A method for attitude control of a rocket during a vertical recovery landing phase using a combination of RCS and swing nozzle control

Abstract

The application provides a rocket vertical recovery landing section attitude control method of RCS and swing nozzle combined control, the dynamics and kinematics equation of the rocket vertical recovery landing section is deduced, a six-degree-of-freedom model suitable for the rocket attitude control law design is established, then the rocket engine swing nozzle control system and the RCS power auxiliary control system are respectively designed, under the constraint conditions of the limited fuel loading and the control ability of the attitude control power system RCS, the rocket vertical recovery landing section attitude control method of RCS and swing nozzle combined control is provided, the rocket engine re-ignition time is designed by using the trajectory planning method, the real-time calculation amount is met while the rocket reserved fuel loading is reduced, the rocket re-ignition time and the rocket fuel loading are used as the reference values in the actual engineering design process, and the reference basis is provided for improving the rocket carrying efficiency and the actual engineering design of the rocket light weight.

Description

Technical Field

[0001] This invention belongs to the field of attitude control for rocket recovery phase, specifically relating to an attitude control method for the vertical recovery and landing phase of a rocket using a combination of RCS and oscillating nozzle control. Background Technology

[0002] Vertical rocket recovery is an important method of rocket reuse, achieved by landing the rocket vertically at a fixed point outside the atmosphere. Rocket attitude control is one of the core functions of the vertical recovery stage control system. It needs to maintain the rocket's stable flight and track the attitude control commands required in real time, and drive the actuators to make corresponding actions to generate the torque needed to adjust the rocket's attitude.

[0003] The RCS (Reaction Control System) is an actuator composed of multiple thrusters that uses the reverse thrust of the lateral jet to control attitude. Compared to continuous aerodynamic control surfaces, its advantage lies in not being constrained by conditions such as atmospheric density. However, it is an on / off actuator that can only provide constant discrete torque. Therefore, pulse modulation technology is required to convert continuous control quantities into RCS pulse commands for attitude control.

[0004] Because the rocket is initially positioned at high altitude during the vertical landing phase, the air is thin and atmospheric density is low. Traditional aerodynamic control surfaces generate insufficient control torque and have limited control capability, making it difficult to meet the rocket's attitude control requirements. To ensure a smooth vertical landing, current technology uses the RCS (Rapid Cross Section) as another actuator for attitude control and employs a combined control scheme to complete the attitude control task during the vertical landing phase. Specifically, the timing of the rocket engine's re-ignition is designed using trajectory planning, and this serves as a marker point for attitude control using different actuators.

[0005] During the specific testing process, it was found that when using RCS for attitude control of the pitch and roll channels, the actuators of the two channels would interfere with each other, resulting in control coupling. This prevented the simultaneous output of control commands from the pitch channel controller and the roll channel controller, ultimately rendering the attitude control scheme using RCS unusable. In engineering, pulse-type control commands are often used to achieve attitude control, for example:

[0006] The patent document with publication number CN114184093A discloses a liquid rocket single-thrust RCS layout and attitude control method. It controls 12 thrust chambers arranged circumferentially or tangentially along the rocket body by outputting pulse-form commands to control the attitude of the rocket's pitch and roll channels. The structure is complex and the functions of multiple thrusters are redundant. When used for attitude control of vertical recovery and landing, the amount of command allocation calculation is too large, the reliability is low, and it will also increase the fuel load, resulting in an increase in rocket mass, which does not meet the actual engineering needs of rocket vertical recovery and landing lightweighting. Summary of the Invention

[0007] To address the issues of complex structures, redundant functions of multiple thrusters, and excessive computational burden in existing pitch and roll channel attitude control methods, which make them unsuitable for vertical recovery and landing attitude control, this invention proposes a rocket vertical recovery and landing attitude control method based on a combination of RCS and oscillating nozzle control.

[0008] The inventive concept of this invention:

[0009] During the applicant's practical engineering verification of the attitude control problem for the vertical landing phase of a rocket, considering the recovery requirements of vertical landing, it was necessary to control the attitude of the rocket's pitch and roll channels using pulse-type commands. However, due to the high computational accuracy requirements for vertical landing and recovery, the computational complexity of the 12 thrusters increased exponentially, requiring an excessive amount of computational resources. This made it difficult to solve the control commands in real time, often leaving more computational time margin, which resulted in an increase in the rocket's reserved fuel load, failing to meet the practical engineering needs of lightweight vertical landing. This invention reduces the number of thrusters from 12 to 6, reducing the computational load and thruster consumption. It can solve for the optimal time for rocket engine re-ignition, delaying the ignition time, thereby meeting the high-precision computational requirements for real-time control command solution, while simultaneously reducing fuel consumption.

