Halo轨道的ASRE非线性留位控制方法

针对Halo轨道的留位控制问题,提出一种跟踪名义参考轨道的非线性最优跟踪控制策略.首先得到日-地系统第二平动点附近的有控制力作用下的轨道动力学方程,其次利用微分修正法得到要跟踪的名义参考轨道,然后将ASRE非线性最优跟踪控制方法与精细积分法相结合,针对Halo轨道的留位设计非线性控制器,最后利用数值算例验证了本文方法的...     

航天器终端接近的有限时间输入饱和避碰控制

针对航天器终端接近问题,解决了追踪航天器在跟踪到达期望目标点的过程中不与目标航天器发生碰撞的难题。首先,在目标航天器轨道系下建立了航天器的相对运动和避碰模型。其次,考虑外界扰动上界已知和未知两种情形,均给出了有限时间避碰控制器,且所设计的控制器都具有输入饱和特性。最后,应用Lyapunov稳定性理论证明了在所提出的控制器作用下系统是有限时间收敛的,并且,利用避碰势函数证明了所设计的控制器能够实现避碰。仿真结果表明,所提出的控制器是有效的。     

基于视线运动模型的椭圆轨道交会最优控制

针对航天器自主交会对接实际存在的接近方位角约束, 在视线坐标系内讨论了椭圆轨道最优交会控制设计问题. 根据椭圆轨道视线动力学模型具有时变非线性的特点, 分别采用状态相关Riccati方程(state-dependent riccati equation, SDRE)方法和\theta-D方法进行了最优交会控制器设计. 考虑到实际施加的控制力沿原轨道坐标系各轴向更易于实现, 结合SDRE方法中系统输入矩阵可与系统状态量相关, 进而设计了控制力沿轨道坐标系轴向的最优交会控制器. 数值仿真表明: 两种方法均实现了带有方位角约束的交会; \theta-D控制算法计算效率更高, 而SDRE控制算法精度较高, 且可以实现控制力沿轨道坐标系各轴定向施加.      

考虑防御系统延迟使其预测误差最大的突防弹道设计

对中段多脉冲机动突防弹道的设计问题进行了研究。采用的原理与方法有别于成熟的航天器多脉冲变轨,而是基于路径规划的思想对弹道设计问题简化。考虑敌方防御系统延迟,改进多脉冲点火模型,并基于变射面的思想对关机点参数进行了设计及优化。然后,从使敌方预测误差最大的角度提出评价函数,并利用遗传算法进行优化。最后,给出了一种同时满足导弹机动突防与打击精度要求的多脉冲弹道设计方法。从模型的可行性,方法的有效性、灵活性、迭代效率及精度等方面进行了仿真验证分析。在PC机仿真中,20 s内就设计出一条保证打击精度的中段突防弹道。结果表明,建立的模型是可行的,提出的突防弹道设计方法是快速有效的。     

基于微分进化算法的深空轨道全局优化设计

针对多目标多任务的深空探测轨道设计问题,提出一种新的将探测目标、探测方式、探测顺序以及发射窗口同时作为优化变量, 并采用微分进化算法进行全局优化的设计方法. 使用该方法在只考虑太阳中心引力作用的二体模型下,基于圆锥曲线拼接法建立第三届全国深空轨道设计竞赛问题的优化模型并进行求解. 最后利用该方法求解ESA的ACT研究团队的深空探测任务算例并对结果进行对比分析. 结果表明, 提出的全局优化设计方法对解决多目标、多任务深空探测轨道优化设计问题是可行和有效的.      

基于深度强化学习的多无人车系统编队控制

针对多智能体编队控制问题,研究了基于DDQN深度强化学习算法的多无人车系统的编队控制器,采用一致性控制与伴随位形相结合的方法对编队控制问题进行建模和简化.建立了基于相对距离和速度的状态空间,使得控制输入不依赖于全局信息,然后设计了基于九大典型运动方向的动作空间,并设计了基于相对距离和相对速度的奖励函数,基于以上参数进行了神经网络架构的设计和网络训练与运动仿真环境的搭建,并成功训练出有效的控制器.该控制器可以直接应用于带有非完整约束的欠驱动无人车的编队任务,且控制器的网络训练只需要运动数据而不需要精确模型,是一种无模型控制方法.最后,通过大量不同场景下的运动仿真验证了控制器的有效性,包括多队形、多位置、多轨迹仿真以及时变队形、时变通讯和通讯故障等特殊情况的检验,该控制器在所有场景中均能有效完成控制任务.最后优化了编队起始阶段的策略,定义了等候条件与启动条件,有效节约了控制的能耗,利用运动仿真和对比分析验证了优化作用.     

