An online trajectory planning and lateral adjustment method for reentry process

Abstract

The application discloses an online trajectory planning and lateral adjustment method in a reentry process and belongs to the technical field of aircraft guidance and control. The method comprises the following steps: S1, a D-V constraint corridor composed of a heat flux density constraint, a dynamic pressure constraint and an overload constraint is determined by real-time calculation; a reference D-V profile is obtained by solving, and is compared with the D-V constraint corridor to generate a longitudinal guidance instruction; S2, a lateral error corridor is determined by real-time calculation; based on a current flight state, trajectory prediction is carried out, and is compared with the lateral error corridor to generate a longitudinal adjustment amount; S3, a combined resistance acceleration instruction is generated; and S4, steps S1-S3 are repeated to realize an online rolling planning cycle. The method can realize online trajectory planning and lateral range control of a hypersonic unpowered aircraft in a reentry return process, and solves the problem that a traditional method cannot realize online real-time trajectory re-planning and accurate range control under strong uncertainty and strict path constraints.

Description

Technical Field

[0001] This invention belongs to the field of aircraft guidance and control technology, and particularly relates to an online trajectory planning and lateral adjustment method for the reentry process. Background Technology

[0002] Existing reentry guidance methods based on standard trajectory tracking have inherent defects such as poor robustness, inability to reprogram online, and difficulty in coordinating longitudinal and lateral coupled motions due to the influence of aircraft model deviations and complex flight environments. As a result, it is difficult to achieve accurate and reliable maneuvering to the predetermined landing site while ensuring strict compliance with thermal flux, dynamic pressure, and overload constraints. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide an online trajectory planning and lateral adjustment method for the reentry process. This method is computationally lightweight and has a fast response, enabling the rapid online generation of feasible and optimal trajectories. It can also intelligently coordinate the guidance of longitudinal and lateral motions, realizing online trajectory planning and lateral range control for the reentry and return process of hypersonic unpowered aircraft. This solves the problem that traditional methods cannot perform online real-time trajectory replanning and precise range control under strong uncertainty and strict path constraints.

[0004] To address the aforementioned technical problems, this invention discloses an online trajectory planning and lateral adjustment method for the reentry process, comprising: S1. Real-time calculation determines the DV constraint corridor composed of heat flux density constraint, dynamic pressure constraint, and overload constraint; based on quasi-equilibrium gliding conditions, a reference DV profile is obtained and compared with the DV constraint corridor determined in real-time calculation to generate longitudinal guidance commands. ; S2, calculate and determine the lateral error corridor in real time; based on the current flight status, perform trajectory prediction and compare it with the lateral error corridor determined in real time to generate the longitudinal adjustment amount. ; S3, according to and Generate resultant drag acceleration command ; S4. Repeat steps S1 to S3 to realize online rolling planning loop and complete online trajectory planning and lateral adjustment in the entire reentry process.

[0005] In the online trajectory planning and lateral adjustment method of the above reentry process, the DV constraint corridor, consisting of heat flux density constraints, dynamic pressure constraints, and overload constraints, is calculated and determined in real time, including: The upper limit of drag acceleration corresponding to the heat flux density constraint is obtained through real-time calculation. Upper limit of drag acceleration corresponding to dynamic pressure constraint The upper limit of drag acceleration corresponding to overload constraints : ···(1) ···(2) ···(3) in, Indicates the maximum heat flux density. Indicates the maximum dynamic pressure. Indicates the maximum overload. This represents a constant related to the radius of curvature of the aircraft's nose. Indicates flight speed. Indicates the drag coefficient. Indicates the lift-to-drag ratio. Indicates the mass of the aircraft. This represents the maximum cross-sectional area of ​​the aircraft. This represents the acceleration due to gravity on Earth. according to , and Determine the range of drag acceleration of the aircraft at different flight speeds: ···(4) in, This indicates taking the minimum value. Indicates drag acceleration; Will The upper and lower boundaries vary with flight speed By continuously drawing, the DV-constrained corridor is obtained, which serves as the feasible region for the safe flight of the aircraft.

[0006] In the online trajectory planning and lateral adjustment method of the reentry process described above, a baseline DV profile is calculated based on quasi-equilibrium gliding conditions and compared with the DV constraint corridor determined in real time to generate longitudinal guidance commands. ,include: Determine the quasi-equilibrium gliding conditions: ···(5) in, Indicates lift acceleration. Indicates the tilt angle; Indicates the distance from the Earth's center. , Represents the Earth's radius. Indicates altitude; Sure , , The expression: ···(6) ···(7) ···(8) in, Indicates atmospheric density. Indicates the lift coefficient; Substituting equations (6) to (8) into equation (5), we derive the analytical relationship between drag acceleration and flight speed and roll angle: ···(9) Parametric functions for constructing the baseline DV profile: ···(10) in, Indicates the reference DV profile. Denotes the coefficient of the quadratic term. Denotes the coefficient of the linear term. Indicates the coefficient of the constant term; Establish the differential equation for the journey: ···(11) in, Indicates the energy of the aircraft. Indicates the remaining distance; Integral result: ···(12) in, Indicates current flight speed The corresponding spacecraft energy, Indicates terminal flight speed The corresponding spacecraft energy; Substituting equation (10) into equation (12), and introducing the relationship between flight speed and aircraft energy... , to obtain The analytical integral expression: ···(13) Three boundary conditions are introduced: Boundary condition 1, current flight speed Corresponding reference DV profile Compared with the current actual drag acceleration Consistency: ···(14) Boundary condition 2, terminal flight speed Corresponding reference DV profile With the actual resistance acceleration at the terminal Consistency: ···(15) Boundary condition 3: The integrated range equals the current remaining range. : ···(16) Solving the equations (14) to (16) simultaneously, we get... The value; The solution obtained Substituting the value into equation (10), we obtain the baseline DV profile; The obtained baseline DV profile is compared with the DV constraint corridor determined by real-time calculation. If every point on the reference DV profile lies within the upper and lower boundaries of the DV constraint corridor determined in real-time calculation, then the reference DV profile is used as the longitudinal guidance command. ; If a segment on the reference DV profile exceeds the upper or lower boundary of the DV constraint corridor determined in real-time calculation, an "active fitting" strategy is adopted to correct the excess portion to the upper or lower boundary of the DV constraint corridor determined in real-time calculation. The drag acceleration corresponding to the upper or lower boundary of the DV constraint corridor determined in real-time calculation is then used as the longitudinal guidance command for that segment. .

