection. (It can also be called the estimated value of the absolute position and velocity of the primary star, which is calculated by the following formula (8)), and the obtained absolute position estimate The navigation calculation unit includes a pulse TOA update module, which is used to aggregate the photon data set from the photon TOA information update module, and then perform interpolation, sorting and other processing on the photon data, and then use the contour folding method to realize pulse folding, and finally use the cross-correlation method to obtain the latest pulse TOA, that is, to obtain the updated observation value. The hardware of the navigation calculation unit is mainly composed of a microprocessor, and the software runs a navigation filtering calculation algorithm. The software steps mainly include: filtering iteration, adaptive noise estimation and iteration number determination; these three steps correspond to the distributed pulsar navigation method in sequence: the filtering iteration step refers to steps ①②③, the adaptive noise estimation step refers to formulas (5) to (6), and the iteration number determination step refers to step ③;

[0072] The inter-satellite distance measurement module A is used to obtain the distance and azimuth information of each slave satellite relative to the master satellite, and send the inter-satellite distance measurement data to the positioning calculation module described below; it is also used to form an inter-satellite link with other spacecraft for interconnection;

[0073] A positioning calculation module is connected to the navigation calculation unit and the inter-satellite ranging module A respectively; and is used to calculate the absolute position estimate value given by the navigation calculation unit according to the inter-satellite ranging data given by the inter-satellite ranging module A and the and an orbital dynamics model, updating the absolute position estimate of each of the slave satellites; and sending the updated absolute position estimate of each of the slave satellites to the orbital prediction update module described below; wherein the orbital dynamics model adopts an existing model, which will not be described in detail herein;

[0074] An orbit prediction update module is connected to the positioning calculation module; it is used to predict the position and speed of each of the slave satellites within a certain time range based on the current absolute position estimate of each of the slave satellites given by the positioning calculation module and in combination with the orbital dynamics model; and transmit the above-mentioned prediction value to the photon TOA information update module described below;

[0075] A photon TOA information update module is connected to the orbit prediction update module and the data preprocessing module of the slave star; it is used to collect the pulsar photon TOA sequence transmitted from each slave star, and then obtain the latest position corresponding to the photon TOA of each slave star by interpolating the prediction value provided by the orbit prediction update module, and then project it in the direction of the pulsar to form a set of photon sequence TOA and corresponding projection position, recorded as {time, position}, and then summarize the {time, position} set of each slave star into a photon data set and transmit it to the pulse TOA update module inside the navigation calculation unit;

[0076] Wherein, the slave stars include:

[0077] A pulsar detector, used to detect pulsars, obtain pulsar photon sequences, and pass the pulsar photon sequences to the following data preprocessing module;

[0078] A data preprocessing module is connected to the pulsar detector; it is used to preprocess the pulsar photon sequence (using conventional processing methods, such as photon signal collection, time stamping, encoding, etc.), and transmit the processed pulsar photon sequence to the primary star photon TOA information update module;

[0079] The intersatellite ranging module B is used for ranging and forming intersatellite links with other spacecraft for interconnection.

[0080] Figure 1 1 to N in the figure represent the spacecraft numbers; specifically, the "Photon TOA information update N" in the figure is a module in the primary satellite, corresponding to processing the photon sequence received from the Nth spacecraft; the "Inter-satellite ranging N" is similarly understandable and will not be repeated here.

[0081] Furthermore, the master satellite also includes a task scheduling module A, which sends scheduling instructions to each of the slave satellites through an intersatellite link according to a unified time reference, and unifies the detection and data transmission tasks of the spacecraft system; specifically, the specific functions are to coordinate the scheduling of each spacecraft grouping, collaborative detection of pulsars, coordinate data transmission cycles, etc.

[0082] Furthermore, the slave satellite also includes a task scheduling module B, which mainly plans and runs related actions according to the task instructions of the master satellite, such as performing pulsar detection, intersatellite ranging, etc. In addition, the task scheduling module A and the task scheduling module B back up each other to prevent damage.

