CN113176787B - Power descent trajectory planning online triggering method based on drop point prediction - Google Patents
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Abstract
The invention relates to a power descent trajectory planning online triggering method based on drop point prediction, belonging to the technical field of power descent guidance of reentry return landing aircrafts; step one, judging the flight speed of an aircraft pneumatic deceleration section; when the flying speed is lower than the speed threshold A, entering a step two; step two, adopting a soft landing trajectory planning equation set to predict the position [ r ] of the landing point y (t f ),r z (t f )](ii) a Step three, calculating a flight path predicted value S in real time according to the predicted landing point position predicted And voyage expected value S desired (ii) a Step four, when the voyage predicted value S predicted Less than desired range value S desired When the aircraft flies continuously according to the pneumatic deceleration section; when voyage predicted value S predicted Greater than or equal to voyage expected value S desired Entering the step five; establishing an online track planning model, solving an optimal solution, and completing online planning; the method can effectively avoid unreasonable initial triggering conditions, thereby improving the reliability of the return landing on-line track planning technology and further improving the safety and success rate of return landing.
Description
Technical Field
The invention belongs to the technical field of power descent guidance of a reentry return landing aircraft, and relates to a power descent trajectory planning online triggering method based on drop point prediction.
Background
Repeatable, low-cost and intelligent development is the development direction of a future space transport system, an online trajectory planning technology is used as a core technology for realizing the return landing guidance system of the next generation of reusable space transporters, and the optimal or feasible trajectory meeting comprehensive terminal constraints and process states and control complex constraints is solved online in the original problem reachable domain so as to meet the harsh landing safety constraints and high-precision requirements. The main difficulty of the technology is that the optimal or feasible fuel track meeting the process, terminal state and control constraint needs to be planned on line at the ignition backstepping moment of the engine so as to eliminate the large dispersion deviation of the initial state of the ignition moment accumulated in the pre-landing stage.
At present, related technical research mainly focuses on a track planning algorithm based on real-time optimization, generally takes flight time, speed or altitude as a trigger condition of an ignition opportunity, actual flight deviation cannot be considered in the trigger mode, and the initial state is often greatly dispersed when the trigger condition is reached, so that a track with large flight distance transfer needs to be planned, difficulty and challenge are added to the track planning algorithm, and even when the trigger opportunity is not correct, the track planning algorithm cannot be solved under current constraint, so that landing failure is caused.
The complexity and feasibility of an online trajectory planning algorithm are directly influenced by the power descent trajectory planning triggering method, and if an inappropriate power descent initial ignition opportunity is triggered, a feasible solution cannot be searched by the trajectory planning algorithm, so that landing failure is caused.
Disclosure of Invention
The invention solves the technical problems that: the method overcomes the defects of the prior art, provides the power descent trajectory planning online triggering method based on the drop point prediction, and can effectively avoid unreasonable initial triggering conditions, thereby improving the reliability of the return landing online trajectory planning technology and further improving the safety and success rate of return landing.
The technical scheme of the invention is as follows:
a power descent trajectory planning online triggering method based on drop point prediction comprises the following steps:
step one, setting a speed threshold A; judging the flight speed of the pneumatic deceleration section in the reentry and return process of the aircraft; when the flying speed is not lower than the speed threshold A, continuing flying according to the pneumatic deceleration section; when the flying speed is lower than the speed threshold A, entering a step two;
step two, adopting a soft landing trajectory planning equation set to predict the position [ r ] of the landing point y (t f ),r z (t f )]；
Step three, calculating a flight path predicted value S in real time according to the predicted landing point position predicted And voyage expected value S desired ；
Step four, predicting the voyage value S predicted And voyage expected value S desired Comparing, and obtaining the predicted value S of the voyage predicted Less than desired range value S desired When the aircraft flies continuously according to the pneumatic deceleration section; when voyage predicted value S predicted Greater than or equal to voyage expected value S desired Triggering the online track planning of power reduction, and entering a fifth step;
step five, establishing an online track planning model, and solving a thrust vector instruction T of the planned engine according to the online track planning model * (t) nominal post-planning trajectory position r * (t) and the post-planning velocity vector v * And (t), completing the online planning.
