阅读说明：本技术 一种火箭软着陆制导方法 (Rocket soft landing guidance method ) 是由 宋征宇 王聪 胡海峰 巩庆海 于 2020-12-15 设计创作，主要内容包括：本发明提供了一种火箭软着陆制导方法,属于运载火箭控制技术领域。本发明通过自适应发动机开机方法获取发动机开机指令,为发动机开机后的着陆过程创造良好初始接入条件,而且根据火箭着陆飞行状态建立的火箭动力软着陆段在线轨迹规划方程,可以实时在线滚动规划后续飞行过程偏差适应能力最强的标称轨迹；通过制导跟踪方法,可以将火箭导引向实时生成的标称轨迹,大大降低火箭着陆过程中干扰的影响；此外,本发明还通过小步长预测关机方法确定发动机关机条件,进一步提升火箭的着陆精度。(The invention provides a rocket soft landing guidance method, and belongs to the technical field of carrier rocket control. The method obtains the starting instruction of the engine by a self-adaptive engine starting method, creates a good initial access condition for the landing process after the engine is started, and can perform real-time online rolling planning on the nominal track with the strongest deviation adaptability in the subsequent flight process according to the rocket power soft landing stage online track planning equation established according to the rocket landing flight state; by means of a guidance tracking method, the rocket can be guided to a nominal track generated in real time, and the influence of interference in the rocket landing process is greatly reduced; in addition, the invention also determines the engine shutdown condition through a small step length prediction shutdown method, thereby further improving the landing precision of the rocket.)

1. A rocket soft landing guidance method is characterized by comprising the following steps:

obtaining an engine starting instruction by adopting a self-adaptive engine starting method;

opening a rocket engine according to the engine starting instruction, and enabling the rocket to enter a soft landing stage;

establishing a first motion equation of a rocket power soft landing section and a first state constraint equation of the rocket power soft landing section according to the rocket soft landing motion process;

establishing an online trajectory planning equation of the rocket power soft landing section according to the first motion equation of the rocket power soft landing section and the first state constraint equation of the rocket power soft landing section;

acquiring the current state quantity and the current control quantity of the rocket; the current state quantity comprises a speed and a position; the current control quantity comprises a thrust amplitude and a program angle;

obtaining ideal control quantity of the rocket according to the current state quantity and the online trajectory planning equation of the rocket power soft landing section; the ideal control quantity comprises an ideal thrust amplitude and an ideal program angle;

correcting the deviation between the ideal controlled variable and the current controlled variable by adopting a guidance tracking method;

obtaining a standard speed shutdown quantity and a standard altitude shutdown quantity of a rocket power soft landing section;

obtaining a rocket engine shutdown instruction according to the standard speed shutdown quantity, the standard altitude shutdown quantity and the small step length prediction shutdown method;

and closing the engine according to the engine shutdown instruction, and completing the rocket soft landing.

2. A rocket soft landing guidance method as recited in claim 1, wherein said obtaining an engine start command using an adaptive engine start method comprises:

establishing a second motion equation of a rocket power soft landing section and a second state constraint equation of the rocket power soft landing section according to the rocket soft landing motion process;

establishing an ideal starting speed trajectory planning equation of the rocket according to the second motion equation of the rocket power soft landing section and the second state constraint equation of the rocket power soft landing section;

acquiring the current position and the current speed of the rocket;

obtaining the ideal landing time of the current position and the ideal starting speed of the current position of the rocket according to the current position of the rocket and the ideal starting speed trajectory planning equation of the rocket;

and determining the engine starting instruction according to the ideal landing time of the current position, the ideal starting speed of the current position and the current speed.

3. A rocket soft landing guidance method as recited in claim 1, wherein said rocket powered soft landing segment first equation of motion comprises:

D＝0.5ρS_refC_D||V||V

wherein r ═ x, y, z]^TIs a position vector, x is the position of the rocket on the x axis, y is the position of the rocket on the y axis, z is the position of the rocket on the z axis, and V is [ V ]_x,V_y,V_z]^TIs a velocity vector, V_xVelocity of rocket in x-axis, V_yVelocity of rocket in y-axis, V_zIs the velocity of the rocket in the z-axis, m is the rocket mass, psi is the yaw angle,is a pitch angle, ω_ψIn order to be able to determine the yaw rate,for pitch angular velocity, T for engine thrust amplitude, delta_TIs the engine thrust amplitude change rate, D is the aerodynamic drag vector, rho is the atmospheric density, S_refAs reference area, C_DIs the aerodynamic drag coefficient, g is the vector of gravitational acceleration, I_spIs specific impulse of engine, g₀Is the sea level gravitational acceleration.