[0083] The pulsar navigation system is modeled as:

[0084] x k =F k x k-1 +w k-1 (1)

[0085]

[0086] Wherein, the subscript k represents the filter cycle number, (1) is the state equation, which is obtained based on the kinematic and dynamic modeling of the system, and x k represents the spacecraft position, velocity and other states at time k, F k is the state transfer matrix; (2) is the observation equation, It is the observation quantity finally obtained by using the pulsar photon sequence detected by each spacecraft detector after data preprocessing, large-scale space-time conversion, profile folding and pulse TOA estimation, namely pulse TOA. k is the observation equation matrix, w k-1 and v k Generally it is white noise, ε k is the model residual. To simplify the explanation, k The noise of the measurement system itself k It is approximately equivalent to a time-varying white noise model, whose mean and variance are recorded as v k and R k .

[0087] Further, the navigation calculation method in the navigation calculation unit implements the SIEKF algorithm, specifically comprising the following steps:

[0088] 1) Set the system initial value:

[0089] in, is the estimated value of the absolute position of the primary star at the initial time (k = 0);

[0090] is the initial estimated variance;

[0091] is the initial observation noise mean;

[0092] is the initial observation noise variance;

[0093] 2) Assign an initial value to the state starting at time k, which is calculated from the state last updated at time k-1;

[0094]

[0095]

[0096] Among them, the superscript i * The marked value is the latest estimated value; the superscript T represents the transposition of the matrix; k represents the filter cycle number, k = 1, 2, ..., K, the initial value of k is 1, and it gradually accumulates with the cycle; P k represents the filtering variance at time k; P k / k-1 represents the prediction variance from time k-1 to time k; Q k represents the state noise variance;

[0097] 3) Perform filtering iterative calculation, the specific steps include:

[0098] ①Use Get observation updates: (i.e. using The pulse TOA is updated, and this process is mainly completed in the pulse TOA update module), and then the latest observation and Recalculate and

[0099]

[0100]

[0101] in,

[0102] Where i represents the number of iterations in a cycle, i = 0, 1, 2, ..., N max , the initial value of i is 0, and it gradually accumulates with the cycle; d k Represents the adaptive factor. Generally,

[0103] ②Use Implementing EKF filtering:

[0104]

[0105]

[0106] in,

[0107] in, is the nonlinear state propagation function of the observation equation; T is Linearized form; represents the gain of the ith update at time k;

[0108] ③ Loop through steps ① and ② in step 3); if the current number of iterations i is greater than or equal to the set maximum number of iterations N max (Set the maximum number of iterations N max This is to prevent the algorithm from entering an infinite loop when the filter does not converge). This round of iteration ends and goes to step 2) to continue the navigation calculation of the next cycle. If the current number of iterations i is less than the set maximum number of iterations N max , then continue to judge the threshold as follows:

[0109]

[0110] Among them, V th is the set threshold;

[0111] When formula (11) holds true, the current value of i is n, and the output is: and End this round of iteration and go to step 2) to continue the navigation calculation of the next cycle; when formula (11) is not true, go back to step 3) to continue the iterative calculation of this cycle.

[0112] In the above method, the innovative invention is:

[0113] As shown in formula (2), in the iteration, using Get observation updates , the observation model should also be updated more accurately (which is not covered in the current work). Therefore, a residual term ε representing the observation model error is set in the observation equation. k , which also changes accordingly during the iteration process, can be recorded as right There are many methods for processing and estimating , and the present invention only provides a specific method: The noise of the measurement system itself k It is approximately equivalent to a time-varying white noise model, whose mean and variance are recorded as v k and R k In order to estimate the equivalent noise model, the calculation methods of formulas (5), (6) and (7) are used.

[0114] For the master star that realizes navigation filter calculation, design the spacecraft master star onboard electronic system and the slave star minimum system. The scheme is as follows Figure 3The electronic system on the master satellite is configured with modules as shown in the figure to achieve navigation and positioning tasks in coordination with the slave satellite.

[0115] Each spacecraft needs to carry corresponding payloads according to requirements, such as pulsar detectors, star sensors, intersatellite link payloads, time synchronization timing systems, etc. The following is an explanation of the payloads carried by distributed spacecraft:

[0116] (1) Pulsar Detector

[0117] It consists of a photon probe, a signal amplification and acquisition unit, a photon sequence encoding unit, a data processing unit, etc. Among them, the photon probe, the signal amplification and acquisition unit, and the photon sequence encoding unit are mainly used to collect and preprocess pulsar photon data to form photon TOA information.

[0118] (2) Star sensor

[0119] This payload is used to determine the attitude of the spacecraft and assist in completing the pulsar detection function.

