Carrier rocket flight path online planning method considering collision constraint

Abstract

The invention relates to a carrier rocket flight path online planning method considering collision constraints. The method comprises the steps that a flight path online planning dynamic model of a carrier rocket is established; setting a collision constraint condition based on the flight path online planning dynamic model, and solving an orbit injection state of the carrier rocket in avoiding a collision area based on a sequential quadratic programming algorithm; based on the current speed and position information of the carrier rocket, whether orbit degradation is needed or not is judged; and if yes, designing a degraded track. According to the carrier rocket flight path online planning method considering the collision constraint provided by the invention, flight path online planning is carried out based on the real-time speed and position information of the carrier rocket, the collision constraint is considered, and the collision risk with a space object is calculated online, so that a collision area automatic avoidance function is realized, and available launching windows are effectively expanded; and meanwhile, whether orbit degradation is carried out or not is decided, so that on-line re-planning and high-reliability orbit injection of the flight path of the carrier rocket are realized, and hysteresis of traditional off-line planning is avoided.

Description

Technical Field

[0001] This invention relates to the field of online flight trajectory planning technology, and more specifically to an online flight trajectory planning method for launch vehicles that takes into account collision constraints. Background Technology

[0002] In recent years, due to increasingly frequent human space activities, the number of space debris (such as abandoned satellites and rocket fragments) has grown rapidly, posing significant safety hazards to spacecraft and space activities. Space debris is mainly concentrated in low Earth orbit (LEO), the orbit closest to the Earth's surface, at altitudes between 200 and 2000 kilometers. According to ESA statistical models, there are approximately 36,500 pieces of space debris larger than 10 centimeters in Earth orbit. On the other hand, mega-constellations in LEO have developed rapidly in recent years. According to data filed by SpaceX with the Federal Communications Commission (FCC), SpaceX plans to deploy 4,425 satellites by 2024, 7,518 satellites by 2027, and has 30,000 reserve satellites, totaling more than 42,000 satellites, with orbital altitudes concentrated between 300 and 570 kilometers.

[0003] With the number of space objects such as space debris and low-Earth orbit mega-constellations increasing exponentially, the available spacetime for launch vehicles during ascent is severely compressed. They inevitably traverse near-Earth space, where space objects are densely distributed, leading to increasingly severe challenges of space collisions and significantly increasing the complexity and cost of launch missions. Statistics show that there have been numerous instances where the calculated probability of a rocket colliding with a space object during ascent exceeds a threshold, resulting in a usable launch window of only tens or even hundreds of seconds.

[0004] In related technologies, to prevent the risks posed by space collisions to launch missions, a method of "offline planning + pre-launch setup" is generally adopted. On the one hand, the available launch window is greatly compressed, affecting the implementation of the launch mission; on the other hand, the pre-launch offline ballistic planning optimizes the flight trajectory based on the theoretical values ​​of engine parameters and conducts collision analysis calculations accordingly. However, the actual flight trajectory deviates from the theoretical flight trajectory due to the influence of the engine's own energy distribution level and the accuracy of performance predictions, thus reducing the reliability of collision risk calculations. Summary of the Invention

[0005] This application provides an online trajectory planning method for launch vehicles that considers collision constraints, solving the technical problems in related technologies such as the high probability of collisions between launch vehicles and space objects during the ascent phase and the low reliability of collision risk calculation.

[0006] This application provides an online trajectory planning method for a launch vehicle that considers collision constraints, which includes the following steps: Establish an online dynamic model for the flight trajectory planning of a launch vehicle; Based on the online planning dynamics model of the flight trajectory, collision constraints are set, and the orbital state of the launch vehicle in the collision avoidance zone is solved based on the sequential quadratic programming algorithm. Based on the current speed and position information of the launch vehicle, determine whether orbital degradation is necessary; If so, then design a degraded track.

