A morphing aircraft reentry guidance method based on constraint adaptive adjustment

Abstract

The application provides a morphing aircraft reentry guidance method based on constraint adaptive adjustment, and belongs to the field of aircraft guidance, which comprises the following steps: constructing a reentry guidance model with an attack angle, a roll angle, a span length and a sweepback angle as variables; designing a lateral guidance law based on a heading error based on the reentry guidance model, and calculating an aerodynamic lift coefficient required by current guidance in real time to make an indirect longitudinal guidance law; designing a terminal velocity constraint condition which is adaptively adjusted in real time according to a flight state; constructing a longitudinal guidance optimization model of the morphing aircraft; calculating the longitudinal guidance optimization model to obtain the span length, the sweepback angle and the attack angle as a longitudinal guidance law, and combining the lateral guidance law to realize online guidance of the morphing aircraft with configuration change as an auxiliary under terminal target switching. The application can realize multi-dimensional constraint and reentry guidance of the morphing aircraft under terminal target switching in a certain range.

Description

Technical Field

[0001] This invention belongs to the field of aircraft guidance, specifically relating to a reentry guidance method for variable-structure aircraft based on constraint adaptive adjustment. Background Technology

[0002] Modularly configured aircraft, by altering the wingspan, sweep, and tail section, can improve aerodynamic characteristics and enhance maneuverability, showing broad application prospects in aerospace transportation, emergency rescue, and modern agriculture. With advancements in materials science and intelligent control technologies, modularity has become a crucial development direction for next-generation aerospace vehicles, including reusable and space-to-space vehicles. Reentry guidance is key to the precise achievement of the reentry trajectory and terminal target for aerospace vehicles, and superior guidance laws are essential for the safe, accurate, and efficient completion of reentry missions. During reentry, the aircraft improves its aerodynamic characteristics through configuration changes, potentially reducing the rudder deflection load required for guidance. However, the strong coupling between configuration and aerodynamic characteristics means that the reentry corridor, composed of aerodynamic overload, heat flux density, and dynamic pressure, dynamically changes during configuration changes. Guidance commands must be matched in real-time to the aerodynamic characteristics under the current configuration to avoid touching the reentry corridor and affecting the reentry mission's success. In mission spaces with large airspace, wide speed range, and target reconstruction, the dynamic strong coupling relationship between configuration, aerodynamic characteristics, and reentry corridor poses challenges to the reentry guidance technology of variable-configuration aircraft.

[0003] Existing research on guidance problems for fixed-configuration aircraft is relatively abundant. The literature "Energy Tube Control Guidance Method for Long-Range Maneuvering Aircraft" (Tong Wei, Jia Pinghui, Zhang Ning, et al. Energy Tube Control Guidance Method for Long-Range Maneuvering Aircraft [J]. Missiles and Space Launch Vehicle Technology, 2021, (4): 88-92.) provides an energy tube control guidance method, which uses an energy management method to correct flight altitude online for terminal velocity control. It has the advantages of high terminal velocity accuracy and easy engineering implementation. However, guidance methods for fixed-configuration aircraft do not involve the coupling changes of aircraft configuration and aerodynamic characteristics. Therefore, velocity control requires sacrificing terminal altitude control accuracy. Moreover, this method does not address the feasible range of terminal velocity and ignores the limitations imposed by process constraints on terminal velocity. Some methodological research has been conducted both domestically and internationally on the guidance problem of deformable aircraft. The literature "Guidance Method for No-Fly Zone Evasion of Retractable Deformable Aircraft" (Zheng Jinku, Yao Qingrui, Huang Ding, et al. Guidance Method for No-Fly Zone Evasion of Retractable Deformable Aircraft [J]. Tactical Missile Technology, 2024, (4): 64-71+102.) utilizes the additional maneuverability brought by the deformability to meet the requirements of maneuver evasion missions. In the guidance process, the configuration state is preset as a discrete state. It does not involve continuous deformation or reentry guidance under terminal target switching requirements, and the utilization of deformation is not yet sufficient. In view of the reentry guidance mission requirements under terminal target switching within a certain range, a new reentry guidance method for deformable aircraft is urgently needed, which uses configuration change to assist guidance and considers the dynamic strong coupling relationship between configuration, aerodynamic characteristics and reentry corridor. Summary of the Invention