[0007] In the online trajectory planning and lateral adjustment method of the above reentry process, the lateral error corridor is calculated and determined in real time, including: The maximum permissible lateral deviation for the remaining flight range is calculated in real time: ···(17) in, Indicates the remaining flight distance The maximum permissible lateral deviation. This indicates the preset maximum permissible lateral deviation saturation value. Indicates the narrowing coefficient; based on The lateral error corridor is determined; the lateral error corridor is based on the line of sight from the aircraft's current position to the target point, and is bounded by a left boundary and a right boundary; the left boundary refers to the leftward shift of the line of sight. The right boundary refers to the rightward shift of the line of sight. .

[0008] In the online trajectory planning and lateral adjustment method described above for the reentry process, trajectory prediction is performed based on the current flight status and compared with the lateral error corridor determined in real time to generate the longitudinal adjustment amount. ,include: state variables Over time The change is described by the following system of equations: Position kinematic equations: ···(18) in, Indicates longitude. Indicates latitude, Indicates the inclination angle of the flight path. Indicates the heading angle; Velocity dynamics equations: ···(19) Track tilt dynamic equation: ···(20) Heading angle dynamic equation: ···(twenty one) Based on the current flight status For initial value, To determine the integration step size, the fourth-order Runge-Kutta method is used to integrate equations (18) to (21) until the integration termination condition is met, thus obtaining the prediction time domain. Latitude and longitude sequence of inland ground projection points As a trajectory prediction; among which, This represents the distance from the Earth's center at the current moment. Indicates the longitude at the current moment. Indicates the latitude at the current moment. Indicates the current flight speed. This indicates the inclination angle of the flight path at the current moment. Indicates the heading angle at the current moment. This indicates the tilt angle at the current moment. Indicates the current moment; This represents the number of ground projection points in the prediction time domain. , Indicates the prediction time domain, Indicates rounding down; and Representing the prediction time domain The longitude and latitude of the ground projection point at any given time. ; according to Determine the sequence of lateral deviations of ground projection points relative to the nominal heading within the prediction time domain. ; The lateral deviations of the ground projection points relative to the nominal heading at each time point within the prediction time domain are compared with the lateral error corridor determined by real-time calculation. Specifically, if the lateral deviations of the ground projection points relative to the nominal heading at all times within the prediction time domain satisfy... If the trajectory prediction does not exceed the lateral error corridor, then the longitudinal adjustment amount is determined. If the lateral deviation of the ground projection point relative to the nominal heading at any moment in the prediction time domain does not satisfy... If the trajectory prediction exceeds the lateral error corridor, a lateral adjustment is triggered, and the longitudinal adjustment amount is determined based on the lateral adjustment result. ; Indicates the prediction time domain Lateral deviation of the ground projection point relative to the nominal heading at any given time; express The remaining flight distance at that moment, Indicates the remaining flight distance The maximum permissible lateral deviation.

[0009] In the online trajectory planning and lateral adjustment method of the above reentry process, when using the fourth-order Runge-Kutta method to integrate equations (18) to (21), the integration termination condition takes the minimum value of the following three: 1) Achieve prediction in the time domain; 2) The aircraft's energy drops below the terminal energy threshold; 3) The remaining range is less than zero.

[0010] In the online trajectory planning and lateral adjustment method of the reentry process described above, lateral adjustment is triggered, and the longitudinal adjustment amount is determined based on the lateral adjustment result. ,include: Find the ground projection point that is furthest from the lateral error corridor within the prediction time domain, and denote it as point A. ; Determine the point Corresponding remaining range Flight speed Lateral deviation relative to nominal heading Remaining flight distance Maximum permissible lateral deviation ; Calculation points The magnitude of the lateral error corridor and determine the direction sign. : ···(twenty two) ···(twenty three) in, , indicating leftward deviation; , indicates rightward deviation; according to The required heading angle correction is calculated. : ···(twenty four) in, Indicates the conversion factor; Mapping the heading angle correction to the roll angle adjustment yields the required roll angle adjustment. : The relationship between the rate of change of heading angle and the heel angle is given by the following lateral dynamics equation: ···(25) in, Indicates the rate of change of heading angle; If you expect to have the remaining time If the correction is completed within the timeframe, the required average rate of change of heading angle is... for: ···(26) According to equations (25) to (26), we have: ···(27) but: ···(28) Taking the partial derivative of equation (9) with respect to the tilt angle, we obtain the sensitivity of drag acceleration to the tilt angle: ···(29) Then, by The resulting longitudinal adjustment amount is : ···(30) That is: ···(31) ···(32) in, This represents the overall gain, determined through simulation calibration.