[0010] Therefore, as Figure 15As shown, this invention first reduces the number of thrusters from 12 to 6 and establishes a usage strategy model, thereby creating a new rocket dynamics and kinematic model. To avoid rocket roll and the resulting decrease in rocket control performance, an attitude angle controller for the pitch and roll channels is designed by solving equivalent rudder deflection commands to maintain rocket stability. However, the actuators of the two channels interfere with each other, resulting in control coupling. Therefore, a PWM modulation stage is introduced to convert the continuous torque into an RCS switching command that conforms to engineering implementation. A periodic control solution is adopted to solve the RCS interference problem of the pitch and roll channels. Then, the controller parameters corresponding to the two actuators are calculated and the solution is obtained. The control commands for calculating the RCS are used to design the rocket engine oscillating nozzle control system and the RCS power-assisted control system, respectively. The attitude control of each channel is realized based on the periodic control scheme. Finally, by establishing the dynamic equations of the rocket's vertical recovery segment, and based on the constraints of the rocket's vertical recovery landing segment set according to actual requirements, the rocket mass at the end of the vertical recovery landing segment is used as the performance index. The optimal time for the rocket's re-ignition is solved using the trajectory planning method, and the rocket fuel loading amount can be calculated based on this. This calculation is then handed over to the actuators for execution, serving as reference values ​​for the rocket's re-ignition time and rocket fuel loading amount in the actual engineering design process.

[0011] To achieve the above objectives, the technical solution provided by this invention is:

[0012] A method for attitude control during the vertical recovery and landing phase of a rocket using a combination of RCS and oscillating nozzle control is characterized by the following steps:

[0013] Step 1: Establish a usage strategy model for the 6 RCS thrusters;

[0014] Step 2: Establish the dynamics and kinematics model of the arrow body;

[0015] Step 3: Design an attitude angle controller for two channels;

[0016] Step 4: Calculate the control command based on the RCS of the PWM waveform;

[0017] Step 5: Determine the optimal time for the rocket engine to reignite, including the following sub-steps:

[0018] Step 5.1: Establish a periodic control scheme and select the control period;

[0019] Step 5.2: Establish the dynamic equations for the vertical recovery and landing phase of the rocket;

[0020] Step 5.3: Set the constraints on the rocket's vertical recovery and landing segment according to actual requirements, including initial state constraints, engine throttle constraints, attitude angular rate constraints, rocket mass constraints, and terminal state constraints. Use the rocket mass at the terminal moment of the vertical recovery and landing segment as the performance index to establish the trajectory optimization problem for the rocket's vertical recovery and landing segment.

[0021] Step 5.4: Solve for the optimal time for the rocket engine to reignite in the trajectory optimization problem of the rocket's vertical recovery landing segment in Step 5.3.

[0022] Furthermore,

[0023] Step 1.1: Define the positive direction of the oscillation direction of the oscillating nozzle;

[0024] The projection of the rocket engine's oscillation direction onto the rocket body's YOZ plane can form any angle with the rocket body's Y-axis or Z-axis, with the maximum angle with the negative X-axis being δ. max Looking from the tail of the rocket towards the head, the X-axis is perpendicular to the paper and points inward, the Y-axis is upward, and the Z-axis is to the right, which conforms to the right-hand rule. The oscillating nozzle oscillates in the positive direction of the Y-axis in the pitch channel.

[0025] Step 1.2: Arrange the six thrusters in a "T" shape at the nose of the rocket, respectively in the roll channel, pitch channel, and radial direction;

[0026] Six thrusters are used, divided into two groups and set at both ends of the Z-axis. Three thrusters in one group point in the positive Y-axis direction, negative Y-axis direction, and positive Z-axis direction, respectively. Three thrusters in the other group point in the positive Y-axis direction, negative Y-axis direction, and negative Z-axis direction, respectively.

[0027] Step 1.3: Define the RCS thruster usage strategy and assign functions to each RCS thruster.