[0004] To address the shortcomings of existing methods in terms of autonomy regarding the utilization of aerodynamic improvements introduced by configuration changes and dynamic matching of reentry corridors, this invention proposes a constraint-adaptive adjustment-based reentry guidance method for variable-configuration aircraft, targeting reentry guidance missions under terminal target switching within a certain range. From the perspective of configuration-assisted guidance, within a predictive correction guidance framework, a terminal velocity constraint condition that adaptively adjusts in real time according to flight status is designed. An optimized reentry guidance model for the variable-configuration aircraft is constructed, and the optimal angle of attack and deformation are calculated in real time using a sequential quadratic programming algorithm. Combined with a lateral guidance law, online guidance for variable-configuration aircraft with configuration changes as an aid is achieved under multi-dimensional constraints and terminal target switching. This invention can realize reentry guidance for variable-configuration aircraft under multi-dimensional constraints and terminal target switching within a certain range.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment includes the following steps:

[0007] The first step is to construct a reentry guidance model based on the kinematics and dynamics model of the variable-structure aircraft, combined with process constraints and terminal constraints, with angle of attack, bank angle, span, and sweep angle as variables.

[0008] The second step is to design a lateral guidance law based on the reentry guidance model and the quasi-equilibrium gliding condition and prediction correction algorithm to calculate the aerodynamic lift coefficient required for the current guidance in real time and make an indirect longitudinal guidance law.

[0009] The third step is to introduce terminal velocity prediction variables that are related to aerodynamic drag and terminal altitude, and design terminal velocity constraints that are adaptively adjusted in real time according to flight status.

[0010] The fourth step is to construct a longitudinal guidance optimization model for the variable-structure aircraft, with the minimum drag coefficient of the aircraft as the optimization objective, the angle of attack, the roll angle, and the span as longitudinal guidance variables, and the indirect longitudinal guidance law, the range constraint of the guidance variable, the rate of change constraint of the guidance variable, the aerodynamic coefficient constraint, and the terminal velocity constraint as comprehensive constraints.

[0011] The fifth step is to solve the longitudinal guidance optimization model to obtain the longitudinal guidance law formed by the span, sweep angle and angle of attack, and combine it with the lateral guidance law to realize the online guidance of the variable-configuration aircraft with configuration change as an auxiliary under the terminal target switching.

[0012] Beneficial effects:

[0013] To address the reentry guidance problem of variable-configuration aircraft, this invention, under comprehensive constraints including quasi-equilibrium gliding conditions, process constraints, physical constraints, and terminal constraints, ensures the feasibility of the reentry mission by employing a lateral guidance law based on heading error and an indirect longitudinal guidance law based on prediction correction. Configuration parameters are incorporated into the guidance variables to construct a reentry guidance optimization model, which solves for the optimal deformation and angle of attack in real time. Configuration changes are used to minimize aerodynamic drag and increase terminal velocity. Simultaneously, a terminal velocity constraint condition that adaptively adjusts with flight status is designed, combined with aerodynamic coefficient constraints, to achieve real-time dynamic matching between configuration, aerodynamic characteristics, and the reentry corridor. This prevents the aircraft from touching the reentry corridor and ensures the success of the reentry guidance mission. This invention enhances the ability of existing methods to improve aerodynamic characteristics, solves the problem of insufficient autonomy in dynamic matching of the reentry corridor, and realizes online guidance for variable-configuration aircraft with configuration changes as an aid under multi-dimensional constraints and terminal target switching. Attached Figure Description

[0014] Figure 1 This is a flowchart of a constrained adaptive adjustment-based reentry guidance method for a variable-structure aircraft according to the present invention.

