WO2017005052A1 - 航天器脉冲交会轨迹的梯度分割区间优化设计方法 - Google Patents
航天器脉冲交会轨迹的梯度分割区间优化设计方法 Download PDFInfo
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- the invention belongs to an orbit design and optimization technology in the field of orbital dynamics and control of a spacecraft, and relates to a spacecraft using a thrust device such as a rocket engine carried by a spacecraft to generate a thrust action which is identical to a predetermined natural object or another spacecraft.
- a thrust device such as a rocket engine carried by a spacecraft to generate a thrust action which is identical to a predetermined natural object or another spacecraft.
- the design technique of the intersection orbit that arrives at the same position at the same speed, especially the intersection orbit design technique based on the global optimization solution of the spacecraft intersection trajectory calculated by the interval arithmetic mathematical model.
- orbital design occupies an important position.
- the design of a rendezvous orbit that exerts a force on a spacecraft to reach the same position at the same speed as a predetermined natural object or another spacecraft is a prerequisite for the realization of multiple space missions.
- These tasks include: space platforms operating in orbit (such as space stations) and other spacecraft (such as manned reciprocating aircraft, space transport cargo ships) rendezvous and docking, natural celestial body detection and landing, on-orbit spacecraft on-orbit maintenance.
- the number of possible orbits for realizing the rendezvous is theoretically infinite.
- the reconciliation orbit design task becomes a trajectory optimization task, that is, finding the track with the least cost from the above infinite orbits as the result of the design of the rendezvous orbit.
- the so-called minimum cost can be the shortest flight time, minimum fuel consumption, and the like.
- the benefits of this optimization include the reduction of the cost of space missions and the efficiency of space missions. Therefore, the optimized design technology of the spacecraft rendezvous orbit has a very important position in aerospace engineering.
- a conventional rocket engine that uses a chemical propellant to generate a short-time, pulse-like ignition at a predetermined time by commanding a rocket engine to generate a force that causes the spacecraft to fly in a predetermined orbit.
- a type of propeller that uses advanced, currently not yet mature, continuously outputting small thrusts, uses a command thruster to perform long-term thrust output during or during part of the flight, resulting in the ability to achieve rendezvous.
- the optimization design method of spacecraft rendezvous orbit can be divided into three categories: indirect method, direct method and hybrid method.
- the indirect method uses the variational principle and the Pontiac maximum principle to transform the spacecraft intersection orbit optimization problem into a two-point boundary value problem that satisfies the optimal conditions. Under certain conditions, the indirect method can be used to obtain the analytical solution of the orbital optimization of the spacecraft, but in most cases, the sensitivity of the integral operation caused by the nonlinearity of the problem to the initial value of the co-state will change the solution of the problem. It is extremely difficult.
- the direct method uses the discretization and parameterization of the state quantity and control function to transform the spacecraft intersection orbit optimization problem into a multi-dimensional nonlinear programming problem.
- the disadvantage of sequential quadratic programming is its sensitivity to the initial guess of the parameter and its Ensure that the characteristics of the local optimal solution are obtained.
- the disadvantage of the intelligent optimization algorithm is that it cannot guarantee the global optimality of its solution.
- the hybrid method combines the direct method with the indirect method. On the one hand, it introduces the co-state to determine the necessary conditions for optimality, and on the other hand introduces the parameterization method to solve the optimal control problem. Research on the hybrid method often uses the same solution method as the direct method, and therefore has similar disadvantages as in the direct method study.
- bionics-based intelligent optimization algorithms are all random optimization methods.
- the basic principle of the stochastic optimization method is to generate a new guess from the initial guess value and generate a new guess by random perturbation of the initial guess value, and repeat the process until the predetermined abort condition is reached.
- the stochastic optimization method can theoretically obtain a solution that approximates the global optimal solution with a very high probability.
- the global optimality of the operation results of the random optimization method cannot be proved.
- the deterministic optimization method converges the sequence to the global optimal solution or the global optimal solution through an iterative process by constructing a sequence consisting of a finite number of points or an infinite number of points within a given limit. Contained within a sufficiently small boundary.
- the interval optimization method is a deterministic global optimization method that has received much attention in recent years.
- the interval optimization method is based on the explicit and systematically proposed interval analysis theory published by American scholar Ramon Edgar Moore in 1966, Interval Analysis. By subdividing the interval, it is gradually excluded that it is impossible to include the global optimal solution. The interval, and finally the list of intervals that satisfy the predetermined requirements that contain the global optimal solution.
- Erik-Jan van Kampen presented an analysis of the interval optimization method and the gradient optimization method in the paper "Optimization of spacecraft rendezvous and docking using interval analysis" published at AIAA Guidance, Navigation, and Control Conference.
- the gradient optimization method converges to the non-global optimal solution when it is close to the actual non-convex optimization problem, and the interval optimization method can still obtain the global optimal solution.
- the interval optimization algorithm is also constrained in practice because of the large storage space required for calculation, large computational complexity, and slow convergence.
- Chen Cheng applied for a master's degree at Shanghai University as “parallel global search based on interval mathematics.
- the paper also gives the above viewpoints in the research and system implementation of the algorithm. Many studies have attempted to solve the above problems by combining interval optimization methods with other optimization methods.
- This method first uses interval optimization method to find some interval widths that do not meet the predetermined requirements.
- the interval containing the global optimal value is then used to perform the local optimization calculation using the gradient optimization method, which improves the optimization efficiency, but the cost is that the global optimality of the optimization result cannot be guaranteed.
- the optimized design method of the spacecraft pulse intersection trajectory has many existing methods available, each has its own Each shortcoming, and generally cannot guarantee the global optimality of the optimization results.
- the shortcomings of the existing interval optimization methods that can guarantee the global optimal solution in theory are mainly the two methods of large computational complexity and high storage requirements when applied to practical problems.
- the existing methods for solving these two problems often The guarantee of destroying the global optimality comes at the cost.
- the present invention proposes a method based on interval optimization theory for the optimization design of spacecraft pulse intersection trajectory.
- the global optimization problem based on interval analysis theory is constructed and the global optimization problem is solved according to the following steps:
- Step 1 Interval processing the spacecraft pulse intersection trajectory optimization model, including the following sub-steps:
- Sub-step 1.3 taking the interval expansion of the fuel optimal condition as the objective function And given the value of the upper bound J min of the value of the objective function;
- Sub-step 1.4 setting the number of decision variable intervals M for each test, the predetermined positive number ⁇ u and the predetermined positive number ⁇ J ;
- Step 2 Perform interval segmentation on the decision variable interval [u] according to the spacecraft pulse intersection trajectory optimization model, which is called “symbol segmentation method” and includes the following sub-steps:
- Sub-step 2.3 arbitrarily combining the component interval and the time interval of the speed increment obtained in sub-step 2.1 and sub-step 2.2 to obtain Q decision variable intervals, wherein the Q decision variable intervals constitute an interval group queue L;
- step 4 the gradient-based optimization algorithm is used to solve the spacecraft pulse intersection trajectory optimization problem in each of the decision variable intervals in the sub-interval queue L1 selected in step 3, and one of the following operations is performed according to the solution result:
- Step 4 Result 1 On any of the decision variable intervals [u ⁇ ] in the sub-interval queue L1, the gradient-based optimization algorithm has a solution, and the following sub-step 4.1 and sub-step 4.2 are performed:
- Sub-step 4.1 the gradient segmentation method, that is, the value of the decision variable is extended to the extended interval [I ⁇ ] of the solution containing the gradient-based optimization algorithm, with the value of the decision variable corresponding to the solution as the center and the radius of the given value as the radius.
- the decision variable interval [u ⁇ ] each variable divided into three sections Interval or 2 intervals, and combine them as interval queue Lnew;
- Sub-step 4.2 the upper bound update of the value of the objective function based on the gradient, that is, the value of the decision variable is expanded to a radius containing a gradient-based optimization algorithm with the value of the decision variable corresponding to the solution as a center and a very small value as a radius.
- the extended interval [I ⁇ 1 ] is calculated by the interval analysis theory on the extended interval [I ⁇ 1 ] to check whether it satisfies the constraint condition of the spacecraft pulse intersection trajectory optimization model, and whether the corresponding upper bound of the objective function interval is smaller than the target function.