[0028] Furthermore,

[0029] Step 2.1: Perform small-disturbance linearization modeling for the pitch channel, with the transfer function as follows:

[0030]

[0031] in, ω is the pitch angle. z For pitch rate, δ z The angle of attack is the equivalent elevator deflection, α is the angle of attack, and n is the angle of attack. y For the overload of the Y-axis of the rocket body, θ is the trajectory angle, V is the velocity, a1 is the pitch damping dynamic coefficient, a2 is the pitch static stability dynamic coefficient, a3 is the pitch control dynamic coefficient, a4 is the pitch normal force dynamic coefficient, a5 is the pitch control surface dynamic coefficient, and g is the gravity constant.

[0032] Step 2.2: Perform small-disturbance linearization modeling on the roll channel;

[0033] The transfer function is:

[0034]

[0035] Where γ is the roll angle, ω x δ is the roll rate. x b1 is the equivalent aileron deflection angle, b2 is the roll damping dynamic coefficient, and b2 is the roll control dynamic coefficient.

[0036] Furthermore,

[0037] Step 3.1: Calculate the control dynamic coefficient a3 and design the rocket pitch channel attitude angle controller;

[0038] The formula for calculating the control power coefficient a3 is:

[0039]

[0040] in, J is the partial derivative of the pitch moment with respect to a 1° equivalent elevator deflection. z Let F be the moment of inertia of the rocket along its Z-axis. RCS This indicates the magnitude of the thrust of the thruster, where P is the rocket engine thrust and L is the thrust. p X is the distance from the point of thrust application to the apex of the rocket. cg This is the distance from the center of mass to the apex of the rocket;

[0041] For a sway nozzle, a 1° deflection angle is defined as a 1° equivalent elevator deflection angle, and the partial derivative of the pitch moment with respect to the 1° equivalent elevator deflection angle is used as the basis for this definition. Calculate the control force coefficient a3;

[0042] For the RCS thruster, one RCS element is defined as a 1° equivalent elevator deflection angle, and according to... Calculate the control power coefficient a3. The equivalent elevator deflection angle is the number of RCS units that need to be activated.

[0043] Step 3.2: Calculate the control dynamic coefficient b2 and design the rocket roll channel attitude angle controller;

[0044] The formula for calculating the handling power coefficient b2 is:

[0045]

[0046] in, J is the partial derivative of the rolling moment with respect to a 1° equivalent aileron deflection angle. x Let D be the moment of inertia of the rocket along its X-axis. refGiven the rocket diameter, one RCS element is defined as an equivalent aileron deflection angle of 1°. The size of the equivalent aileron deflection angle is then the number of RCS elements that need to be activated.

[0047] Step 3.3: Calculate the parameters of the controllers corresponding to the two actuators;

[0048] Using the pole placement method, the parameter K of the pitch channel attitude angle controller is calculated separately. w , and And the parameter K of the roll channel attitude angle controller γ K γI and K wx ;

[0049] Furthermore,

[0050] Step 4.1: Define the thrust of the nozzle in the RCS based on the jet characteristics of the RCS;

[0051] Because the jet flow rate of the RCS is difficult to adjust uniformly and continuously, once the RCS is open, the thrust generated by its nozzle cannot be adjusted. Therefore, the RCS nozzle only has two states: open and closed. The mathematical description of the thrust of the nozzle in the RCS is as follows:

[0052]

[0053] Among them, F i F represents the thrust generated by the i-th nozzle. RCS is the reaction thrust of the nozzle; U is the nozzle switching command, 0 means off, 1 means on;

[0054] Step 4.2: Perform PWM waveform modulation;

[0055] Step 4.3: Calculate the on-time of the RCS in each control cycle;

[0056]

[0057] Where, τ n This represents the pulse width of the nth control cycle; T is the controller's calculation cycle.

[0058] Step 4.4: Calculate the fixed torque generated by the RCS during the control cycle. The calculation formula is as follows:

[0059]

[0060] Furthermore,

[0061] Step 5.4 employs the Gauss pseudospectral method to solve for the optimal time for the rocket engine to reignite in the trajectory optimization problem of the rocket's vertical recovery landing segment in step 5.3.

[0062] The advantages of this invention are:

[0063] 1. This invention utilizes trajectory planning to optimize the design of rocket engine re-ignition timing, and reduces the rocket's reserved fuel load while meeting real-time computational requirements. As a reference value for rocket re-ignition timing and rocket fuel load in actual engineering design, it provides a reference basis for improving rocket carrying efficiency and rocket lightweighting in practical engineering design.