[0015] Figure 2 A schematic diagram of the reentry guidance trajectory of the aircraft when switching to the terminal target.

[0016] Figure 3a , Figure 3b This is a curve showing the deformation during the guidance process; among which... Figure 3a For the exhibition length, Figure 3b It is the sweep angle.

[0017] Figure 4 This is a graph showing the predicted flight speed and terminal velocity during the guidance process. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0019] like Figure 1 As shown, the reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment proposed in this invention includes the following steps:

[0020] The first step is to construct a reentry guidance model based on the kinematics and dynamics model of the variable-structure aircraft, combined with process constraints and terminal constraints, with angle of attack, bank angle, span, and sweep angle as variables.

[0021] The second step is to design a lateral guidance law based on the reentry guidance model and the quasi-equilibrium gliding condition and prediction correction algorithm to calculate the aerodynamic lift coefficient required for the current guidance in real time and make an indirect longitudinal guidance law.

[0022] The third step is to introduce terminal velocity prediction variables that are related to aerodynamic drag and terminal altitude, and design terminal velocity constraints that are adaptively adjusted in real time according to flight status.

[0023] The fourth step is to construct a longitudinal guidance optimization model for the variable-structure aircraft, with the minimum drag coefficient of the aircraft as the optimization objective, the angle of attack, the roll angle, and the span as longitudinal guidance variables, and the indirect longitudinal guidance law, the range constraint of the guidance variable, the rate of change constraint of the guidance variable, the aerodynamic coefficient constraint, and the terminal velocity constraint as comprehensive constraints.

[0024] The fifth step is to solve the longitudinal guidance optimization model to obtain the longitudinal guidance law based on the span, sweep angle, and angle of attack, and combine it with the lateral guidance law to achieve online guidance of the variable-configuration aircraft with configuration changes as an auxiliary under terminal target switching.

[0025] Example:

[0026] Taking a variable-structure aircraft with variable span and sweep angle as the application object, with a maximum span of 1.1m, a minimum span of 0m, a maximum sweep angle of 90 degrees, and a minimum sweep angle of 67 degrees, the specific steps of the present invention are further explained as follows:

[0027] Specifically, the first step includes:

[0028] The kinematic and dynamic model of the variable-structure aircraft is established as follows:

[0029] (1)

[0030] in, The distance from the Earth's center. and They are longitude and latitude, respectively. The velocity of the aircraft in the ground coordinate system. For velocity tilt angle, For speed and heading angle, , , , , , The first derivative of the corresponding variable; and Lift and drag are respectively, expressed as: and ,in and These are the lift coefficient and drag coefficient, respectively. Atmospheric density, For the reference area of ​​the aircraft; The tilt angle, For the mass of the aircraft, This refers to gravitational acceleration. The lift coefficient is... and drag coefficient To the sweep angle Exhibition length ,Mach number Angle of attack Related nonlinear polynomial functions; atmospheric density To match the altitude of the aircraft Related atmospheric index models, ,in Indicates atmospheric density at reference altitude. This indicates the standard atmospheric altitude. For this variable-structure aircraft, the aircraft's mass... Aircraft reference area Atmospheric density at reference altitude Atmospheric standard altitude .

[0031] The process constraints are divided into dynamic pressure constraints, heat flux density constraints, and overload constraints, and their expressions are as follows:

[0032] (2)

[0033] in, For dynamic pressure, For heat flux density, For total overload, This represents the maximum feasible value for dynamic pressure. The maximum feasible value for heat flux density, This represents the maximum feasible value for overload. The constant coefficient, This is the standard gravitational acceleration. (This is for the variable-structure aircraft.) , , , .

[0034] The terminal constraints are:

[0035] (3)

[0036] in, , , The altitude, longitude, and latitude of the terminal target, respectively. , , They are respectively The altitude, longitude, and latitude of the target at all times. Indicates the terminal heading error. This represents the maximum permissible value for the terminal heading error. The superscript T indicates the transpose of the matrix.

