Non-cooperative spacecraft relative pose identification method for space cell robot

Abstract

The application relates to a relative attitude identification method of a non-cooperative spacecraft fixed space cell robot, and relates to the field of spacecraft parameter identification. Firstly, a proper cell connection topological structure is selected according to the number of the space cell robot and the geometric configuration of the target spacecraft, and a cell robot body coordinate system located at a topological center position is selected as a base coordinate system according to an information link topological structure. Then, the rotation matrix of the body coordinate system is identified by using a recursive least square method according to the data collected by the angular velocity sensors of each cell robot and the base cell, so that an attitude identification model of the space cell robot is given. The method of the application obtains the transformation matrix between the body coordinate systems of the space cell robot, and provides a basis for the control distribution of the momentum wheel on each cell star. The identification method has high identification precision.

Description

Technical Field

[0001] This invention relates to the field of spacecraft parameter identification, specifically to a method for relative attitude identification of a fixed space cell robot in a non-cooperative spacecraft. Background Technology

[0002] With the development of space technology, space cellular robots, with their advantages of standardization, reconfigurability, and system flexibility, are receiving increasing attention in space missions such as attitude takeover, on-orbit servicing, and target detection. In attitude takeover missions, multiple space cellular robots are fixedly coupled to a target spacecraft to form a combined spacecraft. Attitude takeover of the target spacecraft is achieved through actuators such as momentum wheels on the space cellular robots. Since the target spacecraft may be non-cooperative, and its shape and geometry cannot be known in advance, the configuration topology of the space cellular robots connected to it varies in different missions. Furthermore, the attitude of the fixed space cellular robots may contain errors; therefore, it is necessary to identify the relative attitude of the space cellular robots to improve the control accuracy of the combined spacecraft.

[0003] Existing technologies rely on measurements from angular velocity sensors to identify the relative attitude between two space targets. However, publicly available methods for identifying the relative attitude of combined spacecraft only involve the identification of a small number of spacecraft, and their application in a large number of space cellular robots faces communication and computational challenges. Summary of the Invention

[0004] The technical problem to be solved by this invention is:

[0005] Multiple maneuverable space cellular robots are fixedly connected to a non-cooperative target spacecraft in a specific topology, forming a combined spacecraft. Attitude control of the combined spacecraft is achieved through the coordinated action of momentum wheels on all the space cellular robots. However, because the topological configurations of the space cellular robots connected to the target spacecraft vary in different missions, and because the fixed attitudes of the space cellular robots may contain errors, the relative attitudes between the space cellular robots are difficult to ascertain.

[0006] To avoid the shortcomings of existing technologies, this invention provides a relative attitude identification method for a fixed space cell robot in a non-cooperative spacecraft. Based on the distributed characteristics of the space cell robot, a parameter identification method based on inter-cell communication topology is designed.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for relative attitude recognition of a non-cooperative spacecraft-attached space cellular robot, characterized by the following steps:

[0009] Step 1: Establish a body coordinate system containing n space cell robots and a combined spacecraft;

[0010] Step 2: Determine the communication topology links between the space cell robots and draw the communication topology diagram between all n space cell robots;

[0011] Step 3: Using a distributed election algorithm, find the cell robot located at the topology center, which can communicate with all other cell robots with the shortest information link;

[0012] Step 4: Establish the angular velocity transfer matrix expression for the space cell robot located on the master node and other space cell robots to be identified at other locations;

[0013] Step 5: Identify the parameters in the transition matrix using the least squares method with constraints.

[0014] A further technical solution of the present invention: Step 3 includes:

[0015] Step S3.1: When there is no Leader node or the Leader node crashes, initialize the election, set all nodes to Follower state, and initialize the Term term to 0.

[0016] Step S3.2: If a Follower node does not receive a heartbeat from the Leader node or a vote request (Request Vote) from the Candidate node within the specified time, its state changes to Candidate, the Term increments, and it sends a vote request to all other nodes.

[0017] Step S3.3: When a node receives a voting request, it compares the requesting node's Term with its own Term. If the requesting node's Term is greater than its own Term, and the node has not yet voted for any other node, it accepts the voting request and casts its vote for the requesting node. If the requesting node's Term is less than its own Term, and the node has not yet voted, it rejects the request and casts its vote for itself. In each election round, each node can only cast one vote.

[0018] Step S3.4: After one round of election, if a Candidate node receives votes from more than half of the nodes (n2+1), it will win and be promoted to Leader node. Then, it will periodically send heartbeats to other nodes. Other nodes will become Follower nodes and keep synchronized with the Leader node, and this round of election will end. If no Candidate node receives more than half of the votes, the next round of election will begin until a Leader node is elected.