- Step 4 Result 2 On any decision variable interval [u ⁇ ] in the sub-interval queue L1, the gradient-based optimization algorithm does not get a solution, and the interval midpoint of each interval variable on the decision variable interval [u ⁇ ] Dividing each interval variable separately, dividing each interval variable of the decision variable interval [u ⁇ ] into two intervals, and combining them as the interval queue Lnew;
- Step 5 The interval deletion strategy, that is, performing interval analysis on each decision variable interval of the interval queue Lnew obtained in step 4, and performing the following sub-steps 5.1 to 5.4:
- Sub-step 5.2 checking whether each decision variable interval in the interval queue Lnew updated in step 5.1 satisfies the relative distance constraint condition, and deleting the decision variable interval that does not satisfy the relative distance constraint condition from the interval queue Lnew;
- the variable can be expressed as a function of other decision variables, so that the spacecraft pulse intersection trajectory optimization model is transformed into a spacecraft pulse intersection trajectory optimization model with other variables except three specified variables as decision variables, and the objective function J is examined.
- the first-order partial derivative interval of the new decision variable in each decision variable interval in the interval queue Lnew includes 0. If the check result is no, the corresponding decision variable interval is deleted from the interval queue Lnew;
- Sub-step 5.4 respectively, check the relationship between the objective function interval and the upper bound J min of the objective function value in each decision variable interval in the interval queue Lnew processed by the sub-step 5.3, and perform the following steps 5.4.1 And the operation of Sun Step 5.4.2:
- Step 7 checking each decision variable interval termination condition in the interval queue Lnew, that is, checking the width A of each decision variable interval in the interval queue Lnew and the objective function interval corresponding to each decision variable interval in the interval queue Lnew Width B, where the width of the decision variable interval is the maximum of the widths of all interval variables within the decision variable interval, perform the following sub-step 7.1 and sub-step 7.2 operations:
- Sub-step 7.1 when the width A is less than the predetermined positive number ⁇ u , or the width B is less than the predetermined positive number ⁇ J , the corresponding decision variable interval is deleted from the interval queue Lnew, and the corresponding decision variable interval is set Enter the design result interval queue R;
- Sub-step 7.2 after completing the operation of step 7.1 for each decision variable interval in the interval queue Lnew, the interval group queue L is updated, that is, the interval queue Lnew is inserted into the interval group queue L.
- step 3 at most M selected are deleted. The deletion point of the interval, the interval group queue L after the insertion of the interval queue Lnew is taken as the new interval group queue L;
- Step 8 Check the number of decision variable intervals in the interval group queue L, and perform one of the following operations according to the results:
- Step 8 Result 1 the number of decision variable intervals in the interval group queue L is not 0, then go to step 3 and continue the design operation.
- Step 8 result 2 the number of decision variable intervals in the interval group queue L is 0, and the design ends;
- step 9 a design result interval is taken from the design result interval queue R, and any value is selected in the value interval of each interval variable in the selected design result interval, and the corresponding last pulse thrust effect is calculated. Tracking the speed increment brought by the spacecraft, an optimized design solution for the aforementioned spacecraft pulse intersection trajectory is obtained.
- the specified position in step 3 of the above method is the tail of the interval group queue L, and the sub-step 7.2 corresponding to the interval queue 7.2 is placed at the end of the interval group queue L to form a new interval group queue. L.
- the specified location in step 3 of the foregoing method is the head of the interval group queue L, and the sub-step 7.2 corresponding to the interval group queue L is placed at the end of the interval queue Lnew to form a new interval group queue. L.
- the two preferred schemes of the above step 3 make the deletion and update operation of the interval group queue L more convenient.
- the upper bound of the corresponding objective function interval is taken from the design result interval queue R as the design result interval of the upper bound J min of the objective function value, in the selected design result interval.
- any value is combined, and the corresponding last impulse thrust is applied to the speed increment brought by the tracking spacecraft, and an optimized design of the aforementioned spacecraft pulse intersection trajectory is obtained. solution.
- the preferred scheme of the above step 9 will ensure that the objective function value corresponding to the design result is not higher than J min .
- the invention has the beneficial effects of ensuring the global optimality of the obtained design results.
- a gradient-based optimization method that cannot guarantee a global optimal solution depending on the initial value selection is used in the step 4.
- the running result of the gradient-based optimization method is only used to determine the upper bound of the interval segmentation point and the update objective function value.
- the present invention is completely an interval optimization method, and thus inherits the global optimality of the interval optimization method.
- the invention also has the beneficial effect that the maximum value of the requirement for the computer storage space is determined in advance, and thus the storage space shortage (overflow) which may occur in the interval optimization algorithm is avoided.
- the design process is abnormally interrupted. This benefit is mainly provided by step 3 of the above technical solution. According to step 3, only a limited number (maximum M) intervals are selected from the to-be-processed interval group for processing, and the M value can be set according to the storage space of the computer used, and thus the design process does not appear. Storage space overflow.
- the beneficial effects of the present invention are also an improvement in design efficiency, that is, a reduction in the time required to obtain a design result.
- This beneficial effect is mainly provided by step 2 and step 4 - step 6 in the above technical solution.
- the entire search interval is divided into multiple intervals, which avoids the excessively extensive interval expansion caused by the interval including 0. It facilitates the early execution of the interval deletion operation and the resulting rapid reduction in the number of intervals to be processed, and thereby reduces the time required for the design process.
- the use of the operation result of the gradient-based optimization method is advantageous for quickly updating the upper bound of the value of the target function by using the information of the local optimal solution or the global optimal solution.
- step 4 the segmentation is performed by using the gradient-based optimization method, which is beneficial to quickly obtain the decision variable interval with local optimal value and smaller interval width, and is also beneficial for other non-optimal solution intervals. Discard quickly.
- step 4 clearly contribute to the reduction in time required for the design process.
- step 5 it is advantageous to reduce the number of intervals to be processed and the upper bound of the value of the updated target function, and thus it is advantageous to reduce the time required for the design process.
- step 6 the local monotonicity on the constraint condition is used to further reduce the width of the interval to be processed, which is beneficial to the reduction of the interval expansion in the interval analysis operation, and thus facilitates the early execution of the interval deletion operation, thereby generating Reduce the time required for the design process.
- FIG. 1 is a schematic flow chart of a gradient segmentation interval optimization design method for a spacecraft pulse intersection trajectory provided by the present invention
- FIG. 2 is a schematic diagram of interval group queue change in the process of step 3 - step 7 of the method provided by the present invention
- FIG. 3 is a schematic diagram of an update process of an upper bound based on a value of a gradient objective function in the method provided by the present invention
- FIG. 4 is a schematic diagram of relative motion trajectories between two spacecrafts obtained in accordance with an embodiment of the present invention
- Figure 5 is a schematic illustration of an optimized design result interval queue obtained in accordance with one embodiment of the present invention.
- the relative coordinate system X-axis is along the flight direction of the target spacecraft in the orbital plane
- the Z-axis is from the centroid of the target spacecraft to the center of the earth
- the Y-axis is in the right-hand orthogonal coordinate system.
- ⁇ is the orbital angular velocity of the target spacecraft
- x, y, and z are the relative positions of the tracking spacecraft in the X, Y, and Z directions, respectively. Tracking the relative speed of the spacecraft in the X, Y, and Z directions, respectively. The relative acceleration of the spacecraft in the X, Y, and Z directions is tracked separately.
- a spacecraft tracking pulse is applied for the first time, the pulse to the thrust force caused by tracking the spacecraft velocity increments v 1 (v 1x, v 1y , v 1z).
- the tracking spacecraft applies a second pulse, and the impulse thrust brings the speed increment brought by the tracking spacecraft to v 2 (v 2x , v 2y , v 2z ), two spacecraft rendezvous.
- (3) is the constraint condition of the spacecraft pulse intersection trajectory optimization model with t 1 , t f , v 1 , v 2 as the decision variables, which are relative distance constraint and relative velocity constraint respectively.
- the objective function of the spacecraft pulse intersection trajectory optimization model is:
- the gradient optimization interval design method of the spacecraft pulse intersection trajectory is used to solve the above optimization model.