[0037] The reentry guidance model of the modified aircraft includes kinematic and dynamic models, process constraints and terminal constraints, with angle of attack, bank angle, span and sweep angle as guidance variables.

[0038] Specifically, the second step includes:

[0039] In this invention, the reentry guidance problem of the variable-structure aircraft is solved from both lateral and longitudinal aspects. Lateral guidance is performed within the heading error corridor framework, with the roll angle as the guidance variable, satisfying the terminal heading error constraint. Longitudinal guidance is performed within the predictive correction guidance framework, around the quasi-equilibrium gliding condition, with deformation and angle of attack as longitudinal guidance variables, satisfying the process constraints and terminal position constraints during reentry.

[0040] In terms of lateral guidance, heading error Defined as the angle between the line of sight from the current position of the aircraft to the terminal target and the velocity direction in the current horizontal plane, the expression is:

[0041] (4)

[0042] in, For heading error, The viewing angle is obtained using spherical trigonometry theory:

[0043] (5)

[0044] To eliminate this heading error, the heel angle amplitude is designed. It is a proportional error gain feedback form:

[0045] (6)

[0046] in, This is the proportional error gain coefficient.

[0047] To meet heading error constraints, a roll angle sign reversal strategy is determined based on the heading error corridor. When the heading error exceeds the constraint upper limit, the roll angle sign is reversed. A typical heading error corridor is set according to the flight speed range, and the boundaries of the corridor are determined iteratively. The design goal is to minimize the number of roll angle reversals while ensuring that the terminal bearing meets accuracy requirements.

[0048] In terms of longitudinal guidance, at the vehicle's velocity tilt angle Smaller and rate of change Under the near-zero assumptions, the expression for the quasi-equilibrium gliding condition is: Lift Lift coefficient in The deformation (sweep angle) in the longitudinal guidance law Exhibition length and angle of attack Related. To obtain the lift coefficient that satisfies the terminal position constraints and quasi-equilibrium gliding conditions, the aircraft's ready-to-fly range is defined. Satisfying the equation The superscript "." indicates the first derivative. For the Earth's radius, Let be the aircraft altitude. Based on the aircraft's kinematics and dynamics equations, a differential relationship exists between the expected flight range and the flight altitude. Considering the current position information of the variable-structure aircraft and terminal target location Integrating, we can obtain:

[0049] (7)

[0050] in, This indicates the flight distance from the current location to the target location. Flight distance Alternatively, a geometric solution can be performed based on the current position and the terminal target position using the spherical triangle theory, then the reference velocity tilt angle can be calculated. .

[0051] To track the reference velocity tilt angle A velocity tilt angle control law is designed using feedback linearization control theory. The known velocity tilt angle derivative equation can be transformed into... ,in The dynamic characteristics of the system are represented by the following expression: , This indicates the control input section, and the expression is: Introducing intermediate control variables satisfy Simplify the equation for the derivative of the velocity angle as follows: ,design It is in the following form:

[0052] (8)

[0053] in, is the time constant. Reference velocity tilt angle The first derivative.

[0054] With the aerodynamic lift coefficient required for current guidance As an indirect longitudinal guidance law, its expression is:

[0055] (9)

[0056] Specifically, the third step includes:

[0057] Introducing terminal speed prediction variables The expression is:

[0058] (10)

[0059] in, To account for the terminal velocity deviation due to atmospheric drag, the expression is: intermediate variables ; To account for the terminal velocity deviation due to Earth's gravity, the expression is: , The Earth's gravitational constant. Terminal velocity predictor variable. Taking into account atmospheric drag and Earth's gravity, an analytical relationship was established that is related to aerodynamic drag and terminal altitude. Typically, the accuracy of terminal velocity prediction is low at the initial moment, and the accuracy increases as the distance to the terminal target increases.

[0060] The terminal velocity constraint is designed to be adaptively adjusted in real time according to flight conditions. ,in The maximum feasible terminal speed based on process constraint transformation.