[0007] In one implementation, the online flight trajectory planning dynamics model is represented as: ; in, V For the flight speed of the launch vehicle, r For the geocentric radius, The gravitational constant of Earth, m For the mass of the launch vehicle, For engine thrust, For fixed constant values, For the engine's specific impulse. Indicates the direction of the thrust vector.

[0008] In one implementation, the step of setting collision constraints based on the online flight trajectory planning dynamics model and solving the orbital state of the launch vehicle's collision avoidance zone based on a sequential quadratic programming algorithm includes: The initial state and collision constraints of the launch vehicle are set. The initial state includes the initial position, initial velocity, initial attitude and initial mass of the launch vehicle at the initial moment. Based on the online flight trajectory planning dynamics model and the initial state, the position and velocity of the launch vehicle at the moment of orbit insertion are calculated. To avoid the orbital insertion time of the collision zone and fuel demand Set as comprehensive performance index J , is represented as: ; Determine whether the collision constraint conditions are met; If so, then the orbital insertion state of the launch vehicle in the collision avoidance zone is obtained.

[0009] In one implementation, the collision constraint conditions include: Endpoint constraints are expressed as follows: ,in, This refers to the initial time when the launch vehicle's engines are started. The time of engine shutdown is the time of orbit insertion. x This indicates the real-time location of the launch vehicle. This represents the initial position of the launch vehicle at the moment the engine is started. The position of the launch vehicle at the moment the engine is shut down; The attitude angle constraint is expressed as: ,in, , , For the final order angle in the geocentric system xyz The magnitude of the components in the three directions; Process constraints are expressed as follows: ,in, , These are the position components of the launch vehicle and the space objects in the collision zone, respectively. Minimum distance to prevent collisions.

[0010] In one implementation, the shortest orbital insertion time to avoid the collision zone is set as the overall performance index, expressed as: .

[0011] In one implementation, if not, the initial state and collision constraints of the launch vehicle are reset.

[0012] In one implementation, determining whether orbital degradation is needed based on the launch vehicle's current velocity and position information includes: Based on the current speed and position information of the launch vehicle, the required fuel mass to reach the original orbit is calculated in real time. Determine the relationship between the available fuel mass and the required fuel mass of the launch vehicle; If the available fuel mass is less than the required fuel mass, then orbital degradation is performed.

[0013] In one implementation, if the available fuel mass is greater than or equal to the required fuel mass, then the aircraft will fly along the original trajectory.

[0014] In one implementation, the orbital degradation includes: Determine whether orbit degradation can be performed based on whether the perigee altitude of the degraded orbit is greater than the set altitude; If so, orbital degradation can be performed; Adjust the perigee altitude of the degraded orbit until the available fuel mass equals the required fuel mass.

[0015] In one implementation, if not, the downgraded trajectory does not exist, and the aircraft flies along the original trajectory.

[0016] The beneficial effects of the technical solutions provided in this application include: This application provides an online trajectory planning method for launch vehicles that considers collision constraints. Based on the real-time velocity and position information of the launch vehicle, online trajectory planning is performed, avoiding the "false alarm" problem that may arise from pre-launch planning. It considers collision constraints and calculates the collision risk with space objects online to achieve automatic collision zone avoidance, effectively expanding the available launch window. Simultaneously, it decides whether to perform orbit degradation based on this information, enabling online replanning of the launch vehicle's trajectory and high-reliability orbit insertion, improving the success rate of flight missions, providing the ability for autonomous mission reconfiguration, enhancing the rocket's autonomous adaptability to unexpected events during flight, and avoiding the lag of traditional offline planning. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the steps of an online trajectory planning method for a launch vehicle that considers collision constraints in one embodiment of the present invention.

[0019] Figure 2 This is a flowchart of the track degradation steps in one embodiment of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0021] This application provides an online trajectory planning method for launch vehicles that considers collision constraints, which can solve the technical problems in related technologies such as the high probability of collision between launch vehicles and space objects during the ascent phase and the low reliability of collision risk calculation.