4. A rocket soft landing guidance method as recited in claim 3, wherein said rocket powered soft landing segment first state constraint equation comprises: a first initial state constraint equation, a first terminal state constraint equation and a first process constraint equation;

the first initial state constraint equation comprises:

[r₀,V₀,m₀]＝[r,V,m](t₀)

wherein, t₀Indicates the current time, r₀Indicating the position of the rocket at the current moment, V₀Representing the velocity of the rocket at the current moment, m₀Representing the mass of the rocket at the current moment;

the first terminal state constraint equation comprises:

V_yf≤V_y(t_f)≤0,|V_x(t_f)|≤V_xf,|V_z(t_f)|≤V_zf,m(t_f)≥m_min

wherein, t_fIndicating the terminal time, y_fIndicating the desired end position of the rocket in the y-axis, x_fIndicating the desired end position of the rocket in the x-axis, z_fIndicating the desired end position of the rocket in the z-axis, V_yfIs the lower bound of the terminal velocity of the rocket in the y-axis, V_xfDesired terminal velocity, V, for rocket in x-axis_zfDesired terminal velocity, T, for rocket in z-axis_yRepresenting the magnitude of engine thrust in the y-axis direction of the rocket,representing the desired pitch angle, m, of the rocket at the terminal location_minRepresents a rocket minimum mass;

the first process constraint equation comprises:

T_min≤T(t)≤T_max,|δ_T(t)|≤δ_Tmax,

|ω_ψ(t)|≤ω_ψmax,y(t)≥0,V_y(t)≤0

wherein the content of the first and second substances,representing the maximum value of pitch angle, T_minRepresenting the minimum value of the thrust amplitude of the engine, T_maxRepresenting the maximum magnitude of engine thrust, δ_TmaxRepresents the maximum value of the rate of change of the magnitude of the engine thrust,at maximum pitch rate, ω_ψmaxIs the maximum value of the yaw rate.

5. A rocket soft landing guidance method as recited in claim 4, wherein said establishing rocket powered soft landing segment on-line trajectory planning equation based on said rocket powered soft landing segment first equation of motion and said rocket powered soft landing segment first state constraint equation comprises:

establishing a first motion equation of the rocket power soft landing section and a first state constraint equation of the rocket power soft landing section simultaneously, and establishing an online trajectory planning equation of the rocket power soft landing section by taking the fuel minimum of the power soft landing section as an optimization target;

the rocket power soft landing segment online trajectory planning equation comprises the following steps:

min J＝-m(t_f)

[r₀,V₀,m₀]＝[r,V,m](t₀),y(t_f)＝y_f,|x(t_f)|≤x_f,|z(t_f)|≤z_f,

V_yf≤V_y(t_f)≤0,|V_x(t_f)|≤V_xf,|V_z(t_f)|≤V_zf,m(t_f)≥m_min,

T_min≤T≤T_max,|δ_T(t)|≤δ_Tmax,y(t)≥0,V_y(t)≤0。

6. a rocket soft landing guidance method as recited in claim 2, wherein said rocket powered soft landing segment second equations of motion comprise:

7. a rocket soft landing guidance method as recited in claim 6, wherein the rocket powered soft landing segment second state constraint equation comprises: a second initial state constraint equation, a second terminal state constraint equation and a second process constraint equation;

the second initial state constraint equation comprises:

r₀＝r(t₀),m₀＝m(t₀).

wherein, t₀Denotes the initial point time, r₀Denotes the rocket initial position, m₀Representing the initial mass of the rocket;

the second terminal state constraint equation comprises:

r(t_f)＝r_f,V(t_f)＝V_f,m(t_f)≥m_min.

r_findicating the desired end position of the rocket, V_fRepresenting the velocity of the rocket at the desired terminal location;

the second process constraint equation comprises:

wherein, T_midIs the median value of the engine thrust adjustment range.