[0019] A further technical solution of the present invention: the expression for the angular velocity transfer matrix is:

[0020]

[0021] Among them, [ω itX ω itY ω itZ ] T The three elements represent the angular velocity measurements of the three axes of the i-th spatial cell robot; [ω 1tX ω 1tY ω 1tZ ] T The three elements represent the angular velocity measurements of the three axes of the spatial cellular robot, which serves as the master node. The matrix to be identified.

[0022] A computer system is characterized by comprising: one or more processors, and a computer-readable storage medium for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method described above.

[0023] A computer-readable storage medium is characterized by storing computer-executable instructions, which, when executed, are used to implement the above-described method.

[0024] A computer program product is characterized by including computer-executable instructions, which, when executed, are used to implement the above-described method.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention provides a relative attitude identification method for fixed space cell robots in non-cooperative spacecraft, achieving relative attitude identification for all space cell robots while minimizing the communication link. First, a suitable cell connection topology is selected based on the number of space cell robots and the geometry of the target spacecraft. Then, based on the information link topology, the cell robot's body coordinate system located at the topology center is selected as the base coordinate system. Next, based on data collected by angular velocity sensors on each cell robot and the base cell, the rotation matrix of the body coordinate system is identified using a recursive least squares method. This yields the attitude identification model for the space cell robots. This invention obtains the transformation matrix between the space cell robot's body coordinate systems, providing a basis for the control allocation of momentum wheels on each cell. The identification method of this invention has high identification accuracy. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 This is a schematic flowchart of a method for relative attitude recognition of a non-cooperative spacecraft-attached space cell robot provided by an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the coordinate system involved in the embodiments of the present invention;

[0030] Figure 3 This is a schematic diagram illustrating coordinate transformation between two spatial cellular robot coordinate systems in an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the communication link topology between space cell robots in an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram comparing the measured angular velocity value with the actual value provided in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the spatial cell robot rotation matrix identification results provided in an embodiment of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] See Figure 1 This invention proposes a method for relative attitude recognition of a fixed space cell robot in a non-cooperative spacecraft, comprising:

[0036] Step S1: Establish a body coordinate system containing n space cell robots and the combined spacecraft;

[0037] Step S2: Determine the communication topology links between the space cell robots and draw the communication link topology diagram between all n space cell robots;

[0038] Step S3: Using a distributed election algorithm, find the cell robot located at the topology center, which can communicate with all other cell robots with the shortest information link.

[0039] Step S4: Establish the angular velocity transfer matrix expression for the space cell robot located on the master node and other space cell robots to be identified at other locations;

[0040] Step S5: The parameters in the transition matrix are identified using the least squares method with constraints.

[0041] The specific steps described above are as follows:

[0042] Step S1, establish as follows Figure 2 The coordinate system shown.

[0043] Where Σ I {O I X I Y I Z I} is the Earth's inertial coordinate system, with its origin O. I Fixed to the Earth's center of mass, O I X I The axis points to the vernal equinox at a specific epoch within the equatorial plane. I Z I The axis is perpendicular to the equatorial plane and points towards the geographic North Pole, O I Y I The axis is determined according to the right-hand rule; Σ t {O t X t Y t Z t Σ{OXYZ} is the target spacecraft coordinate system, with its origin fixed at the target spacecraft's center of mass, and its coordinate axes parallel to the symmetry axes of the target spacecraft's geometry. Considering that the target spacecraft is non-cooperative, the target spacecraft coordinate system cannot guarantee that its orientation is along its principal inertial axes; Σ{OXYZ} is the combined spacecraft coordinate system, fixed to the combined spacecraft, with its origin O located at the combined spacecraft's center of mass, and its coordinate axes parallel to the target spacecraft's coordinate axes; Σ i {O ci X ci Y ci Z ci} is the coordinate system of the i-th spatial cell robot, Σ i It is fixedly connected to the i-th spatial cell robot, with its origin O ci Located at the centroid of the i-th spatial cell robot, with coordinate axes parallel to the geometric symmetry axis of the spatial cell robot.

[0044] Let's assume there are n cellular stars connected to the target spacecraft. In the attitude takeover mission, the position of each space cellular robot fixed to the target spacecraft is uncertain, and the connector may also be uncertain. The coordinate systems of any two space cellular robots are not strictly parallel. Figure 3 This is a schematic diagram of the coordinate transformation between the coordinate systems of the first and nth spatial cell robots. From the origin of the first spatial cellular robot coordinate system Pointing to the origin of the coordinate system of the nth spatial cell robot set up The projections onto the three axes of Σ1 are: Δrx 1n ,Δry 1n ,Δrz 1n Then from Σ1 to Σ n Homogeneous transformation matrix T 1n The expression for is shown in equation (1):

[0045]

[0046] Each space cell robot is equipped with three momentum wheels to control the attitude of the combined spacecraft. The directions of the angular momentum of the three momentum wheels are parallel to the three coordinate axes of the space cell robot's coordinate system.

