Small celestial body center gravity on-orbit identification method based on multi-source measurement information
Through the comprehensive utilization of multi-source measurement information, the high accuracy of the gravitational coefficient in the autonomous identification center of the in-orbit detection task is achieved, and the problems of difficult gravitational identification and poor orbital accuracy on the ground measurement are solved.
Patent Information
- Application Number
- CN202411989765.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2025-05-06
AI Technical Summary
In small celestial object detection missions, the gravitational force of the target celestial object is weak and it is difficult to accurately identify through the prior art, especially when the orbital accuracy is poor on the ground.
Using a method based on multi-source measurement information, the multi-source position relationship data of the detector relative to the small celestial body is obtained, including the relative navigation method based on the image landmark, central line of sight + ranging and point cloud features, the optimization indicators of the variable to be identified are determined, and the exact value of the center gravitational coefficient of the small celestial body is obtained through iterative correction.
It realizes high accuracy of independently identifying the center of a small celestial body in orbit, and does not require support from ground measurement rails at all, improving detection accuracy and safety.
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Figure CN119937040A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of deep space small celestial body detection, and in particular relates to an on-orbit identification method of the central gravity of a small celestial body based on multi-source measurement information. Background Art
[0002] In the mission of small celestial body detection, accurate identification of the gravity of small celestial bodies plays an important role, mainly reflected in:
[0003] (1) As a key parameter in the dynamic extrapolation equation in relative navigation, the gravitational parameters can be used on board to achieve higher-precision relative position and velocity navigation;
[0004] (2) Since the small celestial body is significantly affected by gravity when it flies near it, gravity needs to be a known quantity if the guidance law is to be calculated on board, which is conducive to achieving a more accurate guidance transfer process.
[0005] The gravity of small celestial bodies is generally weak and difficult to accurately identify through Kalman filtering, so it is necessary to accumulate data from a long period of free motion arc. This data can be transmitted to the ground for high-precision identification, and parameters such as the central gravity coefficient and perturbation coefficient can be identified. However, when implementing small celestial body gravity identification activities on orbit, in order to ensure safety, it is generally necessary to realize the function of on-orbit identification of small celestial body gravity on the satellite. At this time, it is generally only necessary to perform preliminary identification of several main variables such as central gravity.
[0006] When identifying the gravity of a small celestial body, the satellite can generally use relevant information including relative navigation based on image landmarks, relative navigation based on central line of sight + ranging, and relative navigation based on point cloud features. Small celestial body detectors are generally equipped with sensors such as wide-field cameras, ranging sensors, and laser point cloud navigation sensors. Before performing relative navigation, it is necessary to first complete the three-dimensional terrain modeling of the small celestial body, and extract the landmark library and point cloud feature library. At a long distance, the wide-field camera can directly measure the central line of sight direction of the target celestial body, and the position information of the detector can be directly given in combination with the ranging information of the ranging sensor. At a close distance, the wide-field camera can use the natural terrain features on the surface of the small celestial body in the sunlit area for landmark navigation. The output information is the direction vector of the landmark in the wide-field camera measurement system and the position of the corresponding landmark in the fixed connection of the small celestial body. In addition, the detector can also use the laser point cloud navigation sensor to perform point cloud navigation that is not dependent on lighting conditions through active point cloud scanning.
[0007] Based on the above problems and actual engineering situations, the present invention proposes a method for autonomously identifying the gravity of small celestial bodies on board based on multi-source measurement information. By making full use of various effective relative navigation measurement information, the on-orbit identification accuracy of the central gravity of small celestial bodies can be improved as much as possible. Summary of the invention
[0008] The problem to be solved by the present invention is: in view of the difficult problems that the target celestial body has weak gravity and is difficult to identify in the small celestial body detection mission, and the poor accuracy of the ground orbit determination makes it difficult to support identification, an on-orbit identification method of the central gravity of small celestial bodies based on multi-source measurement information is proposed, which can realize the autonomous identification of the central gravity coefficient of small celestial bodies on board.