8. A rocket soft landing guidance method as recited in claim 7, wherein said establishing a rocket ideal starting speed trajectory planning equation based on said rocket powered soft landing segment second equation of motion and said rocket powered soft landing segment second state constraint equation comprises:

establishing a second motion equation of a rocket power soft landing section and a second state constraint equation of the rocket power soft landing section simultaneously, and establishing an ideal starting speed trajectory planning equation of the rocket by taking the fuel minimum of the power soft landing section as an optimization target;

the ideal starting speed trajectory planning equation of the rocket comprises the following steps:

Technical Field

The invention belongs to the technical field of carrier rocket control, and particularly relates to a rocket soft landing guidance method.

Background

At present, 9 Merlin 1D engines are configured at one stage or a boosting stage of the Falcon series rocket capable of realizing vertical landing of the rocket, and the thrust-weight ratio can be greatly reduced by only starting a few engines instead of all the engines in the landing process, the thrust symmetry can be kept, and the attitude control stability is maintained. The rocket makes the thrust-weight ratio equal to 1 before landing by adjusting the thrust of the engine, and realizes constant-speed landing at safe landing speed. However, at present, a plurality of active rockets are only connected with a small number of engines in parallel at one stage or boosting stage, such as CZ-5 rockets and CZ-7 rockets in China, European Ariane 6 rockets and Japanese H3 rockets, and the like, and only two engines are arranged at one stage. If one platform is closed in the landing process, the attitude is difficult to keep stable; if the engine is not closed, the engine is required to have deep throttling capacity, and the deep throttling of a high-thrust engine is always a difficult problem. If the guidance method can still realize the fixed-point soft landing of the rocket under the condition that the minimum thrust is still larger than the large thrust-weight ratio of the gravity of the rocket, the pressure of deep throttling of the engine can be relieved, so that the in-service rocket can be economically upgraded to a reusable carrier rocket through the proper adjustment of the throttling capacity of the engine, and the design of a plurality of engines connected in parallel for reuse is avoided. However, under the condition of large thrust-weight ratio, the physical feasible region of the rocket power landing section is greatly compressed and easily flies out of the feasible region under the interference state, so that fixed-point soft landing is difficult to realize.

Disclosure of Invention

The invention aims to provide a rocket soft landing guidance method, and aims to solve the problem that when an existing rocket is vertically landed, the existing rocket is easy to fly out of a feasible region in an interference state, so that the soft landing position is inaccurate.

In order to achieve the purpose, the invention adopts the technical scheme that:

a rocket soft landing guidance method comprises the following steps:

obtaining an engine starting instruction by adopting a self-adaptive engine starting method;

opening a rocket engine according to the engine starting instruction, and enabling the rocket to enter a soft landing stage;

establishing a first motion equation of a rocket power soft landing section and a first state constraint equation of the rocket power soft landing section according to the rocket soft landing motion process;

establishing an online trajectory planning equation of the rocket power soft landing section according to the first motion equation of the rocket power soft landing section and the first state constraint equation of the rocket power soft landing section;

acquiring the current state quantity and the current control quantity of the rocket; the current state quantity comprises a speed and a position; the current control quantity comprises a thrust amplitude and a program angle;

obtaining ideal control quantity of the rocket according to the current state quantity and the online trajectory planning equation of the rocket power soft landing section; the ideal control quantity comprises an ideal thrust amplitude and an ideal program angle;

correcting the deviation between the ideal controlled variable and the current controlled variable by adopting a guidance tracking method;

obtaining a standard speed shutdown quantity and a standard altitude shutdown quantity of a rocket power soft landing section;

obtaining a rocket engine shutdown instruction according to the standard speed shutdown quantity, the standard altitude shutdown quantity and the small step length prediction shutdown method;

and closing the engine according to the engine shutdown instruction, and completing the rocket soft landing.