日地系统L_2点Halo轨道绳系卫星编队动力学

研究平动点附近周期轨道上旋转多体绳系卫星编队系统的非线性耦合动力学问题。编队系统为各卫星质量接近的轮辐状结构,位于日地系统第二平动点附近,整个系统的旋转保持系绳处于张紧状态,建立Hill限制性三体问题的绳系编队系统动力学模型。针对处于留位阶段的典型对称三星编队,在位于较大Halo轨道上无控制力作用的情况下,进行母卫星轨道运动与系绳摆动耦合运动的动力学模拟,分析轨道方向、卫星质量比、系绳长度以及初始旋转速度对编队系统整体稳定性的影响。     

基于虚拟中心引力场方法的航天器转移轨道设计

空间机动技术是实现空间操作任务的基础,具有重要的研究价值. 研究了连续推力作用下航天器转移轨道设计问题,提出了一种基于虚拟中心引力场的轨道设计方法. 该方法有两大特点:(1) 能够将机动轨道设计问题转化为虚拟中心引力场参数的优化问题,简化了设计过程;(2) 对轨道形状或推力方向、大小不做任何假定,能够应用于一般情况下的机动轨道设计. 将该方法应用于航天器二维和三维的转移轨道设计,并和形状方法进行了对比分析. 仿真结果分析表明,采用该方法简化了轨道设计过程,为航天器快速轨道设计提供了新思路.      

地月低能转移的发生条件及轨迹构造

应用平动点理论研究了地月低能转移的发生条件和轨迹构造. 由于空间双圆模型存在周期性扰动,传统的平动点概念不再适用;根据Hill瞬时边界的连接情况定义了等效平动点LL_{1}和LL_{2}. 通过构造合适的Poincaré截面以获得所有可能的月球捕获轨道的近月距和偏心率分布,从而获得了完全不同于Hill和圆型限制性三体问题的月面捕获能量. 在空间双圆模型下,平动点和Halo轨道不变流形的渐近结构遭到破坏:到达或离开平动点的时间,由无穷转变为有限值;运动方向由双向变为单向. 经由LL_{1}点穿越获得了最小能量的低能转移,借助LL_{1}-Halo轨道穿越得到了(M,N)-圈穿越轨道,经由LL_{2}点穿越获得了最小能量的弱稳定边界转移,借助LL_{2}-Halo轨道穿越得到了弱稳定边界逃逸和捕获窗口. 最后,以地月转移和大幅值逆行轨道的切入为例,给出低能转移的小推力、脉冲和弱稳定边界等转移的实现方式.      

多储液腔航天器刚液耦合动力学与复合控制

采用复合控制方法对充液航天器的姿态和轨道机动进行高精度控制.通过傅里叶-贝塞尔级数展开法,将低重力环境下液体的弯曲自由表面的动态边界条件转化为简单的微分方程,其中耦合液体晃动方程的状态向量由相对势函数的模态坐标和波高的模态坐标组成.通过广义准坐标下的拉格朗日方程得到航天器刚体部分运动和液体燃料晃动的耦合动力学方程,提出了自适应快速终端滑模策略和输入整形技术相结合的复合控制器,并分别用于控制携带有一个燃料腔和四个燃料腔航天器的轨道机动和姿态机动.通过数值模拟来验证控制器的效率和精度.结果表明,对于多储液腔航天器,如果在设计航天器的姿态和轨道控制器时没有充分考虑燃料晃动效应,那么在受控航天器系统中将会出现刚-液-控耦合问题并导致航天器姿态不稳定.而本研究中的复合自适应终端滑模控制器可以实现航天器机动的高精度控制并有效抑制液体燃料晃动.     