[0009] The technical solution provided by the present invention is as follows:
[0010] In the first aspect, a method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information comprises:
[0011] Acquire multi-source information during the free descent of the probe toward the small celestial body; the multi-source information is the position relationship data of the probe relative to the small celestial body obtained by relative navigation based on image landmarks, relative navigation based on central line of sight combined with ranging, and relative navigation based on point cloud features;
[0012] Determine the position and velocity of the probe relative to the small celestial body and the gravitational coefficient of the small celestial body at the initial moment as the variables to be identified, and determine the optimization index of the variables to be identified based on the variables to be identified and their prior values and the multi-source information obtained;
[0013] The variables to be identified are iteratively corrected to obtain the central gravitational coefficient of the small celestial body corresponding to the minimized optimization index of the variables to be identified.
[0014] In the second aspect, a small celestial body central gravity on-orbit identification device based on multi-source measurement information comprises:
[0015] The first module is used to obtain multi-source information during the free descent of the probe toward the small celestial body; the multi-source information is the position relationship data of the probe relative to the small celestial body obtained by relative navigation based on image landmarks, relative navigation based on central line of sight combined with ranging, and relative navigation based on point cloud features;
[0016] The second module is used to determine the position and velocity of the probe relative to the small celestial body and the gravitational coefficient of the small celestial body at the initial moment as the variables to be identified, and determine the optimization index of the variables to be identified based on the variables to be identified and their prior values and the multi-source information obtained;
[0017] The third module is used to iteratively correct the variables to be identified and obtain the central gravitational coefficient of the small celestial body corresponding to the minimization of the optimization index of the variables to be identified.
[0018] In the third aspect, a small celestial body central gravity on-orbit identification device based on multi-source measurement information comprises:
[0019] one or more processors;
[0020] a storage device for storing one or more programs,
[0021] When the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information.
[0022] In a fourth aspect, a readable storage medium stores a computer program thereon, which, when executed by a processor, implements the aforementioned method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information.
[0023] The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information provided by the present invention has the following beneficial effects:
[0024] The present invention provides an on-orbit identification method of the central gravity of a small celestial body based on multi-source measurement information, including obtaining multi-source information during the free descent of the probe toward the small celestial body; the multi-source information is the position relationship data of the probe relative to the small celestial body obtained by relative navigation based on image landmarks, relative navigation based on central line of sight combined with ranging, and relative navigation based on point cloud features; determining the position and speed of the probe relative to the small celestial body and the central gravity coefficient of the small celestial body as variables to be identified at the initial moment, determining the optimization index of the variables to be identified according to the variables to be identified and their prior values and the obtained multi-source information; iteratively correcting the variables to be identified, and obtaining the central gravity coefficient of the small celestial body corresponding to the minimum optimization index of the variables to be identified. The method realizes the measurement of the central gravity coefficient of small celestial bodies in deep space exploration by making full use of various effective relative navigation measurement information, and does not require ground orbit determination support at all. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is a flow chart of an on-orbit identification method of the central gravity of a small celestial body based on multi-source measurement information;
[0026] Figure 2 Schematic diagram of the probe's ascent and descent toward a small celestial body. DETAILED DESCRIPTION
[0027] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.
[0028] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
[0029] The present invention provides a method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information. Figure 1 As shown, the following steps are included:
[0030] Step (1) is to obtain multi-source information during the free fall of the probe toward the small celestial body. The multi-source information is the position relationship data of the probe relative to the small celestial body obtained by relative navigation based on image landmarks, relative navigation based on central line of sight + ranging, and relative navigation based on point cloud features.
[0031] like Figure 2 As shown, the free descent process of the probe toward the small celestial body is realized by the following methods;
[0032] (a) Initially, the small celestial body probe is in a stable parking process at the base camp point (generally more than 3 km away from the small celestial body);
[0033] (b) After the mission start command is sent from the ground, the probe autonomously moves to the vicinity of the nominal position (generally 250-350m away from the small celestial body) and eliminates the position and velocity residuals;
[0034] (c) After the position and velocity residuals are less than the set threshold, the probe autonomously applies a velocity increment toward the center of the small celestial body to start the descent process. After applying the velocity increment at the starting point to make the probe move toward the small celestial body, the acceleration increment is immediately stopped to put the probe in a free descent process, and the momentum wheel is used for attitude control to avoid jet disturbance;
[0035] The specific size of the velocity increment should be determined based on the estimated range of the small celestial body's gravity, the initial velocity navigation error, the total descent time requirement, etc. Its typical value is generally not more than 3 cm / s;
[0036] (d) After reaching the set minimum altitude, the detector will autonomously apply a set pulse velocity increment (e.g. 0.3 m / s) to leave the surface of the asteroid. The altitude information can generally be directly measured by the ranging sensor. The minimum altitude should generally be set based on the size of the asteroid, the maximum possible range of the central gravity and safety. The typical value can generally be set to 20-40 m.