Preferably, the obtaining of the engine starting instruction by the adaptive engine starting method includes:

establishing a second motion equation of a rocket power soft landing section and a second state constraint equation of the rocket power soft landing section according to the rocket soft landing motion process;

establishing an ideal starting speed trajectory planning equation of the rocket according to the second motion equation of the rocket power soft landing section and the second state constraint equation of the rocket power soft landing section;

acquiring the current position and the current speed of the rocket;

obtaining the ideal landing time of the current position and the ideal starting speed of the current position of the rocket according to the current position of the rocket and the ideal starting speed trajectory planning equation of the rocket;

and determining the engine starting instruction according to the ideal landing time of the current position, the ideal starting speed of the current position and the current speed.

Preferably, the rocket power soft landing segment first equation of motion comprises:

D＝0.5ρS_refC_D||V||V

wherein r ═ x, y, z]^TIs a position vector, x is the position of the rocket on the x axis, y is the position of the rocket on the y axis, z is the position of the rocket on the z axis, and V is [ V ]_x,V_y,V_z]^TIs a velocity vector, V_xVelocity of rocket in x-axis, V_yVelocity of rocket in y-axis, V_zIs the velocity of the rocket in the z-axis, m is the rocket mass, psi is the yaw angle,is a pitch angle, ω_ψIn order to be able to determine the yaw rate,for pitch angular velocity, T for engine thrust amplitude, delta_TIs the engine thrust amplitude change rate, D is the aerodynamic drag vector, rho is the atmospheric density, S_refAs reference area, C_DIs the aerodynamic drag coefficient, g is the vector of gravitational acceleration, I_spIs specific impulse of engine, g₀Is the sea level gravitational acceleration.

Preferably, the rocket power soft landing stage first state constraint equation comprises: a first initial state constraint equation, a first terminal state constraint equation and a first process constraint equation;

the first initial state constraint equation comprises:

[r₀,V₀,m₀]＝[r,V,m](t₀)

wherein, t₀Indicates the current time, r₀Indicating the position of the rocket at the current time,V₀representing the velocity of the rocket at the current moment, m₀Representing the mass of the rocket at the current moment;

the first terminal state constraint equation comprises:

V_yf≤V_y(t_f)≤0,|V_x(t_f)|≤V_xf,|V_z(t_f)|≤V_zf,m(t_f)≥m_min

wherein, t_fIndicating the terminal time, y_fIndicating the desired end position of the rocket in the y-axis, x_fIndicating the desired end position of the rocket in the x-axis, z_fIndicating the desired end position of the rocket in the z-axis, V_yfIs the lower bound of the terminal velocity of the rocket in the y-axis, V_xfDesired terminal velocity, V, for rocket in x-axis_zfDesired terminal velocity, T, for rocket in z-axis_yRepresenting the magnitude of engine thrust in the y-axis direction of the rocket,representing the desired pitch angle, m, of the rocket at the terminal location_minRepresents a rocket minimum mass;

the first process constraint equation comprises:

wherein the content of the first and second substances,representing the maximum value of pitch angle, T_minRepresenting the minimum value of the thrust amplitude of the engine, T_maxIndicating maximum magnitude of engine thrustValue delta_TmaxRepresents the maximum value of the rate of change of the magnitude of the engine thrust,at maximum pitch rate, ω_ψmaxIs the maximum value of the yaw rate.

Preferably, the establishing of the rocket power soft landing section online trajectory planning equation according to the rocket power soft landing section first motion equation and the rocket power soft landing section first state constraint equation comprises:

establishing a first motion equation of the rocket power soft landing section and a first state constraint equation of the rocket power soft landing section simultaneously, and establishing an online trajectory planning equation of the rocket power soft landing section by taking the fuel minimum of the power soft landing section as an optimization target;

the rocket power soft landing segment online trajectory planning equation comprises the following steps:

min J＝-m(t_f)

[r₀,V₀,m₀]＝[r,V,m](t₀),y(t_f)＝y_f,|x(t_f)|≤x_f,|z(t_f)|≤z_f,

V_yf≤V_y(t_f)≤0,|V_x(t_f)|≤V_xf,|V_z(t_f)|≤V_zf,m(t_f)≥m_min,

T_min≤T≤T_max,|δ_T(t)|≤δ_Tmax,y(t)≥0,V_y(t)≤0。

preferably, the rocket power soft landing segment second equation of motion comprises:

D＝0.5ρS_refC_D||V||V

preferably, the second state constraint equation of the rocket power soft landing segment comprises: a second initial state constraint equation, a second terminal state constraint equation, and a second process constraint equation:

the second initial state constraint equation comprises:

r₀＝r(t₀),m₀＝m(t₀).

wherein, t₀Denotes the initial point time, r₀Denotes the rocket initial position, m₀Representing the initial mass of the rocket;

the second terminal state constraint equation comprises:

r_findicating the desired end position of the rocket, V_fRepresenting the velocity of the rocket at the desired terminal location;

the second process constraint equation comprises:

wherein, T_midIs the median value of the engine thrust adjustment range.