An improved nonlinear control strategy for deep space formation flying spacecraft

This paper aims to provide further study on the nonlinear modeling and controller design of formation flying spacecraft in deep space missions. First, in the Sun-Earth system, the nonlinear formation dynamics for the circular restricted three-body problem （CRTBP） and elliptic restricted three-body problem （ERTBP） are presented. Then, with the Floquet mode method, an impulsive controller is developed to keep the Chief on the desired Halo orbit. Finally, a nonlinear adaptive control scheme based on Nonzero set- point LQR and neural network is proposed to achieve high precision formation maneuver and keeping. The simulation results indicate that the proposed nonlinear control strategy is reasonable as it considers not only the orbit keeping of the Chief, but also the formation modeling inaccuracy. Moreover, the nonlinear adaptive control scheme is effective to improve the control accuracy of the formation keeping.     

木卫停泊轨道间低耗能小推力转移轨道设计方法研究

对木卫停泊轨道间的低耗能小推力转移轨道设计方法进行了研究,提出基于"类halo轨道截面"法的低耗能转移轨道参数化方法和基于配点法的多体Lambert问题求解算法,并利用全局优化算法得出了燃耗最少的初步优化结果;利用多体同伦法和固定近心点高度的多圈转移控制律得到了各段小推力转移轨道的有效设计结果.所提方法同样适用于其他天体间的转移轨道设计,为多体环境下低耗能小推力转移轨道提出了新的设计思路和方法.     

Trajectory optimization and applications using high performance solar sails

The high performance solar sail can enable fast missions to the outer solar system and produce exotic non-Keplerian orbits. As there is no fuel consumption, mission trajectories for solar sail spacecraft are typically optimized with respect to flight time. Several investigations focused on interstellar probe missions have been made, including optimal methods and new objective functions. Two modes of interstellar mission trajectories, namely “direct flyby” and “angular momentum reversal trajectory”, are compared and discussed. As a foundation, a 3D non-dimensional dynamic model for an ideal plane solar sail is introduced as well as an optimal control framework. A newly found periodic double angular momentum reversal trajectory is presented, and some properties and potential applications of this kind of inverse orbits are illustrated. The method how to achieve the minimum periodic inverse orbit is also briefly elucidated.     

基于星历匹配法的载人小行星探测轨迹优化问题求解

对基于星历匹配法的载人小行星探测轨迹优化问题解法进行了研究. 提出星历匹配法的概念,利用其求出最优发射窗口初值与候选最优探测序列,然后利用遗传算法对特定探测序列的时间节点等参数进行优化,最后利用基于庞德里亚金极大值原理的同伦法进行小推力转化以求得最终探测轨道及其推力控制律. 结果显示星历匹配法可以快速准确地求出最优发射窗口初值与候选探测序列,这大大提高了载人小行星探测等多目标交会探测问题的求解效率.     

Model-free chaos control based on AHGSA for a vibro-impact system

For a vibro-impact system with clearance, the model-free chaos control method based on adaptive hybrid gravitational search algorithm (or AHGSA algorithm for short) is proposed. Nonparametric time-varying dynamic linear model based on pseudo-partial-derivative is established using input/output data of the controlled system, and on this basis, the optimal controller is designed according to the quadratic performance index, and the controller parameters is optimized using AHGSA algorithm. By combining the artificial bee colony search operator and chaos optimization strategy, gravitational search algorithm (or GSA algorithm for short) is improved from three aspects (i.e., population initialization, velocity and position update, gravity coefficient adjustment) to achieve a balance between the global detection ability and the local development ability. AHGSA algorithm has good optimization accuracy and efficiency: The arbitrariness is avoided in controller parameters selection, and the quality of the chaos control is ensured as well. In simulation experiment, the model-free controller optimized is used to control the chaotic motion of a single-degree-of-freedom vibro-impact system with clearance to verify the validity and feasibility of the proposed chaos control method. The simulation results show that the control effect is good, and the proposed chaos control method has the following advantages: the proposed chaos control method does not depend on the precise model of the controlled system, and the controller is easy to be designed and implemented.     