[0022] like Figure 1 As shown, Figure 1 This is a flowchart illustrating the steps of an online trajectory planning method for a launch vehicle that considers collision constraints in one embodiment of the present invention.

[0023] This embodiment provides an online trajectory planning method for launch vehicles that considers collision constraints, which includes the following steps: Step S1: Establish an online dynamic model for the flight trajectory planning of the launch vehicle; Step S2: Based on the online planning dynamic model of flight trajectory, set collision constraints and solve the orbital state of the launch vehicle in the collision avoidance zone based on the sequential quadratic programming algorithm; Step S3: Based on the launch vehicle's current speed and position information, determine whether orbital degradation is necessary; If so, then design a degraded track.

[0024] This embodiment provides an online trajectory planning method for launch vehicles that considers collision constraints. Based on the real-time velocity and position information of the launch vehicle, online trajectory planning is performed, avoiding the "false alarm" problem that may arise from pre-launch planning. Collision constraints are considered, and the risk of collision with space objects is calculated online to achieve automatic collision zone avoidance, effectively expanding the available launch window. Simultaneously, decisions are made based on this to determine whether to perform orbital degradation, enabling online replanning of the launch vehicle's trajectory and high-reliability orbit insertion, improving the success rate of flight missions, providing the ability for autonomous mission reconfiguration, enhancing the rocket's autonomous adaptability to unexpected events during flight, and avoiding the lag of traditional offline planning.

[0025] The following provides a detailed explanation of each step.

[0026] In one embodiment, the dynamic model for online flight trajectory planning in step S1 is represented as follows: ; in, V For the flight speed of the launch vehicle, r For the geocentric radius, The gravitational constant of Earth, m For the mass of the launch vehicle, For engine thrust, For fixed constant values, For the engine's specific impulse. Indicates the direction of the thrust vector.

[0027] In one embodiment, step S2, setting collision constraints based on the online flight trajectory planning dynamics model and solving the orbital state of the launch vehicle in the collision avoidance zone based on the sequential quadratic programming algorithm, includes: Step S21: Set the initial state and collision constraints of the launch vehicle. The initial state includes the initial position, initial velocity, initial attitude and initial mass of the launch vehicle at the initial moment. Step S22: Calculate the position and velocity of the launch vehicle at the moment of orbit insertion based on the online flight trajectory planning dynamic model and initial state; Step S23, orbital insertion time to avoid collision zone and fuel demand Set as comprehensive performance index J , is represented as: ; Step S24: Determine whether the collision constraint conditions are met; Step S25: If yes, then the orbital insertion status of the launch vehicle in the collision avoidance zone is obtained.

[0028] Sequential Quadratic Programming (SQP) is an iterative algorithm for solving nonlinear constrained optimization problems. It transforms the original problem into a series of quadratic programming (QP) subproblems that progressively approximate the optimal solution. Its core ideas are: local approximation (at the current iteration point, approximating the objective function with a quadratic model and the constraints with a linear model) and iterative updating (obtaining the search direction by solving the QP subproblems and updating variables along this direction until convergence). It achieves a high efficiency balance between accuracy and speed through sequential quadratic approximation, rigorously handles nonlinear constraints (such as collision avoidance), and has strong engineering applicability (no parameter tuning required, reliable convergence).

[0029] It should also be noted that when solving the problem based on the sequential quadratic programming algorithm, since the engine nozzle cannot be deflected, i.e. It directly represents the projection of the final stage attitude angle onto the geocentric frame. This is the final optimized control quantity.

[0030] The above scheme unifies orbital insertion time and fuel consumption into a comprehensive performance index using a sequential quadratic programming algorithm, enabling dual-objective optimization of fuel and time. Simultaneously, the comprehensive performance index is calculated as the outer function, and the dynamic model is calculated as the inner function (e.g., the orbital analysis method based on velocity increments and the orbital analysis calculation method based on the two-body model). By combining dynamic collision constraint modeling with sequential quadratic programming (SQP) optimization, highly reliable trajectory planning for the launch vehicle in complex space environments is achieved. This allows for further expansion of rocket propulsion types to include purely solid, purely liquid, or hybrid solid-liquid systems; or expansion of the number of rocket stages to a certain range, such as two, three, or four stages.