[0037] (e) After reaching the designated safe altitude (usually 250-350m from the small celestial body), the aircraft will autonomously brake and stop to await further instructions from the ground.
[0038] During the free fall, every ΔT mea Time (such as 1min) records the following data:
[0039] (a) If there are two or more landmark directions currently visible, record:
[0040] Landmark measurement time t LM , the quaternion q of the small celestial body's solid relation relative to the inertial system FI , the quaternion q of the detector system relative to the inertial system BI , landmark sight measurement vector nmea , the position vector R of the landmark under the fixed connection of the small celestial body LM . Where t LM 、n mea , R LM Can be directly output by image processing computer, q FI From the extrapolated model of small celestial bodies, q BI Directly measured by star sensors.
[0041] (b) Otherwise, if the current point cloud matching algorithm is valid, record:
[0042] Measuring time t m , the quaternion q of the small celestial body's solid relation relative to the inertial system FI , the quaternion q of the detector system relative to the inertial system BI , the position of the detector relative to the fixed point of the small celestial body determined by the laser point cloud navigation sensor F,mea . Where t m 、r F,mea Given by the image processing computer through the point cloud matching algorithm, q FI From the extrapolated model of small celestial bodies, q BI Directly measured by star sensors.
[0043] (c) Otherwise, if the central line of sight + ranging navigation mode is valid, record:
[0044] Current star time m , the quaternion q of the small celestial body's solid relation relative to the inertial system FI , the quaternion q of the detector system relative to the inertial system BI , the position r of the detector relative to the inertial system of the small celestial body is directly given by the center line of sight + ranging relative navigation filter I,mea .
[0045] Step (2) determines the position and velocity of the detector at the initial moment and the gravitational coefficient of the small celestial body as the variables to be identified, and determines the optimization index of the variables to be identified based on the variables to be identified and their prior values and the multi-source information obtained in step (1).
[0046] Assume the variable to be identified is:
[0047]
[0048] Where r0 and v0 are the relative position and velocity of the detector corresponding to the first measurement moment, μ A is the central gravitational coefficient of the small celestial body to be estimated.
[0049] The following optimization index form based on the least squares method is adopted:
[0050]
[0051] in:
[0052] Indicates the prior values of the probe position, velocity, and gravitational coefficient of the small celestial body at the first measurement moment;
[0053] P0=diag([R 0_err ,R 0_err ,R 0_err ,V 0_err ,V 0_err ,V 0_err ,μ err ]) is the 7×7 dimensional diagonal variance matrix of the variable to be estimated, where R 0_err V is the a priori error of the relative position, which can generally be set to 5% to 10% of the initial position; 0_err is the prior error of relative speed, which can generally be set to about 0.1 to 0.3 m / s; μ err is the prior error of the gravity coefficient, which should be set according to the initial estimation result on the ground and should generally be larger than the maximum possible range of the gravity coefficient of a small celestial body;
[0054] N m is the number of measurements for landmark matching, n k is the number of landmarks during the kth landmark sight measurement, n mea (k,i) is the sight measurement vector of the i-th landmark during the k-th sight measurement;
[0055] N F is the number of position measurements given by relative navigation using point cloud features, r F,mea (k F ) is the kth F The position solution result of the secondary point cloud navigation;
[0056] N l is the number of position measurements given by direct use of the central line of sight + ranging relative navigation, r I,mea (k L ) is the kth L The position measurement result given by the relative navigation method;
[0057] is the diagonal matrix of the line of sight measurement variance of each landmark navigation, σ n Generally, it can be set to the measurement error size of the landmark direction, which can generally be set within 0.001745rad (0.1°);
[0058] is the diagonal matrix of the position measurement variance of each point cloud relative navigation, σ FGenerally, it can be set to the size of the position measurement error. Generally, it should be set according to the error characteristics of point cloud navigation. The typical value can be set within 1% to 3% of the relative position modulus.