Multi-objective transfer to libration-point orbits via the mixed low-thrust and invariant-manifold approach

The multi-objective optimization of transfer trajectories from an orbit near Earth to a periodic libration-point orbit in the Sun–Earth system using the mixed low-thrust and invariant-manifold approach is investigated in this paper. A two-objective optimization model is proposed based on the mixed low-thrust and invariant-manifold approach. The circular restricted three-body model (CRTBP) is utilized to represent the motion of a spacecraft in the gravitational field of the Sun and Earth. The transfer trajectory is broken down into several segments; both low-thrust propulsion and stable manifolds are utilized based on the CRTBP in different segments. The fuel cost, which is generated only by the low-thrust trajectory for transferring the spacecraft from an orbit near Earth to a stable manifold, is minimized. The total flight time, which includes the time during which the spacecraft is controlled by the low-thrust trajectory and the time during which the spacecraft is moving on the stable manifold, is also minimized. Using the nondominated sorting genetic algorithm for the resulting multi-objective optimization problem, highly promising Pareto-optimal solutions for the transfer of the spacecraft are found. Via numerical simulations, it is shown that tradeoffs between time of flight and fuel cost can be quickly evaluated using this approach. Furthermore, for the same time of flight, transfer trajectories based on the mixed-transfer method can save a larger amount of fuel than the low-thrust method alone.     

A survey on orbital dynamics and navigation of asteroid missions

Asteroid exploration is currently one of the most concerned topics among international space agencies. Or- bital dynamics and navigation are obviously crucial for asteroid exploration. This paper aims to give a brief review on the dynamics, control and navigation of asteroid reconnaissance orbits, including the heliocentric transfer orbit and near as- teroid orbit. The developments in optimization techniques of the transfer segment are discussed in detail. We surveyed global researches in this field and made comments on several important progresses. The final section proposed a prospec- tive of future studies with emphasis on the key techniques of these issues in the asteroid exploration missions.     

Barrier Lyapunov functions-based fixed-time stabilization of nonholonomic systems with unmatched uncertainties and time-varying output constraints

The fixed-time stabilization problem is addressed in this paper for a kind of nonholonomic systems in chained form with unmatched uncertainties and time-varying output constraints. A novel tan-type barrier Lyapunov function is introduced to deal with time-varying output constraints. Under the unified framework of the considered system with and without output constraints, a state feedback controller is designed with the aid of adding a power integrator technique and switching control strategy. It is shown that the suggested controller ensures the states of closed-loop system to zero in a given fixed time without disobeying the constraints. Finally, simulation results are given to confirm the efficacy of the presented control scheme.

     

A multi-objective optimization method for uncertain structures based on nonlinear interval number programming method

A multi-objective optimization method for uncertain structures is developed based on nonlinear interval number programming (NINP) method. The NINP method is employed to transform each uncertain objective function into a deterministic single-objective optimization problem. Using the constraint penalty function method, a deterministic multi-objective and non-constraint optimization problem is formulated in terms of penalty functions. Then the micro multi-objective genetic algorithm and the intergeneration projection genetic algorithm are adopted as outer layer and inner optimization operator to solve the nesting optimization problem, respectively. Finally, four numerical examples are provided to demonstrate the effectiveness of the present method.     

Stabilization problems for a system with output feedback (review)

Algorithms for solving the problem of design of static output feedback controllers for stationary linear systems with continuous and discrete time are reviewed. The inverse problem is considered. The algorithms of synthesis of output feedback controllers are generalized to the case of a periodic discrete-time system. To solve such problems, it might be more natural to use an approach based on multi-criterion optimization. It is also shown that these algorithms can be used for the optimal stabilization of unstable systems with delay. In this connection, the parameters of a controller with given structure for a controlled unstable scalar system with delay are optimized. To this end, the system is first approximated by a system without delay, with the exponent approximated by a fractionally rational function. Since the structure of the controller is given, the quality of approximation is estimated as the difference (in the space of controller coefficients) between the stability domains of the original and approximating systems. At the next stage, the gain coefficients of the controller for the reduced system are optimized. The efficiency of the thus synthesized controller is assessed through mathematical modeling of a system with delay whose feedback loop is defined by the gain coefficients found. The approach is illustrated by stabilizing an inverted simple pendulum with a proportional–derivative controller with delay. The problem of synthesis of a robust controller for this example is considered. Some examples of designing a robust controller, including for a third-order system in which the delay rather than some parameter is uncertain are presented