[0064] 2. This invention introduces a PWM modulation stage to convert continuous torque into RCS switching commands that conform to engineering implementation. It also adopts a periodic control solution to address the RCS interference problem in the pitch and roll channels. In engineering terms, this invention can meet the design requirements of a rocket landing smoothly in a vertical attitude under the constraint of limited fuel.

[0065] 3. This invention uses only 6 thrusters to control the attitude of the rocket's pitch and roll channels. The attitude control of the two channels is carried out alternately through a periodic control scheme. The number of control units is small, the reliability is high, and the gas consumption of RCS is reduced, thus reducing the rocket's mass. Attached Figure Description

[0066] Figure 1 Flowchart of attitude control process for the pitch channel of the rocket's vertical recovery and landing section;

[0067] Figure 2 Flowchart of attitude control process for the roll channel of the rocket's vertical recovery landing section;

[0068] Figure 3 Schematic diagram defining the positive direction of the rocket pitch channel nozzle oscillation;

[0069] Figure 4 : A schematic diagram of the distribution and installation of one RCS unit of a rocket;

[0070] Figure 5 Schematic diagram of the definition of the positive deflection direction of the rudder equivalent to the RCS of the rocket pitch channel;

[0071] Figure 6 Schematic diagram of the definition of the positive deflection direction of the rudder equivalent to the RCS of the rocket roll channel;

[0072] Figure 7 : Block diagram of rocket pitch channel attitude angle controller;

[0073] Figure 8 : Block diagram of the rocket roll channel attitude angle controller;

[0074] Figure 9 : Curve showing the change in altitude of the rocket's vertical recovery landing section over time;

[0075] Figure 10 : Pitch angle tracking command curve for the rocket's vertical recovery and landing phase;

[0076] Figure 11 : Roll angle tracking command curve for the rocket's vertical recovery and landing phase;

[0077] Figure 12 A diagram comparing fuel consumption between optimized ignition timing and early ignition in rockets;

[0078] Figure 13 A diagram comparing the throttle commands for optimized rocket ignition timing and early ignition.

[0079] Figure 14 : Schematic diagram of the rocket engine's swing direction;

[0080] Figure 15 Flowchart of attitude control method for rocket vertical recovery and landing phase. Detailed Implementation

[0081] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0082] A method for attitude control during the vertical recovery and landing phase of a rocket using a combination of RCS and oscillating nozzle control includes the following steps:

[0083] Step 1: Establish the usage strategy model for the 6 RCS thrusters, including the following sub-steps:

[0084] Step 1.1: Define the positive direction of the oscillation direction of the oscillating nozzle;

[0085] like Figure 14 As shown, the projection of the rocket engine's oscillation direction onto the rocket body's YOZ plane can form any angle with the rocket body's Y-axis or Z-axis, with the maximum angle with the negative X-axis being δ. max ;like Figure 3 As shown, looking from the tail of the rocket towards the head, the X-axis is perpendicular to the paper and points inward, the Y-axis is upward, and the Z-axis is to the right, which conforms to the right-hand rule. The oscillating nozzle oscillates in the positive direction of the Y-axis in the pitch channel.

[0086] Step 1.2: Arrange the six thrusters in a "T" shape at the nose of the rocket, respectively in the roll channel, pitch channel, and radial direction;

[0087] like Figure 4 , Figure 5 , Figure 6As shown, in this embodiment, six thrusters are used, divided into two groups and respectively set at both ends of the Z-axis. The three thrusters in one group point in the positive Y-axis direction, the negative Y-axis direction, and the positive Z-axis direction, respectively. The three thrusters in the other group point in the positive Y-axis direction, the negative Y-axis direction, and the negative Z-axis direction, respectively.