[0011] The online trajectory planning and lateral adjustment method for the above reentry process also includes: monitoring and determining in real time whether the heat flux density, dynamic pressure, overload and lateral deviation exceed the limits throughout the entire process of steps S1 to S3; if any parameter of heat flux density, dynamic pressure, overload and lateral deviation exceeds the limits, the current cycle is immediately interrupted and the emergency replanning mode is started.

[0012] In the online trajectory planning and lateral adjustment method of the above reentry process, real-time monitoring and determination of whether heat flux density, dynamic pressure, overload, and lateral deviation exceed limits are performed, including: The current heat flux density is calculated in real time. And based on a simplified heat conduction model, future predictions are obtained. Internal heat flow changes ;like Make If the heat flux density exceeds the limit, it is determined that the heat flux density exceeds the limit; otherwise, it is determined that the heat flux density does not exceed the limit. Represents the time domain for heat flux prediction. Indicates the heat flow warning coefficient; Real-time calculation to obtain the current dynamic pressure And based on the rate of change of atmospheric density, future predictions are obtained. Internal dynamic pressure changes ;like Make If the dynamic pressure exceeds the limit, it is determined that the dynamic pressure has exceeded the limit; otherwise, it is determined that the dynamic pressure has not exceeded the limit. This indicates the time domain for dynamic pressure prediction. Indicates the dynamic pressure warning coefficient; Real-time calculation to obtain the current overload And based on aerodynamic changes, future predictions are obtained. Internal overload changes ;like Make If the load exceeds the limit, it is determined that the overload has exceeded the limit; otherwise, it is determined that the overload has not exceeded the limit. Indicates the overload prediction time domain. Indicates the overload warning coefficient; The current lateral deviation is calculated in real time. Determine emergency corridors : ;like If the deviation exceeds the limit, the lateral deviation is determined to be out of bounds; otherwise, the lateral deviation is determined to be within the limit. Indicates the emergency response coefficient. .

[0013] In the online trajectory planning and lateral adjustment method of the above reentry process, the heat flux density constraint is: The dynamic pressure constraint is: The overload constraint is: ;in, Represents heat flux density, Indicates dynamic pressure. Indicates overload.

[0014] The present invention has the following advantages: (1) This invention discloses an online trajectory planning and lateral adjustment method for reentry process, which realizes online real-time trajectory replanning during the reentry process of the aircraft. Its unique longitudinal and lateral coordination logic deeply couples the heading correction with heat flow / energy management, realizes longitudinal and lateral intelligent collaborative control, and improves the overall control quality while effectively adapting to state and environmental disturbances.

[0015] (2) This invention discloses an online trajectory planning and lateral adjustment method for reentry process, which has fault prediction and emergency replanning capabilities. It can automatically switch to emergency mode in abnormal situations to ensure the safe arrival of the aircraft at the landing site and has high reliability. Attached Figure Description

[0016] Figure 1 This is a flowchart of an online trajectory planning and lateral adjustment method for a reentry process according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a drag acceleration-velocity profile and a constraint corridor in an embodiment of the present invention; Figure 3 This is a schematic diagram of a lateral error corridor and heading adjustment logic in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments disclosed in the present invention will be described in further detail below with reference to the accompanying drawings.

[0018] Reference Figure 1 In this embodiment, the online trajectory planning and lateral adjustment method for the reentry process includes: S1. Real-time calculation determines the DV constraint corridor composed of heat flux density constraint, dynamic pressure constraint, and overload constraint; based on quasi-equilibrium gliding conditions, a reference DV profile is obtained and compared with the DV constraint corridor determined in real-time calculation to generate longitudinal guidance commands. .

[0019] In this embodiment, before the spacecraft re-enters, the landing site coordinates and path constraint thresholds (including but not limited to: maximum heat flux density) can be set. Maximum dynamic pressure Maximum overload (etc.), aircraft aerodynamic parameters (including but not limited to: lift coefficient) drag coefficient The onboard computer is loaded with information such as the aircraft's position, speed, and attitude during reentry.

[0020] Preferably, the specific implementation process of step S1 is as follows: S11, real-time calculation determines the DV constraint corridor, which consists of heat flux density constraints, dynamic pressure constraints, and overload constraints. Specifically: 111) The upper limit of drag acceleration corresponding to the heat flux density constraint is calculated in real time. .

[0021] The heat flux density constraint is: , Let heat flux density be represented, then:

[0022] Heat flux density can be calculated using the Sutton-Graves formula: when expressing heat flux density as a relationship between flight speed and drag acceleration, atmospheric density is introduced. Due to drag acceleration Definition The solution can be found Substituting into the Sutton-Graves formula, we get: ···(1) in, This represents a constant related to the radius of curvature of the aircraft's nose. Indicates flight speed. Indicates the mass of the aircraft. This represents the maximum cross-sectional area of ​​the aircraft.

