X-ray attitude determination method and system based on differential scanning of double detectors

Abstract

The invention discloses an X-ray attitude determination method and system based on differential scanning of double detectors, and aims to solve the problems of insufficient ground verification means, mismatch of models and signals, imperfect precision evaluation and the like of the existing X-ray attitude measurement method. By constructing an experimental platform integrating an X-ray source, a differential detection module, an electric control turntable and a height-adjustable device, a scanning process under various attitude parameter combinations is simulated, and a dual-channel photon counting time sequence signal is obtained. Parameters such as a pitch angle and a rotation angular velocity are solved by combining a differential response model with nonlinear fitting, and error statistical analysis and method effectiveness evaluation are carried out on an estimation result. According to the invention, positive and negative discrimination of the pitch angle, high-fidelity data acquisition and closed-loop precision evaluation are realized, and the engineering verifiability of the differential scanning attitude determination method and the robustness of the system are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of measurement, and further relates to a kind of X-ray attitude determination method and system based on double probe difference scanning in the field of space precision measurement and spacecraft measurement.The present application can be used to simulate the dynamic process of differential scanning X-ray source of spacecraft in orbit, effectively calibrates and verifies the key performance indicators of attitude information obtained by differential scanning system, especially the accurate determination of pitch angle sign and the calculation accuracy of attitude parameters. BACKGROUND

[0002] X-ray attitude measurement technology is a method for solving spacecraft attitude by using the radiation characteristics of cosmic natural X-ray source, which has the unique advantages of strong anti-interference, independence on sunlight and visible starlight, and thus shows good adaptability and development potential in extreme scenarios such as near space, high-speed vehicle periphery, deep space environment, etc.Under the conditions that GNSS is unavailable and traditional optical star sensor is limited, this kind of technology can still stably obtain attitude information, providing basic support for autonomous navigation and control.At present, X-ray attitude measurement mainly includes two technical paths: one is the sky map recognition method based on X-ray imager, and the other is the photon response curve matching method based on X-ray scanner.The former usually adopts coding imaging, focusing imaging or Fourier modulation to obtain star map image, and uses the pre-established X-ray star table for recognition and matching to obtain the pointing information of the optical axis of the sensor in the celestial coordinate system.This method is suitable for scenarios with large field of view, high resolution and stable recognition, but requires high hardware complexity, photon flux and processing capacity.The X-ray scanner method records the curve of photon counting rate changing with time (i.e.response envelope or scanning signal) from one or more known X-ray sources during scanning by rotating X-ray detector with spacecraft rotation or platform control, and obtains the attitude information of spacecraft based on trajectory fitting or parameter inversion technology.Especially in the environment of near space where the number of strong X-ray sources is limited and the space atmosphere interference is weak but the visible light is extremely unstable, the scanner scheme can realize higher attitude solving capacity at lower hardware cost.

[0003] Xidian University in its application of the patent literature "Spacecraft attitude and position measurement system and method based on X-ray pulsar" (application number: 201310320673.0 authorized announcement number: CN 103389099 B) proposed a kind of technical scheme using single X-ray detector observation single X-ray pulsar, and the vector information obtained by combining the horizon sensor, the spacecraft attitude and position are jointly calculated. The scheme first controls the observation direction of X-ray detector through collimator, captures X-ray signal from a specific pulsar and extracts the incident direction; second, the earth direction vector is obtained by using the horizon sensor, which together constitutes the direction constraint required for attitude calculation; finally, the star-ground vector obtained is input into the solving algorithm, the attitude and position parameters of spacecraft in the celestial coordinate system are calculated. The characteristics of this scheme are that only one pulsar is needed for observation, and the system structure is relatively simple. However, this scheme still has the following shortcomings: it is highly dependent on vector observation, lacks the ability to extract attitude information from time series signals, and there is a risk of non-unique symbol judgment for pitch angle and other attitude parameters. At the same time, this scheme combines angle, TOA and angle, etc. The observation noise modeling is complex, and it puts forward higher requirements for on-board computing resources and algorithm stability.

[0004] Beijing Control Engineering Institute in its application of the patent literature "A near space X-ray angular second level star tracker" (application number: 202210301101.7 application date: 2022.03.24 application publication number: CN 115265524 A) discloses an X-ray star tracking method for near space high-speed aircraft. The implementation steps of this method are: first, receiving natural X-ray source signal through hard X-ray Fourier modulation imaging assembly, and modulating the incident photons by using the built-in double collimator system; second, obtaining X-ray star source image by Fourier inversion, and completing star point extraction and attitude calculation by focal plane semiconductor detection assembly; third, adjusting the pitch and yaw of the imaging device field of view by means of two-dimensional precision tracker to realize wide field of view coverage; finally, obtaining the attitude output of the aircraft in the celestial coordinate system through coordinate conversion. This patent is based on imaging instrument method and has high angular second level measurement accuracy, but this method still has the following shortcomings: its attitude calculation process is highly dependent on imaging quality, and the core observation data must be extracted before it can be used for attitude calculation, which is limited by the sparse distribution of X-ray star sources, the field of view of the detector and the signal-to-noise ratio conditions, and it is difficult to ensure the continuous recognition rate of star points in actual application. At the same time, this scheme does not design system error modeling mechanism, and also lacks experimental platform for high-fidelity verification of solving accuracy and pitch angle symbol judgment ability under ground controllable conditions. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides an X-ray attitude determination method and system based on double-probe differential scanning, aiming to solve the problem that there is a lack of a high-fidelity and controllable experimental platform in the verification process of the existing X-ray attitude measurement method, especially the mismatch between the theoretical model and the actual scanning signal under the differential collimator structure, which makes it difficult to accurately evaluate the algorithm precision and stability.