[0031] In one embodiment, in step S21, the collision constraint conditions include: Endpoint constraints are expressed as follows: ,in, This refers to the initial time when the launch vehicle's engines are started. The time of engine shutdown is the time of orbit insertion. x This indicates the real-time location of the launch vehicle. This represents the initial position of the launch vehicle at the moment the engine is started. The position of the launch vehicle at the moment the engine is shut down; The attitude angle constraint is expressed as: ,in, , , For the final order angle in the geocentric system xyz The magnitude of the components in the three directions; Process constraints are expressed as follows: ,in, , These are the position components of the launch vehicle and the space objects in the collision zone, respectively. Minimum distance to prevent collisions.

[0032] The above scheme transforms the positional uncertainty of space objects (such as satellites and debris) into mathematical constraints and embeds them into the dynamic model, while satisfying the above collision constraints, thus achieving both avoiding space objects in the collision zone and entering the target orbit.

[0033] In one embodiment, in step S23, the shortest orbital insertion time to avoid the collision zone is set as the comprehensive performance index, expressed as: .

[0034] By utilizing the above scheme, which takes advantage of the fact that the engine is always running during the launch vehicle's orbit change process, resulting in a fixed engine consumption per second, the shortest orbit change time and the most fuel-efficient operation can be achieved. This further simplifies the overall performance indicators and effectively saves propellant.

[0035] In one embodiment, if not, the initial state and collision constraints of the launch vehicle are reset.

[0036] like Figure 2 As shown, Figure 2 This is a flowchart of the track degradation steps in one embodiment of the present invention.

[0037] In one embodiment, step S3, determining whether orbital degradation is needed based on the launch vehicle's current velocity and position information, includes: Step S31: Based on the current speed and position information of the launch vehicle, calculate in real time the required fuel mass to reach the original orbit.

[0038] Specifically, let the parameters of the elliptical orbit entered by the launch vehicle after velocity correction be denoted as and the perigee be denoted as . apogee is The original orbit, i.e. the target orbit, has a perigee of... apogee is (In particular, if the target orbit is a circular orbit, then...) ).

[0039] Elliptical orbit at height The velocity at that point is as follows: ; in, The radius of the Earth's equator. The semi-major axis (subscript 1 indicates the elliptical orbit the launch vehicle enters after velocity correction, the same below). The distance from the geocentric point to the apogee. The distance from the geocentric point of perigee. For eccentricity, It is the semi-nominal diameter. For true near point angle, For the lateral component of velocity, This represents the radial component of the velocity.

[0040] The target orbit is at an altitude of The velocity at that point is as follows: ; in, The distance from the geocentric point to the apogee (subscript 2 represents the original orbit, i.e., the target orbit, and the same applies below). The distance from the geocentric point of perigee. For the lateral component of velocity, This represents the radial component of the velocity.

[0041] The velocity increment required by the final stage of the launch vehicle is: ; The corresponding propellant mass, i.e. the required fuel mass, is: .

[0042] Step S32: Determine the available fuel mass of the launch vehicle. m r With the required fuel mass ∆ m Relationship; Step S33: If the available fuel mass m r <Required fuel mass ∆ m If so, orbital degradation will be performed.

[0043] The above scheme provides an analytical calculation method for orbit based on a two-body model to achieve rapid and efficient calculation of velocity increments, assess the rocket's remaining flight capability and fuel status, and significantly improve the mission reliability and survivability of the launch vehicle in the event of insufficient fuel or sudden failure by combining real-time fuel assessment with a dynamic degradation mechanism.

[0044] In one embodiment, if the available fuel mass m r ≥Required fuel mass ∆ m Then it will fly along the original trajectory.