[0023] 112) The upper limit of the drag acceleration corresponding to the dynamic pressure constraint is calculated in real time. .

[0024] The dynamic pressure constraint is: , Indicates dynamic pressure.

[0025] Dynamic pressure Defined as: ,use eliminate We can obtain:

[0026] After sorting, it is as follows: ···(2) in, This represents the drag coefficient.

[0027] 113) The upper limit of the drag acceleration corresponding to the overload constraint is calculated in real time. .

[0028] The overload constraint is: , Indicates overload.

[0029] Overload The definition is: the ratio of aerodynamic force to gravity, that is: .

[0030] Under quasi-equilibrium gliding conditions, lift acceleration and drag acceleration Through the lift-to-drag ratio Related: Then we have: .

[0031] After sorting, it is as follows: ···(3) in, This represents the lift-to-drag ratio, which is usually preset as a function of flight speed; It represents the acceleration due to gravity on Earth.

[0032] 114) Formation of DV-constrained corridors.

[0033] according to , and Determine the range of drag acceleration of the aircraft at different flight speeds: ···(4) in, This indicates taking the minimum value.

[0034] Will The upper and lower boundaries vary with flight speed Continuous drawing yields the following results: Figure 2 The DV-constrained corridor shown (i.e., flight speed) v With drag acceleration D The relationship between these factors serves as a feasible domain for the safe flight of aircraft.

[0035] S12, based on quasi-equilibrium gliding conditions, calculates the baseline DV profile and compares it with the DV constraint corridor determined in real time to generate longitudinal guidance commands. Specifically: 121) The baseline DV profile is obtained by calculation.

[0036] In quasi-equilibrium gliding flight, the longitudinal motion of the aircraft satisfies the balance relationship between lift, gravity, and centrifugal force, which can be expressed as: ···(5) in, Indicates lift acceleration. Indicates the tilt angle; Indicates the distance from the Earth's center. , Represents the Earth's radius. Indicates altitude.

[0037] As mentioned above, , , The definition is as follows: ···(6) ···(7) ···(8) in, Indicates atmospheric density. This represents the lift coefficient.

[0038] Substituting equations (6) to (8) into equation (5), we derive the analytical relationship between drag acceleration and flight speed and roll angle: ···(9) To achieve rapid online calculation, the baseline DV profile is designed as a parameterized function of flight velocity. This embodiment adopts a quadratic polynomial form to balance fitting accuracy and solution simplicity: ···(10) in, Indicates the reference DV profile. Denotes the coefficient of the quadratic term. Denotes the coefficient of the linear term. This represents the coefficient of the constant term.

[0039] The aircraft from its current flight speed (corresponding energy) ) Gliding to terminal flight speed (corresponding energy) The remaining distance traveled can be calculated using the energy-distance integral formula; with energy as the independent variable, the differential equation for the distance is: ···(11) in, Indicates the energy of the aircraft. Indicates the remaining distance.

[0040] Integral result: ···(12) in, Indicates current flight speed The corresponding spacecraft energy, Indicates terminal flight speed The corresponding spacecraft energy.

[0041] Substituting equation (10) into equation (12), and introducing the relationship between flight speed and aircraft energy... , to obtain The analytical integral expression: ···(13) To determine Three coefficients, introducing three boundary conditions: Boundary condition 1, current flight speed Corresponding reference DV profile Compared with the current actual drag acceleration Consistency: ···(14) Boundary condition 2, terminal flight speed Corresponding reference DV profile With the actual resistance acceleration at the terminal Consistency: ···(15) Boundary condition 3: The integrated range equals the current remaining range. : ···(16) Solving the equations (14) to (16) simultaneously, we get... The value of .

[0042] The solution obtained Substituting the value into equation (10), we obtain the baseline DV profile.

[0043] 122) Generate longitudinal guidance commands .

[0044] The obtained baseline DV profile is compared with the DV constraint corridor determined by real-time calculation; if every point on the baseline DV profile is within the upper and lower boundaries of the DV constraint corridor determined by real-time calculation, then the baseline DV profile is used as the longitudinal guidance command. If a segment on the reference DV profile exceeds the upper or lower boundary of the DV constraint corridor determined in real-time calculation, an "active fitting" strategy is adopted to correct the excess portion to the upper or lower boundary of the DV constraint corridor determined in real-time calculation. The drag acceleration corresponding to the upper or lower boundary of the DV constraint corridor determined in real-time calculation is then used as the longitudinal guidance command for that segment. .

[0045] S2, calculate and determine the lateral error corridor in real time; based on the current flight status, perform trajectory prediction and compare it with the lateral error corridor determined in real time to generate the longitudinal adjustment amount. Specifically: S21, real-time calculation to determine the lateral error corridor.

[0046] Before performing lateral deviation determination, the boundary of the lateral error corridor must be calculated in real time based on the current remaining range. The lateral error corridor is defined as: the acceptable lateral deviation range of the aircraft's ground projection point relative to the nominal heading; the lateral error corridor consists of two curves symmetrical about the nominal heading, and its half-width... Defined as the maximum allowable lateral deviation within the current remaining range.