[0061] Based on the height of the terminal target The maximum permissible terminal speed corresponding to each process constraint is obtained as follows:

[0062] (11)

[0063] in, , , These represent the maximum feasible terminal speeds based on dynamic pressure constraints, heat flux density constraints, and overload constraints at the terminal height, respectively. The maximum feasible terminal speed based on process constraint transformation is also mentioned. The expression is For this variable-structure aircraft, in order to ensure constraint margins, the design... .

[0064] Specifically, in the fourth step, the expression for the longitudinal guidance optimization model of the modified aircraft is as follows:

[0065] (12)

[0066] Here, find means to search, and st means constraint. For the vertical guidance variable to be solved, This indicates that the optimization objective is to minimize the aerodynamic drag coefficient. This represents the objective function to be optimized. This indicates the lift coefficient equation constraint; guidance variable range constraints include... , , ,in , These are the maximum and minimum values ​​of the sweep angle, respectively. , These are the maximum and minimum span values, respectively. , These represent the maximum and minimum angles of attack, respectively; the constraints on the rate of change of guidance variables include... , , ,in , , Let be the first derivatives of the sweep angle, span, and angle of attack, respectively. , , The upper limit of the rate of change of each guidance variable; aerodynamic coefficient constraints include , ,in , The lower limit constraint of the lift coefficient is based on the transformation of quasi-equilibrium gliding conditions and dynamic pressure constraints. This represents the lower limit constraint of the lift coefficient based on the transformation of quasi-equilibrium gliding conditions and heat flux density constraints; , Transformation for overload constraints The upper boundary is expressed as: ; This represents the terminal velocity constraint. For this variable-structure aircraft, the angle-of-attack range constraint is... The constraint magnitude of the rate of change of the guided variable is , , .

[0067] This invention transforms the longitudinal guidance law design problem of a variable-configuration aircraft into a reentry guidance optimization problem. Under the comprehensive constraints of indirect longitudinal guidance law, physical constraints of guidance variables, process constraints, and terminal velocity constraints, deformation and angle of attack are used as optimization variables. Through the real-time solution of this optimization problem, configuration-assisted reentry guidance can be achieved.

[0068] Specifically, the terminal target switching in the fifth step can be defined as:

[0069] (13)

[0070] in, For the time of terminal target switching, , , These are the altitude, longitude, and latitude of the original terminal target, respectively. , , These are the altitude, longitude, and latitude of the new terminal target after the switch; Indicates the switchable range of terminal targets. The angle between the line-of-sight angle and the velocity-heading angle is expressed as follows: , The maximum allowable line-of-sight angle and velocity heading angle are switched for the terminal target. For this variant aircraft, , , , .

[0071] By combining terminal target constraints, based on the longitudinal guidance optimization model, and using the sequential quadratic programming algorithm to solve for the optimal angle of attack and deformation in real time, and combined with the tilt angle obtained by the second-step lateral guidance law, online guidance of the variable-configuration aircraft with configuration changes as an aid is realized under terminal target switching.

[0072] like Figure 2The image shows the reentry guidance trajectory under terminal target switching, as shown below. Figure 3a , Figure 3b The figure shows the deformation curve during the guidance process, where, Figure 3a For the exhibition length, Figure 3b This is the sweep angle. For example... Figure 4 The image shows the predicted flight speed and terminal velocity curves during the guidance process. Analysis Figure 2 , Figure 3a , Figure 3b , Figure 4 It can be seen that during reentry, the reentry trajectory of the deformable spacecraft is relatively stable overall, with no significant fluctuations even after the terminal target switch, and it can reach the designated terminal target. The rate of change of deformation is small, with significant fluctuations only occurring at the instant of terminal target switch, and the fluctuation amplitude is small, which facilitates the physical control. Although the predicted terminal velocity fluctuates significantly at the instant of terminal target switch, the adaptive adjustment mechanism of the constraints in the longitudinal optimization guidance model can achieve rapid limiting of the terminal velocity. Based on the above analysis, it can be concluded that the present invention can effectively complete the reentry guidance task under terminal target switch, with continuous deformation and satisfying the terminal velocity constraint.