- the flow diagram of the gradient segmentation interval optimization design method for the spacecraft pulse intersection trajectory is shown in Figure 1, which includes the following steps:
- Step 1 Interval processing the spacecraft pulse intersection trajectory optimization model, including the following sub-steps:
- Sub-step 1.1 assuming that two spacecraft move in the orbital plane of the target spacecraft, there is a decision variable interval
- Sub-step 1.4 setting the number of decision variable intervals M for each test, the predetermined positive number ⁇ u and the predetermined positive number ⁇ J ;
- Step 2 using the symbol segmentation method, includes the following substeps:
- Sub-step 2.1 the components of the speed increment [v 1x ] and [v 1z ] brought by the first impulse thrust to the tracking spacecraft are divided into two with positive values and only negative values. Component interval of speed increments;
- Sub-step 2.2 the interval between the second pulse thrust action time [t f ], the second pulse thrust action time and the first pulse thrust action time [t 1 ⁇ f ], to use the spacecraft
- the quadrant of the trigonometric function in the pulse intersection trajectory optimization model is divided into multiple time intervals;
- Sub-step 2.3 arbitrarily combining the component interval and the time interval of the speed increment obtained in sub-step 2.1 and sub-step 2.2 to obtain Q decision variable intervals, wherein the Q decision variable intervals constitute an interval group queue L;
- the sub-interval queue L1 at the same time, deletes the selected M-th decision variable interval from the interval group queue L, and the steps of the interval group queue change in the process of performing the steps 2 to 7 continuously, as shown in FIG. 2;
- step 4 the gradient-based optimization algorithm is used to solve the spacecraft pulse intersection trajectory optimization problem in each of the decision variable intervals in the sub-interval queue L1 selected in step 3, and one of the following operations is performed according to the solution result:
- Step 4 Result 1 On any of the decision variable intervals [u ⁇ ] in the sub-interval queue L1, the gradient-based optimization algorithm has a solution, and the following sub-step 4.1 and sub-step 4.2 are performed:
- Sub-step 4.1 extending the decision variable value to the extended interval [I ⁇ ] of the solution containing the gradient-based optimization algorithm by using the value of the decision variable corresponding to the solution as the center and the radius of the given size as the radius to expand the interval [
- the boundary values of the respective interval variables of I ⁇ ] respectively divide the respective interval variables of the decision variable interval [u ⁇ ], and divide each interval variable of the decision variable interval [u ⁇ ] into three intervals or two intervals. And combine them as an interval queue Lnew;
- Sub-step 4.2 updating the upper bound of the value of the objective function based on the gradient, that is, extending the value of the decision variable to a solution containing the gradient-based optimization algorithm with the value of the decision variable corresponding to the solution as the center and using a very small value as a radius
- the extended interval [I ⁇ 1 ] is calculated by the interval analysis theory on the extended interval [I ⁇ 1 ] to check whether it satisfies the constraint condition of the spacecraft pulse intersection trajectory optimization model, and whether the corresponding upper bound of the objective function interval is smaller than the objective function.
- Step 4 Result 2 On the decision variable interval [u ⁇ ] in the sub-interval queue L1, the gradient-based optimization algorithm is not solved, and each interval variable is divided into each interval variable in the decision variable interval [u ⁇ ] Dividing each interval variable of the decision variable interval [u ⁇ ] into two intervals and combining them as the interval queue Lnew;
- Step 5 the interval deletion strategy, that is, each decision variable interval of the interval queue Lnew obtained in step 4 is separately entered.
- Sub-step 5.2 checking whether each decision variable interval in the interval queue Lnew updated in step 5.1 satisfies the relative distance constraint condition, and deleting the decision variable interval that does not satisfy the relative distance constraint condition from the interval queue Lnew;
- the variable can be expressed as a function of other decision variables, so that the spacecraft pulse intersection trajectory optimization model is transformed into a spacecraft pulse intersection trajectory optimization model with other variables except three specified variables as decision variables, and the objective function J is examined. If the first-order partial derivative interval of the new decision variable contains 0 in each decision variable interval in the interval queue Lnew processed in sub-step 5.2, if the check result is no, the corresponding decision variable interval is deleted from the interval queue Lnew. ;
- Sub-step 5.4 respectively, check the relationship between the objective function interval and the upper bound J min of the objective function value in each decision variable interval in the interval queue Lnew processed by the sub-step 5.3, and perform the following steps 5.4.1 And the operation of Sun Step 5.4.2:
- Each interval variable in [u] is monotonic, and the following substep 6.1 is performed:
- Step 7 checking each decision variable interval termination condition in the interval queue Lnew, that is, checking the width A of each decision variable interval in the interval queue Lnew and the objective function interval corresponding to each decision variable interval in the interval queue Lnew Width B, where the width of the decision variable interval is the maximum of the widths of all interval variables within the decision variable interval, perform the following sub-step 7.1 and sub-step 7.2 operations:
- Sub-step 7.1 when the width A is less than the predetermined positive number ⁇ u , or the width B is less than the predetermined positive number ⁇ J , the corresponding decision variable interval is deleted from the interval queue Lnew, and the corresponding decision variable interval is set Enter the design result interval queue R;
- Sub-step 7.2 after completing the operation of step 7.1 for each decision variable interval in the interval queue Lnew, updating the interval group queue L, that is, the interval queue Lnew is inserted into the end of the interval group queue L;
- Step 8 Check the number of decision variable intervals in the interval group queue L, and perform one of the following operations according to the results:
- Step 8 result 1, the number of decision variable intervals in the interval group queue L is not 0, then proceeds to step 3 to continue the design operation;
- Step 8 Result 2 the number of decision variable intervals in the interval group queue L is 0, and the design ends.
- Step 9 selecting the optimized results, taking the design results bound J min interval on upper bound of interval corresponding to a result of design objective function objective function value interval from design result queue R interval, the selected design results interval In the value interval of each decision variable, any value is combined to calculate the speed increment brought by the corresponding last impulse thrust to the spacecraft, and an optimized design solution of the spacecraft pulse intersection trajectory is obtained. .
- the simulation operation shows that the upper bound of the value of the objective function under the current precision and the corresponding solution interval are shown in Table 1.
- the value of the objective function is in the [J] interval, and the upper bound J min of the objective function is the upper limit of [J] is 8.750384691131890m ⁇ s - 1 .
- the relative distance gradually decreases to 0 with time, and the error is within the specified 0.015 m range. From the path, the correctness of the solution of the present invention is visually verified.
- the genetic algorithm is used to solve the problem.
- the decision variables are t 1 ⁇ f and t f .
- the search range is [0,8000]s.
- the initial population is 100, the maximum genetic algebra is 100 generations, and the solution is 10 times.
- the results are shown in Table 2. .
- the optimal value of the objective function of the 10th genetic algorithm in Table 2 is the optimal value of the objective function of the sixth operation, 8.750384691363504, which is similar to the upper bound value of the objective function of the global optimization algorithm proposed by the present invention, 8.750384691131890 m ⁇ s -1 . It proves the correctness of the solution of the present invention and also supports the overall advantages of the invention.