In the above power descent trajectory planning online triggering method based on the drop point prediction, in the first step, the pneumatic deceleration section is a preceding flight stage of the power descent section, and the flight speed is a relative landing planetary speed.
In the above on-line triggering method for power descent trajectory planning based on drop point prediction, in the second step, the soft landing trajectory planning equation set is:
s,t.
r(t 0 )＝r 0 ,v(t 0 )＝v 0 ,m(t 0 )＝m 0
r x (t f )＝0,v(t f )＝0
T(t f )＝[T x (t f )≠0 0 0]
0<m dry ≤m(t f )
0<T min ≤||T(t)||≤T max
wherein, | | x | | is a model for solving the vector long;
r (t) is a position vector which changes along with time in the landing process;
v (t) is a velocity vector;
g＝[-g 0 ,0,0]is a constant gravitational acceleration vector; wherein, g 0 The gravity acceleration of the earth surface is obtained;
t (T) is a rocket engine thrust vector;
m (t) is mass;
S ref is the effective cross-sectional area of the landing aircraft;
C D is the aerodynamic drag coefficient;
ρ is the atmospheric density;
α＝1/(I sp g 0 )，I sp specific impulse for an aircraft rocket engine;
r 0 for landing flightPredicting an initial time position vector;
v 0 predicting an initial moment velocity vector for the landing aircraft;
m 0 predicting initial moment quality for a landing aircraft;
t 0 predicting an initial moment;
t f predicting the terminal time;
r x (t f ) Is the landing terminal altitude;
T x (t f ) The magnitude of the thrust;
m dry is the structural mass of the rocket;
T min is the minimum thrust of the rocket engine;
T max the maximum thrust of the rocket engine;
calculating the terminal horizontal position of the soft landing trajectory planning equation set, namely the landing point position [ r y (t f ),r z (t f )]。
In the above on-line triggering method for power descent trajectory planning based on drop point prediction, in the third step, the flight distance predicted value S predicted The calculation method comprises the following steps:
S predicted ＝||[r y (t 0 )-r y (t f ),r z (t 0 )-r z (t f )] T ||
in the formula, r y (t 0 ) Predicting the horizontal position of the y direction at the initial moment;
r z (t 0 ) Predicting the horizontal position of the z direction at the initial moment;
voyage expected value S desired The calculation method comprises the following steps:
S desired ＝||[r y (t 0 ),r z (t 0 )] T ||。
in the above power down trajectory planning online triggering method based on drop point prediction, in the fifth step, the online trajectory planning model is:
v(t plan )＝v(t 0 )+a(t 0 )·(t plan -t 0 )
r(t plan )＝r(t 0 )+v(t 0 )·(t plan -t 0 )+a(t 0 )·(t plan -t 0 ) 2 /2
in the formula, t plan Time for starting flying according to the planning instruction after the track planning is finished;
t plan -t 0 consuming time for planning algorithms
v(t plan ) The flight speed after the planning for recursion is completed;
r(t plan ) A position vector after the recursive planning is completed;
r(t 0 ) The position when the online planning is triggered;
v(t 0 ) Speed when triggering on-line planning;
a(t 0 ) An acceleration vector when triggering the online planning;
with t plan 、r(t plan )、v(t plan ) And performing online track planning calculation as initial state input of the online track planning.