Preferably, the establishing of the ideal rocket starting speed trajectory planning equation according to the second motion equation of the rocket power soft landing segment and the second state constraint equation of the rocket power soft landing segment includes:

establishing a second motion equation of a rocket power soft landing section and a second state constraint equation of the rocket power soft landing section simultaneously, and establishing an ideal starting speed trajectory planning equation of the rocket by taking the fuel minimum of the power soft landing section as an optimization target;

the ideal starting speed trajectory planning equation of the rocket comprises the following steps:

minJ＝-m(t_f)

the rocket soft landing guidance method provided by the invention has the beneficial effects that: compared with the prior art, the invention provides a method for obtaining the starting instruction of the engine by a self-adaptive engine starting method, creates a good initial access condition for the landing process after the engine is started, and can real-timely and online roll-plan the nominal track with the strongest deviation adaptability in the subsequent flight process according to the rocket power soft landing section online track planning equation established by the rocket landing flight state; by means of a guidance tracking method, the rocket can be guided to a nominal track generated in real time, and the influence of interference in the rocket landing process is greatly reduced; in addition, the invention also determines the engine shutdown condition through a small step length prediction shutdown method, thereby further improving the landing precision of the rocket.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a flow chart of a rocket soft landing guidance method provided by an embodiment of the invention;

fig. 2 is a schematic diagram of a rocket soft landing guidance method provided by an embodiment of the invention.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is 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 of the invention and are not intended to limit the invention.

Referring to fig. 1 and 2, a description will now be given of a rocket soft landing guidance method provided by the present invention. A rocket soft landing guidance method comprises the following steps:

step 101: obtaining an engine starting instruction by adopting a self-adaptive engine starting method;

in order to obtain the starting condition of the engine of the rocket entering the power soft landing section, the invention provides a self-adaptive engine starting method for the power soft landing section of the reusable carrier rocket, so that the rocket can enter the power soft landing section under the condition of the largest feasible region, and the deviation adaptive capacity of the power soft landing section is improved.

Step 101 specifically includes:

and S1, establishing a second motion equation of the rocket power soft landing section and a second state constraint equation of the rocket power soft landing section according to the rocket soft landing motion process.

As will be further described below with respect to a process, a target coordinate system is defined under which the motion of the rocket-powered soft landing stage is described. Target coordinate system origin O at landingAnd point, an OY axis is vertical to the target point local horizontal plane and points to the sky, an OX axis points to the emission point in the target point local horizontal plane, and an OZ axis meets the right-hand rule. When describing the three-degree-of-freedom centroid motion equation of the dynamic soft landing segment, the rocket is considered as particles, the influence of engine thrust, aerodynamic force and mass change on the motion process of the rocket is considered, the dynamic process of motion around the centroid attitude is ignored, and the rocket attitude can respond to the program angle command in real time. Defining the thrust of the engine to be always along the axial direction of the rocket, wherein the included angle between the thrust vector and the OXY plane is a yaw angle psi, and the included angle between the projection of the thrust vector in the OXY plane and the OX axis is a pitch angle

The established second equation of motion of the rocket power soft landing segment is as follows:

wherein r ═ x, y, z]^TIs a position vector, x is the position of the rocket on the x axis, y is the position of the rocket on the y axis, z is the position of the rocket on the z axis, and V is [ V ]_x,V_y,V_z]^TIs a velocity vector, V_xVelocity of rocket in x-axis, V_yVelocity of rocket in y-axis, V_zIs the velocity of the rocket in the z-axis, m is the rocket mass, psi is the yaw angle,is a pitch angle, ω_ψIn order to be able to determine the yaw rate,pitch angular velocity, T engine thrust amplitude, D aerodynamic drag vector, ρ atmospheric density, S_refAs reference area, C_DIs the aerodynamic drag coefficient, g is the vector of the gravitational acceleration (the projected vector of the gravitational acceleration under the target system), I_spIs specific impulse of engine, g₀Is the sea level gravitational acceleration.