[0120] (3) Intersatellite link payload

[0121] The intersatellite link payload can realize functions such as communication and precise distance measurement between spacecraft. The information necessary for navigation of each spacecraft is transmitted and shared through the intersatellite link. In addition, the intersatellite link can realize the synchronization of spacecraft clocks and the precise measurement of relative positions.

[0122] (4) Time synchronization timing system

[0123] It consists of on-board clocks, inter-satellite links, embedded systems and clock synchronization algorithm software to ensure the accuracy and synchronization of the timing of each spacecraft.

[0124] The following is a description of the main satellite onboard electronic system:

[0125] The onboard electronic system of the master satellite is composed of a photon TOA information update module, a pulse TOA update module, a navigation calculation unit, a task scheduling module, a positioning calculation module, an intersatellite ranging module, and an orbit prediction update module. These modules realize information transmission and sharing through the internal bus, and jointly complete functions such as photon sequence processing, intersatellite ranging, positioning calculation, orbit prediction, and navigation calculation. In terms of external interfaces, the photon TOA information update module also collects photon sequences sent by other spacecraft (slave satellites) through intersatellite links, and processes and integrates these photon sequences. The task scheduling module sends scheduling instructions to the slave satellites through the intersatellite links based on a unified time reference, unifying the detection and data transmission tasks of the spacecraft system. The master satellite sends the calculated absolute positions of each spacecraft (slave satellite) to each slave satellite through the intersatellite link. The intersatellite ranging module mainly completes the measurement of the distance between each satellite and the collection of data such as related attitude angles.

[0126] The following is a description of the satellite electronic system:

[0127] The electronic system of the slave satellite can have the same configuration as the master satellite, but when the master satellite is specified, the minimum electronic system of the slave satellite includes: pulsar detector, data preprocessing module, task scheduling module and intersatellite ranging module. Among them, the pulsar detector and data preprocessing module mainly realize the preprocessing of pulsar detection and its photon sequence, and the task scheduling module mainly plans and runs related actions according to the task instructions of the master satellite, such as executing pulsar detection, intersatellite ranging, etc. The intersatellite ranging module mainly realizes ranging and communication with other spacecraft.

[0128] In the spacecraft system interconnected by the intersatellite link, the navigation master star is first set, and the spacecraft must have the functional modules required by the present invention. In addition, when the mission is started, an initial value of the absolute position of the master star orbit is set first, which is used to preliminarily realize the calculation of pulse TOA, and the master star position is continuously updated in the subsequent filtering iteration.

[0129] Specifically, Figure 2 As shown, a distributed spacecraft positioning method based on an iterative estimation method comprises the following steps:

[0130] S1. Set the absolute position estimate of the primary star orbit The initial value of

[0131] S2. In the current cycle k, after the task starts, under the unified time reference and task scheduling, each slave satellite is divided into three groups to detect three different pulsars respectively, and each slave satellite obtains the corresponding pulsar photon sequence; at the same time, the master satellite obtains the intersatellite distance of each slave satellite from the master satellite through the intersatellite link, and obtains the attitude of each slave satellite through a camera or other instrument, that is, the master satellite obtains the distance and azimuth information of each slave satellite;

[0132] S3. The positioning calculation module uses the distance and azimuth information of each slave star obtained in S2 to first calculate the relative position of each slave star in the constellation, and then combines it with the absolute position estimate of the master star orbit Determine the absolute position estimate of each slave star; at the same time, each slave star records the pulsar photon sequence detected and transmits it to the master star;

[0133] S4. Based on the estimated absolute positions of the satellites, the orbit prediction update module performs orbit prediction for a certain time range and sends these prediction data to the photon TOA information update module;

[0134] S5. The master satellite uses the prediction data provided by the orbit prediction update module to update the photon data of each slave satellite in the photon TOA information update module;

[0135] S6. The pulse TOA update module in the navigation calculation unit calculates the pulse TOA based on the latest photon data provided in S5; then uses the navigation calculation method to perform navigation positioning calculation to obtain the latest absolute position estimate of the primary star. Then, S2 to S6 are executed in a loop.