[0006] The technical idea for achieving the purpose of the present application is that the present application constructs a multi-degree-of-freedom precision experimental system integrating an X-ray source, a double-X-ray-probe differential scanning module, an electrically controlled turntable and a controllable height adjusting device. The system allows independent setting of the pitch angle and the rotation angle speed, supports continuous adjustment in positive and negative directions, and can reconstruct the dynamic attitude change process of the scanning X-ray source when the spacecraft rotates in orbit. At the same time, based on the accurate control of the scanning speed and direction of the electrically controlled platform, the system can carry out repeated experiments and attitude solution error analysis, thereby expanding the platform simulation dimension, accurately controlling the parameters and improving the reliability of the system verification. The present application designs a double-X-ray-probe differential scanning structure and proposes a differential scanning response model based on two-way photon counting time sequence signals. The model comprehensively utilizes the relative intensity change and difference characteristics of two different pitch angle probes in the same phase scanning process of the same X-ray source, so that the pitch angle, rotation angle speed and source apparent flow intensity can be solved from the waveform peak value and width of the differential scanning signal without relying on prior source intensity information, and the positive and negative directions of the pitch angle can be accurately judged through the difference size. At the same time, through joint parameter fitting of the differential response model, the common parameter set corresponding to the two-channel signals is solved, the recognizability, precision and robustness of the attitude solution result are improved, and the defects in pitch angle direction discrimination and attitude information complete acquisition are avoided. The present application introduces a joint parameter fitting framework and a multi-working-condition error analysis mechanism in the method. Through nonlinear optimization fitting of the double-channel photon counting time sequences repeatedly collected under different pitch angle and angular velocity combinations, the best estimated value of each attitude parameter is obtained, and the absolute error, relative error, fitting residual and error distribution characteristics of the corresponding parameters are calculated in combination with the parameter preset value, thereby constructing a statistical model of systematic error and random error, and quantifying the efficiency boundary and accuracy of different algorithms.

[0007] The X-ray attitude determination system of the application comprises a ground experiment system composed of an X-ray source, a mechanical motion platform, a double X-ray detector differential scanning module and a data acquisition module; the double X-ray detector differential scanning module comprises two independent X-ray detectors and respective beam collimation devices; the double X-ray detector differential scanning module synchronously receives photon signals from the X-ray source; the data acquisition module is connected with the double X-ray detector differential scanning module, the photon signals are transmitted from the double X-ray detector differential scanning module to the data acquisition module, and photon counting time sequence signals corresponding to two X-ray detector acquisition channels are generated; the data acquisition module uses a differential attitude determination algorithm and a performance evaluation algorithm to fit and solve the attitude parameters of the photon counting time sequence signals.

[0008] Further, the mechanical motion platform comprises an electrically controlled turntable for carrying and driving the double detector module to rotate and scan, and a controllable height adjusting device installed on the electrically controlled turntable for adjusting the relative spatial pose between the double X-ray detector differential scanning module and the X-ray source to simulate different pitch angles.

[0009] The X-ray attitude determination method of the application comprises the following steps:

[0010] Step 1: evaluating the environmental background and the characteristics of the X-ray source;

[0011] Step 2: installing the double X-ray detector differential scanning module in parallel at the center of the electrically controlled turntable to ensure that the rays emitted by the X-ray source can be scanned by the two detectors in turn during the rotation of the two detectors, and to calibrate the relative pitch angle difference;

[0012] Step 3: measuring the effective horizontal distance D between the exit point of the X-ray source and the center of the rotation axis of the electrically controlled turntable;

[0013] Step 4: disassembling the double X-ray detector differential scanning module and setting it perpendicular to the electrically controlled turntable to record the initial state of the pitch angle;

[0014] Step 5: adjusting the simulated pitch angle θ by driving the controllable height adjusting device H ;

[0015] Step 6: setting the electrically controlled turntable to rotate at a constant angular velocity Ω set according to the experimental requirements, and the two detectors of the double X-ray detector differential scanning module receive the photons output by the X-ray source during the entire rotation scanning period and transmit them to the data acquisition module respectively to generate double-channel photon counting time sequence signals C1(t) and C2(t);

[0016] Step 7, change the height of the controllable height adjustment device to make the dual-probe differential scanning module generate a series of vertical height differences AH, which include zero value, a plurality of positive and negative values with different amplitudes; each height difference corresponds to an equivalent simulated pitch angle in the range of [-a0, a0-△a0] angle, thereby forming a plurality of groups of attitude parameter combinations covering positive and negative directions, wherein a0 represents the half field of view angle of the X-ray detector; for each height or rotation angular velocity setting, at least 10 times of differential rotation scanning and data acquisition operations are repeatedly performed to obtain a photon counting time sequence signal for joint parameter fitting and attitude solution error evaluation; x ] angle range, thereby forming a plurality of groups of attitude parameter combinations covering positive and negative directions, wherein a0 represents the half field of view angle of the X-ray detector; for each height or rotation angular velocity setting, at least 10 times of differential rotation scanning and data acquisition operations are repeatedly performed to obtain a photon counting time sequence signal for joint parameter fitting and attitude solution error evaluation;

[0017] Step 8, pre-process the dual-channel photon counting time sequence signals C1(t) and C2(t) and the photon counting time sequence signal for joint parameter fitting and attitude solution error evaluation;

[0018] Step 9, based on the differential scanning signal mathematical model, a suitable nonlinear optimization algorithm is used to perform joint parameter fitting on the pre-processed two scanning sequence signals to solve the best estimation value of each parameter in the joint parameter set X containing the target attitude information to be determined;

[0019] Step 10, compare the parameter best estimation value obtained by the joint parameter fitting with the simulated pitch angle θ H and the preset rotation angular velocity Ω set , calculate the absolute error and relative error of each attitude parameter, and repeatedly calculate under a plurality of attitude parameter combinations to obtain the statistical characteristic values of the pitch angle estimation error and the angular velocity estimation error.

[0020] Further, the steps of evaluating the environmental background and the X-ray source characteristics are as follows:

[0021] First, without enabling the X-ray source, the environmental background noise signals B of the two X-ray detectors are collected and recorded respectively;

[0022] Second, the X-ray source and its corresponding beam collimation device are enabled, the center of the X-ray source and the detector are aligned, the output stability of the X-ray source is evaluated, and the reference peak flow intensity R is recorded.