In the above on-line triggering method for power descent trajectory planning based on drop point prediction, the on-line trajectory planning calculation method is:
establishing a fixed point landing fuel optimal nonlinear equation system calculated by on-line trajectory planning:
s,t.
r(t plan )＝r(t 0 )+v(t 0 )·(t plan -t 0 )+a(t 0 )·(t plan -t 0 ) 2 /2,
v(t plan )＝v(t 0 )+a(t 0 )·(t plan -t 0 ),m(t plan )＝m 0
r(t f )＝0,v(t f )＝0
T(t f )＝[0 T y (t f )≠0 0]
0<m dry ≤m(t f )
0<T min ≤||T(t)||≤T max
|||T(t i+1 )||-||T(t i )|||≤ΔT max
||[r x (t),r z (t)] T ||cotθ gs ≤r y (t),θ gs ∈[0,90°)
in the formula, r (t) f ) Planning the position of an equation for the three-dimensional vector of the landing terminal position and the fixed-point landing track;
t i+1 and t i Two adjacent time points are taken in the calculation process;
ΔT max the maximum value allowed by the thrust change between two beats;
θ T,max Is an angle constraint between the thrust direction and the plumb line;
θ gs is the connecting line between the rocket and the landing point and the horizonThe included angle between the two is restricted;
solving the optimal solution T of the fixed point landing fuel optimal nonlinear equation set calculated by the online track planning * (t)、r * (t)、v * (t); wherein, T * (t) a planned engine thrust vector command; r is * (t) nominal trajectory position after planning; v. of * And (t) is a planned velocity vector.
Compared with the prior art, the invention has the beneficial effects that:
(1) The online trigger condition judgment of the power descent section at the beginning of the pneumatic deceleration section is selected, and the flight maneuver capacity of the power descent section of the aircraft is judged in real time through the drop point prediction in the flight process, so that the failure risk of power descent trajectory planning can be effectively reduced;
(2) The selection and implementation of the drop point prediction algorithm and the power descent trajectory planning algorithm can be realized through the adjustment of the terminal position constraint, and the use is convenient;
(3) According to the method, the influence of the time consumption of planning calculation is fully considered when the power descending trajectory planning is triggered, the influence of the time consumption of the trajectory planning on the planning result can be eliminated through a motion state recursion strategy, and the precision of real-time trajectory planning is improved;
(4) The invention realizes the improvement of the reliability of the power-down online trajectory planning
Drawings
Fig. 1 is an on-line triggering flow chart of the power descent trajectory planning of the present invention.
Detailed Description
The invention is further illustrated by the following examples.
The invention provides a power descent trajectory planning online triggering method based on drop point prediction, which solves the problem of determining the ignition reverse thrust opportunity of a power descent section of a returned landing aircraft and ensures that a feasible solution exists when an online trajectory planning algorithm is started.
An online trigger method for power descent trajectory planning based on drop point prediction is shown in fig. 1, and specifically comprises the following steps:
step one, setting a speed threshold A; judging the flight speed of the pneumatic deceleration section in the reentry and return process of the aircraft; when the flying speed is not lower than the speed threshold A, continuing flying according to the pneumatic deceleration section; when the flying speed is lower than the speed threshold A, entering a step two; the pneumatic deceleration section is a preorder flight stage of the power descending section, and the flight speed is the relative landing planetary speed.
Step two, adopting a soft landing trajectory planning equation set to predict the position [ r ] of the landing point y (t f ),r z (t f )](ii) a The soft landing trajectory planning equation set is as follows:
s,t.
