Control distribution method for spacecraft with eight-thruster structure

Abstract

The invention discloses a control distribution method for a spacecraft with an eight-thruster structure, and belongs to the technical field of spacecraft control. The problem that after the number of thrusters of an existing spacecraft is reduced, decoupling control requirements of force / torque in all directions cannot be met is solved. Comprising the steps that eight thrusters are arranged on a spacecraft, so that the eight thrusters are distributed in an axial symmetry mode in a structure installation coordinate system, nozzles face an evasion limiting area, and the axes of the nozzles evade the centroid deviation range of a whole-satellite structure center area; for the combined control of the expected single-axis force and the expected three-axis torque, establishing a relational expression by taking the longest total ignition duration of the four thrusters as a target, and calculating the ignition duration of each thruster; and for combined control of the expected triaxial force and the expected triaxial torque, six thrusters are selected from the eight thrusters to establish a relational expression between the ignition duration and the expected triaxial force and the expected triaxial torque, and the ignition duration of the six thrusters is calculated. The method is used for ignition control of the spacecraft.

Description

Technical Field

[0001] This invention relates to a control allocation method for an eight-thrust spacecraft, belonging to the field of spacecraft control technology. Background Technology

[0002] Existing spacecraft thruster layout schemes mostly employ traditional multi-thrust redundant orthogonal configurations to provide independent control forces / torques in each direction. While this allocation method reduces the complexity of control allocation, it typically requires more than 12 thrusters, making it unsuitable for low-cost microsatellite applications. Some studies have proposed simplified thruster layout schemes based on the control coupling approach, reducing the number of thrusters to 6 to 8. However, their control coupling design binds control forces / torques in certain directions, failing to meet the requirement of independent control in a single direction.

[0003] Existing control force / torque allocation methods for thruster assemblies theoretically employ optimization allocation algorithms based on directly solving the pseudo-inverse of the installation matrix. These methods suffer from high computational complexity and are difficult to implement on spaceborne computers with severely limited computational resources. In engineering practice, the commonly used lookup table method lacks robustness to installation deviations and centroid shifts, requiring frequent re-addition of the allocation matrix to prevent a decrease in control accuracy, and exhibits poor on-orbit autonomy. Summary of the Invention

[0004] To address the problem that reducing the number of thrusters in existing spacecraft cannot meet the decoupling control requirements of forces / torques in various directions, this invention provides a control allocation method for an eight-thrust spacecraft.

[0005] The present invention provides a control allocation method for an eight-thrust spacecraft, comprising:

[0006] Eight thrusters are arranged on the spacecraft so that the eight thrusters are symmetrically distributed in the structural installation coordinate system, and the nozzles are oriented to avoid the restricted area and the nozzle axis avoids the center of mass offset range of the whole satellite structure center area.

[0007] For the combined control of desired uniaxial force and desired triaxial torque: Select four thruster combinations corresponding to the desired uniaxial force direction based on the nozzle positions and directions of the eight thrusters; Based on the selected four thruster combinations, with the goal of maximizing the total ignition time of the four thrusters within one control cycle, establish the relationship between the desired triaxial torque and the thruster shutdown time by adjusting the shutdown time of different thrusters within one control cycle, and then calculate and determine the ignition time of each thruster in the current four thruster combinations;

[0008] For the combination control of the expected triaxial force and the expected triaxial moment: selecting six thrusters from the eight thrusters to establish the relationship between the ignition time length of the six thrusters and the expected triaxial force and the expected triaxial moment, and then calculating and determining the ignition time length of the six thrusters.

[0009] According to the control distribution method of the eight-thruster structure spacecraft of the application, the layout of the eight thrusters on the spacecraft satisfies:

[0010] ,

[0011] In the formula, is the included angle between the thruster nozzle direction and the horizontal direction, is the included angle between the line connecting the thruster and the nominal mass center of the whole spacecraft structure and the horizontal direction, is the longitudinal coordinate of the thruster in the nominal structure coordinate system, is the transverse coordinate of the thruster in the nominal structure coordinate system, is the force arm of the first thruster relative to the actual mass center of the whole spacecraft structure, is the maximum distance of the mass center deviation estimation, is the force arm of the second thruster relative to the actual mass center of the whole spacecraft structure.

[0012] According to the control distribution method of the eight-thruster structure spacecraft of the application, the four thrusters on one side surface of the whole spacecraft structure are sequentially recorded as thruster T1, thruster T2, thruster T3 and thruster T4 in clockwise direction, and the corresponding four thrusters on the opposite surface are sequentially recorded as thruster T5, thruster T6, thruster T7 and thruster T8;

[0013] For the combination control of the expected single-axis force and the expected triaxial moment, the four thruster combination corresponding to the expected single-axis force direction selected according to the nozzle position and the nozzle direction of the eight thrusters includes:

[0014] +X-axis control force, the corresponding four thruster combination is T1+T2+T3+T4;

[0015] -X-axis control force, the corresponding four thruster combination is T5+T6+T7+T8;

[0016] +Y-axis control force, the corresponding four thruster combination is T1+T4+T5+T8;

[0017] -Y-axis control force, the corresponding four thruster combination is T2+T3+T6+T7;

[0018] +Z-axis control force, the corresponding four thruster combination is T3+T4+T7+T8;

[0019] -Z-axis control force, the corresponding four thruster combination is T1+T2+T5+T6.