[0023] Further, the steps of calibrating the relative pitch angle difference △a0 x are as follows:

[0024] First, the electrically controlled turntable is rotated at a known and stable angular velocity Ω cal , and the dual X-ray detector differential scanning module collects the photon signals emitted by the X-ray source in a complete scanning period, and transmits the data to the connected data acquisition module to generate a photon signal for calibrating the relative pitch angle difference △a0 xtwo groups of photon counting time series;

[0025] Secondly, analyze the two groups of photon counting time series, find the time when the intensity of each signal reaches the peak value through phase fitting method, and measure the relative time difference△t between the two time points;

[0026] Thirdly, calculate the actual relative pitch angle difference△δ cal according to the relative time difference△t and the angular velocity of the electrically controlled turntable Ω x ; the operation is repeated for multiple times until the termination condition is met, the arithmetic mean of the multiple fitting results is taken as the calibration result, and the mean value and the standard deviation are recorded;

[0027] The termination condition refers to one of the following two conditions: condition 1, the difference between the consecutive fitting results is less than the preset convergence threshold; condition 2, the effective sampling number reaches not less than 5 times.

[0028] Further, the step of disassembling the double X-ray detector differential scanning module and setting it perpendicular to the electrically controlled turntable and recording the initial state of the pitch angle is as follows:

[0029] Firstly, disassemble the double X-ray detector differential scanning module which has completed the relative pitch angle difference calibration from the parallel installation state, flip it by 90° along the main field of view axis of the detector, and then install it in the center of the controllable height adjusting device, so that the two detectors of the double X-ray detector differential scanning module are arranged in sequence from left to right; the controllable height adjusting device is arranged on the plane of the electrically controlled turntable, and the geometric centers of the two device planes overlap;

[0030] Secondly, adjust the initial position of the controllable height adjusting device so that the reference axis of the double X-ray detector differential scanning module is aligned with the exit point of the X-ray source, record the reference position reading H0 of the controllable height adjusting device at this time, and define this state as the simulated zero pitch angle

[0031] Further, the step of adjusting the simulated pitch angle θ H by driving the controllable height adjusting device is as follows:

[0032] Firstly, drive the controllable height adjusting device to change the position of the double X-ray detector differential scanning module from the reference height H0 to a new set height H1, and generate a vertical height difference△H; the value range of the new height H1 depends on the corresponding equivalent pitch angle θ H , and the range of θ H is [-α0, α0-△δ x ], where α0 is the half field of view angle of the X-ray detector;

[0033] Secondly, the equivalent pitch angle θ formed between the X-ray detector differential scanning module and the X-ray source is calculated according to the following formula H : Wherein, arctan represents the inverse tangent operation, and D represents the effective horizontal distance between the measured exit point of the X-ray source and the center of the rotation axis of the electrically controlled turntable.

[0034] Further, the preprocessing refers to, but is not limited to, baseline subtraction, noise filtering, signal timestamp alignment, and specific selection of processing methods according to the data characteristics of the two original scanning signals.

[0035] Further, the differential scanning signal to be subjected to joint parameter fitting has the following mathematical model:

[0036] Y j (t i ;X) = A·△t·[B j +s j ·t i +R·T scan,j (t i ,i p ,Ω,△δ z,j )·T pitch,j (θ0,△δ x,j )]

[0037] Wherein, Y j (t i ;X) represents the number of photons received by the jth detector corresponding to the ith sampling point at time t i ; j = 1, 2, X represents the joint parameter set to be solved, including the pitch angle θ0and the rotation angular velocity Ω of the target attitude information; A represents the effective detection area of the jth detector, which can be used as the comprehensive response coefficient of the scanning signal amplitude after normalization;△t represents the data sampling time interval; B j , s j respectively represent the parameters of the background signal of the jth detector; R represents the apparent flow intensity of the X-ray source to be solved; i p is the sampling point number corresponding to the time of the signal peak value; Ω represents the rotation angular velocity to be solved; θ0represents the simulated pitch angle to be solved; T scan,j , T pitch,j respectively represent the normalized collimator response functions of the jth detector in the rotation scanning direction and the pitch direction, and the specific form depends on the geometric shape and actual response characteristics of the used collimator;△δ z,j represents the relative angle difference between the detector j and the main viewing axis in the scanning direction, and△δ x,j represents the relative pitch angle difference between the detector j and the main viewing axis.

[0038] Further, the joint parameter fitting step is as follows:

[0039] First, the two detector theoretical scanning signals Y1(t,X) and Y2(t,X) described in the joint differential scanning signal mathematical model are used to construct a target function about the joint parameter set X, which is defined as the weighted residual square sum between the actual photon counting time series signals C1(t), C2(t) and the theoretical scanning signals;

[0040] Second, the fitting initial value of the joint parameter set X is reasonably selected according to the scanning motion characteristics and the actual scanning signal, and the least square method or other nonlinear optimization algorithm is used to iteratively solve the target function to obtain the optimal joint parameter estimation value that minimizes the residual function

[0041] Third, set the convergence threshold ε and the maximum iteration number N max , if the optimization process converges within the threshold or reaches the maximum iteration step, it is terminated;

[0042] Fourth, record the final optimal estimation parameter set fitting residual distribution, compare the parameter estimation value with the system simulation value, and calculate the absolute error and relative error of each attitude parameter;

[0043] Fifth, repeat the joint parameter fitting at least 10 times under different attitude parameter combinations, and obtain the statistical characteristic values of the pitch angle estimation error and the angular velocity estimation error, and finally combine the optimal estimation parameters obtained in the fourth step as the output of the attitude parameter solution.

[0044] Compared with the prior art, the present application has the following advantages:

[0045] First, the present application integrates an X-ray source module, a double-detector differential scanning module, an electric control turntable and a controllable height adjusting device into a multi-degree-of-freedom precision ground experiment X-ray attitude determination system, which has the functions of controllable setting of attitude parameters, high repeatability, independent adjustment of rotation angle and pitch angle, etc., and can more accurately simulate the dynamic process of the on-orbit differential scanning X-ray source of the spacecraft. The system overcomes the shortcomings of the prior art, such as simplified structure, lack of precise control ability and inability to simulate the whole process of attitude change, and significantly improves the verification ability of the differential scanning algorithm in real working conditions in terms of repeatability, high precision and high consistency.