[0047] Preferably, the maximum permissible lateral deviation for the remaining flight distance can be calculated in real time using the following formula (17): ···(17) in, Indicates the remaining flight distance The maximum permissible lateral deviation is given, and the remaining range can be calculated from the spherical distance between the current position and the target point. This represents the preset maximum permissible lateral deviation saturation value (ranging from 30km to 100km), used to characterize the upper limit of the width of the lateral error corridor when the remaining range is sufficiently large; This represents the narrowing coefficient (with a value of 0.001 to 0.01), used to control the narrowing rate of the lateral error corridor as the remaining range decreases.

[0048] based on The lateral error corridor is determined. The lateral error corridor is defined by the line-of-sight direction from the aircraft's current position to the target point, and is bounded by its left and right boundaries; the left boundary refers to the leftward shift of the line-of-sight direction. The right boundary refers to the rightward shift of the line of sight. ,like Figure 3 As shown.

[0049] The lateral error corridor is independent of the longitudinal DV constraint corridor, but it is triggered when lateral adjustments are made (i.e., the predicted trajectory exceeds the limit). At that time, the system will calculate the longitudinal adjustment amount. This enables longitudinal and lateral coupling control.

[0050] S22 performs trajectory prediction based on the current flight status.

[0051] To determine whether a lateral maneuver has crossed the boundary, the onboard computer needs to predict the trajectory of the ground projection point in the future time domain based on the current flight state. The prediction process uses numerical integration with a fixed step size: state variables Over time The change is described by the following system of equations: Position kinematic equations: ···(18) in, Indicates longitude. Indicates latitude, Indicates the inclination angle of the flight path. Indicates the heading angle.

[0052] Velocity dynamics equations: ···(19) Track tilt dynamic equation: ···(20) Heading angle dynamic equation: ···(twenty one) Based on the current flight status For initial value, The integration step size ( The value is 0.1~0.5 seconds. The fourth-order Runge-Kutta method is used to integrate equations (18)~(21) until the integration termination condition is met, and the predicted time domain is obtained. Latitude and longitude sequence of inland ground projection points , as trajectory prediction. This represents the distance from the Earth's center at the current moment. Indicates the longitude at the current moment. Indicates the latitude at the current moment. Indicates the current flight speed. This indicates the inclination angle of the flight path at the current moment. Indicates the heading angle at the current moment. This indicates the tilt angle at the current moment. Indicates the current moment; This represents the number of ground projection points in the prediction time domain. , Indicates the prediction time domain, Indicates rounding down; and Representing the prediction time domain The longitude and latitude of the ground projection point at any given time. , , .

[0053] Preferably, when using the fourth-order Runge-Kutta method to solve equations (18) to (21) by integration, the integration termination condition is the minimum of the following three: 1) reaching the prediction time domain; 2) the aircraft energy is reduced to below the terminal energy threshold; 3) the remaining range is less than zero.

[0054] Furthermore, according to Determine the sequence of lateral deviations of ground projection points relative to the nominal heading within the prediction time domain. .

[0055] S23, Lateral error determination, generation of longitudinal adjustment amount. .

[0056] The lateral deviation of the ground projection point relative to the nominal heading at each time point in the prediction time domain is compared with the lateral error corridor determined by real-time calculation.

[0057] If the lateral deviation of the ground projection point relative to the nominal heading at all times within the prediction time domain satisfies If the trajectory prediction does not exceed the lateral error corridor, then the longitudinal adjustment amount is determined. .in, Indicates the prediction time domain Lateral deviation of the ground projection point relative to the nominal heading at any given time; express The remaining flight distance at that moment, Indicates the remaining flight distance The maximum permissible lateral deviation.

[0058] If the lateral deviation of the ground projection point relative to the nominal heading at any moment in the prediction time domain does not satisfy... If the trajectory prediction exceeds the lateral error corridor, a lateral adjustment is triggered, and the longitudinal adjustment amount is determined based on the lateral adjustment result. Specifically: Find the ground projection point that is furthest from the lateral error corridor within the prediction time domain, and denote it as point A. ; Determine the point Corresponding remaining range Flight speed Lateral deviation relative to nominal heading Remaining flight distance Maximum permissible lateral deviation .

[0059] Calculation points The magnitude of the lateral error corridor and determine the direction sign. : ···(twenty two) ···(twenty three) in, , indicating leftward deviation; , indicates rightward deviation.

[0060] according to The required heading angle correction is calculated. : ···(twenty four) in, This represents the conversion factor, which is usually taken as... Radius conversion factor, dimensionless.

[0061] Furthermore, the heading angle correction is mapped to the roll angle adjustment to obtain the required roll angle adjustment. : The relationship between the rate of change of heading angle and the heel angle is given by the following lateral dynamics equation: ···(25) in, This represents the rate of change of heading angle.

[0062] If you expect to have the remaining time If the correction is completed within the timeframe, the required average rate of change of heading angle is... for: ···(26) According to equations (25) to (26), we have: ···(27) For small adjustments, the result can be linearized as follows: ···(28) Furthermore, by taking the partial derivative of equation (9) with respect to the tilt angle, we obtain the sensitivity of drag acceleration to the tilt angle: ···(29) Then, by The resulting longitudinal adjustment amount is : ···(30) Furthermore, the formula is simplified and synthesized into a practical engineering formula: ···(31) ···(32) in, This represents the overall gain, which can be simplified to a constant value determined through simulation calibration.