[0020] According to the control allocation method for an eight-thrust spacecraft of the present invention, the relationship between the desired triaxial torque and the thruster shutdown time is established as follows:

[0021] ,

[0022] In the formula The torque allocation matrix for the four thrusters, The theoretical thrust of the four thrusters. To control the cycle, The torque distribution matrix for three of the four thrusters. This represents the theoretical thrust of three out of the four thrusters. The shutdown time for three of the four thrusters. This represents the expected value of the three-axis attitude control torque.

[0023] According to the control allocation method of the eight-thrust spacecraft of the present invention, the torque allocation matrix of three of the four thrusters at the current moment is obtained. The methods include:

[0024] Calculate the estimated center of mass deviation CP_Est at the current moment, then calculate the installation position matrix of the four thrusters at the current moment, and finally obtain the torque distribution matrix of the four thrusters at the current moment. Simultaneously, obtain the torque distribution matrix of any three of the four thrusters at the current moment. .

[0025] According to the control allocation method of the eight-thrust structure spacecraft of the present invention, assuming that the control force direction is the +Z axis control force, the four thruster combinations are T3+T4+T7+T8, which includes four thruster shutdown groups: T3+T4+T7, T3+T4+T8, T3+T7+T8, and T4+T7+T8.

[0026] Based on the four thruster combinations and four thruster shutdown groups, the ignition duration of the four thrusters in each control cycle is calculated. ,include:

[0027] right Process it so that each component is limited to 0 to Within the interval, and for The ratio to the minimum pulse width is rounded off, then multiplied by the minimum pulse width to obtain the updated value. ;

[0028] but ,

[0029] In the formula is a 4x1 column vector for each component.

[0030] The control distribution method of the eight-thruster structure spacecraft according to the present application, in the combined control of the desired single-axis force and the desired three-axis torque, the method for determining the final thruster shutdown grouping is:

[0031] Calculate the distribution error The serial number of the thruster shutdown grouping:

[0032]

[0033] Select the thruster shutdown grouping with the minimum distribution error Output the ignition duration of the four thrusters

[0034] The control distribution method of the eight-thruster structure spacecraft according to the present application, for the combined control of the desired three-axis force and the desired three-axis torque, the relationship between the ignition duration of the six thrusters and the desired three-axis force and the desired three-axis torque is established as:

[0035]

[0036] In the formula, is the force and torque joint distribution matrix of the six thrusters among the eight thrusters, is the theoretical thrust size of the eight thrusters, is the ignition time of the selected six thrusters among the eight thrusters, is the control period, is the desired control quantity including the desired three-axis force and the desired three-axis torque;

[0037]

[0038] In the formula, is the installation direction matrix of the six thrusters, is the vector cross product, is the installation position matrix of the six thrusters;

[0039]

[0040] In the formula, is the desired three-axis force, is the desired three-axis torque.

[0041] The control distribution method of the eight-thruster structure spacecraft according to the present application, obtains six-thruster combinations from the eight thrusters;

[0042] ​​​​​​​​For each six-thrust assembly, calculate the ignition time of each of the six thrusters. :

[0043] ;

[0044] right Process it so that each component is limited to 0 to Within the interval, and for The ratio to the minimum pulse width is rounded off, then multiplied by the minimum pulse width to obtain the updated value. .

[0045] According to the control allocation method for an eight-thrust spacecraft of the present invention, the allocation error is calculated. , The serial number of the six-thrust assembly:

[0046] ,

[0047] In the formula This is the upper limit value for controlling the amplitude.

[0048] Selecting the allocation error The smallest six-thrust assembly achieves the ignition timing of all six thrusters. This leads to a control cycle. Ignition timing of the eight internal thrusters ;

[0049] Ignition time of eight thrusters The method of obtaining it is: The ignition timing of the corresponding six-thrust combination is assigned, while the ignition timing of the other two thrusters is set to zero.

[0050] The beneficial effects of the present invention are as follows: By rationally arranging the installation positions of the eight thrusters, the method of the present invention can achieve independent output of single-axis control force / control torque under the nominal installation matrix; by selecting different thruster combinations, it can also achieve output of attitude and orbit coupling control force / torque, which has strong task versatility.

[0051] Considering the practical problem of center of mass shift during on-orbit operation, the method of this invention allocates control forces / torques in conjunction with structural layout. By combining the advantages of both lookup table methods and direct solution methods, it achieves high-precision allocation of control quantities with low computational complexity, thus improving the robustness of allocation to structural parameter deviations. Specifically:

[0052] Optimization of the number and structural layout of thrusters: Compared with the traditional thruster layout method, the layout scheme proposed by the method of the application significantly reduces the number of thrusters (from 12-16 to 8) while still ensuring the independent output characteristics of the control force / control torque in each direction. Not only does this provide a foundation for simplifying subsequent control allocation algorithms, but it also enhances the adaptability of the spacecraft thruster system to complex control scenarios.

[0053] Mode differentiation of the control force / torque allocation algorithm: Compared with the traditional allocation method, which directly allocates control quantities to all thrusters, the method of the application differentiates between single-axis force + three-axis torque and three-axis force + three-axis torque working modes, thereby reducing the overall complexity of the algorithm while enhancing the fault tolerance of the propulsion system. In the event of a thruster failure, the entire allocation algorithm does not need to be reconfigured; instead, a new thruster combination can be selected to continue executing most orbit control tasks in the single-axis force + three-axis torque mode.