[0046] Secondly, the application proposes a method for attitude determination based on double-probe differential scanning, which synchronously acquires two light counting time sequences and constructs a differential response model to jointly solve parameters such as pitch angle, rotation angular velocity and source intensity, effectively introduces phase difference and response difference information to distinguish the positive and negative directions of the pitch angle. This method overcomes the problems of non-uniqueness in the sign judgment of the pitch angle and high dependence on the source intensity prior in the traditional single-probe scanning, realizes reliable solution of the sign of the pitch angle under the driving of real differential signals, and improves the practicality and robustness of attitude measurement.

[0047] Thirdly, the application introduces a joint parameter fitting and multi-condition repeated experiment method, statistically analyzes the attitude solution error, fitting residual and error propagation characteristics under different combinations of pitch angle and angular velocity, and realizes comprehensive identification and quantitative evaluation of the sources of systematic error and random error. This method overcomes the limitations of the existing technology that the differential scanning verification process lacks error modeling capability and cannot perform precision and stability statistics, and significantly improves the ability of the application in attitude solution accuracy verification, algorithm reliability testing and system performance quantification. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 FIG. 1 is a structural schematic diagram of the system of the application;

[0049] Figure 2 FIG. 2 is a flowchart of the method steps of the application;

[0050] Figure 3 FIG. 3 is a schematic diagram of the relative pitch angle difference calibration method of the application. DETAILED DESCRIPTION

[0051] Embodiments of the application provide a method and system for attitude determination based on differential rotation scanning of double X-ray detectors. The method is suitable for simulating differential scanning of an X-ray source by an X-ray star sensor in a simulated on-orbit space environment, relies on a high-integration ground experimental system, and constructs a controllable and repeatable attitude parameter adjustment and data acquisition process. The X-ray attitude determination system of the application includes a ground experimental system composed of an X-ray source, a mechanical motion platform, a double X-ray detector differential scanning module and a data acquisition module; under the system framework, the double X-ray detector realizes accurate setting of simulated pitch angle and rotation angular velocity through an electrically controlled turntable and an adjustable height platform, acquires and transmits differential photon counting time sequence signals; then through a pre-processing and joint nonlinear fitting process, key parameters containing attitude information are extracted, and error statistical analysis and method effectiveness evaluation are performed in combination with multi-condition experiments.

[0052] The specific structure of the attitude verification system based on differential rotation scanning of double X-ray detectors according to the application will be further described below. Figure 1 The specific structure of the attitude verification system based on differential rotation scanning of double X-ray detectors according to the application will be further described below.

[0053] The system is mainly composed of the following core modules: an X-ray source 1, which is internally provided with an X-ray generator and is equipped with a front-end collimating component to generate a stable and approximately parallel X-ray beam, simulating a distant celestial X-ray source; a double X-ray detector differential scanning module 2, which integrates two independent X-ray detection units, which can be selected as a silicon drift detector (SSD), and is divided into a detector 201 and a detector 202, each of which is equipped with a rectangular collimator of the same specification to define its own field of view, and the two detectors have a preset small relative pitch angle difference Δδ x is rigidly fixed and installed; a controllable multi-degree-of-freedom precision mechanical motion platform 5, including an electrically controlled turntable 3 with a settable angular velocity Ω for carrying and driving the double X-ray detector differential scanning module 2 to perform circumferential rotation scanning, and a controllable height adjustment device 4 for accurately adjusting the overall vertical height of the double X-ray detector differential scanning module 2 to change the relative pitch angle θ H between it and the X-ray source 1, which is a precision lifting platform driven by a stepping motor and can realize precise control of the height difference ΔH; and a data acquisition module 6, i.e., a computer and supporting software and hardware connected between the double X-ray detector differential scanning module 2 and the mechanical motion platform 5, which is responsible for synchronously acquiring the output signals of the two detectors, controlling the entire experimental process, and performing subsequent signal processing and attitude parameter solving algorithms.

[0054] The implementation steps of the X-ray attitude determination method of the present application will be further described below. Figure 2 .

[0055] Step 1, environmental background and source characteristic evaluation.

[0056] The environmental background and source characteristic evaluation refers to acquiring background noise without enabling the X-ray source 1, and evaluating the output intensity and stability of the source after it is enabled to establish a reference benchmark for the experimental environment. The specific steps are described as follows:

[0057] Step 1.1, under the condition that the X-ray source 1 is turned off, the two detectors in the double X-ray detector differential scanning module 2 are caused to respectively acquire and record the environmental background noise signals within a sufficient time period, which are denoted as B1(t) and B2(t) respectively.

[0058] Step 1.2, the X-ray source 1 and its beam collimating device are enabled, and after the working state reaches stability, any one of the detectors in the double X-ray detector differential scanning module 2 is used to calibrate the emission direction of the X-ray source 1, and the X-ray signals are continuously acquired within a short time; the relative fluctuation of the short-time average count rate is calculated to evaluate the short-term output stability and record the reference peak flow intensity R.

[0059] Step 2, relative pitch angle difference precision calibration.

[0060] The precise calibration of the relative pitch angle difference refers to fixing the differential scanning module 2 of the dual X-ray detector in parallel on the electrically controlled turntable 3, and completing the precise calibration of the pitch angle of the main line of sight by scanning the photon signal and calculating the relative phase difference.

[0061] Combination Figure 3 The steps of the relative pitch angle difference calibration method of the present invention are described in detail below.

[0062] Step 2.1: Install the dual X-ray detector differential scanning module 2, which has two X-ray detectors rigidly fixed, parallel to each other at the center of the electrically controlled turntable 3; adjust the initial orientation of the module to ensure that the approximately parallel X-ray beam emitted by the X-ray source 1 can be effectively scanned by the respective fields of view of the two detectors during its rotation and scanning process with the turntable; based on the actual detector field of view and the required angular resolution, set the electrically controlled turntable 3 to a known and stable angular velocity Ω. cal The turntable rotates circumferentially; simultaneously, data acquisition module 6 synchronously and at equal intervals samples and records the photon counting time-series signals output by the two detectors within a complete scan cycle, denoted as C. 1,cal (t) and C 2,cal (t).