[0136] Specifically, in the navigation calculation unit, the collected photon TOA information of each star is first integrated in the pulse TOA update module in the navigation calculation unit, such as sorting, interpolation, splicing, etc., and further processed to obtain the pulse TOA. The SIEKF method is used to perform navigation positioning calculations to obtain the latest absolute position estimate of the primary star. And judge the number of iterations i, if i is not less than the maximum number of iterations N max , then the current iteration ends and the navigation positioning calculation of the next filtering cycle begins, that is, the detection and calculation of a new cycle begins from step 2); if i is less than the maximum number of iterations N max , then further determine whether it satisfies formula (11). If not, return to step 3) and use the latest estimated value to re-update the absolute position of each spacecraft, thereby realizing the updated calculation of the pulse TOA and further realizing the updated calculation of the estimated value. If it satisfies formula (11), the latest estimated value of the absolute position of the master star is It is output as the navigation positioning result and enters the navigation positioning calculation of the next filtering cycle, that is, starting from step 2) to perform detection and calculation of a new cycle.

[0137] Specifically, the data processing flow implementation plan is as follows:

[0138] (1) Under the scheduling of the master star, the pulsar detection mission starts at time t0 and lasts for a navigation period T. During this period, the pulsar detectors of each spacecraft continuously detect the arrival time series P of the photons radiated by the pulsar. h ; The spacecraft constellation system uses the inter-satellite link payload to measure and infer the inter-satellite distance L, and the star sensor to measure and calculate the spacecraft attitude C.

[0139] (2) After pre-processing the detected photon data, each spacecraft transmits it to the navigation master satellite through the intersatellite link under unified scheduling; the navigation master satellite also collects the intersatellite ranging information in the corresponding time period.

[0140] (3) The navigation satellite task scheduling module first calls the program in the positioning module, uses the intersatellite link for relative positioning, and then estimates the position of the satellite based on the estimated position of the satellite. Perform absolute position determination of all spacecraft

[0141] Then, the orbital position of each spacecraft is predicted and calculated using the orbit prediction module. Combined with the photon detection sequence, the {photon-position} set is constructed through interpolation method. Using information such as attitude angle, the position of each spacecraft is further projected toward the corresponding pulsar direction, and the {photon-projection distance} set can be obtained.

[0142] Finally, the pulse TOA update module is used to convert the photon sequence into the solar system center of mass coordinate system through large-scale space-time transformation, and the contour folding and pulse TOA calculation are performed to obtain the observed pulse TOA.

[0143] (4) The task scheduling module calls the program of the navigation calculation unit, implements the SIEKF algorithm, and performs navigation calculation. If the number of iterations i is less than the maximum number of iterations N max , then continue to iterate, that is, use the estimated position to recalculate TOA. In the SIEKF algorithm, its adaptive estimator can iterate the model error, thereby improving the iterative estimation accuracy. If the number of iterations i is greater than or equal to the set value N max , the filtering calculation of the current cycle is completed, the position information is output, and the navigation calculation of the next navigation cycle is continued.

[0144] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A distributed spacecraft positioning system based on an iterative estimation method, characterized in that: Including the main star and N slave stars; Wherein, the main star includes: The navigation calculation unit is used to implement navigation calculations and obtain the absolute position estimate of the main satellite based on the latest pulse TOA. The absolute position estimate obtained is The navigation calculation unit includes a pulse TOA update module, which is used to aggregate the photon data set from the photon TOA information update module, and then process the photon data, and then use the contour folding method to achieve pulse folding, and finally use the cross-correlation method to obtain the latest pulse TOA; The inter-satellite distance measurement module A is used to obtain the distance and azimuth information of each slave satellite relative to the master satellite, and send the inter-satellite distance measurement data to the positioning calculation module described below; it is also used to form an inter-satellite link with other spacecraft for interconnection; A positioning calculation module is connected to the navigation calculation unit and the inter-satellite ranging module A respectively; and is used to calculate the absolute position estimate value given by the navigation calculation unit according to the inter-satellite ranging data given by the inter-satellite ranging module A and the and an orbital dynamics model, updating the absolute position estimate of each of the slave satellites; and sending the updated absolute position estimate of each of the slave satellites to the orbital prediction update module described below; An orbit prediction update module is connected to the positioning calculation module; it is used to predict the position and speed of each of the slave satellites within a certain time range based on the current absolute position estimate of each of the slave satellites given by the positioning calculation module and in combination with the orbital dynamics model; and transmit the above-mentioned prediction value to the photon TOA information update module described below; A photon TOA information update module, connected to the orbit prediction update module and the data preprocessing module of the slave star; used to collect the pulsar photon sequence transmitted from each slave star, then obtain the latest position corresponding to the photon TOA of each slave star by interpolating the prediction value provided by the orbit prediction update module, and then project it in the direction of the pulsar to form a set of photon sequence TOA and corresponding projection position, recorded as {time, position}, and then summarize the {time, position} set of each slave star into a photon data set and transmit it to the pulse TOA update module inside the navigation calculation unit; Wherein, the slave stars include: A pulsar detector, used to detect pulsars, obtain pulsar photon sequences, and pass the pulsar photon sequences to the following data preprocessing module; A data preprocessing module, connected to the pulsar detector; used to preprocess the pulsar photon sequence and transmit the processed pulsar photon sequence to the primary star photon TOA information updating module; The intersatellite ranging module B is used for ranging and forming intersatellite links with other spacecraft for interconnection.