[0054] Four-thruster control allocation based on shutdown time modulation: Compared with the approach of converting the indeterminate equation involving only torque calculation into a determinate equation containing single-axis force + three-axis torque by supplementing a control force equation, the method of the application selects three thrusters to modulate the shutdown time and keeps the remaining thruster on for the entire control period. This reduces the dimension of the equation set and the amount of calculation while naturally ensuring the maximum output of single-axis control force during the control period without considering the influence of the selection of the desired control force in the supplemental control force equation on equation solving. The effect of the control force is only driven by time.

[0055] Eight-thruster dimension reduction six-degree-of-freedom control quantity allocation: Compared with the traditional grouping lookup table method and pseudo-inverse solution method, the method of the application pre-classifies eight thrusters into different six-thruster combinations, successfully converting the solution of high-dimensional indeterminate equations into the solution of equations of the same dimension, and converting complex optimization problems into simple optimization extraction problems between different combinations. This saves computational resources for robust design of on-orbit real-time calculation of mass center offset and update of installation / distribution matrix, and eliminates the need for frequent updates of the distribution matrix. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is a control allocation method for the eight-thruster structural spacecraft described in the application, which is a layout diagram of eight thrusters;

[0057] Figure 2 is a diagram showing that the layout of the eight thrusters on the spacecraft satisfies ; and

[0058] Figure 3 is a diagram showing that the layout of the eight thrusters on the spacecraft satisfies .

[0059] Figure 4 is an error quaternion diagram of the spacecraft body coordinate system and the orbit coordinate system in embodiment one;

[0060] Figure 5 is an error attitude angle diagram of the spacecraft body coordinate system and the orbit coordinate system in embodiment one;

[0061] Figure 6 is a distribution error diagram of the expected moment in the simulation process in embodiment one;

[0062] Figure 7 is a cumulative ignition time diagram of the four thrusters in embodiment one;

[0063] Figure 8 is a cumulative velocity increment size diagram of the control force output by the four thrusters in the body coordinate system in embodiment one;

[0064] Figure 9 is a cumulative velocity increment size diagram of the control force output by the four thrusters in the orbit coordinate system in embodiment one;

[0065] Figure 10 is an error quaternion diagram of the spacecraft body coordinate system and the orbit coordinate system in embodiment two;

[0066] Figure 11 is an error attitude angle diagram of the spacecraft body coordinate system and the orbit coordinate system in embodiment two;

[0067] Figure 12 is a distribution error diagram of the expected moment in the simulation process in embodiment two;

[0068] Figure 13 is a cumulative ignition time diagram of the four thrusters in embodiment two;

[0069] Figure 14 is a cumulative velocity increment size diagram of the control force output by the four thrusters in the body coordinate system in embodiment two;

[0070] Figure 15 is a cumulative velocity increment size diagram of the control force output by the four thrusters in the orbit coordinate system in embodiment two;

[0071] Figure 16 is a force distribution error statistical diagram of different expected force / moment test groups in the X axis in embodiment three;

[0072] Figure 17 is a force distribution error statistical diagram of different expected force / moment test groups in the Y axis in embodiment three;

[0073] Figure 18 is a force distribution error statistical chart on the X-axis of different expected force / torque test groups in Example Three;

[0074] Figure 19 is a torque distribution error statistical chart on the X-axis of different expected force / torque test groups in Example Three;

[0075] Figure 20 is a torque distribution error statistical chart on the Y-axis of different expected force / torque test groups in Example Three;

[0076] Figure 21 is a torque distribution error statistical chart on the Z-axis of different expected force / torque test groups in Example Three;

[0077] Figure 22 is a normalized proportion error statistical chart of different expected force / torque test groups in Example Three. DETAILED DESCRIPTION

[0078] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0079] DETAILED DESCRIPTION Figures 1 to 3 As shown in the drawings, the present application provides a control distribution method of a spacecraft with eight thrusters, comprising:

[0080] Eight thrusters are arranged on the spacecraft, so that the eight thrusters meet the axisymmetric distribution in the structural installation coordinate system, and the nozzles are oriented to avoid the restricted areas of other single machines such as antennas / cameras and the mass center shift range of the nozzle axis to avoid the center area of the whole satellite structure;

[0081] For the combined control of the expected single-axis force and the expected three-axis torque: according to the nozzle positions and directions of the eight thrusters, four thruster combinations corresponding to the expected single-axis force direction are selected; according to the selected four thruster combinations, the relationship between the expected three-axis torque and the thruster shutdown time is established by adjusting the shutdown time of different thrusters in a control period, so as to calculate and determine the ignition time of each thruster in the current four thruster combinations;

[0082] For the combined control of the expected three-axis force and the expected three-axis torque: six thrusters are selected from the eight thrusters to establish the relationship between the ignition time of the six thrusters and the expected three-axis force and the expected three-axis torque, so as to calculate and determine the ignition time of the six thrusters.

[0083] Figure 1 Center of mass b X b Y b Z b Nominal structure coordinate system, with the origin at the nominal center of mass. Figure 1 Thrust 1 to thrust 8 correspond to thrust T1 to thrust T8 in Table 1. Figure 2 And Figure 3 F1 is the nozzle direction of thrust T1, and F2 is the nozzle direction of thrust T2.