[0047] Since the position of the angular momentum acting on the rigid body does not affect the result of the rigid body's motion, i.e., Δrx in formula (1) 1n ,Δry 1n ,Δrz 1n This has no impact on the control effect of the combined spacecraft. To achieve takeover control of the combined spacecraft's attitude, only parameter a needs to be identified. ij There are 9 constants (i,j=1,2,3), which can be written in matrix form. The matrix to be identified is shown in equation (2) below:

[0048]

[0049] Step S2: Based on the connection topology between the space cell robots, draw the communication link topology diagram between all n space cell robots.

[0050] Figure 4 This is a schematic diagram of the communication link topology between 12 space cell robots. Each space cell robot is described as a node, and the line connecting two nodes represents the information transmission link between the space cell robots.

[0051] Step S3: Using a distributed election algorithm, the topology node containing the space cell robot that can communicate with all other space cell robots and has the shortest communication link is elected as the master node. Nodes are divided into three states: Leader, Follower, and Candidate. Follower nodes maintain a heartbeat with the Leader node and respond to vote requests from Candidate nodes. Candidate nodes are responsible for voting in the election. When the cluster starts up or the Leader node crashes, a node in the Follower state will become a Candidate node to initiate the election. After winning the election, it transitions from the Candidate state to the Leader state. The specific election process is as follows.

[0052] Step S3.1: When there is no Leader node or the Leader node crashes, initialize the election, set all nodes to Follower state, and initialize Term to 0.

[0053] In step S3.2, if a Follower node does not receive a heartbeat from the Leader node or a vote request from the Candidate node within the specified time, its state changes to Candidate, its Term increments, and it sends a vote request to all other nodes.

[0054] Step S3.3: When a node receives a voting request, it compares the requesting node's Term with its own Term. If the requesting node's Term is greater than its own Term, and the node has not yet voted for any other node, it accepts the voting request and casts its vote for the requesting node. If the requesting node's Term is less than its own Term, and the node has not yet voted, it rejects the request and casts its vote for itself. In each round of election, each node can only cast one vote.

[0055] Step S3.4: After one round of elections, if a Candidate node receives more than half of the votes... The candidate node receives the majority of votes and becomes the leader node. It then periodically sends heartbeats to the other nodes. The other nodes become followers and synchronize with the leader node, ending the current election round. If no candidate node receives more than half of the votes, the next election round begins until a leader node is elected.

[0056] Step S4: Establish the angular velocity transfer matrix expression for the space cell robot located on the master node and other space cell robots to be identified at other locations.

[0057] Assuming the index of the master node spatial cellular robot is 1, and the angular velocity measured by its angular velocity sensor in the t-th measurement is ω. 1t The t-th measurement of the angular velocity of the spatial cellular robot with index i. it The following relationship must be satisfied:

[0058] ω it =A 1i ω 1t (3)

[0059] Among them, A 1i The matrix form is shown in equation (2). Equation (3) can be written in matrix form as shown in equation (4):

[0060]

[0061] In equation (4), [ω itX ω itY ω itZ ] T The three elements represent the angular velocity measurements of the three axes of the i-th spatial cell robot; [ω 1tX ω 1tY ω 1tZ ] T The three elements represent the angular velocity measurements of the three axes of the spatial cellular robot, which serves as the master node.

[0062] Step S5, for matrix A 1i Identify the elements in the text.

[0063] Let y t =ω it ∈R 3×1 , blkdiag represents a diagonal matrix with matrix blocks as its diagonal, θ = [a 11 a 12 a 13 a 21 a 22 a 23 a 31 a 32 a 33 ] T .

[0064] Equation (4) can be written as a linear regression equation in the following form:

[0065]

[0066] Define the least squares objective function:

[0067]

[0068] Where N represents the dimension of the collected sample data. Due to the rotation matrix A... 1i It is an orthogonal matrix, and θ satisfies the following constraints:

[0069]

[0070] g4(θ)=θ1θ4+θ2θ5+θ3θ6=0 (10)

[0071] g5(θ)=θ1θ7+θ2θ8+θ3θ9=0 (11)

[0072] g6(θ)=θ7θ4+θ8θ5+θ9θ6=0 (12)

[0073] g7(θ)=det(θ)-1=0 (13)

[0074] Define the Lagrange function:

[0075]

[0076] L(θ,λ i ) respectively for θ and λ i Taking the partial derivative and setting it to zero, we obtain the following equation:

[0077]

[0078] g i ′(θ)=0 (16)

[0079] Satisfying (15) and (16) This is the least squares estimate of θ. Matrix A 1i Identification results The format is as follows:

[0080]

[0081] in, express The j-th element in.