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Abstract
一种航天器脉冲交会轨迹的梯度分割区间优化设计方法,属于航天器轨道动力学与控制领域中的轨道设计及优化技术,特别是基于利用区间算术数学模式计算得到的航天器交会轨迹全局优化解的交会轨道设计技术。针对方法的全局性问题,将梯度优化结果只用于确定区间分割点和更新目标函数取值上界,保全了区间优化算法的全局性;针对区间优化算法计算量大的问题,引入梯度优化方法,以便快速更新目标函数取值上界和使用梯度分割法,结合符号分割法和区间优化策略,有效地分离和去除不包含最优解的区间,提高了运算效率;为解决区间优化算法的存储需求高的问题,每一次迭代只选取有限个区间进行处理,保证运算中不出现存储空间溢出现象。
Description
本发明属于航天器轨道动力学与控制领域中的轨道设计及优化技术,涉及一个航天器利用由其携带的火箭发动机等喷射推力装置产生的推力作用与预定的自然天体或者另一个航天器在同一时间以相同速度到达同一位置的交会轨道的设计技术,特别是基于利用区间算术数学模式计算得到的航天器交会轨迹全局优化解的交会轨道设计技术。
在航天器的任务分析中,轨道设计占有重要位置。在轨道设计任务中,在一个航天器上施加作用力,使其与预定自然天体或者另一个航天器在同一时间以相同速度到达同一位置的交会轨道的设计是多种航天任务实现的先决条件。这些任务包括:在轨运行的空间平台(如空间站)和其它航天器(如载人往返飞行器、空间运输货船)的交会对接、自然天体探测与着陆、在轨航天器的在轨维护等。实现交会的可能轨道的数量在理论上是无穷多的,所以,交会轨道设计任务就成为一个轨迹优化任务,即从上述无穷多个轨道中找出某种代价最小的轨道作为交会轨道设计的结果。所谓代价最小可以是飞行时间最短、燃料消耗最小等。这一优化带来的好处包括航天任务成本的降低、航天任务效率的提高等。因此,航天器交会轨道的优化设计技术在航天工程中具有非常重要的位置。
航天器交会轨道的实现一般可分为两种途径。一种使用传统的、成熟的使用化学推进剂的各种火箭发动机,通过指令火箭发动机在预定时刻进行短时间的、可视为脉冲作用的点火,产生使航天器按预定交会轨道飞行的作用力。另一种使用先进的、目前尚未发展成熟的、可连续输出小推力的各种推进器,通过指令推力器在整个或部分飞行过程中进行长时间的推力输出,产生实现交会的作用力。
航天器交会轨道的优化设计方法可分为间接法、直接法和混合法三大类。间接法利用变分原理和庞特里亚金极大值原理将航天器交会轨道优化问题转化为满足最优性必要条件的两点边值问题进行求解。在某些特定条件下,使用间接法可以获得航天器交会轨道优化的解析解,但大多数情况下,由问题的非线性引起的积分运算对协状态初值的敏感性将使问题的求解变得异常困难。直接法利用对状态量和控制函数的离散化和参数化将航天器交会轨道优化问题转化为多维的非线性规划问题进行求解。关于直接法的研究大多使用基于梯度的序列二次规划法或者基于仿生学的智能优化算法,如遗传算法、模拟退火算法、人工免疫算法、粒子群算法、蚁群算法。序列二次规划法的缺点在于其对参数的初始猜测值的敏感性和其只能
保证获得局部最优解的特性。智能优化算法的缺点在于其无法保证其解的全局最优性。混合法将直接法和间接法结合起来使用,一方面引入协状态以确定最优性必要条件,另一方面引入参数化方法求解最优控制问题。关于混合法的研究往往使用与直接法相同的求解方法,因此也具有与直接法研究中相似的缺点。
上面提到的基于仿生学的智能优化算法都属于随机性优化方法。随机性优化方法的基本原理为:从选定的初始猜测值开始,通过对初始猜测值的随机扰动来生成新的猜测值,并重复这一过程直至达到事先给定的中止条件。当运算时间足够长时,随机性优化方法在理论上可以以极高的概率获得逼近全局最优解的解。但实际使用中,随机性优化方法的运算结果的全局最优性是无法证明的。相对于随机性优化方法,确定性优化方法通过构造确定的由有限个点或给定界限内的无限个点组成的序列,通过迭代过程使该序列收敛于全局最优解或将全局最优解包含在足够小的界限范围内。
区间优化方法就是一种近年来备受关注的确定性全局优化方法。区间优化方法以由美国学者Ramon Edgar Moore在1966年出版的著作《Interval Analysis》中明确地和系统地提出的区间分析理论为基础,通过对区间的细分,逐步排除不可能包含全局最优解的区间,并最终获得包含着全局最优解的、满足预定要求的区间的列表。2010年Erik-Jan van Kampen在AIAA Guidance,Navigation,and Control Conference上发表的论文“Optimization of spacecraft rendezvous and docking using interval analysis”给出了一个区间优化方法与梯度优化方法的比较,结果表明在处理更接近实际的非凸优化问题时梯度优化方法收敛于非全局最优解,而区间优化方法仍能得到全局最优解。但是区间优化算法也因为运算所需存储空间过大,计算量大,收敛速度慢等缺点,在实用中受到牵制,2014年陈诚在上海大学申请硕士学位的名为“基于区间数学的并行全局寻优算法的研究与系统实现”的论文也给出了上述观点。许多研究试图通过将区间优化方法与其他优化方法相结合以解决上述问题。2012年关守平和房少纯在《东北大学学报(自然科学版)》上发表的名为“一种新型的区间-粒子群优化算法”的论文公开了一种将粒子群算法与区间优化方法结合的方法,但文中给出的计算结果表明,目标函数值域区间很接近但不包括实际最优值。2013年Tong Chen等人在《Journal of Guidance,Control and Dynamics》上发表的名为“Optimization of time-open constrained Lambert rendezvous using interval analysis”的论文指出了区间优化方法存储需求过大、运算中内存容易溢出等不足,并公开了一种用于航天器脉冲交会轨迹优化设计的、区间优化方法和梯度优化方法相结合的方法,该方法先使用区间优化方法求得一些区间宽度尚不满足预定要求的包含全局最优值的区间,然后改用梯度优化方法进行局部优化计算,提高了优化效率,但其代价是无法保证优化结果的全局最优性。
综上可知,航天器脉冲交会轨迹的优化设计方法虽然有很多现有方法可供使用,但各有
各的短处,且一般无法保证优化结果的全局最优性。而理论上能够保证求得全局最优解的现有的区间优化方法的短处主要为应用于实际问题时运算量大、存储需求高这两点,现有的解决这两个问题的方法往往以破坏全局最优性的保证为代价。
发明内容
针对上述现有技术存在的不足,本发明提出了一种用于航天器脉冲交会轨迹优化设计的、基于区间优化理论的方法。
为解决上述技术问题,本发明的技术方案如下:
根据所采用或建立的航天器脉冲交会轨迹优化模型,构造基于区间分析理论的全局优化问题并依照下列步骤对所建立的全局优化问题进行求解:
步骤1,对航天器脉冲交会轨迹优化模型进行区间化处理,包括以下子步骤:
子步骤1.1,给定航天器脉冲交会过程中应使用的脉冲推力作用次数N(N为大于等于2的自然数),取最后一次脉冲推力作用时间tf、最后一次脉冲推力作用时间tf与除最后一次脉冲推力外的各次脉冲推力作用时间之间的间隔时间ti→f(i=1,2...N-1)、各次脉冲推力作用给追踪航天器带来的速度增量的分量(vix,viy,viz)(i=1,2,...,N)作为决策变量,并按各决策变量的可能取值范围构成决策变量区间[u]=[[v1x],[v1y],[v1z],...,[v(N-1)x],[v(N-1)y],[v(N-1)z],[t1→f],[t2→f],...,[tN-1→f],[tf]]。
子步骤1.2,将相对坐标系下航天器交会时的X、Y、Z三轴方向上的相对距离约束Si(u)=0(i=x,y,z)转化为不等式约束|[Si]([u])|<ε(ε为小正实数;i=x,y,z)和等式特征形式0∈[Si]([u])(i=x,y,z)。[Si]([u])(i=x,y,z)表示i方向的相对距离函数;
子步骤1.4,设定每次检验的决策变量区间个数M、预定正数δu和预定正数δJ;