[0084] In this embodiment, the nozzle axes (and their extensions) of the eight thrusters should not pass through the center of mass of the center region of the whole satellite structure, so as to ensure sufficient torque output, i.e. Figure 2 And Figure 3 In this embodiment, d1 and d2 should be greater than or equal to the corresponding set threshold. Figure 2 And Figure 3 In this embodiment, the vertices of the rectangular structure schematic shape are used as the mounting positions of the thrusters.

[0085] Further, according to Figure 2 And Figure 3 , the calculation formula of the equivalent projection force arm can be obtained, i.e. the layout of the eight thrusters on the spacecraft satisfies:

[0086] ,

[0087] In the formula, is the angle between the nozzle direction of the thruster and the horizontal direction, is the angle between the line connecting the thruster and the nominal center of mass of the whole satellite structure and the horizontal direction, is the longitudinal coordinate of the thruster in the nominal structure coordinate system, is the transverse coordinate of the thruster in the nominal structure coordinate system, is the force arm of the first thruster relative to the actual center of mass of the whole satellite structure, is the maximum distance of the center of mass deviation estimation, which is generally required to be controlled within 3 cm by the design of the whole satellite structure; is the force arm of the second thruster relative to the actual center of mass of the whole satellite structure.

[0088] According to the above requirements and design method, a layout design example as shown in Table 1 is given, which is suitable for a microsatellite with a nearly cubic main structure (about 1 m in length) of the whole satellite.

[0089] Table 1: Eight-thruster structure layout design example

[0090]

[0091] According to the above design result, the thruster combination for single-axis control force / control torque independent output can be easily obtained as shown in Table 2, and the entire set of actuators only uses 8 thrusters, and the number of thrusters to be installed is reduced to almost the minimum while achieving control output decoupling.

[0092] The four thrusters on one side surface of the whole satellite structure are sequentially recorded as thruster T1, thruster T2, thruster T3 and thruster T4 in clockwise direction, and the corresponding four thrusters on the opposite surface are sequentially recorded as thruster T5, thruster T6, thruster T7 and thruster T8;

[0093] For the combination control of expected single-axis force and expected three-axis torque, the four thruster combination corresponding to the expected single-axis force direction selected according to the jet port position and jet port direction of the eight thrusters includes:

[0094] +X-axis control force, the corresponding four thruster combination is T1+T2+T3+T4;

[0095] -X-axis control force, the corresponding four thruster combination is T5+T6+T7+T8;

[0096] +Y-axis control force, the corresponding four thruster combination is T1+T4+T5+T8;

[0097] -Y-axis control force, the corresponding four thruster combination is T2+T3+T6+T7;

[0098] +Z-axis control force, the corresponding four thruster combination is T3+T4+T7+T8;

[0099] -Z-axis control force, the corresponding four thruster combination is T1+T2+T5+T6.

[0100] Table 2 Thruster combination for single-axis control force / control torque output

[0101]

[0102] Control force / torque distribution algorithm:

[0103] The control force / torque distribution algorithm is executed according to the following flow:

[0104] Working mode selection: According to the experience of thruster combination in orbit use, it can be divided into (1) single-axis force + three-axis torque and (2) three-axis force + three-axis torque two working modes. Among them (1) single-axis force + three-axis torque working mode needs the spacecraft to adjust the whole satellite attitude to the desired inertial pointing direction of output single-axis force in advance. This step belongs to the conventional attitude control. It needs to be pointed out that the control effect of this working mode stabilizes the whole satellite attitude at the desired pointing direction. Large angle attitude maneuvering can be executed in theory, but it will destroy the control force effect and further affect the orbit control. And (2) three-axis force + three-axis torque can realize the simultaneous control of attitude and orbit, and has good applicability to the scene of attitude-orbit coupling control. It needs to be pointed out here that the two working modes can also enhance the fault tolerance of the control allocation algorithm. That is, in the case of failure of a certain thruster, the entire allocation algorithm does not need to be reconfigured, and only a new thruster combination can continue to execute most of the orbit control tasks in the single-axis force + three-axis torque mode.

[0105] Specific algorithm execution:

[0106] (1) Single-axis force + three-axis torque working mode:

[0107] In this working mode, the basic principle of the control force / torque allocation algorithm is to modulate the shutdown time of the four inclined orbit control engines (installation method is required) within a control period to ensure attitude stability while ensuring maximum output of the orbit control force. The total impulse of the control force execution is determined by the length of time after entering this working mode.

[0108] The relationship between the desired three-axis torque and the shutdown time of the thruster is established as follows:

[0109] ,

[0110] In the formula, is the torque allocation matrix of the four thrusters, position x thrust direction, the centroid drift error is time-varying, and the direction error is fixed. The mechanical installation accuracy is better than ±1mm in position and better than ±1° in angle; is the theoretical thrust size of the four thrusters, which can be obtained through the design of the propulsion system; is the control period, is the torque allocation matrix of three thrusters among the four thrusters, position x thrust direction, there are four combinations under the four inclined layout, and the installation matrix is invertible; is the theoretical thrust size of three thrusters among the four thrusters, corresponding to ; is the shutdown time of three thrusters among the four thrusters in this control period, The expected value of the three-axis attitude control torque is 0.06 Nm. To ensure the solvability of the allocation, the magnitude of the control torque needs to be proportionally limited. According to the structural layout design given in this embodiment, the value can be taken as 0.06 Nm.