The second state constraint equation of the rocket power soft landing segment comprises the following steps: a second initial state constraint equation, a second terminal state constraint equation and a second process constraint equation;

the second initial state constraint equation includes:

r₀＝r(t₀),m₀＝m(t₀). (2)

wherein, t₀Denotes the initial point time, r₀Denotes the rocket initial position, m₀Representing the initial mass of the rocket;

the second terminal state constraint equation comprises:

r_findicating the desired end position of the rocket, V_fRepresenting the velocity of the rocket at the desired terminal location,representing the desired pitch angle, m, of the rocket at the terminal location_minRepresents a rocket minimum mass;

the second process constraint equation includes:

wherein, T_midThe value of the middle value of the thrust adjusting range of the engine is represented by a subscript max, wherein the subscript max represents the maximum value allowed by the corresponding state quantity and control quantity in the landing process, the height and speed inequality constraint represents that the height cannot be lower than a target point in the landing process, and the longitudinal speed is always downward.

S2, establishing an ideal starting speed trajectory planning equation of the rocket according to a second motion equation of the rocket power soft landing section and a second state constraint equation of the rocket power soft landing section;

further, according to the constraint conditions described in (1) to (4), an ideal starting speed trajectory planning problem with the largest feasible region is constructed by taking the fuel economy of the dynamic soft landing segment as an optimization target, and the specific form is as follows:

wherein minJ ═ m (t)_f) And optimizing an objective function for the fuel of the rocket power soft landing stage.

S3, acquiring the current position and the current speed of the rocket;

s4, obtaining the ideal landing time of the current position and the ideal starting speed of the current position of the rocket according to the current position of the rocket and the ideal starting speed trajectory planning equation of the rocket;

and solving the ideal starting speed trajectory planning problem with the largest feasible region by using a numerical optimization algorithm (such as an interior point method or a sequential quadratic programming algorithm) to obtain an optimal solution. The terminal time of the optimal solution is t_f ^optI.e. the ideal landing time; initial velocity vector V of the optimal solution₀ ^optI.e. the ideal boot speed corresponding to the current position.

And S5, determining an engine starting instruction according to the ideal landing time of the current position, the ideal starting speed of the current position and the current speed.

Specifically, the allowable shortest flight time of the dynamic soft landing segment is defined as t_fminIf t is_fmin≥t_f ^optIf not, evaluating the deviation between the current time speed of the rocket and the ideal starting speed. Defining a boot characteristic quantity DeltaV_IFor quantifying the deviation between the current time speed of the rocket and the ideal starting speed, the specific calculation mode is as follows,

wherein p is_x、p_y、p_zWeight parameters respectively representing the speed deviation of the rocket in the three directions of the x axis, the y axis and the z axis can adjust the proportion of the speed deviation in different directions to the startup characteristic quantity according to task requirements, and further,p_xweight parameter, p, representing the velocity deviation of the rocket in the direction of the x-axis_yWeight parameter, p, representing the velocity deviation of the rocket in the y-axis direction_zWeight parameter, V, representing the velocity deviation of the rocket in the direction of the z-axis_x0 ^optRepresents the component of the ideal starting speed of the current position of the rocket in the direction of the x axis, V_y0 ^optRepresenting the component of the ideal starting speed of the current position of the rocket in the direction of the y axis, V_z0 ^optRepresenting the component of the ideal boot speed of the current position of the rocket in the z-axis direction.

Defining the last control period as corresponding to time t_oldIf Δ V_I(t)≥ΔV_I(t_old) Otherwise, the engine is started, otherwise, the next control cycle is continued, and the steps S3-S5 are repeatedly executed until the engine is started.