[0063] S3, according to and Generate resultant drag acceleration command .

[0064] In this embodiment, The flight control system can track the aircraft by adjusting its angle of attack and roll angle. Among them, the angle of attack mainly affects the longitudinal direction, which is used to change the drag coefficient and directly control the energy consumption rate of the aircraft. At the same time, the larger the angle of attack, the more severe the aerodynamic heating and the higher the heat flux density. The roll angle affects the lateral direction by generating lateral forces to change the flight direction, and also affects the longitudinal direction through quasi-equilibrium gliding conditions. Thus, while controlling the flight direction, it also enables fine-tuning of the aircraft's energy consumption and heat flux density.

[0065] S4. Repeat steps S1 to S3 to realize online rolling planning loop and complete online trajectory planning and lateral adjustment in the entire reentry process.

[0066] In this embodiment, the online rolling planning cycle is triggered once every 10 seconds or every 0.5km descent. Through the online rolling planning cycle (planning-execution-feedback-replanning) in steps S1 to S4 above, the aircraft continuously adjusts its angle of attack and roll angle in real time based on its current position, velocity, attitude information, landing site coordinates, and path constraint thresholds throughout the reentry process. This allows for precise tracking or replanning of the flight trajectory, ultimately achieving precise and reliable maneuvering to the predetermined landing site while ensuring strict compliance with thermal flux, dynamic pressure, and overload constraints.

[0067] In this embodiment, the online trajectory planning and lateral adjustment method for the reentry process further includes: throughout steps S1 to S3, real-time monitoring and determination of whether heat flux density, dynamic pressure, overload, and lateral deviation exceed limits; if any one of these parameters exceeds the limit, the current cycle is immediately interrupted, and an emergency replanning mode is initiated. The limit determination employs a prediction + margin strategy, not only monitoring whether the current value exceeds the limit but also predicting whether it will exceed the limit in the future, thus triggering an emergency response in advance. Specifically: (1) Monitor and determine whether the heat flux density exceeds the limit by means of the following: The current heat flux density is calculated in real time. And based on a simplified heat conduction model, future predictions are obtained. Internal heat flow changes ;like Make If the heat flux density exceeds the limit, it is determined that the heat flux density exceeds the limit; otherwise, it is determined that the heat flux density does not exceed the limit. This represents the time domain for heat flux prediction, typically taken as 3 seconds. This represents the heat flow warning coefficient, which is usually taken as 0.9~0.95, allowing for short-term approaches but not exceeding the threshold.

[0068] (2) Monitor and determine whether the dynamic pressure exceeds the limit by means of the following: Real-time calculation to obtain the current dynamic pressure And based on the rate of change of atmospheric density, future predictions are obtained. Internal dynamic pressure changes ;like Make If the dynamic pressure exceeds the limit, it is determined that the dynamic pressure has exceeded the limit; otherwise, it is determined that the dynamic pressure has not exceeded the limit. This represents the time domain for dynamic pressure prediction, typically taken as 3 seconds. This represents the dynamic pressure warning coefficient, typically taken as 0.9. 0.95.

[0069] (3) Monitor and determine whether the overload exceeds the limit using the following methods: Real-time calculation to obtain the current overload And based on aerodynamic changes, future predictions are obtained. Internal overload changes ;like Make If the load exceeds the limit, it is determined that the overload has exceeded the limit; otherwise, it is determined that the overload has not exceeded the limit. This represents the overload prediction time domain, typically taken as 3 seconds. This represents the overload warning factor, typically taken as 0.9. 0.95.

[0070] (4) Monitor and determine whether the lateral deviation exceeds the limit by means of the following: The current lateral deviation is calculated in real time. Determine emergency corridors : ;like If the deviation exceeds the limit, the lateral deviation is considered to be out of bounds; otherwise, the lateral deviation is considered not to have exceeded the limit. Indicates the emergency response coefficient. .

[0071] If any of the aforementioned critical parameters is detected to be about to exceed the limit, the current loop is immediately interrupted, and an emergency replanning mode is initiated. This emergency replanning mode is a special planning mode with the primary objective of preserving the aircraft. This mode prioritizes lateral control, generating a conservative flight profile that strictly satisfies all path constraints and directly conforms to the lower boundary of the thermal flow constraint to reduce thermal load. Then, based on this conservative profile, a feasible trajectory capable of reaching the landing site is recalculated. If the current trajectory cannot safely reach the original landing site, it is automatically replanned to a pre-stored alternate landing site.

[0072] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0073] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for online trajectory planning and lateral adjustment during reentry, characterized in that, include: S1. Real-time calculation determines the DV constraint corridor composed of heat flux density constraint, dynamic pressure constraint, and overload constraint; based on quasi-equilibrium gliding conditions, a reference DV profile is obtained and compared with the DV constraint corridor determined in real-time calculation to generate longitudinal guidance commands. ; S2, real-time calculation to determine the lateral error corridor; Based on the current flight status, trajectory prediction is performed and compared with the lateral error corridor determined in real time to generate the longitudinal adjustment amount. ; S3, according to and Generate resultant drag acceleration command ; S4. Repeat steps S1 to S3 to realize online rolling planning loop and complete online trajectory planning and lateral adjustment in the entire reentry process.