[0111] The specific execution steps are as follows:

[0112] Based on the actual situation of the propulsion system and the direction of the single-axis force, a suitable thruster combination is selected to generate... Considering the shift in the center of mass of the entire satellite due to fuel consumption, the following method is adopted to reduce the error of the installation matrix:

[0113] Obtain the torque distribution matrix of three out of the four thrusters at the current moment. The methods include:

[0114] Calculate the estimated centroid deviation CP_Est at the current moment, then calculate the installation position matrix of the four thrusters at the current moment, and finally obtain the torque distribution matrix of the four thrusters at the current moment. Simultaneously, obtain the torque distribution matrix of any three of the four thrusters at the current moment. .

[0115] Assuming the control force direction is the +Z axis control force, the corresponding four thruster combinations are T3+T4+T7+T8, which includes four thruster shutdown groups: T3+T4+T7, T3+T4+T8, T3+T7+T8, and T4+T7+T8.

[0116] Based on the four thruster combinations and four thruster shutdown groups, the ignition duration of the four thrusters in each control cycle is calculated. ,include:

[0117] right Process it so that each component is limited to 0 to Within the interval, and for The ratio to the minimum pulse width is rounded off, then multiplied by the minimum pulse width to obtain the updated value. ;

[0118] but ;

[0119] In the formula Each component is a control cycle. The 4×1 column vector. The difference operation of each component in the above formula should strictly correspond to the number of each thruster, and the shutdown time of the thruster that is not selected for shutdown should be set to zero.

[0120] In the combined control of desired uniaxial force and desired triaxial torque, the method for determining the final thruster shutdown group is as follows:

[0121] Calculate the allocation error That is, the magnitude of the vector error. The sequence number for the thruster shutdown group:

[0122] ,

[0123] Selecting the allocation error The smallest thruster shutdown group outputs the ignition duration of four thrusters. Or the duty cycle of power-on time The power-on time of the remaining four unselected thrusters is set to zero, i.e., they are turned off.

[0124] Triaxial force + triaxial torque working mode:

[0125] In this working mode, the basic principle of the control force / torque distribution algorithm is: within a control cycle, by modulating the start-up time of the 8 inclined thrusters (with requirements for installation method), the distribution error of the theoretically calculated control force and control torque output by the control algorithm is minimized.

[0126] For the combined control of desired triaxial force and desired triaxial torque, the relationship between the ignition time of the six thrusters and the desired triaxial force and desired triaxial torque is established as follows:

[0127] ,

[0128] In the formula The force and torque joint allocation matrix for six of the eight thrusters. The theoretical thrust of the eight thrusters. The ignition timing of six thrusters selected from eight thrusters, and Correspondingly; To control the cycle, The desired control quantity includes the desired triaxial force and the desired triaxial torque;

[0129] ,

[0130] In the formula This is the installation direction matrix for the six thrusters, opposite to the thrust direction; For vector cross product, The matrix represents the installation positions of the six thrusters; the center of gravity drift error is time-varying, while the directional error is fixed. Mechanical installation accuracy: position better than ±1mm, angle better than ±1°;

[0131] ,

[0132] In the formula For the desired triaxial force, The desired triaxial torque.

[0133] To ensure the solvability of the allocation, the desired control quantity needs to be limited. According to the structural layout design given in this embodiment, the values ​​can be 0.5N and 0.05Nm.

[0134] In this operating mode, the specific execution steps of the control force / torque allocation algorithm are as follows:

[0135] Theoretically, it is possible to obtain power from eight thrusters. There are six thruster combinations, some of which may be rank-deficient and can be discarded; calculate their allocation matrix using the same method described above. Furthermore, the computational load on the satellite can be further reduced by pre-storing data on the ground.

[0136] Perform the following steps 28 times:

[0137] For each six-thrust assembly, calculate the ignition time of each of the six thrusters. :

[0138] ;

[0139] right Process it so that each component is limited to 0 to Within the interval, and for The ratio to the minimum pulse width is rounded off, then multiplied by the minimum pulse width to obtain the updated value. .

[0140] Calculate the allocation error , The serial number of the six-thrust assembly:

[0141] ,

[0142] In the formula This is the upper limit value for controlling the amplitude.

[0143] Selecting the allocation error The smallest six-thrust assembly achieves the ignition timing of all six thrusters. This leads to a control cycle. Ignition timing of the eight internal thrusters Or the duty cycle of power-on time ;

[0144] Ignition time of eight thrusters The method of obtaining it is: The ignition timing of the corresponding six-thrust combination is assigned, while the ignition timing of the other two thrusters is set to zero.