[0045] In one embodiment, the orbit degradation in step S33 includes: Step S331: Determine whether orbit degradation can be performed based on whether the perigee altitude of the degraded orbit is greater than the set altitude; Step S332: If so, orbital degradation can be performed; Step S333: Adjust the perigee altitude of the degraded orbit until the usable fuel mass is reached. m r =Required fuel mass ∆ m .

[0046] The above approach determines whether orbit degradation is feasible based on the minimum capacity requirements of the degraded orbit.

[0047] In one embodiment, in step S332, if not, then the downgraded trajectory does not exist, and the aircraft flies along the original trajectory.

[0048] Furthermore, a "degraded orbit does not exist" command can be issued.

[0049] Through the above scheme, the launch vehicle has the ability to autonomously reconfigure its flight mission, realize intelligent propellant management, and improve the rocket's autonomous adaptability to unexpected events during flight. By introducing a downgraded orbit, such as reducing orbital altitude and other parameters, the launch vehicle's energy requirements for entering orbit are reduced, enabling the launch vehicle to make the most efficient use of remaining propellant after collision avoidance maneuvers, improving orbital flexibility and reliability, and ultimately achieving the goal of sending the mission payload into the predetermined orbit.

[0050] Before entering a region with a high density of objects in orbit, the launch vehicle's flight trajectory is planned online. Based on whether the engine has the capability for multiple ignitions, the appropriate propulsion unit is selected to complete speed correction and on-orbit maneuvers.

[0051] The flight sequence of the launch vehicle's flight trajectory is planned online as follows: 1) When there is a high-collision-risk area that needs to be avoided on the predetermined flight trajectory, the method provided in this application embodiment performs online replanning based on the real-time position and velocity information of the launch vehicle, and determines whether speed correction is needed to reduce the collision risk based on the collision probability of the predetermined flight trajectory passing through the high-collision-risk area; if so, speed correction power is provided by starting the final stage engine, that is, power is provided by optimizing the nozzle action of the engine, planning the working time of the speed correction segment and the starting attitude, and adjusting the attitude to the starting attitude; 2) Speed ​​correction phase: The engine starts operating based on the online replanning results; 3) Based on the launch vehicle's current speed and position information, calculate in real time the remaining flight capacity (such as the required fuel mass) needed to reach the original orbit. If the capacity is sufficient (i.e., the available fuel mass...) m r ≥Required fuel mass ∆ mIf the remaining flight capacity is less than the required remaining flight capacity (i.e., available fuel mass), then it will continue to fly along the original target trajectory; m r <Required fuel mass ∆ m If the minimum capability requirements for the degraded orbit are not met (such as whether the perigee altitude of the degraded orbit is greater than the set altitude), it will be determined whether orbit degradation can be carried out. If the requirements are not met, a "degraded orbit does not exist" command will be issued; if the requirements are met, a degraded orbit can be selected for orbit degradation based on the actual remaining flight capacity. 4) Plan the entry trajectory for the final stage taxiing phase, plan the ignition attitude of the entry phase and the second engine start-up time, and adjust the attitude to the second start-up attitude; 5) After the engine is started for the second time, iterative guidance calculations are performed. Once the orbital insertion conditions are met, the engine is shut down.

[0052] It should be noted that the sequence numbers of the embodiments in this application are merely for descriptive purposes and do not represent the superiority or inferiority of the embodiments. The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices. The terms "first," "second," and "third," etc., are used to distinguish different objects, etc., and do not represent a sequential order, nor do they limit "first," "second," and "third" to different types.

[0053] In the description of the embodiments of this application, terms such as "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a concrete manner.

[0054] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more.

[0055] In some processes described in the embodiments of this application, multiple operations or steps are included in a specific order. However, it should be understood that these operations or steps may not be executed in the order they appear in the embodiments of this application, or they may be executed in parallel. The sequence number of the operation is only used to distinguish the different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed sequentially or in parallel, and these operations or steps may be combined.