步骤2,根据航天器脉冲交会轨迹优化模型对决策变量区间[u]进行区间分割,称为“符号分割法”,包括以下子步骤:
子步骤2.1,将各次脉冲推力作用给追踪航天器带来的速度增量的分量([vix],[viy],[viz])(i=1,2,...,N)以0为界各分为仅含正值和仅含负值的两个速度增量的分量区间;
子步骤2.2,将最后一次脉冲推力作用时间[tf]、最后一次脉冲推力作用时间与除最后一次脉冲推力外的各次脉冲推力作用时间之间的间隔时间[ti→f](i=1,2...N-1),以所使用的航天器脉冲交会轨迹优化模型中三角函数的象限为界各分为多个时间区间;
子步骤2.3,将子步骤2.1和子步骤2.2所得的速度增量的分量区间和时间区间任意组合得到Q个决策变量区间,所述的Q个决策变量区间组成区间群队列L;
步骤3,区间选择策略,根据设定的每次检验的决策变量区间个数M,若Q≤M,则令M=Q,从区间群队列L指定位置选择至多M个决策变量区间组成子区间队列L1,同时从区
间群队列L中删除选择的至多M个决策变量区间;
步骤4,使用基于梯度的优化算法分别在步骤3所选出的子区间队列L1中的每一个决策变量区间上求解航天器脉冲交会轨迹优化问题,按求解结果分别进行如下操作之一:
步骤4结果1:在子区间队列L1中的任意一个决策变量区间[u□]上,基于梯度的优化算法有解,进行以下子步骤4.1和子步骤4.2的操作:
子步骤4.1,梯度分割法,即以该解对应的决策变量值为中心、以给定大小的数值为半径将决策变量值扩展为包含有基于梯度的优化算法的解的扩展区间[IΔ],以扩展区间[IΔ]的各个区间变量的边界值分别分割所述的决策变量区间[u□]的各个相应的区间变量,将决策变量区间[u□]的各个区间变量分为3个区间或2个区间,并将其组合作为区间队列Lnew;
子步骤4.2,基于梯度的目标函数取值的上界更新,即以该解对应的决策变量值为中心、以非常小的数值为半径将决策变量值扩展为包含有基于梯度的优化算法的解的扩展区间[IΔ1],利用区间分析理论在扩展区间[IΔ1]上计算,检查其是否满足航天器脉冲交会轨迹优化模型的约束条件、其对应的目标函数区间上界是否小于目标函数取值的上界Jmin,当上述两项检查的结果都为“是”时,以扩展区间[IΔ1]对应的目标函数区间的上界更新目标函数取值的上界Jmin,否则保持现有目标函数取值的上界Jmin不变;
步骤4结果2:在子区间队列L1中的任意一个决策变量区间[u□]上,基于梯度的优化算法没有得到解,以决策变量区间[u□]上的的各个区间变量的区间中点分别分割各个区间变量,将决策变量区间[u□]的各个区间变量分为2个区间,并将其组合作为区间队列Lnew;
步骤5,区间删除策略,即在步骤4所得区间队列Lnew的每一个决策变量区间上分别进行区间分析,并进行以下子步骤5.1~子步骤5.4的操作:
子步骤5.1,若相对距离约束Si(u)=0(i=x,y,z)中各脉冲速度是线性相关的,则利用决策变量区间[u]中除第j次脉冲推力作用给追踪航天器带来的速度增量的分量之外的决策变量通过
[Si]([u])=0(i=x,y,z)解出第j次脉冲推力作用给航天器带来的速度增量的分量区间
[[vjx_f],[vjy_f],[vjz_f]](j=1,2...N-1),并计算其与[u]中[[vjx],[vjy],[vjz]]的交集
[[vjx_new],[vjy_new],[vjz_new]],若该交集为空集,则将该决策变量区间[u]从区间队列Lnew中删除,否则,更新决策变量区间[u]中的第j次脉冲推力作用给追踪航天器带来的速度增量的分量区间为[[vjx_new],[vjy_new],[vjz_new]],并同时得到更新的区间队列Lnew;
子步骤5.2,检查经步骤5.1更新后的区间队列Lnew中的每一个决策变量区间是否满足相对距离约束条件,并将不满足相对距离约束条件的决策变量区间从区间队列Lnew中删除;
子步骤5.3,在决策变量中任取一次脉冲作用对应的3个速度增量变量,根据相对距离约束Si(u)=0(i=x,y,z),指定的3个速度增量变量可以表达为其他决策变量的函数,以此将航天器脉冲交会轨迹优化模型转化为以除3个指定变量外的其他变量为决策变量的航天器脉冲交
会轨迹优化模型,检查目标函数J在经步骤5.2处理后的区间队列Lnew中的每一个决策变量区间上对新决策变量的一阶偏导数区间是否包含0,如检查结果为否,则将相应的决策变量区间从区间队列Lnew中删除;
子步骤5.4,对经子步骤5.3处理后的区间队列Lnew中的每一个决策变量区间分别检查目标函数区间与目标函数取值的上界Jmin之间的关系,并进行如下孙步骤5.4.1和孙步骤5.4.2的操作:
孙步骤5.4.1,若目标函数区间的下界大于目标函数取值的上界Jmin,则将相应的决策变量区间从区间队列Lnew中删除;
孙步骤5.4.2,若目标函数区间的上界小于目标函数取值的上界Jmin,则更新目标函数取值的上界Jmin为目标函数区间的上界;
步骤6,区间紧缩策略,即检查相对距离函数[Si]([u])(i=x,y,z)在经步骤5处理后的区间队列Lnew中每一个决策变量区间[u]上对[u]中各个区间变量的单调性,并进行如下子步骤6.1的操作:
子步骤6.1,若对区间队列Lnew中的任意一个决策变量区间,相对距离函数[Si]([u])对决策变量区间[u]中的第k个区间变量[uk]是单调的,且[uk]下界处[Si]([uk].inf)或[uk]上界处
[Si]([uk].sup)的符号为正或为负,则在[uk]内寻找大于[uk]下界且对应的[Si]与[uk]下界处
[Si]([uk].inf)同号的uk1,若没有,则令uk1=[uk].inf;寻找小于[uk]上界且对应的[Si]与[uk]上
界处[Si]([uk].sup)同号的uk2,若没有,则令uk2=[uk].sup;用区间[uk1,uk2]更新该区间队列Lnew中的相应决策变量区间[u]的第k个区间变量[uk],其中,[uk].inf表示[uk]的下界,[uk].sup表示[uk]的上界;
步骤7,检查区间队列Lnew中的每一个决策变量区间终止条件,即检查区间队列Lnew中的每一个决策变量区间的宽度A和对应于区间队列Lnew中的每一个决策变量区间的目标函数区间的宽度B,其中决策变量区间的宽度为决策变量区间内所有区间变量的宽度的最大值,执行以下子步骤7.1和子步骤7.2的操作:
子步骤7.1,当上述宽度A小于预定正数δu,或宽度B小于预定正数δJ时,将相应的决策变量区间从区间队列Lnew中删除,并将所述的相应的决策变量区间置入设计结果区间队列R中;
子步骤7.2,在对区间队列Lnew中的每一个决策变量区间都完成步骤7.1的操作后,更新区间群队列L,即将区间队列Lnew插入至区间群队列L在步骤3中删除选择的至多M个区间的删除点,将插入区间队列Lnew之后的区间群队列L作为新的区间群队列L;
步骤8,检查区间群队列L中决策变量区间的个数,并根据结果分别进行以下操作之一:
步骤8结果1,区间群队列L中决策变量区间的个数不为0,则转入步骤3,继续设计操
作;
步骤8结果2,区间群队列L中决策变量区间的个数为0,则设计结束;
步骤9,从设计结果区间队列R中任取一个设计结果区间,在所选取的设计结果区间的每个区间变量的取值区间内任意取值进行组合,并计算相应的最后一次脉冲推力作用给追踪航天器带来的速度增量,就得到了前述航天器脉冲交会轨迹的一个优化设计解。
优选的,上述方法的步骤3中所述指定位置是区间群队列L的队尾,与之相对应的子步骤7.2中将区间队列Lnew置于区间群队列L队尾以形成新的区间群队列L。
优选的,上述方法的步骤3中所述指定位置是区间群队列L的队首,与之相对应的子步骤7.2中将区间群队列L置于区间队列Lnew队尾以形成新的区间群队列L。
上述步骤3的两种优选方案使得区间群队列L的删除和更新操作更加便利。
优选的,上述方法的子步骤6.1中在[uk]内寻找大于[uk]下界且对应的[Si]与[uk]下界处[Si]([uk].inf)同号的最大值uk3,若没有,则令uk3=[uk].inf,寻找小于[uk]上界且对应的[Si]与[uk]上界处[Si]([uk].sup)同号最小值uk4,若没有,则令uk4=[uk].sup,用区间[uk3,uk4]更新该区间队列Lnew中的相应决策变量区间[u]的第k个区间变量[uk]。