[0145] Example 1:

[0146] Single force + three torque mode:

[0147] Initial attitude: Earth pointing;

[0148] Direction of maneuver: Tangential (path direction, Y direction in LVLH, X direction in VVLH);

[0149] Thruster combination: 3478 (+Zb axis thrust, refer to Figure 1 );

[0150] Initial mass: 71 kg, dry mass: 68.5 kg, fuel mass: 2.5 kg (fully loaded 6.5 kg);

[0151] Nominal thrust magnitude: 0.52 N (varies with pressure fitting law), minimum control pulse width 20 ms;

[0152] Inertias exist 5% deviation from nominal inertias (diag([7.92 5.84 7.96])), mounting matrix exists 1°, ±5 mm mounting deviation, mass center deviation along Zb axis direction

[0153] Simulation time: 150 s; control period: 500 ms;

[0154] The results are shown in Figures 4 to 9 .

[0155] Example Two:

[0156] Single force + three torque mode:

[0157] Initial attitude: Earth pointing;

[0158] Direction of maneuver: Tangential (path direction, Y direction in LVLH, X direction in VVLH);

[0159] Thruster combination: 1234 (+Xb axis thrust);

[0160] Initial mass: 71 kg, dry mass: 68.5 kg, fuel mass: 2.5 kg (fully loaded 6.5 kg);

[0161] Nominal thrust magnitude: 0.52 N (varies with pressure fitting law), minimum control pulse width 20 ms;

[0162] Inertias exist 5% deviation from nominal inertias (diag([7.92 5.84 7.96])), mounting matrix exists 1°, ±5 mm mounting deviation, mass center deviation along Zb axis direction

[0163] Simulation time: 150 s; control period: 500 ms;

[0164] The results are shown inFigures 10 to 15 As shown.

[0165] Examples 1 and 2 show that:

[0166] 1) When there is a constant deviation of the center of mass that is not along the direction of the resultant thrust axis of the four inclined thrusters, in order to ensure attitude stability, as above... Figure 13 As shown, the thruster on one side must be shut down to balance the eccentric torque caused by the deviation of the center of mass.

[0167] 2) In single-axis force + three-axis torque mode, the algorithm proposed in this invention can achieve a control effect with an attitude better than 0.1 degrees, such as... Figure 5 and Figure 11 As shown, the results meet the requirements for actual on-orbit use. It should be noted that the attitude control accuracy and the severity of its oscillations are related to changes in inertia / center of mass offset, etc. The simulation results are applicable to general, gradually changing conditions.

[0168] 3) Even if there is a constant deviation of the center of mass not along the direction of the resultant thrust axis, the excess velocity increment of other axes due to pulse width modulation is less than 10% of the main shaft velocity increment using the method of this invention. Figure 8 , Figure 9 , Figure 14 and Figure 15 As shown, for scenarios with an ignition duration of less than 10 minutes, there will be no significant impact on the macroscopic effect of track control.

[0169] Example 3:

[0170] Triaxial force + triaxial torque mode:

[0171] Desired control variables are randomly generated for target practice based on different sample groups. The generation method of the desired control variables is shown below:

[0172] Generation Method 1: The generation methods for desired control force / control torque are consistent, simulating the working condition where the quantity to be allocated simultaneously has triaxial force + triaxial torque:

[0173] ,

[0174] in Let [the function] be the random number generation function within the closed interval [0,1]. In the above formula, The function's intrinsic parameter indicates that it generates a 3×1 random number vector;

[0175] Table 3 Parameter Settings for Generation Method 1

[0176]

[0177] Generation Method 2: Simulate working conditions where the quantities to be allocated only involve uniaxial force + triaxial torque or biaxial force + triaxial torque.

[0178] Table 4: Calculation formula of the second generation method

[0179]

[0180] Initial mass: 71 kg, dry mass 68.5 kg, fuel mass 2.5 kg, 5% deviation of inertia relative to nominal inertia (diag([7.92 5.84 7.96])), 1° installation deviation, ±5 mm installation deviation, mass center deviation along Zb axis

[0181] Nominal thrust: 0.52 N, change with pressure fitting rule, minimum control pulse width 20 ms

[0182] Thrust installation error: 1° angle deviation, ±5 mm position deviation

[0183] Control period: 500 ms, total number of sample groups 11

[0184] The results are shown in the following figure Figures 16 to 21 The vertical axis is the proportion of the total sample group, and the horizontal axis is the sample group number. The sample details are shown in Tables 3 and 4 above.

[0185] Figures 16 to 21 The statistical analysis shows that for the above sample groups, the absolute amount of allocation error is basically consistent, that is, more than 80% of the errors are less than 0.01 N and 0.004 Nm. For a thrust of 0.52 N, the error magnitude is within a minimum pulse width (20 ms), which meets the accuracy requirements of allocation and meets the needs of on-orbit service.

[0186] Figure 22 The simulation results show that when the expected control amount to be allocated is too small, it will result in a larger relative error, that is, the allocation effect is worse. It must be pointed out that this allocation error is directly related to the minimum pulse width of the thruster. The shorter the time length of the minimum pulse width, the smaller the allocation error will be.

[0187] In summary, the method of the present application can complete low-complexity control allocation with high precision while resisting mass center shift in on-orbit operation and improving robustness. It is based on the traditional grouping table lookup method, divides the thrusters into different combinations, successfully converts the solving problem of high-dimensional indefinite equations into the solving problem of same-dimensional definite equations, and converts the complex optimization problem into a simple selection and extraction problem among different combinations, thereby saving computing resources for robust design of on-orbit real-time calculation of mass center shift and updating of installation / distribution matrix.