[0082] Based on the above technical solution, this embodiment of the invention conducted a simulation experiment on the relative attitude recognition of a fixed space cell robot on a non-cooperative spacecraft. The rotation matrix between the two space cell robots (numbered 1 and 2), their rotational angular velocity in their own body coordinate system, angular velocity measurement error, sampling period, and other parameter settings are shown in Table 1.

[0083] Table 1

[0084]

[0085] Based on the above simulation parameters, according to Figure 1The technical solution shown was verified by simulation, and the simulation results are as follows:

[0086] Figure 5 This diagram illustrates a comparison between the measured angular velocity values ​​of the space cell robot provided in an embodiment of the present invention and the actual values. Figure 6 A schematic diagram of the rotation matrix identification result provided by an embodiment of the present invention is shown. Figure 6 Substituting the result into equation (17), we can obtain the identification value of the rotation matrix.

[0087]

[0088] because and The identification method provided in this embodiment of the invention has high identification accuracy in simulation.

[0089] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for relative attitude recognition of a fixed space cellular robot in a non-cooperative spacecraft, characterized in that, The steps are as follows: Step 1: Create a system containing The body coordinate system of a space cell robot and a combined spacecraft; Step 2: Determine the communication topology links between space cell robots and draw all of them. Communication link topology diagram between individual space cell robots; Each space cell robot is described as a node, and the line connecting two nodes represents an information transmission link between space cell robots. Step 3: Using a distributed election algorithm, find the cell robot located at the topology center, which can communicate with all other cell robots with the shortest information link; Nodes are divided into three states: Leader, Follower, and Candidate. Follower nodes maintain a heartbeat with the Leader and respond to vote requests from Candidate nodes. Candidate nodes are responsible for election voting. When the cluster starts up or the Leader node crashes, a node in the Follower state will become a Candidate node to initiate an election. After winning the election, it transitions from the Candidate state to the Leader state. The specific election process is as follows: Step S3.1: When there is no Leader node or the Leader node crashes, initialize the election, set all nodes to Follower state, and initialize Term (term of office) to 0. Step S3.2: If a Follower node does not receive a heartbeat from the Leader node or a vote request (Request Vote) from the Candidate node within the specified time, its state changes to Candidate, the Term is incremented, and a vote request is sent to all other nodes. Step S3.3: When a node receives a voting request, it compares the requesting node's Term with its own Term. If the requesting node's Term is greater than its own Term, and the node has not yet voted for any other node, it accepts the voting request and casts its vote for the requesting node. If the requesting node's Term is less than its own Term, and the node has not yet voted for any other node, it rejects the request and casts its vote for itself. In each round of elections, each node can only cast one vote; Step S3.4: After one round of elections, if a Candidate node receives more than half of the votes... The candidate node receives more than half of the votes and is promoted to leader. It then sends heartbeats to other nodes periodically. Other nodes become followers and keep in sync with the leader node, ending the current election. If no candidate node receives more than half of the votes, the next election begins until a leader node is elected. Step 4: Establish the angular velocity transfer matrix expression for the space cell robot located on the master node and other space cell robots to be identified at other locations; Assuming the index of the master node spatial cell robot is 1, its angular velocity sensor is the... The angular velocity measured this time is ; Subscript Space cell robot angular velocity The measurement value of the time The following relationship must be satisfied: Will In matrix form, it is shown in the following equation: In the formula The three elements represent the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth ... Angular velocity measurements of a three-axis spatial cellular robot; The three elements represent the angular velocity measurements of the three axes of the spatial cellular robot, which serves as the master node. Step 5: Identify the parameters in the transition matrix using the least squares method with constraints; make , , This represents a diagonal matrix with matrix blocks as its diagonal. ; The linear regression equation can be written in the following form: Define the least squares objective function: in This indicates the dimension of the collected sample data; due to the rotation matrix It is an orthogonal matrix. The following constraints must be met: Define the Lagrange function: To each and Taking the partial derivative and setting it to zero, we obtain the following equation: satisfy That is Least squares estimation; matrix Identification results The format is as follows: in, express The first in Each element.

2. A computer system, characterized in that... include: One or more processors, a computer-readable storage medium for storing one or more programs, wherein, when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method of claim 1.

3. A computer-readable storage medium, characterized in that... The device stores computer-executable instructions, which, when executed, are used to implement the method of claim 1.

4. A computer program product, characterized in that... It includes computer-executable instructions, which, when executed, are used to implement the method of claim 1.

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