上述子步骤6.1的优选方案将获得更好的区间紧缩结果。
优选的,上述方法的步骤9中,从设计结果区间队列R中取一个对应的目标函数区间的上界为目标函数取值的上界Jmin的设计结果区间,在所选取的设计结果区间中,在每个决策变量的取值区间内任意取值进行组合,并计算相应的最后一次脉冲推力作用给追踪航天器带来的速度增量,就得到了前述航天器脉冲交会轨迹的一个优化设计解。
上述步骤9的优选方案将保证设计结果所对应的目标函数值不高于Jmin。
与现有技术相比,本发明的有益效果在于保证了所得设计结果的全局最优性。在本发明中,因依赖于初值选择而不能保证获得全局最优解的基于梯度的优化方法被用于步骤4中。但基于梯度的优化方法的运行结果只用于确定区间分割点和更新目标函数取值的上界,本发明完全是一种区间优化方法,并因此继承了区间优化方法的全局最优性。
与现有技术相比,本发明的有益效果还在于对计算机存储空间的需求的最大值是事先确定的,并由此避免了区间优化算法可能会出现的存储空间不足(溢出)这一将导致设计过程异常中断的情况出现。这一有益效果主要由上述技术方案中的步骤3提供。依照步骤3,每次只从待处理区间群中选出有限个(最多M个)区间进行处理,而M值可根据所使用的计算机的存储空间进行设置,并因此可以保证设计过程中不出现存储空间溢出现象。
与现有技术相比,本发明的有益效果还在于设计效率的提高,即得到设计结果所需时间的减少。这一有益效果主要由上述技术方案中的步骤2及步骤4-步骤6提供。依照步骤2,将整个搜索区间划分为多个区间,避免了由于区间包括0而导致的过于粗放的区间扩张,有
利于区间删除操作的早期进行以及由此产生的待处理区间数量的快速减少,并由此减少了设计过程所需时间。依照步骤4,基于梯度的优化方法的运算结果的使用,有利于利用局部最优解或全局最优解的信息快速更新目标函数取值的上界。依照步骤4,利用基于梯度的优化方法运算所得结果进行区间分割,有利于快速获得具有包含局部最优值且具有较小的区间宽度的决策变量区间,也有利于其他不包含最优解区间的快速舍弃。这两个由步骤4提供的优势显然有利于设计过程所需时间的减少。依照步骤5的操作,有利于减少待处理区间的个数和更新目标函数取值的上界,并因此有利于设计过程所需时间的减少。依照步骤6,在约束条件上的局部单调性被用于进一步缩小待处理区间的宽度,有利于区间分析运算中区间扩张的减小,并因此有利于区间删除操作的早期进行,由此产生了减少设计过程所需时间的效果。
图1是本发明提供的航天器脉冲交会轨迹的梯度分割区间优化设计方法的流程示意图;
图2是本发明提供的方法的步骤3-步骤7连续执行两次的过程中区间群队列变化的示意图;
图3是本发明提供的方法中基于梯度目标函数取值的上界的更新过程示意图;
图4是根据本发明的一个实施例所得的两个航天器之间相对运动轨迹的示意图;
图5是根据本发明的一个实施例所得的优化设计结果区间队列的示意图。
下面结合附图与具体实施方式对本发明做进一步的详细描述。
以非固定时间的双脉冲交会对接优化问题为例,相对坐标系X轴在轨道平面内沿目标航天器飞行方向,Z轴从目标航天器质心指向地心,Y轴符合右手正交坐标系,垂直于轨道平面,并采用如下的CW方程近似描述建立航天器脉冲交会轨迹优化模型:
通过式(1),可得t时刻追踪航天器相对于目标航天器的相对位置和速度如下:
设追踪航天器和目标航天器交会的时刻为tf。从0时刻开始,在t1时刻,追踪航天器施加第一次脉冲,脉冲推力作用给追踪航天器带来的速度增量为v1(v1x,v1y,v1z)。经过t1→f=tf-t1时间,在tf时刻,追踪航天器施加第二次脉冲,脉冲推力作用给追踪航天器带来的速度增量为v2(v2x,v2y,v2z),两个航天器交会。
通过式(2)可以得到交会时刻tf的相对距离S和相对速度V,并令S=0和V=0。
则(3)式为以t1,tf,v1,v2为决策变量的航天器脉冲交会轨迹优化模型的约束条件,分别为相对距离约束和相对速度约束。
若只考虑对燃料消耗的要求,则航天器脉冲交会轨迹优化模型的目标函数为:
J取最小值,则双脉冲交会燃料消耗最低。
采用航天器脉冲交会轨迹的梯度分割区间优化设计方法对以上优化模型进行求解,航天器脉冲交会轨迹的梯度分割区间优化设计方法的流程示意图,如图1所示,具体包括如下步骤:
步骤1,对航天器脉冲交会轨迹优化模型进行区间化处理,包括以下子步骤:
子步骤1.1,假定两个航天器在目标航天器的轨道平面内运动,则有决策变量区间
[u]=[[v1x],[v1z],[t1→f],[tf]]。
子步骤1.2,航天器交会处的相对速度约束V=0可以由第二次脉冲推力作用给追踪航天器带来的速度增量(v2x,v2y,v2z)得以保证。而对于相对距离约束S=0,由于两个航天器在目标航天器的轨道平面内运动,所以S=0可以分解为Sx=0,Sz=0。将Sx=0,Sz=0转化为不等式约束形式|[Sx]([u])|<ε,|[Sz]([u])|<ε(ε为小正实数)和等式特征形式0∈[Sx]([u]),0∈[Sz]([u])。[Sx]([u])表示x方向的相对距离函数,[Sz]([u])表示z方向的相对距离函数。
子步骤1.4,设定每次检验的决策变量区间个数M、预定正数δu和预定正数δJ;
步骤2,使用符号分割法,包括以下子步骤:
子步骤2.1,将第一次脉冲推力作用给追踪航天器带来的速度增量的分量[v1x]和[v1z]以0为界各分为仅含正值和仅含负值的两个速度增量的分量区间;
子步骤2.2,将第二次脉冲推力作用时间[tf]、第二次脉冲推力作用时间与第一次脉冲推力作用时间之间的间隔时间[t1→f],以所使用的航天器脉冲交会轨迹优化模型中三角函数的象限为界各分为多个时间区间;
子步骤2.3,将子步骤2.1和子步骤2.2所得的速度增量的分量区间和时间区间任意组合得到Q个决策变量区间,所述的Q个决策变量区间组成区间群队列L;
步骤3,根据设定的每次检验的决策变量区间个数M,若Q≤M,则令M=Q,从区间群队列L队尾(或任意位置)中选择至多M个决策变量区间组成子区间队列L1,同时从区间群队列L中删除选择的至多M个决策变量区间,步骤3~步骤7连续执行两次的过程中区间群队列变化的示意,如图2所示;
步骤4,使用基于梯度的优化算法分别在步骤3所选出的子区间队列L1中的每一个决策变量区间上求解航天器脉冲交会轨迹优化问题,按求解结果分别进行如下操作之一:
步骤4结果1:在子区间队列L1中的任意一个决策变量区间[u□]上,基于梯度的优化算法有解,进行以下子步骤4.1和子步骤4.2的操作:
子步骤4.1,以该解对应的决策变量值为中心、以给定大小的数值为半径将决策变量值扩展为包含有基于梯度的优化算法的解的扩展区间[IΔ],以扩展区间[IΔ]的各个区间变量的边界值分别分割所述的决策变量区间[u□]的各个相应的区间变量,将决策变量区间[u□]的各个区间变量分为3个区间或2个区间,并将其组合作为区间队列Lnew;
子步骤4.2,基于梯度的目标函数取值上界的更新,即以该解对应的决策变量值为中心、以非常小的数值为半径将决策变量值扩展为包含有基于梯度的优化算法的解的扩展区间[IΔ1],利用区间分析理论在扩展区间[IΔ1]上进行计算,检查其是否满足航天器脉冲交会轨迹优化模型的约束条件、其对应的目标函数区间上界是否小于目标函数取值的上界Jmin,当上述两项检查的结果都为“是”时,以扩展区间[IΔ1]对应的目标函数区间的上界更新目标函数取值的上界Jmin,否则保持现有目标函数取值的上界Jmin不变,过程示意图如图3所示;
步骤4结果2:在子区间队列L1中的决策变量区间[u□]上,基于梯度的优化算法没有得到解,以决策变量区间[u□]上的各个区间变量中点分别分割各个区间变量,将决策变量区间[u□]的各个区间变量分为2个区间,并将其组合作为区间队列Lnew;
步骤5,区间删除策略,即在步骤4所得区间队列Lnew的每一个决策变量区间上分别进
行区间分析,并进行以下子步骤5.1~子步骤5.4的操作:
子步骤5.1,若相对距离约束Si(u)=0(i=x,y,z)中各脉冲速度是线性相关的,则利用决策变量区间[u]中区间变量[t1→f]和[tf],通过[Si]([u])=0(i=x,z)解出第一次脉冲推力作用给追踪航天器带来的速度增量的分量区间[[v1x_f],[v1z_f]],并计算其与[u]中[[v1x],[v1z]]的交集