2. A distributed spacecraft positioning system based on an iterative estimation method according to claim 1, characterized in that: The master satellite also includes a task scheduling module A, which sends scheduling instructions to each of the slave satellites through an intersatellite link based on a unified time reference to unify the detection and data transmission tasks of the spacecraft system.

3. The distributed spacecraft positioning system based on iterative estimation method according to claim 1, characterized in that: The slave satellite also includes a task scheduling module B, which mainly plans and runs related actions according to the task instructions of the master satellite.

4. A distributed spacecraft positioning system based on an iterative estimation method according to claim 1, characterized in that: The navigation calculation method in the navigation calculation unit specifically comprises the following steps: 1) Set the system initial value: 2) Assign an initial value to the state starting at time k; Among them, the superscript i * The marked value is the latest estimated value; the superscript T represents the transposition of the matrix; k represents the filter cycle number, k = 1, 2, ..., K; P k represents the filtering variance at time k; P k / k-1 represents the prediction variance from time k-1 to time k; Q k represents the state noise variance; 3) Perform filtering iterative calculation, the specific steps include: ①Use Get observation updates: Then using the latest observations and Recalculate and in, Where i represents the number of iterations in a cycle, i = 0, 1, 2, ..., N max ;d k represents the adaptive factor, ②Use Implementing EKF filtering: in, ③ Loop through steps ① and ② in step 3); if the current number of iterations i is greater than or equal to the set maximum number of iterations N max , then the current iteration ends and enters step 2) to continue the navigation calculation of the next cycle; if the current iteration number i is less than the set maximum iteration number N max , then continue to judge the threshold as follows: Among them, V th is the set threshold; When formula (11) holds true, the current value of i is n, and the output is: and End this round of iteration and go to step 2) to continue the navigation calculation of the next cycle; when formula (11) is not true, go back to step 3) to continue the iterative calculation of this cycle.

5. A distributed spacecraft positioning method based on an iterative estimation method, applied to the distributed pulsar navigation system according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Set the absolute position estimate of the primary star orbit The initial value of S2. In the current cycle k, after the task starts, under the unified time reference and task scheduling, each slave satellite is divided into three groups to detect three different pulsars respectively, and each slave satellite obtains the corresponding pulsar photon sequence; at the same time, the master satellite obtains the intersatellite distance of each slave satellite from the master satellite through the intersatellite link, and obtains the attitude of each slave satellite through a camera or other instrument, that is, the master satellite obtains the distance and azimuth information of each slave satellite; S3. The positioning calculation module uses the distance and azimuth information of each slave star obtained in S2 to first calculate the relative position of each slave star in the constellation, and then combines it with the absolute position estimate of the master star orbit Determine the absolute position estimate of each slave star; at the same time, each slave star records the pulsar photon sequence detected and transmits it to the master star; S4. Based on the estimated absolute positions of the satellites, the orbit prediction update module performs orbit prediction for a certain time range and sends these prediction data to the photon TOA information update module; S5. The master satellite uses the prediction data provided by the orbit prediction update module to update the photon data of each slave satellite in the photon TOA information update module; S6. The pulse TOA update module in the navigation calculation unit calculates the pulse TOA based on the latest photon data provided in S5; then uses the navigation calculation method to perform navigation positioning calculation to obtain the latest absolute position estimate of the primary star. Then, S2 to S6 are executed in a loop.

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