[0188] Application scenarios of the method of the present application:

[0189] 1. Attitude and orbit coupling control in micro-satellite rendezvous and docking: applicable to attitude and orbit coupling control in micro-satellite rendezvous and docking, in which the attitude and orbit coupling controller must output a control quantity to be executed including three-axis force + three-axis torque. The application of the eight-thruster structural layout scheme and the control force / torque distribution algorithm proposed in the application will realize high-precision distribution of the attitude and orbit coupling control quantity with relatively low cost and relatively simple algorithm complexity, expanding the on-orbit service capability of micro-satellites.

[0190] 2. General orbit control of micro-satellite: applicable to general orbit control scenarios of micro-satellites, and the micro-satellite only needs to install 4 thrusters on one side of the eight-thruster structural layout scheme proposed in the application and apply a single-axis force + three-axis torque control distribution algorithm to realize the general orbit control requirement, which is low in cost and does not need the intervention of a flywheel or other attitude control execution mechanism. If 8 thrusters are installed, the fault tolerance capability is provided, and the robustness of the whole satellite control is improved.

[0191] In the control force / control torque distribution algorithm, the linear equation system solving algorithm can also be used instead of the inverse matrix operation when solving the equation system.

[0192] The application is based on the control force / control torque distribution method of grouping dimension reduction + real-time update of installation matrix: through the grouping dimension reduction processing of the multi-thruster system, the indefinite equation solving problem is converted into a definite equation solving problem, and a robust operation of real-time updating of the installation matrix in the case of mass center offset is designed, which reduces the complexity of the control force / control torque distribution algorithm while ensuring the distribution accuracy.

[0193] The application can realize the eight-thruster structural layout design of efficient control: through the symmetrical pyramid configuration of the thruster structural layout, the number of thrusters that can realize full-drive control is reduced to 8, while the independent output of single-axis control force / control torque is ensured, and the solving difficulty of the control distribution problem is reduced.

[0194] Selection and fault tolerance of control quantity distribution mode: by designing two control quantity distribution modes, on the one hand, the complexity of the control distribution problem is further reduced, and on the other hand, the problem of complete reconstruction of the whole satellite multi-thruster control distribution algorithm in the case of single thruster failure is avoided, and the flexibility in use is enhanced.

[0195] The high-precision low-computational-load control distribution method of the invention: through the grouping dimension reduction processing of the multi-thruster system, the indefinite equation solving problem is converted into the definite equation solving, compared with the traditional pseudo-inverse method of directly solving the indefinite equation, the computational complexity is significantly reduced, on this basis, the robust operation of real-time updating the installation matrix in the case of centroid offset is designed, avoiding the remote control complexity of the traditional lookup table method which needs to constantly update the new distribution matrix to adapt to the continuous centroid offset, the simulation shows that the attitude control precision can be better than 0.1 deg, and the relative distribution error is less than 20%.

[0196] The low-cost high-efficiency control eight-thruster structure layout design of the invention: through the symmetrical pyramid configuration of the thruster structure layout, while reducing the number of thrusters that can realize the control of full drivability from the traditional 12-16 to 8, the independent decoupling output of single-axis control force / control torque is also ensured, the solving difficulty of the control distribution problem is reduced, and the complex control coupling problem is avoided.

[0197] Flexible control quantity distribution mode selection and fault tolerance of the invention: by designing two control quantity distribution modes, on the one hand, the complexity of the control distribution problem is further reduced from the top layer of the task, on the other hand, the problem of complete reconstruction of the whole satellite multi-thruster control distribution algorithm in the case of single thruster failure is avoided, and the flexibility of use is enhanced.

[0198] Although the present invention is described herein with reference to particular embodiments, it is to be understood that these examples are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It is to be understood that the features of the dependent claims can be combined with those of the parent application in the manner set forth in the description. It is also to be understood that the features described in connection with one embodiment can be used in conjunction with other embodiments described herein.

Claims

1. A control allocation method for an eight-thruster configuration spacecraft, characterized by, The method comprises the following steps: Eight thrusters are arranged on the spacecraft to meet the following conditions: the eight thrusters are arranged in an axisymmetric distribution in a structural mounting coordinate system, and the nozzles are directed to avoid a restricted area and the mass center offset range of the nozzle axis from the center of the whole satellite structure; For combined control of a desired single-axis force and a desired three-axis moment: selecting four thruster combinations corresponding to the direction of the desired single-axis force according to the nozzle positions and directions of the eight thrusters; establishing a relationship between the desired three-axis moment and the shutdown time of the thrusters by adjusting the shutdown time of different thrusters in a control cycle to maximize the total ignition time of the four thrusters in the control cycle, and then calculating and determining the ignition time of each thruster in the current four thruster combination; For combined control of a desired three-axis force and a desired three-axis moment: selecting six thrusters from the eight thrusters to establish a relationship between the ignition time of the six thrusters and the desired three-axis force and the desired three-axis moment, and then calculating and determining the ignition time of the six thrusters.