[[v1x_new],[v1z_new]],若该交集为空集,则将该决策变量区间[u]从区间队列Lnew中删除,否则,更新决策变量区间[u]中的第一次脉冲推力作用给追踪航天器带来的速度增量的分量区间为[[v1x_new],[v1z_new]],并同时得到更新的区间队列Lnew;
子步骤5.2,检查经步骤5.1更新后的区间队列Lnew中的每一个决策变量区间是否满足相对距离约束条件,并将不满足相对距离约束条件的决策变量区间从区间队列Lnew中删除;
子步骤5.3,在决策变量中任取一次脉冲作用对应的3个速度增量变量,根据相对距离约束Si(u)=0(i=x,y,z),指定的3个速度增量变量可以表达为其他决策变量的函数,以此将航天器脉冲交会轨迹优化模型转化为以除3个指定变量外的其他变量为决策变量的航天器脉冲交会轨迹优化模型,检查目标函数J在经子步骤5.2处理后的区间队列Lnew中的每一个决策变量区间上对新决策变量的一阶偏导数区间是否包含0,如检查结果为否,则将相应的决策变量区间从区间队列Lnew中删除;
子步骤5.4,对经子步骤5.3处理后的区间队列Lnew中的每一个决策变量区间分别检查目标函数区间与目标函数取值的上界Jmin之间的关系,并进行如下孙步骤5.4.1和孙步骤5.4.2的操作:
孙步骤5.4.1,若目标函数区间的下界大于目标函数取值的上界Jmin,则将相应的决策变量区间从区间队列Lnew中删除;
孙步骤5.4.2,若目标函数区间的上界小于目标函数取值的上界Jmin,则更新目标函数取值的上界Jmin为目标函数区间的上界;
步骤6,区间紧缩策略,即检查相对距离函数[Si]([u])(i=x,z)在经步骤5处理后的区间队列Lnew中的每一个决策变量区间[u]上对[u]中各个区间变量单调性,并进行如下子步骤6.1的操作:
子步骤6.1,若对区间队列Lnew中的任意一个决策变量区间,相对距离函数[Si]([u])对决策变量区间[u]中的第k个区间变量[uk]是单调的,且[uk]下界处[Si]([uk].inf)或[uk]上界处
[Si]([uk].sup)的符号为正或为负,则在[uk]内寻找大于[uk]下界且对应的[Si]与[uk]下界处
[Si]([uk].inf)同号的最大值uk1,若没有,则令uk1=[uk].inf;寻找小于[uk]上界且对应的[Si]与
[uk]上界处[Si]([uk].sup)同号的最小值uk2,若没有,则令uk2=[uk].sup;用区间[uk1,uk2]更新该区间队列Lnew中的相应决策变量区间[u]的第k个区间变量[uk],其中,[uk].inf表示[uk]的下界,[uk].sup表示[uk]的上界;
步骤7,检查区间队列Lnew中的每一个决策变量区间终止条件,即检查区间队列Lnew中的每一个决策变量区间的宽度A和对应于区间队列Lnew中的每一个决策变量区间的目标函数区间的宽度B,其中决策变量区间的宽度为决策变量区间内所有区间变量的宽度的最大值,执行以下子步骤7.1和子步骤7.2的操作:
子步骤7.1,当上述宽度A小于预定正数δu,或宽度B小于预定正数δJ时,将相应的决策变量区间从区间队列Lnew中删除,并将所述的相应的决策变量区间置入设计结果区间队列R中;
子步骤7.2,在对区间队列Lnew中的每一个决策变量区间都完成步骤7.1的操作后,更新区间群队列L,即区间队列Lnew插入至区间群队列L队尾;
步骤8,检查区间群队列L中决策变量区间的个数,并根据结果分别进行以下操作之一:
步骤8结果1,区间群队列L中决策变量区间的个数不为0,则转入步骤3,继续设计操作;
步骤8结果2,区间群队列L中决策变量区间的个数为0,则设计结束。
步骤9,选取优化设计结果,从设计结果区间队列R中取一个设计结果区间对应的目标函数区间上界为目标函数取值的上界Jmin的设计结果区间,在所选取的设计结果区间中,在每个决策变量的取值区间内任意取值进行组合,并计算相应的最后一次脉冲推力作用给航天器带来的速度增量,就得到了前述航天器脉冲交会轨迹的一个优化设计解。
下面结合一个具体算例进一步展示本发明提供的方法的设计效果。
设目标航天器在400km高的圆轨道上,相对距离精度ε为0.015m,δu和δJ为0.01,设初始决策变量区间[u]=[[-30,30],[-30,30],[0,8000],[0,8000]],目标函数估计值初值为100m·s-1,追踪航天器初始位置为(-10000,0,8000)m,初始速度为(10,0,-15)m·s-1。
仿真运算得出当前精度下目标函数取值的上界及对应的解区间如表1所示
表1 目标函数取值的上界Jmin对应的解区间
在这一组决策变量区间内,任意取值,其目标函数值均在[J]区间内,其中目标函数取值的上界Jmin即为[J]的上限值为8.750384691131890m·s-1。
由图4可知,相对距离随着时间的推移,逐步缩减至0,误差在指定的0.015m范围内。从路径上,直观地验证了本发明求解的正确性。
由图5可知,在指定精度范围内,满足条件的可能包含优化解的可行解区间有5520个,每一个[tf]所对应的[J]均包含了目标函数取值的上界。
采用遗传算法求解该问题,决策变量为t1→f和tf,搜索范围均为[0,8000]s,设初始种群为100个,最大遗传代数100代,求解10次,结果如表2。
表2 遗传算法结果表
由表2可知,遗传算法由于算法特性,依赖于初值选择,容易陷入局部最优,经不起反复运算。表2中10次遗传算法目标函数最优值为第6次运算的目标函数优化值8.750384691363504,与本发明提出的全局优化算法的目标函数取值的上界值8.750384691131890m·s-1相差无几,佐证了本发明求解的正确性,也为本发明的全局性优势提供了支持。
Claims (5)
- 一种航天器脉冲交会轨迹的梯度分割区间优化设计方法,其特征在于,所述方法包括以下步骤:步骤1,对航天器脉冲交会轨迹优化问题进行区间化处理,包括以下子步骤:子步骤1.1,给定航天器脉冲交会过程中应使用的脉冲推力作用次数N,取最后一次脉冲推力作用时间tf、最后一次脉冲推力作用时间tf与除最后一次脉冲推力外的各次脉冲推力作用时间之间的间隔时间ti→f、各次脉冲推力作用给追踪航天器带来的速度增量的分量(vix,viy,viz)作为决策变量,并按各决策变量的可能取值范围构成决策变量区间[u]=[[v1x],[v1y],[v1z],...,[v(N-1)x],[v(N-1)y],[v(N-1)z],[t1→f],[t2→f],...,[tN-1→f],[tf]];N为大于等于2的自然数;间隔时间ti→f中i=1,2...N-1,速度增量的分量(vix,viy,viz)中i=1,2,...,N;子步骤1.2,将相对坐标系下航天器交会时的X、Y、Z三轴方向上的相对距离约束Si(u)=0转化为不等式约束|[Si]([u])|<ε和等式特征形式0∈[Si]([u]);ε为小正实数,i=x,y,z;子步骤1.4,设定每次检验的决策变量区间个数M、预定正数δu和预定正数δJ;步骤2,根据航天器脉冲交会轨迹优化模型对决策变量区间[u]进行区间分割,包括以下子步骤:子步骤2.1,将各次脉冲推力作用给追踪航天器带来的速度增量的分量区间([vix],[viy],[viz])以0为界各分为仅含正值和仅含负值的两个速度增量的分量区间;其中i=1,2,...,N;子步骤2.2,将最后一次脉冲推力作用时间区间[tf]、最后一次脉冲推力作用时间与除最后一次脉冲推力外的各次脉冲推力作用时间之间的间隔时间区间[ti→f],i=1,2...N-1,以所使用的航天器脉冲交会轨迹优化模型中三角函数的象限为界各分为多个时间区间;子步骤2.3,将子步骤2.1所得的仅含正值和仅含负值的两个速度增量的分量区间和子步骤2.2中的多个时间区间任意组合得到Q个决策变量区间,所述的Q个决策变量区间组成区间群队列L;步骤3,根据设定的每次检验的决策变量区间个数M,若Q≤M,则令M=Q,从区间群队列L指定位置选择至多M个决策变量区间组成子区间队列L1,同时从区间群队列L中删除选择的至多M个决策变量区间;步骤4,使用基于梯度的优化算法分别在步骤3所选出的子区间队列L1中的每一个决策变量区间上求解航天器脉冲交会轨迹优化问题,按求解结果分别进行如下操作之一:步骤4结果1:在子区间队列L1中的任意一个决策变量区间[u□]上,基于梯度的优化算 