[0059] It is the position measurement variance diagonal matrix of each central line of sight + ranging relative navigation, which can generally be set according to the error characteristics of the central line of sight + ranging relative navigation mode, and the typical value can be set within 1% to 3% of the relative position modulus;
[0060] n pre (k,i) is the time corresponding to the kth measurement (t k )'s direction vector prediction result in the camera measurement system;
[0061] r I,pre (k F ) is the kth value obtained by extrapolating the orbital dynamics equation of the probe relative to the center of the small celestial body according to the initial value x0 F Second measurement time The predicted value of the probe's relative position to the center of the small celestial body in the central inertial system of ;
[0062] r I,pre (k L ) is the kth value obtained by extrapolating the orbital dynamics equation of the probe relative to the center of the small celestial body according to the initial value x0 L Second measurement time The predicted value of the position of the probe relative to the center of the small celestial body in the central inertial system of ;
[0063] C FI (k F ) is the quaternion q of the small celestial body's fixed relation relative to the inertial system obtained by each measurement when relative navigation is performed using point cloud features. FI (k F ), the corresponding direction cosine matrix is obtained;
[0064] r F ,pre(k F )=C FI (k F )r I,pre (k F ), which is the value obtained based on the initial value x0 at the kth F The predicted position value of the small celestial body under the fixed connection corresponding to the time of the secondary point cloud measurement.
[0065] Step (3), iteratively correct the variables to be identified, and obtain the central gravitational coefficient of the small celestial body corresponding to the minimization of the optimization index of the variables to be identified.
[0066] Step (3.1), determine the prior value of the variable to be identified
[0067] Prior values of the variables to be identified as follows:
[0068]
[0069] Where ΔT mea is the interval between the first two measurements, r I (1) and r I (2) The navigation results of the relative position in the inertial system at the first measurement time and the second measurement time respectively.
[0070] The physical meaning of the above assignment is to use the relative position of the detector measured for the first time as the initial value of the relative position, and to divide the relative position difference between the first two measurements by the measurement time interval to obtain a guess value of the initial velocity of the detector.
[0071] According to the above prior values, the initial value of the variable to be identified can be set as the prior value, that is:
[0072]
[0073] Step (3.2), determine the partial derivative of the observed quantity with respect to the initial state
[0074] According to the initial value x0 of the variable to be identified, and the set time step Δt, the following equation is gradually integrated from the initial time t1 to the terminal time t k :
[0075]
[0076] So we can get the corresponding time t k The position r of the inertial system relative to the center of the small celestial body I,pre (k).
[0077] When integrating the above equation (5), the state transfer matrix Φ(t,t1) is integrated at each step:
[0078]
[0079] in:
[0080]
[0081] Φ(t1,t1)=I7 (8)
[0082] r is the relative position in the integration process of formula (5); I3 is the 3D unit matrix; I7 is the 7D unit matrix.
[0083] According to the above integral, the state transfer matrix Φ(t k ,t1), and from this the partial derivatives of various measured quantities with respect to the initial state can be determined.
[0084] ① Partial derivatives of the landmark sight line relative to the initial state
[0085] Assume n pre (k,i) is the vector prediction result of the sight line direction of the i-th landmark in the k-th measurement, and its calculation formula is:
[0086]
[0087] in:
[0088]
[0089] Among them C CB is the direction cosine matrix of the wide-field camera measurement system relative to the detector system; C BI (k) is the direction cosine matrix of the detector system relative to the inertial system, which is stored by the quaternion q at the corresponding measurement time. BI (k) calculated; C FI (k) is the direction cosine matrix of the small celestial body's solid connection relative to the inertial system, which is given by q FI (k) calculated; R cam is the installation position vector of the wide field camera measurement system under the detector system; r I,pre (k), r I,pre (k L ) and r I,pre (k F ) are the predicted values of the position of the probe relative to the center of the small celestial body in the central inertial system at the time of measurement corresponding to the image landmark navigation, point cloud navigation and central line of sight + ranging relative navigation methods; R LM (k,i) is the position vector of the i-th landmark under the fixed connection of the small celestial body during the k-th line of sight measurement.