[0063] Step 2.2, process the two sets of time series signals C collected in Step 2.1. 1,cal (t) and C 2,cal (t) is analyzed and processed to accurately determine the time when the respective signal envelopes reach their peak values, denoted as t. p1 and t p2 And calculate the absolute value of the time difference between these two characteristic moments:

[0064] △t cal =|t p1 -t p2 |

[0065] Step 2.3, based on the angular velocity Ω of the electrically controlled turntable used in the calibration process. cal and the measured time difference Δt cal Calculate the actual relative elevation angle difference Δδ between the main lines of view of the two detectors. x :

[0066] △δ x =Ω cal ·△t cal ;

[0067] The operation is repeated multiple times to obtain multiple independent Δδ. x,m The measurement is repeated until the termination condition is met; the statistical average of these M sets of measurements is then used to obtain the final accepted relative pitch angle difference calibration result.

[0068]

[0069] Calculate the standard error of the mean or the standard deviation of multiple measurements As delta delta x Evaluation of the uncertainty of calibration.

[0070] The termination condition refers to a situation that meets one of the following two conditions: condition 1, the difference between the consecutive fitting results is less than the preset convergence threshold; condition 2, the effective sampling number reaches no less than 5 times.

[0071] Step 3, measure the distance between the X-ray source and the platform.

[0072] The measurement of the distance between the X-ray source and the platform refers to the accurate measurement of the horizontal distance D between the effective exit point of the X-ray source 1 and the center line of the rotating shaft of the electric control turntable 3 by using a precise distance measurement tool, such as a high-precision laser range finder, a three-coordinate measuring machine or a precise optical theodolite, etc. The measurement of the distance D can be repeated at different positions, and the measurement results are averaged, and the measurement uncertainty is recorded.

[0073] Step 4, vertically install and record the initial attitude.

[0074] The vertical installation and recording of the initial attitude refers to the vertical installation of the double X-ray detector differential scanning module 2 by rotating 90 degrees, and adjusting to align with the exit point of the X-ray source 1, and recording its height as the zero reference of the simulated pitch angle. Combined with the attached Figure 1 , the vertical installation and recording of the initial attitude step is described as follows:

[0075] Step 4.1, the relative pitch angle difference delta delta x The double X-ray detector differential scanning module 2 is removed from the parallel installation state, flipped 90° along the detector main field axis and vertically installed in the center of the controllable height adjustment device 4, so that the two detectors of the double X-ray detector differential scanning module (2) are arranged in sequence from left to right; the controllable height adjustment device (4) is arranged on the plane of the electric control turntable (3), and the geometric centers of the two devices overlap.

[0076] Step 4.2, by fine-tuning the vertical position of the controllable height adjustment device 4, supplemented by turntable motion calibration, so that the reference axis of the double X-ray detector differential scanning module 2, i.e. the main visual axis of the detector 201, is accurately aligned with the effective exit point of the X-ray source 1; the reference position reading H0 of the controllable height adjustment device 4 at this time is recorded in detail, and this state is defined as the simulated zero reference pitch angle of the experiment

[0077] Step 5, adjust the platform height to simulate the pitch angle.

[0078] The simulated pitch angle achieved by adjusting the platform height refers to adjusting the height of the differential scanning module 2 of the dual X-ray detector using the adjustable height device 4 to create different vertical height differences, thereby achieving the desired simulated pitch angle setting. The specific steps are described below:

[0079] Step 5.1: Based on the experimental verification requirements, set a specific non-zero simulated pitch angle θ. H The target value is calculated based on the horizontal distance D between the effective emission point of X-ray source 1 and the center line of the rotation axis of the electrically controlled turntable 3, which has been accurately measured in step 3. The elevation angle θ required to achieve this target is then calculated. H The required height change ΔH of the controllable height adjustment device 4 is calculated as follows:

[0080] △H=D·tan(θ H )

[0081] Step 5.2: By using the precision-driven controllable height adjustment device 4, the stepper motor's step number is controlled, allowing the entire device to move precisely from the reference height H0 by a distance △H to reach the new set height.

[0082] H1 = H0 + ΔH,

[0083] ΔH can be positive or negative, corresponding to different pitch directions.

[0084] Step 6: Differential scanning signal acquisition.

[0085] The differential scanning signal acquisition refers to setting the electrically controlled turntable 3 to rotate at a fixed angular velocity, and having the detector synchronously acquire X-ray signals within the rotation period to form a dual-channel photon time series. The specific steps are described below:

[0086] Step 6.1, after setting the simulated pitch angle θ as in step 5. H Under the given conditions, the electrically controlled turntable 3 is set to rotate stably at a suitable target angular velocity Ω, and the value of Ω should be within 5° / s.

[0087] Step 6.2: While the electrically controlled turntable 3 rotates, the data acquisition module 6 operates at a preset sampling rate F. s The photon counting time series signals output by the two X-ray detectors throughout the entire rotational scanning cycle are synchronously and continuously acquired and stored, denoted as C1(t) and C2(t), respectively. The sampling rate should ensure that there are enough data points to describe the signal envelope when the detectors sweep across the X-ray source, and the scanning range should at least cover the effective angular range of the X-ray source signal and the background on both sides.

[0088] Step 7: Scan with multiple sets of parameters.

[0089] The multi-group parameter combination scanning refers to repeating the acquisition experiment for more than 10 times under the combination of multiple pitch angles and angular velocities, for constructing a data set for joint parameter fitting. The specific steps are described as follows:

[0090] Step 7.1, simulate the sequence variation design of the pitch angle θ H , under the premise of keeping other experimental conditions, such as the setting of the rotation angle speed Ω set of the electric control turntable 3, the output intensity R of the X-ray source 1 is relatively stable, the controllable height adjusting device 4 is controlled by the data acquisition module 6 program or precisely manually operated, so that the overall height difference △H of the double X-ray detector differential scanning module 2 is systematically changed in the preset effective scanning angle range, thereby generating a series of different equivalent pitch angles θ H in the effective range:

[0091]

[0092] The test sequence should cover at least the following ranges: near zero pitch angle; a plurality of different sizes of positive pitch angles; and a plurality of different sizes of negative pitch angles symmetric to the positive pitch angles.