r(t 0 )＝r 0 ,v(t 0 )＝v 0 ,m(t 0 )＝m 0
r x (t f )＝0,v(t f )＝0
T(t f )＝[T x (t f )≠0 0 0]
0<m dry ≤m(t f )
0<T min ≤||T(t)||≤T max
wherein, | | x | | is a model for solving the vector long;
r (t) is a position vector which changes along with time in the landing process;
v (t) is a velocity vector;
g＝[-g 0 ,0,0]is a constant gravity acceleration vector; wherein, g 0 The gravity acceleration of the earth surface is obtained;
t (T) is a rocket engine thrust vector;
m (t) is mass;
S ref is the effective cross-sectional area of the landing aircraft;
C D is the aerodynamic drag coefficient;
ρ is the atmospheric density;
α＝1/(I sp g 0 )，I sp specific impulse for an aircraft rocket engine;
r 0 predicting an initial time position vector for the landing aircraft;
v 0 predicting an initial moment velocity vector for the landing aircraft;
m 0 predicting initial moment quality for a landing aircraft;
t 0 predicting an initial moment;
t f predicting the terminal time;
r x (t f ) Is the landing terminal altitude;
T x (t f ) The magnitude of the thrust;
m dry is the structural mass of the rocket;
T min is the minimum thrust of the rocket engine;
T max the maximum thrust of the rocket engine;
calculating the terminal horizontal position of the soft landing trajectory planning equation set, namely the landing point position [ r y (t f ),r z (t f )]。
Step three, calculating a flight prediction value S in real time according to the predicted landing point position predicted And voyage expected value S desired (ii) a Predicted value S of voyage predicted The calculation method comprises the following steps:
S predicted ＝||[r y (t 0 )-r y (t f ),r z (t 0 )-r z (t f )] T ||
in the formula, r y (t 0 ) Predicting the horizontal position of the y direction at the initial moment;
r z (t 0 ) Predicting the horizontal position of the z direction at the initial moment;
voyage expected value S desired The calculation method comprises the following steps:
S desired ＝||[r y (t 0 ),r z (t 0 )] T ||。
step four, predicting the voyage value S predicted And voyage expected value S desired Comparing, and obtaining the predicted value S of the voyage predicted Less than desired range value S desired When the aircraft flies continuously according to the pneumatic deceleration section; when voyage predicted value S predicted Greater than or equal to voyage expected value S desired Triggering the online track planning of power reduction, and entering a fifth step;
step five, establishing an online track planning model, and solving a thrust vector instruction T of the planned engine according to the online track planning model * (t) post-planning nominal trajectory position r * (t) and the post-planning velocity vector v * And (t), completing the online planning. The online track planning model is as follows:
v(t plan )＝v(t 0 )+a(t 0 )·(t plan -t 0 )
r(t plan )＝r(t 0 )+v(t 0 )·(t plan -t 0 )+a(t 0 )·(t plan -t 0 ) 2 /2
in the formula, t plan Time for starting flying according to the planning instruction after the track planning is finished;
t plan -t 0 consuming time for planning algorithms
v(t plan ) Planning of completed flights for recursionSpeed;
r(t plan ) A position vector after the recursive planning is completed;
r(t 0 ) The position when the online planning is triggered;
v(t 0 ) Speed when triggering on-line planning;
a(t 0 ) An acceleration vector when online planning is triggered;
with t plan 、r(t plan )、v(t plan ) And performing online track planning calculation as the initial state input of the online track planning.
The online track planning calculation method comprises the following steps:
establishing a fixed point landing fuel optimal nonlinear equation system calculated by on-line trajectory planning:
s,t.
r(t plan )＝r(t 0 )+v(t 0 )·(t plan -t 0 )+a(t 0 )·(t plan -t 0 ) 2 /2,
v(t plan )＝v(t 0 )+a(t 0 )·(t plan -t 0 ),m(t plan )＝m 0
r(t f )＝0,v(t f )＝0
T(t f )＝[0 T y (t f )≠0 0]
0<m dry ≤m(t f )
0<T min ≤||T(t)||≤T max
|||T(t i+1 )||-||T(t i )|||≤ΔT max
||[r x (t),r z (t)] T ||cotθ gs ≤r y (t),θ gs ∈[0,90°)
in the formula, r (t) f ) Planning the position of an equation for the three-dimensional vector of the landing terminal position and the fixed-point landing track;
t i+1 and t i Two adjacent time points are taken in the calculation process;
ΔT max the maximum value allowed by the thrust change between two beats;
θ T,max Is an angle constraint between the thrust direction and the plumb line;
θ gs the included angle between a connecting line between the rocket and the landing point and the horizon is restrained;
solving the optimal solution T of the fixed point landing fuel optimal nonlinear equation set calculated by the online track planning * (t)、r * (t)、v * (t); wherein, T * (t) a planned engine thrust vector command; r is * (t) nominal trajectory position after planning; v. of * And (t) is a planned velocity vector.