The self-adaptive engine starting method provided by the invention has the advantages that the standard track of the median thrust landing is planned on line, the ideal initial speed corresponding to the current position is obtained, the deviation between the current speed and the ideal speed is calculated, the engine starting instruction is sent out when the deviation is minimum, meanwhile, the median thrust standard track generated on line can be used as the initial guess value of the on-line track planning equation of the subsequent rocket power soft landing section, and the calculation efficiency of an on-line planning algorithm is improved.

Step 102: opening a rocket engine according to an engine starting instruction, and enabling the rocket to enter a soft landing stage;

step 103: establishing a first motion equation of a rocket power soft landing section and a first state constraint equation of the rocket power soft landing section according to the rocket soft landing motion process;

the first motion equation of the rocket power soft landing segment is established in a target coordinate system and comprises the following steps:

wherein r ═ x, y, z]^TIs a position vector, x is the position of the rocket on the x axis, y is the position of the rocket on the y axis, z is the position of the rocket on the z axis, and V is [ V ]_x,V_y,V_z]^TIs a velocity vector, V_xVelocity of rocket in x-axis, V_yVelocity of rocket in y-axis, V_zIs the velocity of the rocket in the z-axis, m is the rocket mass, psi is the yaw angle,is a pitch angle, ω_ψIn order to be able to determine the yaw rate,for pitch angular velocity, T for engine thrust amplitude, delta_TIs the engine thrust amplitude change rate, D is the aerodynamic drag vector, rho is the atmospheric density, S_refAs reference area, C_DIs the aerodynamic drag coefficient, g is the vector of the gravitational acceleration (the projected vector of the gravitational acceleration under the target system), I_spIs specific impulse of engine, g₀Is the sea level gravitational acceleration.

The first state constraint equation of the rocket power soft landing segment comprises the following steps: a first initial state constraint equation, a first terminal state constraint equation and a first process constraint equation;

the first initial state constraint equation comprises:

[r₀,V₀,m₀]＝[r,V,m](t₀) (8)

wherein, t₀Indicates the current time, r₀Indicating the position of the rocket at the current moment, V₀Representing the velocity of the rocket at the current moment, m₀Representing the mass of the rocket at the current moment;

the first terminal state constraint equation comprises:

V_yf≤V_y(t_f)≤0,|V_x(t_f)|≤V_xf,|V_z(t_f)|≤V_zf,m(t_f)≥m_min (9)

wherein, t_fWhen indicating the terminalM, y_fIndicating the desired end position of the rocket in the y-axis, x_fIndicating the desired end position of the rocket in the x-axis, z_fIndicating the desired end position of the rocket in the z-axis, V_yfIs the lower bound of the terminal velocity of the rocket in the y-axis, V_xfDesired terminal velocity, V, for rocket in x-axis_zfDesired terminal velocity, T, for rocket in z-axis_yRepresenting the magnitude of engine thrust in the y-axis direction of the rocket,representing the desired pitch angle, m, of the rocket at the terminal location_minRepresents a rocket minimum mass;

the first process constraint equation includes:

wherein the content of the first and second substances,representing the maximum value of pitch angle, T_minRepresenting the minimum value of the thrust amplitude of the engine, T_maxRepresenting the maximum magnitude of engine thrust, δ_TmaxRepresents the maximum value of the rate of change of the magnitude of the engine thrust,at maximum pitch rate, ω_ψmaxThe maximum value of the yaw rate is shown, wherein the subscript max represents the maximum value allowed by the corresponding state quantity and control quantity in the landing process, the height and speed inequality constraint represents that the height cannot be lower than the target point in the landing process, and the longitudinal speed is always downward.

Step 104: establishing an online trajectory planning equation of the rocket power soft landing section according to a first motion equation of the rocket power soft landing section and a first state constraint equation of the rocket power soft landing section;

constructing a dynamic soft landing stage trajectory planning proposition with the largest feasible domain by taking the fuel economy of the dynamic soft landing stage as an optimization target according to the constraint conditions described in (7) to (10), wherein the specific form is as follows,

min J＝-m(t_f)