2. The control distribution method of the eight-thruster structure spacecraft according to claim 1, wherein the arrangement of the eight thrusters on the spacecraft meets the following conditions:

3. The control distribution method of the eight-thruster structure spacecraft according to claim 2, wherein the four thrusters on one side surface of the whole satellite structure are sequentially recorded as thruster T1, thruster T2, thruster T3 and thruster T4 in a clockwise direction, and the four thrusters on the opposite side surface are sequentially recorded as thruster T5, thruster T6, thruster T7 and thruster T8. ， wherein is the angle between the thruster nozzle direction and the horizontal direction, is the angle between the line connecting the nominal center of mass of the thruster and the whole satellite structure and the horizontal direction, is the longitudinal coordinate of the thruster in the nominal structure coordinate system, is the transversal coordinate of the thruster in the nominal structure coordinate system, is the force arm of the first thruster relative to the actual center of mass of the whole satellite structure, is the maximum distance of the center of mass deviation estimation, is the force arm of the second thruster relative to the actual center of mass of the whole satellite structure. For combined control of a desired single-axis force and a desired three-axis moment, the selection of four thruster combinations corresponding to the direction of the desired single-axis force according to the nozzle positions and directions of the eight thrusters comprises: +X-axis control force, corresponding to four thruster combination T1+T2+T3+T4; -X-axis control force, corresponding to four thruster combination T5+T6+T7+T8; +Y-axis control force, corresponding to four thruster combination T1+T4+T5+T8; -Y-axis control force, corresponding to four thruster combination T2+T3+T6+T7; +Z-axis control force, corresponding to four thruster combination T3+T4+T7+T8; -Z-axis control force, corresponding to four thruster combination T1+T2+T5+T6.

4. The control distribution method of the eight-thruster structure spacecraft according to claim 3, wherein the relationship between the desired three-axis moment and the shutdown time of the thrusters is:

5. The control distribution method of the eight-thruster structure spacecraft according to claim 4, wherein the relationship between the desired three-axis moment and the shutdown time of the thrusters is:

6. The control distribution method of the eight-thruster structure spacecraft according to claim 5, wherein the relationship between the desired three-axis moment and the shutdown time of the thrusters is: Assuming that the control force direction is +Z-axis control force, corresponding to four thruster combination T3+T4+T7+T8, then it includes four thruster shutdown groupings T3+T4+T7, T3+T4+T8, T3+T7+T8 and T4+T7+T8. ， wherein is the moment distribution matrix for four thrusters, is the theoretical thrust magnitude for four thrusters, is the control period, is the moment distribution matrix for three thrusters out of four thrusters, is the theoretical thrust magnitude for three thrusters out of four thrusters, is the shutdown time for three thrusters out of four thrusters, is the calculated expected value of the three-axis attitude control moment.

7. The control distribution method of the eight-thruster structure spacecraft according to claim 6, wherein the relationship between the desired three-axis moment and the shutdown time of the thrusters is: Obtain the torque distribution matrix of three out of the four thrusters at the current moment. The methods include: The centroid deviation estimation value CP_Est at the current time is calculated, and a mounting position matrix of the four thrusters at the current time is calculated, and then a moment distribution matrix of the four thrusters at the current time is obtained , and at the same time a moment distribution matrix of any three thrusters among the four thrusters at the current time is obtained . ​ ​ According to four thruster combinations and four thruster shutdown groups, the ignition time of the four thrusters in each control cycle is calculated comprising: right Process it so that each component is limited to 0 to Within the interval, and for The ratio to the minimum pulse width is rounded off, then multiplied by the minimum pulse width to obtain the updated value. ; Then , wherein is a 4 x 1 column vector for each component is a 4 x 1 column vector for each component ​ In the combined control of the expected single-axis force and the expected three-axis moment, the method for determining the final thruster shutdown grouping is: Computing assignment errors , Sequence number for thruster shutdown packet ， allocation error minimum thruster shutdown packet, output four thruster firing durations .

8. The control allocation method for an eight-thruster structured spacecraft according to claim 2, wherein, For the combined control of the expected three-axis force and the expected three-axis moment, the relationship between the ignition time length of the six thrusters and the expected three-axis force and the expected three-axis moment is established as: ， wherein is a force, moment joint distribution matrix for six of the eight thrusters, is a theoretical thrust magnitude for the eight thrusters, is a firing time for the selected six of the eight thrusters, is a control period, is a desired control quantity including a desired three-axis force and a desired three-axis moment; ， wherein is a matrix of installation directions of the six thrusters, is a vector cross product, is a matrix of installation positions of the six thrusters; ， wherein is the desired tri-axial force, is the desired tri-axial moment.

9. The control allocation method for an eight-thruster structured spacecraft according to claim 8, wherein, obtained from eight thrusters a six-thruster combination; For each six-thruster combination, the firing times of the six thrusters are calculated : ； right Process it so that each component is limited to 0 to Within the interval, and for The ratio to the minimum pulse width is rounded off, then multiplied by the minimum pulse width to obtain the updated value. .

10. The control allocation method for an eight-thruster structured spacecraft according to claim 9, wherein, Computing assignment errors , Serial number for six thruster assembly: ， In the formula is the upper bound of the control limit amplitude Selectively assigning errors The minimum six thruster combination, obtaining the ignition time of six thrusters , and then obtaining a control cycle The ignition time of eight thrusters in the inner ; Firing times for the eight thrusters The method for obtaining the firing times is to assign the firing times for the six thrusters corresponding to the combination, and to set the firing times for the other two thrusters to zero. The method for obtaining the firing times is to assign the firing times for the six thrusters corresponding to the combination, and to set the firing times for the other two thrusters to zero.

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