2. The online trajectory planning and lateral adjustment method for the reentry process according to claim 1, characterized in that, Real-time calculation determines the DV constraint corridor, which consists of heat flux density constraints, dynamic pressure constraints, and overload constraints, including: The upper limit of drag acceleration corresponding to the heat flux density constraint is obtained through real-time calculation. Upper limit of drag acceleration corresponding to dynamic pressure constraint The upper limit of drag acceleration corresponding to overload constraints : ···（1） ···（2） ···（3） in, Indicates the maximum heat flux density. Indicates the maximum dynamic pressure. Indicates the maximum overload. This represents a constant related to the radius of curvature of the aircraft's nose. Indicates flight speed. Indicates the drag coefficient. Indicates the lift-to-drag ratio. Indicates the mass of the aircraft. This represents the maximum cross-sectional area of ​​the aircraft. This represents the acceleration due to gravity on Earth. according to , and Determine the range of drag acceleration of the aircraft at different flight speeds: ···（4） in, This indicates taking the minimum value. Indicates drag acceleration; Will The upper and lower boundaries vary with flight speed By continuously drawing, the DV-constrained corridor is obtained, which serves as the feasible region for the safe flight of the aircraft.

3. The online trajectory planning and lateral adjustment method for the reentry process according to claim 2, characterized in that, Based on quasi-equilibrium gliding conditions, a baseline DV profile is calculated and compared with the DV constraint corridor determined in real time to generate longitudinal guidance commands. ,include: Determine the quasi-equilibrium gliding conditions: ···（5） in, Indicates lift acceleration. Indicates the tilt angle; Indicates the distance from the Earth's center. , Represents the Earth's radius. Indicates altitude; Sure , , The expression: ···（6） ···（7） ···（8） in, Indicates atmospheric density. Indicates the lift coefficient; Substituting equations (6) to (8) into equation (5), we derive the analytical relationship between drag acceleration and flight speed and roll angle: ···（9） Parametric functions for constructing the baseline DV profile: ···（10） in, Indicates the reference DV profile. Denotes the coefficient of the quadratic term. Denotes the coefficient of the linear term. Indicates the coefficient of the constant term; Establish the differential equation for the journey: ···（11） in, Indicates the energy of the aircraft. Indicates the remaining distance; Integral result: ···（12） in, Indicates current flight speed The corresponding spacecraft energy, Indicates terminal flight speed The corresponding spacecraft energy; Substituting equation (10) into equation (12), and introducing the relationship between flight speed and aircraft energy... , to obtain The analytical integral expression: ···（13） Three boundary conditions are introduced: Boundary condition 1, current flight speed Corresponding reference DV profile Compared with the current actual drag acceleration Consistency: ···（14） Boundary condition 2, terminal flight speed Corresponding reference DV profile With the actual resistance acceleration at the terminal Consistency: ···（15） Boundary condition 3: The integrated range equals the current remaining range. : ···（16） Solving the equations (14) to (16) simultaneously, we get... The value; The solution obtained Substituting the value into equation (10), we obtain the baseline DV profile; The obtained baseline DV profile is compared with the DV constraint corridor determined by real-time calculation. If every point on the reference DV profile lies within the upper and lower boundaries of the DV constraint corridor determined in real-time calculation, then the reference DV profile is used as the longitudinal guidance command. ; If a segment on the reference DV profile exceeds the upper or lower boundary of the DV constraint corridor determined in real-time calculation, an "active fitting" strategy is adopted to correct the excess portion to the upper or lower boundary of the DV constraint corridor determined in real-time calculation. The drag acceleration corresponding to the upper or lower boundary of the DV constraint corridor determined in real-time calculation is then used as the longitudinal guidance command for that segment. .

4. The online trajectory planning and lateral adjustment method for the reentry process according to claim 3, characterized in that, Real-time calculation to determine the lateral error corridor includes: The maximum permissible lateral deviation for the remaining flight range is calculated in real time: ···（17） in, Indicates the remaining flight distance The maximum permissible lateral deviation. This indicates the preset maximum permissible lateral deviation saturation value. Indicates the narrowing coefficient; based on The lateral error corridor is determined; the lateral error corridor is based on the line of sight from the aircraft's current position to the target point, and is bounded by a left boundary and a right boundary; the left boundary refers to the leftward shift of the line of sight. The right boundary refers to the rightward shift of the line of sight. .