[0088] Step 1.3: Define the RCS thruster usage strategy and assign functions to each RCS thruster;

[0089]

[0090]

[0091] Wherein: F RCS The thrust of the thruster is indicated by D, the diameter of the rocket body is indicated by L. RCS This indicates the distance from the point of application of the thrust to the center of mass;

[0092] Step 2: Establish the dynamics and kinematics model of the arrow body;

[0093] Step 2.1: Perform small-disturbance linearization modeling for the pitch channel;

[0094] Considering Earth's gravity, centrifugal inertial force, and Gothic inertial force, aerodynamic data of the rocket is extracted based on the nominal ballistic data. Based on the rigid body motion assumption of the rocket, a small-perturbation linearization model is performed on the pitch channel to establish a standard ellipsoidal model of the standard Earth. The transfer function is:

[0095]

[0096] in, ω is the pitch angle. z For pitch rate, δ z The angle of attack is the equivalent elevator deflection, α is the angle of attack, and n is the angle of attack. y For the overload of the Y-axis of the rocket body, θ is the trajectory angle, V is the velocity, a1 is the pitch damping dynamic coefficient, a2 is the pitch static stability dynamic coefficient, a3 is the pitch control dynamic coefficient, a4 is the pitch normal force dynamic coefficient, a5 is the pitch control surface dynamic coefficient, and g is the gravity constant.

[0097] Step 2.2: Perform small-disturbance linearization modeling on the roll channel;

[0098] The transfer function is:

[0099]

[0100] Where γ is the roll angle, ω x δ is the roll rate. x b1 is the equivalent aileron deflection angle, b2 is the roll damping dynamic coefficient, and b2 is the roll control dynamic coefficient.

[0101] Step 3: By solving the equivalent rudder deflection command, design the attitude angle controller for two channels and design the rocket engine oscillating nozzle control system;

[0102] like Figure 1 As shown, the execution logic of the pitch channel attitude angle controller is as follows:

[0103] First, the deviation between the pitch angle command value and the current rocket pitch angle is obtained. Then, depending on whether the rocket engine is running, the appropriate actuator is selected. If the engine is running, the pitch channel PID algorithm with the oscillating nozzle as the actuator is used to calculate the oscillation angle command of the oscillating nozzle. This command is input to the servo that controls the oscillation of the oscillating nozzle to complete the oscillation command, thereby generating the corresponding control torque. If the engine is off, the pitch channel PID algorithm with the RCS as the actuator is used to calculate the number of RCS units that need to be activated. This number is used as the value of the PWM wave duty cycle. Then, the PWM wave generator is used to generate a PWM wave with the corresponding duty cycle. The generated PWM wave is used as the switching command of the RCS to control the RCS to generate the corresponding reverse thrust, thereby generating the corresponding control torque. Finally, it is determined whether the rocket has reached the ground. If it has not yet reached the ground, the above control process is repeated. If it has reached the ground, the operation of the pitch channel attitude angle controller is stopped.

[0104] like Figure 2 As shown, the execution logic of the roll channel attitude angle controller is as follows:

[0105] First, the deviation between the roll angle command value and the current roll angle of the rocket is obtained. The PID algorithm of the roll channel with RCS as the actuator is used to calculate the number of RCS units that need to be activated, and this number is used as the value of the PWM wave duty cycle. Then, a PWM wave with a corresponding duty cycle is generated using a PWM wave generator. The generated PWM wave is used as the switching command of the RCS to control the RCS to generate the corresponding reverse thrust, thereby generating the corresponding control torque. Finally, it is determined whether the rocket has reached the ground. If it has not yet reached the ground, the above control process is repeated. If it has reached the ground, the operation of the roll channel attitude angle controller is stopped.

[0106] Step 3.1: Calculate the control dynamic coefficient a3 and design the rocket pitch channel attitude angle controller;

[0107] Before ignition, the torque provided by the reaction thrust generated by the RCS is used to control the attitude of the rocket's pitch channel. After ignition, the torque provided by the thrust generated by the oscillating nozzle is used to control the attitude of the rocket's pitch channel.

[0108] Among them, such as Figure 7As shown, the pitch channel attitude angle controller consists of a pitch rate damping loop and a pitch feedback loop. The pitch rate damping loop is used to improve the system damping and enhance the anti-interference capability, while the pitch feedback loop is used to achieve pitch angle stability. In addition, an integral term is added to eliminate the static error of the system.

[0109] The formula for calculating the control power coefficient a3 is:

[0110]

[0111] in, J is the partial derivative of the pitch moment with respect to a 1° equivalent elevator deflection. z Let F be the moment of inertia of the rocket along its Z-axis. RCS This indicates the magnitude of the thrust of the thruster, where P is the rocket engine thrust and L is the thrust. p X is the distance from the point of thrust application to the apex of the rocket. cg This is the distance from the center of mass to the apex of the rocket;

[0112] For a sway nozzle, a 1° deflection angle is defined as a 1° equivalent elevator deflection angle, and the partial derivative of the pitch moment with respect to the 1° equivalent elevator deflection angle is used as the basis for this definition. Calculate the control force coefficient a3;

[0113] For the RCS thruster, one RCS element is defined as a 1° equivalent elevator deflection angle, and according to... Calculate the control power coefficient a3. The equivalent elevator deflection angle is the number of RCS units that need to be activated.