[0073] This invention addresses the reentry guidance problem of variable-configuration aircraft. Under comprehensive constraints including quasi-equilibrium gliding conditions, process constraints, physical constraints, and terminal constraints, it ensures the feasibility of the reentry mission by employing a lateral guidance law based on heading error and a longitudinal guidance law based on prediction correction. Configuration parameters are incorporated into the guidance variables, and a longitudinal guidance optimization model is constructed to solve for the optimal deformation and angle of attack in real time. Configuration changes assist in minimizing aerodynamic drag and increasing terminal velocity. A terminal velocity constraint condition that adaptively adjusts with flight status is designed, combined with aerodynamic coefficient constraints, to achieve real-time dynamic matching between configuration, aerodynamic characteristics, and the reentry corridor, preventing the aircraft from touching the reentry corridor and ensuring the reentry guidance mission. This invention enhances the ability of existing methods to utilize aerodynamic characteristics, solves the problem of insufficient autonomy in dynamic matching of the reentry corridor, and enables online guidance of variable-configuration aircraft assisted by configuration changes under multi-dimensional constraints and terminal target switching.

[0074] The contents not described in detail in this specification are prior art known to those skilled in the art. Those skilled in the art will readily understand that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment, characterized in that, Includes the following steps: The first step is to construct a reentry guidance model based on the kinematics and dynamics model of the variable-structure aircraft, combined with process constraints and terminal constraints, with angle of attack, bank angle, span, and sweep angle as variables. The second step is to design a lateral guidance law based on the reentry guidance model and the quasi-equilibrium gliding condition and prediction correction algorithm to calculate the aerodynamic lift coefficient required for the current guidance in real time and make an indirect longitudinal guidance law. The third step is to introduce terminal velocity prediction variables that are related to aerodynamic drag and terminal altitude, and design terminal velocity constraints that are adaptively adjusted in real time according to flight status. The fourth step is to construct a longitudinal guidance optimization model for the variable-structure aircraft, with the minimum drag coefficient of the aircraft as the optimization objective, the angle of attack, the roll angle, and the span as longitudinal guidance variables, and the indirect longitudinal guidance law, the range constraint of the guidance variable, the rate of change constraint of the guidance variable, the aerodynamic coefficient constraint, and the terminal velocity constraint as comprehensive constraints. The fifth step is to solve the longitudinal guidance optimization model to obtain the longitudinal guidance law formed by the span, sweep angle and angle of attack, and combine it with the lateral guidance law to realize the online guidance of the variable-configuration aircraft with configuration change as an auxiliary under the terminal target switching.

2. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 1, characterized in that, In the first step, the kinematic and dynamic model of the variable-structure aircraft is as follows: （1） in, The distance from the Earth's center. and They are longitude and latitude, respectively. The velocity of the aircraft in the ground coordinate system. For velocity tilt angle, For speed and heading angle, , , , , , The first derivative of the corresponding variable; and Lift and drag are respectively, expressed as: and ,in and These are the lift coefficient and drag coefficient, respectively. Atmospheric density, For the reference area of ​​the aircraft; The tilt angle, For the mass of the aircraft, The lift coefficient is the acceleration due to gravity. and drag coefficient To the sweep angle Exhibition length ,Mach number Angle of attack Related nonlinear polynomial functions; atmospheric density To match the altitude of the aircraft The relevant exponential atmospheric model is expressed as follows: ,in Indicates atmospheric density at reference altitude. Indicates the standard atmospheric altitude.

3. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 2, characterized in that, The process constraints are divided into dynamic pressure constraints, heat flux density constraints, and overload constraints. The conditions for the process constraints are as follows: （2） in, For dynamic pressure, For heat flux density, For total overload, This represents the maximum feasible value for dynamic pressure. The maximum feasible value for heat flux density, This represents the maximum feasible value for overload. The constant coefficient, This is the standard gravitational acceleration.

4. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 3, characterized in that, The conditions for the terminal constraint are: （3） in, , , The altitude, longitude, and latitude of the terminal target, respectively. , , They are respectively The altitude, longitude, and latitude of the target at all times. Indicates the terminal heading error. This represents the maximum permissible value for the terminal heading error; the superscript T indicates the transpose of the matrix. The constructed reentry guidance model for the variable-configuration aircraft includes the kinematics and dynamics model of the variable-configuration aircraft, process constraints, and terminal constraints, with the tilt angle as the reference. sweep angle Exhibition length Angle of attack For guiding variables.

5. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 4, characterized in that, In the second step, the designed lateral guidance law based on heading error is the billing angle, and the expression for the billing angle amplitude is: （6） in, This is a proportional error gain coefficient; The heading error is represented by the sign of the roll angle, which is determined based on the heading error corridor. When the heading error exceeds the upper limit constraint, the sign of the roll angle is reversed, thereby generating a roll angle that satisfies the terminal heading error constraint.

6. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 5, characterized in that, Using quasi-equilibrium gliding conditions and predictive correction algorithms, the aerodynamic lift coefficient required for current guidance is calculated in real time. The expression is: （9） in, The reference velocity tilt angle required for guidance is expressed as follows: ,in For the Earth's radius, For the flight path to take off; The first derivative of the reference velocity angle. is the time constant.

7. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 6, characterized in that, In the third step, the expression for the terminal speed prediction variable is: （10） in, For terminal speed prediction variables, To account for the terminal velocity deviation due to atmospheric drag, the expression is: intermediate variables ; To account for the terminal velocity deviation due to Earth's gravity, the expression is: , is the Earth's gravitational constant.

8. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 7, characterized in that, The expression for the terminal velocity constraint condition that is designed to be adaptively adjusted in real time according to flight conditions is as follows: ； in, The maximum feasible terminal speed based on process constraint transformation is expressed as follows: ; , , Representing the maximum feasible terminal velocity based on the conversion of dynamic pressure constraint, heat flux density constraint, and overload constraint, respectively, the expressions are as follows: , , .

9. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 8, characterized in that, In the fourth step, the expression for the longitudinal guidance optimization model of the modified aircraft is as follows: （12） Here, find means to search, and st means constraint. For the vertical guidance variable to be solved, This indicates that the optimization objective is to minimize the aerodynamic drag coefficient. This indicates the lift coefficient equation constraint; guidance variable range constraints include... , , ,in , These are the maximum and minimum values ​​of the sweep angle, respectively. , These are the maximum and minimum span values, respectively. , These represent the maximum and minimum angles of attack, respectively; the constraints on the rate of change of guidance variables include... , , ,in , , Let be the first derivatives of the sweep angle, span, and angle of attack, respectively. , , The upper limit of the rate of change of each guidance variable; aerodynamic coefficient constraints include , ,in , The lower limit constraint of the lift coefficient is based on the transformation of quasi-equilibrium gliding conditions and dynamic pressure constraints. This represents the lower limit constraint of the lift coefficient based on the transformation of quasi-equilibrium gliding conditions and heat flux density constraints; , Transformation for overload constraints The upper boundary is expressed as: ; This indicates a terminal speed constraint.

10. The reentry guidance method for a variable-structure aircraft based on constraint adaptive adjustment according to claim 1, characterized in that, In the fifth step, the definition of terminal target switching is: （13） in, For the time of terminal target switching, , , These are the altitude, longitude, and latitude of the original terminal target, respectively. , , These are the altitude, longitude, and latitude of the new terminal target after the switch. Indicates the switchable range of terminal targets. The angle between the line-of-sight angle and the velocity-heading angle is expressed as follows: , The maximum allowable line-of-sight angle and velocity heading angle are switched for the terminal target.

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