[0090] n pre The partial derivative of (k,i) with respect to the initial value x0 is calculated as follows:
[0091]
[0092] ② Partial derivatives relative to the initial state during point cloud navigation
[0093] Assume r F,pre (k F ) is the value obtained based on the initial value x0 at the kth F The position prediction value of the small celestial body under the fixed connection corresponding to the time of the second point cloud measurement, then its partial derivative relative to the initial value x0 is calculated as:
[0094]
[0095] Among them C FI (k F ) is the direction cosine matrix of the small celestial body's solid connection relative to the inertial system at the corresponding measurement time, and q FI (k F ) calculated.
[0096] ③ Partial derivative of the central line of sight + ranging navigation relative to the initial state
[0097] Assume r I,mea (k L ) is the value obtained based on the initial value x0 at the kth L The position prediction value of the small celestial body center inertial system corresponding to the secondary central line of sight + ranging navigation measurement time, then its partial derivative relative to the initial value x0 is calculated as:
[0098]
[0099] Step (3.3), iterative solution based on weighted least squares method
[0100] The following formula is used to correct the variables to be identified:
[0101]
[0102] in:
[0103]
[0104]
[0105] According to the correction value of formula (14), the new guess value of x0 is obtained: x0 = x0 + δx0;
[0106] If ||δx0|| is greater than the set threshold, then the integral prediction and partial derivative calculation of step 3.2 are repeated according to the above new guess value, and then equation (14) is continued to be called for iterative correction, otherwise the iterative process is terminated.
[0107] After the iteration process is completed, the estimated result of the central gravitational coefficient of the small celestial body can be obtained as follows:
[0108] μ A,est =x0(7) (17)
[0109] The present invention also provides an on-orbit identification device for the central gravity of a small celestial body based on multi-source measurement information, comprising:
[0110] The first module is used to obtain multi-source information during the free descent of the probe toward the small celestial body; the multi-source information is the position relationship data of the probe relative to the small celestial body obtained by relative navigation based on image landmarks, relative navigation based on central line of sight combined with ranging, and relative navigation based on point cloud features;
[0111] The second module is used to determine the position and velocity of the probe relative to the small celestial body and the gravitational coefficient of the small celestial body at the initial moment as the variables to be identified, and determine the optimization index of the variables to be identified based on the variables to be identified and their prior values and the multi-source information obtained;
[0112] The third module is used to iteratively correct the variables to be identified and obtain the central gravitational coefficient of the small celestial body corresponding to the minimization of the optimization index of the variables to be identified.
[0113] The present invention also provides an on-orbit identification device for the central gravity of a small celestial body based on multi-source measurement information, comprising:
[0114] one or more processors;
[0115] a storage device for storing one or more programs,
[0116] When the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information.
[0117] The present invention also provides a readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the aforementioned method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information.
[0118] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described devices, equipment and readable storage media can refer to the corresponding processes in the aforementioned methods and will not be repeated here.
[0119] The device, equipment and readable storage medium technical solution of the present application can be essentially or partially embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.
[0120] Those skilled in the art will appreciate that in one or more of the above examples, the functions described in the present invention may be implemented in hardware, software, firmware, or any combination thereof. When implemented using software, the functions may be stored in a computer-readable medium or transmitted as one or more instructions or codes on a computer-readable medium. Computer-readable media include computer storage media and communication media, wherein communication media include any media that facilitates the transmission of a computer program from one place to another. The storage medium may be any available medium that a general or special-purpose computer can access.
[0121] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.
[0122] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.