法有解,进行以下子步骤4.1和子步骤4.2的操作:子步骤4.1,梯度分割法,即以该解对应的决策变量值为中心、以给定大小的数值为半径将决策变量值扩展为包含有基于梯度的优化算法的解的扩展区间[IΔ],以扩展区间[IΔ]的各个区间变量的边界值分别分割所述的决策变量区间[u□]的各个相应的区间变量,将决策变量区间[u□]的各个区间变量分为3个区间或2个区间,并将其组合作为区间队列Lnew;子步骤4.2,以该解对应的决策变量值为中心、以非常小的数值为半径将决策变量值扩展为包含有基于梯度的优化算法的解的扩展区间[IΔ1],利用区间分析理论在扩展区间[IΔ1]上计算,检查其是否满足航天器脉冲交会轨迹优化模型的约束条件、其对应的目标函数区间上界是否小于目标函数取值的上界Jmin,当上述两项检查的结果都为“是”时,以扩展区间[IΔ1]对应的目标函数的区间上界更新目标函数取值的上界Jmin,否则保持现有目标函数取值的上界Jmin不变;步骤4结果2:在子区间队列L1中的任意一个决策变量区间[u□]上,基于梯度的优化算法没有得到解,以决策变量区间[u□]上的各个区间变量的区间中点分别分割各个区间变量,将决策变量区间[u□]的各个区间变量分为2个区间,并将其组合作为区间队列Lnew;步骤5,在步骤4所得区间队列Lnew的每一个决策变量区间[u]上分别进行区间分析,并进行以下子步骤5.1~子步骤5.4的操作:子步骤5.1,若相对距离约束Si(u)=0中各脉冲速度是线性相关的,i=x,y,z,则利用决策变量区间[u]中除第j次脉冲推力作用给追踪航天器带来的速度增量的分量之外的决策变量通过相对距离函数[Si]([u])=0解出第j次脉冲推力作用给航天器带来的速度增量的分量区间[[vjx_f],[vjy_f],[vjz_f]],i=x,y,z,j=1,2...N-1,并计算其与决策变量区间[u]中速度增量的分量区间[[vjx],[vjy],[vjz]]的交集[[vjx_new],[vjy_new],[vjz_new]],若该交集为空集,则将该决策变量区间[u]从区间队列Lnew中删除,否则,更新决策变量区间[u]中的第j次脉冲推力作用给追踪航天器带来的速度增量的分量区间为[[vjx_new],[vjy_new],[vjz_new]],并同时得到更新的区间队列Lnew;子步骤5.2,检查经步骤5.1更新后的区间队列Lnew中的每一个决策变量区间[u]是否满足相对距离约束条件,并将不满足相对距离约束条件的决策变量区间从区间队列Lnew中删除;子步骤5.3,在决策变量中任取一次脉冲作用对应的3个速度增量的分量,根据相对距离约束Si(u)=0,i=x,y,z,指定3个速度增量的分量表达为其他决策变量的函数,以此将航天器脉冲交会轨迹优化模型转化为以除3个指定的速度增量的分量外的其他决策变量为决策变量的航天器脉冲交会轨迹优化模型,检查目标函数J在经步骤5.2处理后的区间队列Lnew中的每一个决策变量区间[u]上对新决策变量的一阶偏导数区间是否包含0,如检查结果为否,则将相应的决策变量区间从区间队列Lnew中删除;子步骤5.4,对经子步骤5.3处理后的区间队列Lnew中的每一个决策变量区间[u]分别检查目标函数区间与目标函数取值的上界Jmin之间的关系,并进行如下孙步骤5.4.1和孙步骤5.4.2的操作:孙步骤5.4.1,若目标函数区间的下界大于目标函数取值的上界Jmin,则将相应的决策变量区间从区间队列Lnew中删除;孙步骤5.4.2,若目标函数区间的上界小于目标函数取值的上界Jmin,则更新目标函数取值的上界Jmin为目标函数区间的上界;步骤6,区间紧缩策略,即检查相对距离函数[Si]([u])在经步骤5处理后的区间队列Lnew中每一个决策变量区间[u]上对决策变量区间[u]中各个区间变量的单调性,i=x,y,z,并进行如下子步骤6.1的操作:子步骤6.1,若对区间队列Lnew中的任意一个决策变量区间[u],相对距离函数[Si]([u])对决策变量区间[u]中的第k个区间变量[uk]是单调的,且第k个区间变量[uk]下界处相对距离函数[Si]([uk].inf)或第k个区间变量[uk]上界处相对距离函数[Si]([uk].sup)的符号为正或为负,则在第k个区间变量[uk]内寻找大于第k个区间变量[uk]下界且对应的相对距离函数[Si]与第k个区间变量[uk]下界处相对距离函数[Si]([uk].inf)同号的区间变量uk1,若没有,则令区间变量uk1=[uk].inf,寻找小于第k个区间变量[uk]上界且对应的相对距离函数[Si]与第k个区间变量[uk]上界处相对距离函数[Si]([uk].sup)同号的区间变量uk2,若没有,则令区间变量uk2=[uk].sup,用决策变量区间[uk1,uk2]更新该区间队列Lnew中的相应决策变量区间[u]的第k个区间变量[uk],其中,区间变量[uk].inf表示第k个区间变量[uk]的下界,区间变量[uk].sup表示第k个区间变量[uk]的上界;步骤7,检查区间队列Lnew中的每一个决策变量区间[u]终止条件,即检查区间队列Lnew中的每一个决策变量区间[u]的宽度A和对应于区间队列Lnew中的每一个决策变量区间[u]的目标函数区间的宽度B,其中决策变量区间[u]的宽度为决策变量区间[u]内所有区间变量的宽度的最大值,执行以下子步骤7.1和子步骤7.2的操作:子步骤7.1,当上述宽度A小于预定正数δu,或宽度B小于预定正数δJ时,将相应的决策变量区间从区间队列Lnew中删除,并将所述的相应的决策变量区间置入设计结果区间队列R中;子步骤7.2,在对区间队列Lnew中的每一个决策变量区间[u]都完成步骤7.1的操作后,更新区间群队列L,即将区间队列Lnew插入至区间群队列L在步骤3中删除选择的至多M个决策变量区间的删除点,将插入区间队列Lnew之后的区间群队列L作为新的区间群队列L;步骤8,检查区间群队列L中决策变量区间的个数,并根据结果分别进行以下操作之一:步骤8结果1,区间群队列L中决策变量区间的个数不为0,则转入步骤3,继续设计操 作;步骤8结果2,区间群队列L中决策变量区间的个数为0,则设计结束;步骤9,从设计结果区间队列R中任取一个设计结果区间,在所选取的设计结果区间的每个区间变量的取值区间内任意取值进行组合,并计算相应的最后一次脉冲推力作用给追踪航天器带来的速度增量,就得到了前述航天器脉冲交会轨迹的一个优化设计解。
- 根据权利要求1所述的一种航天器脉冲交会轨迹的梯度分割区间优化设计方法,其特征在于,步骤3所述的指定位置为区间群队列L的队尾,相应的,子步骤7.2中将区间队列Lnew置于区间群队列L队尾以形成新的区间群队列L。
- 根据权利要求1所述的一种航天器脉冲交会轨迹的梯度分割区间优化设计方法,其特征在于,步骤3所述的指定位置为区间群队列L的队首,相应的,子步骤7.2中将区间群队列L置于区间队列Lnew队尾以形成新的区间群队列L。
- 根据权利要求1~3中任意一项权利要求所述的航天器脉冲交会轨迹的梯度分割区间优化设计方法,其特征在于,步骤6.1中,在第k个区间变量[uk]内寻找大于第k个区间变量[uk]下界且对应的相对距离函数[Si]与第k个区间变量[uk]下界处相对距离函数[Si]([uk].inf)同号的最大值uk3,若没有,则令uk3=[uk].inf,寻找小于第k个区间变量[uk]上界且对应的相对距离函数[Si]与第k个区间变量[uk]上界处相对距离函数[Si]([uk].sup)同号最小值uk4,若没有,则令uk4=[uk].sup,用决策变量区间[uk3,uk4]更新该区间队列Lnew中的相应决策变量区间[u]的第k个区间变量[uk]。
- 根据权利要求1~3中任意一项权利要求所述的航天器脉冲交会轨迹的梯度分割区间优化设计方法,其特征在于,步骤9如下:从设计结果区间队列R中取一个对应的目标函数区间的上界为目标函数取值的上界Jmin的设计结果区间,在所选取的设计结果区间的每个区间变量的取值区间内任意取值进行组合,并计算相应的最后一次脉冲推力作用给航天器带来的速度增量,就得到了航天器脉冲交会轨迹的一个优化设计解。
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