[r₀,V₀,m₀]＝[r,V,m](t₀),y(t_f)＝y_f,|x(t_f)|≤x_f,|z(t_f)|≤z_f,

V_yf≤V_y(t_f)≤0,|V_x(t_f)|≤V_xf,|V_z(t_f)|≤V_zf,m(t_f)≥m_min,

T_min≤T≤T_max,|δ_T(t)|≤δ_Tmax,y(t)≥0,V_y(t)≤0

the method introduces the influence of the thrust change rate when describing the planning problem, and constructs the online trajectory planning equation of the rocket power soft landing section with the largest feasible region by limiting the amplitude of the thrust change rate. In each planning period, according to the flight state of the rocket at the current moment, a non-linear programming algorithm (such as a Newton method, an interior point method, sequential quadratic programming and the like) is adopted to solve the discretization optimal flight track state quantity and the thrust control vector meeting the constraint condition in a rolling mode, so that the change of the optimal thrust amplitude control quantity is as smooth as possible, a margin is reserved between the optimal thrust amplitude control quantity and the maximum value and the minimum value, the thrust always has positive and negative adjusting capacity, interference or deviation which possibly occurs in the subsequent flight process is responded, and the adaptability of the rocket to the uncertainty of the subsequent flight process is improved as much as possible in a physical feasible region.

Step 105: acquiring the current state quantity and the current control quantity of the rocket; the current state quantity includes speed and position; the current control quantity comprises a thrust amplitude and a program angle;

step 106: obtaining ideal control quantity of the rocket according to the current state quantity and an online trajectory planning equation of the rocket power soft landing section; the ideal control quantity comprises an ideal thrust amplitude and an ideal program angle;

step 107: correcting the deviation between the ideal controlled variable and the current controlled variable by adopting a guidance tracking method;

furthermore, because the guidance period is shorter than the planning period, at the current flight time of the rocket, appropriate interpolation independent variables (such as time, speed, position and the like) are selected according to task characteristics, and interpolation (such as linear interpolation, quadratic curve interpolation, cubic spline and the like) is carried out on a standard track state sequence which is newly generated by an online track planning equation at the power soft landing section of the rocket to obtain the ideal state quantity and the ideal control quantity at the current time of the rocket. According to the deviation between the current actual state and the ideal state of the rocket, the ideal control quantity is corrected in real time by using a guidance tracking method (such as PID control, LQR control and the like), and the landing precision of the rocket can be greatly improved.

Step 108: obtaining a standard speed shutdown quantity and a standard altitude shutdown quantity of a rocket power soft landing section;

step 109: obtaining a rocket engine shutdown instruction according to the standard speed shutdown quantity, the standard altitude shutdown quantity and the small step length prediction shutdown method;

and calculating the shutdown time speed and altitude value corresponding to the landing at an ideal speed (for example-1 m/s) by combining the effect of the shutdown of the rocket engine and the ideal quality of the rocket during landing, and taking the shutdown time speed and altitude value as the standard speed shutdown quantity and standard altitude shutdown quantity of the rocket power soft landing section. After the rocket enters a power soft landing section, respectively predicting the remaining time of reaching the standard speed shutdown quantity and the standard altitude shutdown quantity according to the current speed and altitude and the speed change rate and altitude change rate of each guidance period, and taking the minimum value of the two values as the predicted time to be flown. In order to reduce the influence of the guidance period on the shutdown precision, a small-step prediction shutdown method is adopted, and when the predicted time to fly is less than N guidance periods (if N can be 1, 2 or 3), 1ms timing is started, so that the sending precision of a shutdown instruction is less than 1ms, and the landing precision is improved.

Step 1010: and closing the engine according to the engine shutdown instruction, and completing the rocket soft landing.

The rocket soft landing guidance method provided by the invention has the beneficial effects that: compared with the prior art, the invention provides a method for obtaining the starting instruction of the engine by a self-adaptive engine starting method, creates a good initial access condition for the landing process after the engine is started, and can real-timely and online roll-plan the nominal track with the strongest deviation adaptability in the subsequent flight process according to the rocket power soft landing section online track planning equation established by the rocket landing flight state; by means of a guidance tracking method, the rocket can be guided to a nominal track generated in real time, and the influence of interference in the rocket landing process is greatly reduced; in addition, the invention also determines the engine shutdown condition through a small step length prediction shutdown method, further improves the landing precision of the rocket, and is suitable for the rocket power reverse thrust soft landing process under the condition of large thrust-weight ratio.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.