[0056] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A launch vehicle flight trajectory online planning method considering collision constraints, characterized in that, It comprises the following steps: An online flight trajectory planning dynamics model of a carrier rocket is established; Collision constraint conditions are set based on the online flight trajectory planning dynamics model, and an orbit entry state of the carrier rocket to avoid a collision zone is solved based on a sequential quadratic programming algorithm; Whether orbit degradation is needed is determined based on current speed and position information of the carrier rocket; If yes, a degraded orbit is designed.

2. The launch vehicle flight trajectory online planning method considering collision constraints of claim 1, wherein, The online flight trajectory planning dynamics model is expressed as: ； wherein, V is the launch vehicle flight velocity, r is the Earth radius, is the Earth gravitational constant, m is the launch vehicle mass, is the engine thrust, is a fixed constant, is the engine specific impulse, denotes the thrust vector direction.

3. The launch vehicle flight trajectory online planning method considering collision constraints of claim 1, wherein, The collision constraint conditions are set based on the online flight trajectory planning dynamics model, and an orbit entry state of the carrier rocket to avoid a collision zone is solved based on a sequential quadratic programming algorithm, which comprises: Initial states of the carrier rocket and collision constraint conditions are set, wherein the initial states comprise initial position, initial speed, initial attitude and initial mass of the carrier rocket at an initial time; Position and speed of the carrier rocket at an orbit entry time are calculated based on the online flight trajectory planning dynamics model and the initial states; Entry time to avoid the collision zone And fuel requirements Set as an overall performance indicator J , is expressed as: ; Whether the collision constraint conditions are met is determined; If yes, the orbit entry state of the carrier rocket to avoid the collision zone is obtained.

4. The launch vehicle flight trajectory online planning method considering collision constraints of claim 3, wherein, The collision constraint conditions comprise: endpoint constraints, denoted as: wherein, is the initial time, i.e. the time when the launch vehicle's engines are started, is the time when the launch vehicle's engines are stopped, i.e. the time of orbit insertion, x is the real-time position of the launch vehicle, is the initial position of the launch vehicle at the time when the engines are started, is the position of the launch vehicle at the time when the engines are stopped. The attitude angle constraint is expressed as: ,in, , , For the final order angle in the geocentric system x y z The magnitude of the components in the three directions; Process constraints, expressed as: wherein, , are position components of the launch vehicle and of the space object in the collision zone, respectively, is the minimum distance for collision avoidance.

5. The launch vehicle flight trajectory online planning method considering collision constraints of claim 3, wherein, The shortest orbit insertion time for avoiding the collision region is set as the comprehensive performance index, which is expressed as: .

6. The launch vehicle flight trajectory online planning method considering collision constraints of claim 3, wherein, If no, the initial states of the carrier rocket and the collision constraint conditions are re-set.

7. The launch vehicle flight trajectory online planning method considering collision constraints of claim 1, wherein, Whether orbit degradation is needed is determined based on the current speed and position information of the carrier rocket, which comprises: Required fuel mass to reach a planned orbit is calculated in real time based on the current speed and position information of the carrier rocket; Relationship between available fuel mass of the carrier rocket and the required fuel mass is determined; If the available fuel mass < the required fuel mass, orbit degradation is performed.

8. The launch vehicle flight trajectory online planning method considering collision constraints according to claim 7, wherein, If the available fuel mass ≥ the required fuel mass, the planned orbit is flown.

9. The launch vehicle flight trajectory online planning method considering collision constraints of claim 7, wherein, The orbit degradation comprises: Whether orbit degradation can be performed is determined according to whether a perigee height of a degraded orbit is greater than a set height; If yes, orbit degradation can be performed; The perigee height of the degraded orbit is adjusted until the available fuel mass = the required fuel mass.

10. The launch vehicle flight trajectory online planning method considering collision constraints of claim 9, wherein, If no, the degraded orbit does not exist, and the planned orbit is flown.

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