5. The online trajectory planning and lateral adjustment method for the reentry process according to claim 4, characterized in that, Based on the current flight status, trajectory prediction is performed and compared with the lateral error corridor determined in real time to generate the longitudinal adjustment amount. ,include: state variables Over time The change is described by the following system of equations: Position kinematic equations: ···（18） in, Indicates longitude. Indicates latitude, Indicates the inclination angle of the flight path. Indicates the heading angle; Velocity dynamics equations: ···（19） Track tilt dynamic equation: ···（20） Heading angle dynamic equation: ···（21） Based on the current flight status For initial value, To determine the integration step size, the fourth-order Runge-Kutta method is used to integrate equations (18) to (21) until the integration termination condition is met, thus obtaining the prediction time domain. Latitude and longitude sequence of inland ground projection points As a trajectory prediction; among which, This represents the distance from the Earth's center at the current moment. Indicates the longitude at the current moment. Indicates the latitude at the current moment. Indicates the current flight speed. This indicates the inclination angle of the flight path at the current moment. Indicates the heading angle at the current moment. This indicates the tilt angle at the current moment. Indicates the current moment; This represents the number of ground projection points in the prediction time domain. , Indicates the prediction time domain, Indicates rounding down; and Representing the prediction time domain The longitude and latitude of the ground projection point at any given time. ; according to Determine the sequence of lateral deviations of ground projection points relative to the nominal heading within the prediction time domain. ; The lateral deviations of the ground projection points relative to the nominal heading at each time point within the prediction time domain are compared with the lateral error corridor determined by real-time calculation. Specifically, if the lateral deviations of the ground projection points relative to the nominal heading at all times within the prediction time domain satisfy... If the trajectory prediction does not exceed the lateral error corridor, then the longitudinal adjustment amount is determined. If the lateral deviation of the ground projection point relative to the nominal heading at any moment in the prediction time domain does not satisfy... If the trajectory prediction exceeds the lateral error corridor, a lateral adjustment is triggered, and the longitudinal adjustment amount is determined based on the lateral adjustment result. ; Indicates the prediction time domain Lateral deviation of the ground projection point relative to the nominal heading at any given time; express The remaining flight distance at that moment, Indicates the remaining flight distance The maximum permissible lateral deviation.

6. The online trajectory planning and lateral adjustment method for the reentry process according to claim 5, characterized in that, When using the fourth-order Runge-Kutta method to integrate equations (18) to (21), the termination condition for integration is the minimum of the following three: 1) Achieve prediction in the time domain; 2) The aircraft's energy drops below the terminal energy threshold; 3) The remaining range is less than zero.

7. The online trajectory planning and lateral adjustment method for the reentry process according to claim 6, characterized in that, Trigger a lateral adjustment, and determine the vertical adjustment amount based on the lateral adjustment result. ,include: Find the ground projection point that is furthest from the lateral error corridor within the prediction time domain, and denote it as point A. ; Determine the point Corresponding remaining range Flight speed Lateral deviation relative to nominal heading Remaining flight distance Maximum permissible lateral deviation ; Calculation points The magnitude of the lateral error corridor and determine the direction sign. : ···（22） ···（23） in, , indicating leftward deviation; , indicates rightward deviation; according to The required heading angle correction is calculated. : ···（24） in, Indicates the conversion factor; Mapping the heading angle correction to the roll angle adjustment yields the required roll angle adjustment. : The relationship between the rate of change of heading angle and the heel angle is given by the following lateral dynamics equation: ···（25） in, Indicates the rate of change of heading angle; If you expect to have the remaining time If the correction is completed within the timeframe, the required average rate of change of heading angle is... for: ···（26） According to equations (25) to (26), we have: ···（27） but: ···（28） Taking the partial derivative of equation (9) with respect to the tilt angle, we obtain the sensitivity of drag acceleration to the tilt angle: ···（29） Then, by The resulting longitudinal adjustment amount is : ···（30） That is: ···（31） ···（32） in, This represents the overall gain, determined through simulation calibration.

8. The online trajectory planning and lateral adjustment method for the reentry process according to claim 7, characterized in that, Also includes: Throughout the entire process of steps S1 to S3, the heat flux density, dynamic pressure, overload, and lateral deviation are monitored and determined in real time to see if they exceed the limits. If any of the parameters of heat flux density, dynamic pressure, overload, and lateral deviation exceeds the limits, the current cycle is immediately interrupted and the emergency replanning mode is initiated.

9. The online trajectory planning and lateral adjustment method for the reentry process according to claim 8, characterized in that, Real-time monitoring and determination of whether heat flux density, dynamic pressure, overload, and lateral deviation exceed limits, including: The current heat flux density is calculated in real time. And based on a simplified heat conduction model, future predictions are obtained. Internal heat flow changes ;like Make If the heat flux density exceeds the limit, it is determined that the heat flux density exceeds the limit; otherwise, it is determined that the heat flux density does not exceed the limit. Represents the time domain for heat flux prediction. Indicates the heat flow warning coefficient; Real-time calculation to obtain the current dynamic pressure And based on the rate of change of atmospheric density, future predictions are obtained. Internal dynamic pressure changes ;like Make If the dynamic pressure exceeds the limit, it is determined that the dynamic pressure has exceeded the limit; otherwise, it is determined that the dynamic pressure has not exceeded the limit. This indicates the time domain for dynamic pressure prediction. Indicates the dynamic pressure warning coefficient; Real-time calculation to obtain the current overload And based on aerodynamic changes, future predictions are obtained. Internal overload changes ;like Make If the load exceeds the limit, it is determined that the overload has exceeded the limit; otherwise, it is determined that the overload has not exceeded the limit. Indicates the overload prediction time domain. Indicates the overload warning coefficient; The current lateral deviation is calculated in real time. Determine emergency corridors : ;like If the deviation exceeds the limit, the lateral deviation is determined to be out of bounds; otherwise, the lateral deviation is determined to be within the limit. Indicates the emergency response coefficient. .

10. The online trajectory planning and lateral adjustment method for the reentry process according to claim 2, characterized in that, The heat flux density constraint is: The dynamic pressure constraint is: The overload constraint is: ;in, Represents heat flux density, Indicates dynamic pressure. Indicates overload.

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