[0093] Step 7.2, simulate the sequence variation design of the rotation angle speed Ω set , under the premise of keeping the simulated pitch angle θ H and other experimental conditions relatively stable, the control software of the data acquisition module 6 is used to set the electric control turntable 3 to work at a series of different target angular velocity values; the test sequence should cover the expected scanning angular velocity range of the spacecraft or the X-ray star sensor, and several test points are selected in the middle.

[0094] Step 7.3, repeated measurement and data acquisition, for each specific parameter combination of the simulated pitch angle θ H and the rotation angle speed Ω set planned in steps 7.1 and 7.2, that is, a specific simulated working condition, the differential rotation scanning and data acquisition operation is strictly repeated M times according to the whole process of differential rotation scanning and synchronous data acquisition described in steps 5 and 6, in order to obtain a group of photon counting time sequence signals for joint parameter fitting and attitude solution error evaluation, M is usually 10 times or more.

[0095] Step 8, scanning signal preprocessing.

[0096] The scanning signal preprocessing refers to operations including but not limited to baseline deduction, noise filtering, signal timestamp alignment, etc. on the original scanning data, the processing method needs to be specifically selected according to the data characteristics of the two original scanning signals, to ensure that the two signals C1(t) and C2(t) are accurately phase-aligned, and to improve the subsequent fitting accuracy and calculation stability.

[0097] Step 9, joint parameter fitting.

[0098] The joint parameter fitting refers to constructing a differential scanning model objective function, and solving the optimal estimation value of the attitude parameter and the sign judgment by a nonlinear optimization algorithm. The specific steps are described as follows:

[0099] Step 9.1, according to the actual parameters of the double X-ray detector differential scanning module 2 and the motion setting of the electric control turntable 3, a differential scanning signal mathematical model for parameter fitting is established, which is described as follows:

[0100] Let the jth detector (j = 1, 2) at time t i , the theoretical model Y j (t i ; X) of the received photon count at the ith sampling point is obtained, wherein X is a parameter vector containing all parameters to be solved. The model can be generally expressed as:

[0101] Y j (t i ; X) = A·△t·[B j +s j ·t i +R·T scan,j (t i ,i p ,Ω,△δ z,j )·T pitch,j (θ0,△δ x,j )],

[0102] Wherein, A represents the effective detection area of the jth detector, which can be normalized as the comprehensive response coefficient of the scanning signal amplitude;△t is the data sampling time interval; B j and s j are parameters for describing the background signal of the detector j; R is the apparent flow intensity of the X-ray source to be solved; i p is the sampling point number corresponding to the peak value of the signal; Ω is the rotation angular velocity to be solved; θ0 is the simulated pitch angle to be solved; T scan,j and T pitch,j are the normalized collimator response functions of the detector j in the scanning direction and the pitch direction respectively, and the specific form depends on the geometric shape and actual response characteristics of the collimator used;△δ z,j represents the relative angle difference between the detector j and the main viewing axis in the scanning direction, and△δ x,j represents the relative pitch angle difference between the detector j and the main viewing axis;

[0103] For the response function T pitch,j (θ0,△θ x,j ) in the pitch direction, the equivalent pointing angle δ x,1and δ x,2 The relative pitch angle difference Δδ, which has been precisely calibrated in step 2, must be reflected. x ;

[0104] The parameter set X to be solved can be specified as:

[0105] X = [B1,s1,B2,s2,i] p ,Ω,θ0,R,...] T ,

[0106] Depending on the complexity of the model and actual needs, other parameters such as detector response coefficient and collimator field of view may also be included.

[0107] Step 9.2: Using a suitable nonlinear optimization algorithm, process the two preprocessed scanning signal data C1(t) from step 8. i ) and C2(t i Perform joint parameter fitting, where i ranges from 0 to N-1, and N is the total number of sampling points; the optimization objective is to minimize the theoretical model prediction value Y. j (t i ;X) and actual observation data C j (t i The weighted sum of squared residuals χ between ) 2 (X), implemented as follows:

[0108]

[0109] Among them, w j,i The weighting factor for the observation data of the j-th detector at the i-th sampling point is usually taken as the variance of the observation data. The reciprocal of the number of photons; if we assume that the photon count follows a Poisson distribution and that the variance can be approximated by the observed count value C when the count value is large. j (t i To ensure that the optimization algorithm can quickly converge to the global optimum or an acceptable local optimum, and to ensure the physical meaning of the solution, reasonable initial estimates and search boundary conditions need to be set for each parameter in the parameter set X to be solved.

[0110] Step 9.3: Obtain the optimal parameter set after the joint parameter fitting converges. In the process, estimated values ​​of core attitude parameters are extracted: simulated pitch angle. Rotational angular velocity Simultaneously, estimates of other relevant parameters can also be obtained; based on the estimated pitch angle... the actual pointing direction of the simulated pitch angle; the M sets of photon counting time series signals obtained by the repeated measurements described in step 7.3 are subjected to the same joint parameter fitting, thereby obtaining multiple independent experimental data sets and their corresponding attitude parameter solving results for each simulated working condition, denoted as where m = 1,..., M is the mth repeated measurement under this working condition.

[0111] Step 10, attitude parameter error statistics and evaluation.

[0112] The attitude parameter error statistics and evaluation refer to comparing the parameter best estimate obtained by the joint parameter fitting in step 9 with the simulated pitch angle θ H and the preset rotation angular velocity Ω set , calculating the absolute error and relative error of each attitude parameter, and repeating the calculation under the multiple attitude parameter combinations described in step 7 to obtain the statistical characteristic values of the pitch angle estimation error and the angular velocity estimation error. The specific steps are described as follows:

[0113] Step 10.1, compare the pitch angle estimation value θ obtained by each measurement with the equivalent pitch angle θ H set by the experiment, calculate the absolute error:

[0114]

[0115] Compare the rotation angular velocity estimation value Ω obtained by the calculation with the angular velocity Ω set set by the electrically controlled turntable, calculate the absolute error

[0116]

[0117] These error values can be used as a preliminary quantitative evaluation of the accuracy of a single specific working condition experiment.