Claims
1. A method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information, characterized in that: include: Acquire multi-source information during the free fall of the probe toward the small celestial body; The multi-source information is the position relationship data of the detector relative to the small celestial body obtained by relative navigation based on image landmarks, relative navigation based on central line of sight combined with ranging, and relative navigation based on point cloud features; Determine the position and velocity of the probe relative to the small celestial body and the gravitational coefficient of the small celestial body at the initial moment as the variables to be identified, and determine the optimization index of the variables to be identified based on the variables to be identified and their prior values and the multi-source information obtained; The variables to be identified are iteratively corrected to obtain the central gravitational coefficient of the small celestial body corresponding to the minimized optimization index of the variables to be identified.
2. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 1, characterized in that: In the step of obtaining multi-source information during the free fall of the probe toward the small celestial body, the probe forms the free fall of the probe toward the small celestial body in the following manner: Initially, the small celestial probe is in a stable parking process at the base camp point; After the mission start command is sent from the ground, the probe autonomously moves to the vicinity of the nominal position and eliminates the position and velocity residuals; the nominal position is 250-350m away from the small celestial body; After the position and velocity residuals are less than the set threshold, the probe will autonomously apply a velocity increment toward the center of the small celestial body to start the descent process. After applying the velocity increment at the starting point to make the probe move toward the small celestial body, the acceleration increment will be immediately stopped, so that the probe is in a free descent process. After reaching the set minimum altitude, the probe autonomously applies a set pulse velocity increment to leave the surface of the small celestial body; After the detector rises to the specified safe height, it brakes and stops autonomously.
3. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 1, characterized in that: In the step of obtaining multi-source information during the free fall of the probe toward the small celestial body, the following data are recorded at set time intervals during the free fall of the probe toward the small celestial body: (a) If there are two or more landmark directions currently visible, record: Landmark measurement time t LM , the quaternion q of the small celestial body's solid relation relative to the inertial system FI , the quaternion q of the detector system relative to the inertial system BI , landmark sight measurement vector n mea , the position vector R of the landmark under the fixed connection of the small celestial body LM ; (b) Otherwise, if the current point cloud matching algorithm is valid, record: Measuring time t m , the quaternion q of the small celestial body's solid relation relative to the inertial system FI , the quaternion q of the detector system relative to the inertial system BI , the position of the detector relative to the fixed point of the small celestial body determined by the laser point cloud navigation sensor F,mea ; (c) Otherwise, if the central line of sight combined with the ranging navigation method is effective, record: Current star time m , the quaternion q of the small celestial body's solid relation relative to the inertial system FI , the quaternion q of the detector system relative to the inertial system BI , the position r of the detector relative to the inertial system of the small celestial body determined by the central line of sight + ranging relative navigation filter I,mea .
4. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 3 is characterized in that: The optimization index of the variable to be identified is: in: Indicates the prior values of the probe position, velocity, and gravitational coefficient of the small celestial body at the first measurement moment; P0=diag([R 0_err ,R 0_err ,R 0_err ,V 0_err ,V 0_err ,V 0_err ,μ err ]) is the 7×7 dimensional diagonal variance matrix of the variable to be estimated, where R 0_err is the a priori error of the relative position; V 0_err is the prior error for relative velocity; μ err is the prior error of gravity coefficient; N m is the number of measurements for landmark matching, n k is the number of landmarks during the kth landmark sight measurement, n mea (k,i) is the sight measurement vector of the i-th landmark during the k-th sight measurement; N F is the number of position measurements given by relative navigation using point cloud features, r F,mea (k F ) is the kth F The position solution result of the secondary point cloud navigation; N l is the number of position measurements given by direct use of the central line of sight + ranging relative navigation, r I,mea (k L ) is the kth L The position measurement result given by the relative navigation method during the first measurement; is the diagonal matrix of the line of sight measurement variance of each landmark navigation, σ n Set to the measurement error size of the landmark direction; is the diagonal matrix of the position measurement variance of each point cloud relative navigation, σ F Set to the position measurement error size; The diagonal matrix of the position measurement variance of each central line of sight combined with the ranging relative navigation; n pre (k,i) is the prediction result of the direction vector of the i-th landmark in the camera measurement system corresponding to the k-th measurement, which is obtained by extrapolation based on the initial value x0, the installation position of the wide-field camera and the orbital dynamics equation of the detector relative to the center of the small celestial body; r I,pre (k F ) is the kth value obtained by extrapolating the orbital dynamics equation of the probe relative to the center of the small celestial body according to the initial value x0 F The predicted value of the position of the probe relative to the center of the small celestial body in the central inertial system during the first measurement; r I,pre (k L ) is the kth value obtained by extrapolating the orbital dynamics equation of the probe relative to the center of the small celestial body according to the initial value x0 L The predicted value of the position of the probe relative to the center of the small celestial body in the central inertial system during the first measurement; C FI (k F ) is the quaternion q of the small celestial body's fixed relation relative to the inertial system obtained by each measurement when relative navigation is performed using point cloud features. FI (k F ), and obtain the corresponding direction cosine matrix.
5. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 4 is characterized in that: The step of iteratively correcting the variables to be identified to obtain the small celestial body central gravity coefficient corresponding to the minimization of the optimization index of the variables to be identified comprises: (1) The following formula is used to correct the variable to be identified and obtain the correction value δx0: in: Among them, r F,pre (k F ) is the value obtained at the kth F The position prediction value of the small celestial body corresponding to the point cloud measurement under the fixed connection; Φ(t k ,t1), are respectively based on the initial value x0 and the orbital dynamics equation of the probe relative to the inertial system of the small celestial body center, from the initial time t1 to the time t k , and The state transition matrix of (2) Based on the correction value of the variable to be identified x0, a new guess value of x0 is obtained, x0=x0+δx0; If ||δx0|| is greater than the set threshold, the iterative correction will continue according to the new guess value of the variable to be identified, otherwise the iterative process ends; (3) After the iteration process is completed, the estimated result of the central gravitational coefficient of the small celestial body can be obtained as follows: m A,est = x0(7).
6. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 5, characterized in that: The pre The partial derivative of (k,i) with respect to the initial state x0 Determined by: in, C CB is the direction cosine matrix of the wide-field camera measurement system relative to the detector system; C BI (k) is the direction cosine matrix of the detector system relative to the inertial system, which is stored by the quaternion q at the corresponding measurement time. BI (k) calculated; C FI (k) is the direction cosine matrix of the small celestial body's solid connection relative to the inertial system, which is given by q FI (k) calculated; R cam is the installation position vector of the wide field camera measurement system under the detector system; r I,pre (k) is the extrapolation to t based on the initial value x0 and the orbital dynamics equation of the probe relative to the center of the small celestial body. k The predicted value of the position of the detector relative to the center of the small celestial body in the central inertial system at the time; R LM (k,i) is the position vector of the i-th landmark under the fixed connection of the small celestial body during the k-th line of sight measurement.
7. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 5, characterized in that: The r F,pre (k F ) relative to the initial value x0 Determined by: Among them C FI (k F ) is the direction cosine matrix of the small celestial body's solid connection relative to the inertial system at the corresponding measurement time, and q FI (k F ) calculated.
8. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 5, characterized in that: The r I,mea (k L ) relative to the initial value x0 Determined by:
9. The method for in-orbit identification of the central gravity of a small celestial body based on multi-source measurement information according to claim 5, characterized in that: The prior value of the variable to be identified as follows: r 0,pre ＝r I (1) v 0,pre =(r I (2)-r I (1)) / ΔT mea m A,pre =0 Where ΔT mea is the interval between the first two measurements, r I (1) and r I (2) The navigation results of the relative position in the inertial system at the first measurement time and the second measurement time respectively.
10. A device for identifying the central gravity of a small celestial body on-orbit based on multi-source measurement information, characterized in that: include: The first module is used to obtain multi-source information during the free fall of the probe toward the small celestial body; The multi-source information is the position relationship data of the detector relative to the small celestial body obtained by relative navigation based on image landmarks, relative navigation based on central line of sight combined with ranging, and relative navigation based on point cloud features; The second module is used to determine the position and velocity of the probe relative to the small celestial body and the gravitational coefficient of the small celestial body at the initial moment as the variables to be identified, and determine the optimization index of the variables to be identified based on the variables to be identified and their prior values and the multi-source information obtained; The third module is used to iteratively correct the variables to be identified and obtain the central gravitational coefficient of the small celestial body corresponding to the minimization of the optimization index of the variables to be identified.