[0114] Step 3.2: Select the control dynamic coefficient b2 and design the rocket roll channel attitude angle controller;

[0115] like Figure 8 As shown, the roll channel attitude angle controller consists of a roll rate damping loop and a roll angle feedback loop. The roll rate damping loop is used to improve the system damping and enhance the anti-interference capability, while the roll angle feedback loop is used to achieve roll angle stability. In addition, an integral term is added to eliminate the static error of the system.

[0116] If the rocket roll channel uses only the torque provided by the reaction thrust generated by the RCS for attitude control, then the formula for calculating the control dynamic coefficient b2 is:

[0117]

[0118] in, J is the partial derivative of the rolling moment with respect to a 1° equivalent aileron deflection angle. x Let D be the moment of inertia of the rocket along its X-axis. refGiven the rocket diameter, one RCS element is defined as an equivalent aileron deflection angle of 1°. The size of the equivalent aileron deflection angle is then the number of RCS elements that need to be activated.

[0119] Step 3.3: Calculate the parameters of the controllers corresponding to the two actuators;

[0120] Using the pole placement method, the parameter K of the pitch channel attitude angle controller is calculated separately. w , and And the parameter K of the roll channel attitude angle controller γ K γI and K wx ;

[0121] Step 4: Based on the control command calculated from the PWM wave, design the RCS power-assisted control system;

[0122] Step 4.1: Define the thrust of the nozzle in the RCS based on the jet characteristics of the RCS;

[0123] Because the jet flow rate of the RCS is difficult to adjust uniformly and continuously, once the RCS is open, the thrust generated by its nozzle cannot be adjusted. Therefore, the RCS nozzle only has two states: open and closed. The mathematical description of the thrust of the nozzle in the RCS is as follows:

[0124]

[0125] Among them, F i F represents the thrust generated by the i-th nozzle. RCS is the reaction thrust of the nozzle; U is the nozzle switching command, 0 means off, 1 means on;

[0126] Step 4.2: Perform PWM waveform modulation;

[0127] The continuous torque in step 3 is modulated into an RCS switching command U, which controls the RCS to generate discrete torques M with different pulse widths. RCS This ensures that the torque impulse is the same in each control cycle, achieving the same control effect as the continuous torque M.

[0128] Step 4.3: Due to the discrete torque M RCS Since the pulse widths are different, the on-time of RCS in each control cycle is calculated;

[0129] Considering the discrete operating characteristics of the actuator's RCS, the continuous torque M required for matching control cannot be directly generated. r Therefore, a PWM wave modulation stage needs to be introduced to modulate the continuous torque M. r The switching command U, modulated into RCS, controls the RCS to generate discrete torques M with different pulse widths.RCS This achieves the same control effect as continuous torque.

[0130] According to the PWM modulation principle, the mathematical description of equal torque impulse in each control cycle is:

[0131]

[0132] Where, τ n M(t) represents the pulse width of the nth control cycle; M(t) represents the torque of the discrete torque at time t.

[0133] Due to the torque M calculated by the control law r It is a continuous torque, a fixed torque M with different pulse widths generated by RCS. RCS It is a discrete torque, therefore the on-time τ of the RCS in each control cycle n for:

[0134]

[0135] Where T is the calculation cycle of the controller;

[0136] Step 4.4: Calculate the fixed torque generated by the RCS;

[0137] The fixed torque M generated by RCS RCS The calculation formula is:

[0138]

[0139] Step 5: Determine the optimal time for the rocket engine to reignite;

[0140] Step 5.1: Establish a periodic control scheme and select the control period;

[0141] To prevent interference and control coupling in some RCS thrusters when simultaneously controlling the pitch and roll paths using the RCS, a control period T is selected. c The pitch and roll channels are controlled separately in cycles;

[0142] Step 5.2: Based on the rocket engine oscillating nozzle control system and the RCS power-assisted control system, establish the dynamic equations for the rocket's vertical recovery and landing phase;

[0143] Step 5.3: Set the constraints on the rocket's vertical recovery and landing segment according to actual requirements, including initial state constraints, engine throttle constraints, attitude angular rate constraints, rocket mass constraints, and terminal state constraints. Use the rocket mass at the terminal moment of the vertical recovery and landing segment as the performance index to establish the trajectory optimization problem for the rocket's vertical recovery and landing segment.