[0118] Step 10.2, statistical evaluation of attitude parameter solving accuracy, for each simulated working condition, compare the attitude parameter estimation value sequence obtained by the M repeated experiments with the corresponding experimental set theoretical value, i.e. the equivalent pitch angle θ H and the angular velocity Ω set set by the electrically controlled turntable under this working condition; calculate the average system deviation of the pitch angle estimation and the average system deviation of the rotation angular velocity estimation under this working condition, and their calculation methods are shown as follows:

[0119]

[0120] The above average system bias is plotted against the simulated pitch angle θ H the size (including positive and negative), the rotation angular velocity Ω set The trend curves of the factors such as fast and slow are drawn to show the accuracy characteristics of the attitude determination method under different conditions.

[0121] Step 10.3, quantitative analysis of measurement uncertainty, for each simulated operating condition, the parameter estimation value sequence obtained by M times of repeated experiments and respectively calculate the sample standard deviation as the quantitative representation of the pitch angle measurement uncertainty and the rotation angular velocity measurement uncertainty under the condition, and the calculation methods are as follows:

[0122]

[0123] Wherein,

[0124]

[0125] By analyzing the variation of these measurement uncertainty indicators with the simulated operating conditions (θ H , Ω set ), the measurement stability and accuracy of the experimental system at different operating points are evaluated.

[0126] The part of the present application not described in detail belongs to the common knowledge of those skilled in the art.

[0127] The above only describes the preferred embodiments of the present application and does not limit the present application. Obviously, for those skilled in the art, after understanding the content and principles of the present application, various modifications and changes in form and details can be made without departing from the principles and structures of the present application. However, these modifications and changes based on the idea of the present application are still within the protection scope of the claims of the present application.

Claims

1. An attitude verification system based on differential rotation scanning with dual X-ray detectors, comprising a ground-based experimental system consisting of an X-ray source (1), a mechanical motion platform (5), a differential scanning module with dual X-ray detectors (2), and a data acquisition module (6); characterized in that, The dual X-ray detector differential scanning module (2) includes two independent X-ray detectors and their respective beam collimation devices; the dual X-ray detector differential scanning module (2) synchronously receives photon signals from the X-ray source (1); the data acquisition module (6) is connected to the dual X-ray detector differential scanning module (2), and the photon signals are transmitted from the dual X-ray detector differential scanning module (2) to the data acquisition module (6), generating photon counting time series signals corresponding to the two X-ray detector acquisition channels; the data acquisition module (6) uses differential attitude determination algorithm and performance evaluation algorithm to fit and solve the attitude parameters of the photon counting time series signals.

2. According to the attitude verification system of claim 1, the mechanical motion platform (5) includes an electrically controlled turntable (3) for carrying and driving the dual detector module to perform rotational scanning, and a controllable height adjustment device (4) installed on the electrically controlled turntable (3) for adjusting the relative spatial pose between the dual X-ray detector differential scanning module (2) and the X-ray source (1) to simulate different pitch angles.

3. An attitude verification method based on differential rotation scanning of dual X-ray detectors according to claim 2, characterized in that, The steps include the following: Step 1: Assess the environmental background B and the characteristics of the X-ray source; Step 2: Install the dual X-ray detector differential scanning module (2) in parallel at the center of the electrically controlled turntable (3) to ensure that the X-rays emitted by the X-ray source can be scanned by the two detectors sequentially during their rotation, and calibrate the relative elevation angle difference Δδ. x ; Step 3: Measure the effective horizontal distance D between the exit point of the X-ray source (1) and the center of the rotation axis of the electrically controlled turntable (3); Step 4: Disassemble the dual X-ray detector differential scanning module (2) and set it perpendicular to the electronically controlled turntable (3), and record the initial state of the pitch angle; Step 5: Adjust the simulated pitch angle θ by driving the controllable height adjustment device (4). H ; Step 6: Set the electronically controlled turntable (3) to rotate at an angular velocity Ω according to the experimental requirements. set Rotating at a constant speed, the two detectors of the dual X-ray detector differential scanning module (2) receive photons output from the X-ray source (1) during the entire rotation scanning cycle and transmit them to the data acquisition module (6) respectively to generate dual-channel photon counting time sequence signals C1(t) and C2(t); Step 7: Change the height of the controllable height adjustment device to generate a series of vertical height differences ΔH in the dual-detector differential scanning module (2). These height differences include zero, multiple positive and negative values ​​of different amplitudes; each height difference corresponds to a value in [-α0, α0-Δδ]. x Equivalent simulated pitch angle θ within the angle range H This forms multiple sets of attitude parameters covering both positive and negative directions, where α0 represents the half field of view of the X-ray detector; for each height or rotation angular velocity setting, at least 10 differential rotation scans and data acquisition operations are repeated to obtain photon counting time series signals for joint parameter fitting and attitude calculation error assessment. Step 8: Preprocess the dual-channel photon counting time series signals C1(t) and C2(t) and the photon counting time series signal used for joint parameter fitting and attitude calculation error assessment; Step 9: Based on the mathematical model of the differential scanning signal, a suitable nonlinear optimization algorithm is used to perform joint parameter fitting on the preprocessed two scanning sequence signals C1(t) and C2(t) to solve for the best estimated value of each parameter in the joint parameter set X containing the attitude information of the target to be determined. Step 10: Combine the best estimated values ​​of the parameters obtained from the joint parameter fitting in Step 9 with the simulated pitch angle θ. H and the preset angular velocity of rotation Ω set By comparing the absolute and relative errors of each attitude parameter, and repeating the calculation under multiple attitude parameter combinations, the statistical characteristic values ​​of pitch angle estimation error and angular velocity estimation error are obtained.

4. The attitude verification method according to claim 3, characterized in that, The steps for evaluating the environmental background B and the characteristics of the X-ray source described in step 1 are as follows: The first step is to collect and record the ambient background noise signal B of each of the two X-ray detectors without using the X-ray source (1). The second step is to activate the X-ray source (1) and its corresponding beam collimation device, align the X-ray source with the center of the detector, evaluate the output stability of the X-ray source and record its reference peak flow intensity R.