The online trigger condition judgment of the power descent section at the beginning of the pneumatic deceleration section is selected, and the flight maneuver capacity of the power descent section of the aircraft is judged in real time through the drop point prediction in the flight process, so that the failure risk of power descent trajectory planning can be effectively reduced; the selection and implementation of a drop point prediction algorithm and a power descent trajectory planning algorithm can be realized through the adjustment of terminal position constraint, and the use is convenient; the influence of the time consumed by planning calculation is fully considered when the power descent trajectory planning is triggered, the influence of the time consumed by the trajectory planning on the planning result can be eliminated through a motion state recursion strategy, and the precision of the real-time trajectory planning is improved; the reliability of the power-down online trajectory planning is improved.
The method provided by the invention comprises the steps of selecting a pneumatic deceleration section returned in reentry to judge the flight speed, adopting a soft landing guidance algorithm to predict the landing point if the flight speed is lower than a set speed threshold, not triggering power descent trajectory planning if the predicted value of the landing point course is smaller than the expected value of the current course to the landing target, triggering power descent on-line trajectory planning if the predicted value of the landing point course is larger than the expected value of the current course to the landing target, and being applied to planetary landing tasks such as rocket return sublevels and Mars landers adopting a pneumatic deceleration plus power descent landing mode.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (6)
1. A power descent trajectory planning online triggering method based on drop point prediction is characterized by comprising the following steps: the method comprises the following steps:
step one, setting a speed threshold A; judging the flight speed of the pneumatic deceleration section in the reentry and return process of the aircraft; when the flying speed is not lower than the speed threshold A, continuing flying according to the pneumatic deceleration section; when the flying speed is lower than the speed threshold A, entering the step II;
step two, adopting soft landing trajectory planningEquation set prediction drop point location [ r ] y (t f ),r z (t f )]；
Step three, calculating a flight path predicted value S in real time according to the predicted landing point position predicted And voyage expected value S desired ；
Step four, predicting the voyage value S predicted And voyage expected value S desired Comparing, and obtaining the predicted value S of the voyage predicted Less than voyage expected value S desired When the aircraft flies continuously according to the pneumatic deceleration section; when voyage predicted value S predicted Greater than or equal to range expected value S desired Triggering the online track planning of power reduction, and entering a fifth step;
step five, establishing an online track planning model, and solving a thrust vector instruction T of the planned engine according to the online track planning model * (t) nominal post-planning trajectory position r * (t) and the post-planning velocity vector v * And (t), completing the online planning.
2. The power-down trajectory planning online triggering method based on the drop point prediction is characterized in that: in the first step, the pneumatic deceleration section is a preorder flight stage of the power descent section, and the flight speed is a relative landing planetary speed.
3. The on-line triggering method for power descent trajectory planning based on drop point prediction as claimed in claim 2, wherein: in the second step, the soft landing trajectory planning equation set is as follows:
s,t.