[0144] Step 5.4: Use the Gauss pseudospectral method to solve for the optimal timing of re-ignition in the trajectory optimization problem of the rocket's vertical recovery landing segment in Step 5.3;

[0145] A rocket attitude control method based on a combination of RCS and oscillating nozzle control was used for the vertical recovery and landing phase. A six-degree-of-freedom attitude control digital simulation was performed, and the simulation results are as follows: Figures 9 to 13 As shown:

[0146] Appendix Figure 9 The curve showing the change of rocket altitude over time shows that the slope of the curve gradually decreases and approaches 0, indicating that the rocket's descent speed gradually decreases to 0 as it approaches the ground, proving that the rocket achieved a smooth landing.

[0147] Appendix Figure 10 The curve shows that the rocket's pitch angle tracking effect on control commands is fast and stable, and can maintain the rocket's vertical landing attitude during descent.

[0148] Appendix Figure 11 The curve shows that the rocket's roll angle tracking effect on control commands is effective. As can be seen from the curve, the rocket's roll attitude angle controller can quickly and stably track control commands and maintain the rocket's attitude stability.

[0149] Appendix Figure 12 This indicates that the rocket consumes less fuel during the descent phase when igniting at the optimal time compared to igniting earlier.

[0150] Appendix Figure 13 The comparison of throttle commands for rocket ignition at the optimal time and ignition in advance shows that ignition at the optimal time allows the rocket engine to decelerate and land at full throttle. At this time, the engine works efficiently and for a short time, thereby reducing fuel consumption during the rocket's descent.

[0151] Simulation results show that the attitude control method for the vertical landing phase of a rocket, which employs a combination of RCS and oscillating nozzle control, involves dynamic and kinematic modeling of the rocket, designing a rocket engine oscillating nozzle control system and an RCS power-assisted control system, and using trajectory planning to design the rocket engine re-ignition timing. This method fully considers engineering feasibility and, under the constraints of limited fuel load and the control capability of the attitude control propulsion system's RCS, achieves high attitude control accuracy and low fuel consumption during the vertical landing phase, ensuring a smooth vertical landing and meeting the attitude control requirements for the vertical landing phase.

[0152] 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 attitude control of a rocket's vertical recovery and landing phase using a combination of RCS and oscillating nozzle control, characterized in that, Includes the following steps: Step 1: Establish a usage strategy model for the 6 RCS thrusters; specifically: Step 1.1: Define the positive direction of the oscillation direction of the oscillating nozzle; The projection of the rocket engine's oscillation direction onto the rocket body's YOZ plane can form any angle with the rocket body's Y-axis or Z-axis, with the maximum angle with the negative X-axis being... Looking from the tail of the rocket towards the head, the X-axis is perpendicular to the paper and points inward, the Y-axis is upward, and the Z-axis is to the right, which conforms to the right-hand rule. The oscillating nozzle oscillates in the positive direction of the Y-axis in the pitch channel. Step 1.2: Arrange the six thrusters in a "T" shape at the head of the rocket, respectively in the roll channel, pitch channel, and radial direction; The six thrusters are divided into two groups and set at both ends of the Z-axis. The three thrusters in one group point in the positive Y-axis direction, the negative Y-axis direction, and the positive Z-axis direction, respectively. The three thrusters in the other group point in the positive Y-axis direction, the negative Y-axis direction, and the negative Z-axis direction, respectively. Step 1.3: Define the RCS thruster usage strategy and assign functions to each RCS thruster; Step 2: Establish the dynamics and kinematics model of the arrow body; Step 3: Design an attitude angle controller for two channels; Step 4: Control instructions based on PWM wave RCS calculation; specifically: Step 4.1: Define the thrust of the nozzle in the RCS based on the jet characteristics of the RCS; Because the jet flow rate of the RCS is difficult to adjust uniformly and continuously, once the RCS is open, the thrust generated by its nozzle cannot be adjusted. Therefore, the RCS nozzle only has two states: open and closed. The mathematical description of the thrust of the nozzle in the RCS is as follows: in, The thrust generated by the i-th nozzle; This is the reaction thrust of the nozzle; This is the on / off command for the nozzle; 0 indicates off, and 1 indicates on. Step 4.2: Perform PWM waveform modulation; Step 4.3: Calculate the on-time of the RCS in each control cycle; in, This represents the pulse width of the nth control cycle; T is the controller's calculation cycle. Indicates continuous torque. Represents discrete torque; Step 4.4: Calculate the fixed torque generated by the RCS during the control cycle. The calculation formula is as follows: ； Step 5: Determine the optimal time for the rocket engine to reignite, including the following sub-steps: Step 5.1: Establish a periodic control scheme and select the control period; Step 5.2: Establish the dynamic equations for the vertical recovery and landing phase of the rocket; Step 5.3: Set the constraints on the rocket's vertical recovery and landing segment according to actual requirements, including initial state constraints, engine throttle constraints, attitude angular rate constraints, rocket mass constraints, and terminal state constraints. Use the rocket mass at the terminal moment of the vertical recovery and landing segment as the performance index to establish the trajectory optimization problem for the rocket's vertical recovery and landing segment. Step 5.4: Solve for the optimal time for the rocket engine to reignite in the trajectory optimization problem of the rocket's vertical recovery landing segment in Step 5.