5. The attitude verification method according to claim 4, characterized in that, The calibration of the relative pitch angle difference Δδ in step 2 x The steps are as follows: The first step is to move the electrically controlled turntable (3) at a known and stable angular velocity Ω. cal The rotating, dual X-ray detector differential scanning module (2) acquires photon signals emitted by the X-ray source (1) during the complete scanning cycle and transmits the data to the connected data acquisition module (6) to generate a calibration of the relative pitch angle difference Δδ. x Two sets of photon counting time series; The second step is to analyze the two sets of photon counting time series signals, find the time when the signal intensity of each signal reaches its peak through the phase fitting method, and measure the relative time difference Δt between the two times. The third step is to determine the relative time difference Δt and the angular velocity Ω of the electrically controlled turntable (3). cal Calculate the actual relative pitch angle difference Δδ x The operation is repeated multiple times until the termination condition is met. The arithmetic mean of the multiple fitting results is taken as the calibration result, and its mean and standard deviation are recorded. The termination condition refers to the situation where one of the following two conditions is met: Condition 1, the difference between consecutive fitting results is less than the preset convergence threshold; Condition 2, the effective sampling number is not less than 5 times.

6. The attitude verification method according to claim 5, characterized in that, The steps described in step 4, namely disassembling the dual X-ray detector differential scanning module (2) and setting it perpendicular to the electronically controlled turntable (3), and recording the initial state of the pitch angle, are as follows: The first step is to complete the relative pitch angle difference Δδ x The calibrated dual X-ray detector differential scanning module (2) is removed from its parallel installation state, rotated 90° along the main field-of-view axis of the detector, and installed at the center of the controllable height adjustment device (4), so that the two detectors of the dual X-ray detector differential scanning module (2) are arranged sequentially from left to right; the controllable height adjustment device (4) is set on the plane of the electrically controlled turntable (3), and the geometric centers of the two devices overlap. The second step is to adjust the initial position of the controllable height adjustment device (4) so ​​that the reference reference axis of the dual X-ray detector differential scanning module (2) is aligned with the emission point of the X-ray source (1), and record the reference position reading H0 of the controllable height adjustment device (4) at this time. This state is defined as the simulated zero pitch angle.

7. The attitude verification method according to claim 6, characterized in that, In step 5, the simulated pitch angle θ is adjusted by driving the controllable height adjustment device (4). H The steps are as follows: The first step is to drive the controllable height adjustment device (4) to change the position of the differential scanning module (2) of the dual X-ray detector from the reference height H0 to the new set height H1, generating a vertical height difference ΔH; the value range of the new height H1 depends on the corresponding equivalent pitch angle θ. H θ H The range is [-α0, α0-Δδ] x ], where α0 is the half field of view of the X-ray detector; The second step is to calculate the equivalent pitch angle θ formed between the X-ray detector differential scanning module (2) and the X-ray source (1) according to the following formula. H : Where arctan represents arctangent operation, and D represents the effective horizontal distance between the measured exit point of the X-ray source (1) and the center of the rotation axis of the electrically controlled turntable (3).

8. The attitude verification method according to claim 7, characterized in that, The preprocessing mentioned in step 8 includes, but is not limited to, baseline subtraction, noise filtering, and signal timestamp alignment, with the specific processing method selected based on the data characteristics of the two original scan signals.

9. The attitude verification method according to claim 8, characterized in that, The mathematical model of the differential scan signal to be fitted with joint parameters in step 9 is as follows: Y j (t i ;X)=A·△t·[B j +s j ·t i +R·T scan,j (t i ,i p ,Ω,△δ z,j )·T pitch,j (θ0,△δ x,j )] Among them, Y j (t i ;X) represents the time t corresponding to the i-th sampling point of the j-th detector. i The number of photons received; j = 1, 2, X represents the set of joint parameters to be solved, including target attitude information such as pitch angle θ0 and rotation angular velocity Ω; A represents the effective detection area of ​​the j-th detector, which, after normalization, can be used as the comprehensive response coefficient of the scan signal amplitude; Δt represents the data sampling time interval; B j s j Represent the parameters of the background signal of the j-th detector; R represents the apparent flux intensity of the X-ray source to be calculated; i p Ω represents the sampling point number corresponding to the moment the signal peak occurs; θ0 represents the rotation angular velocity to be calculated; T represents the simulated pitch angle to be calculated; scan,j T pitch,j Δδ represents the normalized collimator response function of the j-th detector in the rotation scanning direction and the elevation direction, respectively. Its specific form depends on the geometry and actual response characteristics of the collimator used; z,j Δδ represents the relative angular difference between detector j and the main line of sight in the scanning direction. x,j This represents the relative pitch angle difference between detector j and the main line of sight.

10. The attitude verification method according to claim 9, characterized in that, The steps for fitting the joint parameters described in step 9 are as follows: The first step is to construct an objective function for the joint parameter set X using the theoretical scanning signals Y1(t,X) and Y2(t,X) of the two detectors in the mathematical model of the combined differential scanning signal. This objective function is defined as the weighted sum of squared residuals between the actual photon counting time series signals C1(t) and C2(t) and the theoretical scanning signal. The second step involves selecting appropriate initial values ​​for fitting the joint parameter set X based on the characteristics of the scanning motion and the actual scanning signal. Then, using the least squares method or other nonlinear optimization algorithms, the objective function is iteratively solved to obtain the optimal joint parameter estimates that minimize the convergence of the residual function. The third step is to set the convergence threshold ε and the maximum number of iterations N. max The optimization process terminates if it converges within the threshold or reaches the maximum number of iterations. The fourth step is to record the final optimal set of estimated parameters. Fit the residual distribution, compare the parameter estimates with the system simulation values, and calculate the absolute and relative errors of each attitude parameter; Fifth, perform joint parameter fitting at least 10 times under different attitude parameter combinations, and obtain the statistical characteristic values ​​of pitch angle estimation error and angular velocity estimation error. Finally, combine the optimal estimation parameters obtained in the fourth step. As the output of the attitude parameter calculation results.

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