r(t 0 )＝r 0 ,v(t 0 )＝v 0 ,m(t 0 )＝m 0
r x (t f )＝0,v(t f )＝0
T(t f )＝[T x (t f )≠0 0 0]
0<m dry ≤m(t f )
0<T min ≤||T(t)||≤T max
in the formula, | | is a module for solving a vector;
r (t) is a position vector which changes along with time in the landing process;
v (t) is a velocity vector;
g＝[-g 0 ,0,0]is a constant gravity acceleration vector; wherein, g 0 The gravity acceleration of the earth surface is obtained;
t (T) is a rocket engine thrust vector;
m (t) is mass;
S ref effective cross-sectional area of the landing vehicle;
C D is the aerodynamic drag coefficient;
ρ is the atmospheric density;
α＝1/(I sp g 0 )，I sp specific impulse for an aircraft rocket engine;
r 0 predicting an initial time position vector for the landing aircraft;
v 0 predicting an initial moment velocity vector for a landing aircraft;
m 0 predicting initial moment quality for a landing aircraft;
t 0 predicting an initial moment;
t f predicting the terminal time;
r x (t f ) Is the landing terminal altitude;
T x (t f ) The magnitude of the thrust;
m dry is the structural mass of the rocket;
T min is the minimum thrust of the rocket engine;
T max the maximum thrust of the rocket engine;
calculating the terminal horizontal position of the soft landing trajectory planning equation set, namely the position [ r ] of the landing point y (t f ),r z (t f )]。
4. The power-down trajectory planning online triggering method based on the drop point prediction is characterized in that: in the third step, the predicted value S of voyage predicted The calculation method comprises the following steps:
S predicted ＝||[r y (t 0 )-r y (t f ),r z (t 0 )-r z (t f )] T ||
in the formula, r y (t 0 ) Predicting the horizontal position of the y direction at the initial moment;
r z (t 0 ) Predicting the horizontal position of the z direction at the initial moment;
voyage expected value S desired The calculation method comprises the following steps:
S desired ＝||[r y (t 0 ),r z (t 0 )] T ||。
5. the power-down trajectory planning online triggering method based on the drop point prediction is characterized in that: in the fifth step, the online trajectory planning model is as follows:
v(t plan )＝v(t 0 )+a(t 0 )·(t plan -t 0 )
r(t plan )＝r(t 0 )+v(t 0 )·(t plan -t 0 )+a(t 0 )·(t plan -t 0 ) 2 /2
in the formula, t plan Time for starting flying according to the planning instruction after the track planning is finished;
t plan -t 0 consuming time for planning algorithms
v(t plan ) The flight speed after the planning for recursion is completed;
r(t plan ) A position vector after the recursive planning is completed;
r(t 0 ) The position when the online planning is triggered;
v(t 0 ) Speed when triggering on-line planning;
a(t 0 ) An acceleration vector when online planning is triggered;
with t plan 、r(t plan )、v(t plan ) And performing online track planning calculation as initial state input of the online track planning.
6. The power-down trajectory planning online triggering method based on the drop point prediction is characterized in that: the online track planning calculation method comprises the following steps:
establishing a fixed point landing fuel optimal nonlinear equation system calculated by on-line trajectory planning:
s,t.
r(t plan )＝r(t 0 )+v(t 0 )·(t plan -t 0 )+a(t 0 )·(t plan -t 0 ) 2 /2,
v(t plan )＝v(t 0 )+a(t 0 )·(t plan -t 0 ),m(t plan )＝m 0
r(t f )＝0,v(t f )＝0
T(t f )＝[0 T y (t f )≠0 0]
0<m dry ≤m(t f )
0<T min ≤||T(t)||≤T max
|||T(t i+1 )||-||T(t i )|||≤ΔT max
||[r x (t),r z (t)] T ||cotθ gs ≤r y (t),θ gs ∈[0,90°)
in the formula, r (t) f ) Planning the position of an equation for the three-dimensional vector of the landing terminal position and the fixed-point landing track;
t i+1 and t i Two adjacent time points are taken in the calculation process;
ΔT max the maximum value allowed by the thrust variation between two beats;
θ T,max Is an angle constraint between the thrust direction and the plumb line;
θ gs the included angle between a connecting line between the rocket and the landing point and the horizon is restrained;
solving the optimal solution T of the fixed point landing fuel optimal nonlinear equation set calculated by the online track planning * (t)、r * (t)、v * (t); wherein, T * (t) a planned engine thrust vector command; r is * (t) nominal trajectory position after planning; v. of * And (t) is a planned velocity vector.
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