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2. The attitude control method for the vertical recovery and landing phase of a rocket using a combination of RCS and oscillating nozzle control as described in claim 1, characterized in that, Step 2 includes the following sub-steps: Step 2.1: Perform small-disturbance linearization modeling for the pitch channel, with the transfer function as follows: in, The pitch angle, For pitch rate, This is the equivalent elevator deflection angle. For the angle of attack, For overload of the Y-axis of the rocket body, For the trajectory inclination angle, For speed, The pitch damping dynamic coefficient is... The dynamic coefficient for pitch static stability is... For pitch control dynamic coefficient, The dynamic coefficient of the pitch normal force. For pitch control surface dynamics, It is the gravitational constant; Step 2.2: Perform small-disturbance linearization modeling on the roll channel; The transfer function is: in, For roll angle, For the roll rate, For the equivalent aileron deflection, The rolling damping dynamic coefficient is... This is the rolling control power coefficient.

3. The attitude control method for the vertical recovery and landing phase of a rocket using a combination of RCS and oscillating nozzle control as described in claim 2, characterized in that, Step 3 includes the following sub-steps: Step 3.1: Calculate the pitch control dynamic coefficient Design a rocket pitch channel attitude angle controller; Pitch control dynamic coefficient The calculation formula is: in, Let be the partial derivative of the pitch moment with respect to a 1° equivalent elevator deflection. Let Z be the moment of inertia of the rocket along its Z-axis. This indicates the magnitude of the thrust of the thruster, where P is the rocket engine thrust. This is the distance from the point of thrust application to the apex of the rocket. This is the distance from the center of mass to the apex of the rocket; For a sway nozzle, a 1° deflection angle is defined as a 1° equivalent elevator deflection angle, and the partial derivative of the pitch moment with respect to the 1° equivalent elevator deflection angle is used as the basis for this definition. Calculate pitch control dynamic coefficients ; For the RCS thruster, one RCS element is defined as a 1° equivalent elevator deflection angle, and according to... Calculate pitch control dynamic coefficients At this point, the equivalent elevator deflection angle is the number of RCS units that need to be activated. Step 3.2: Calculate the roll control dynamic coefficient Design a rocket roll channel attitude angle controller; Roll control dynamic coefficient The calculation formula is: in, Let be the partial derivative of the rolling moment with respect to a 1° equivalent aileron deflection angle. Let be the moment of inertia of the rocket along its X-axis. Given the rocket diameter, one RCS element is defined as an equivalent aileron deflection angle of 1°. The size of the equivalent aileron deflection angle is then the number of RCS elements that need to be activated. Step 3.3: Calculate the parameters of the controllers corresponding to the two actuators; The pole placement method is used to calculate the parameters of the pitch channel attitude angle controller. , and And the parameters of the roll channel attitude angle controller. , and .

4. The attitude control method for the vertical recovery and landing phase of a rocket using a combination of RCS and oscillating nozzle control as described in claim 1, characterized in that: Step 5.4 employs the Gauss pseudospectral method to solve for the optimal time for the rocket engine to reignite in the trajectory optimization problem of the rocket's vertical recovery landing segment in step 5.3.

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