一类最佳飞行轨迹的计算

 本文给出了一种简化的直接多重打靶算法,并讨论了该算法在求解一类最佳飞行轨迹上的应用。数值计算结果表明,本文所给的算法收敛性好,对初值无很高要求,因而避免了在计算之前对问题进行冗繁的解析分析。     

基于脱靶量数据的发射系航迹参数求解方法

针对当前海态巡航飞行试验末段外测无法跟踪测量的实际问题,基于现有脱靶量测量系统,建立了利用某脱靶量测量数据到发射系的转换模型。此模型将脱靶量测量数据统一到发射系航迹中,有利于航迹分析工作。并建立了转换结果的误差估计模型,误差模型充分考虑了脱靶量测量误差、靶船定位误差以及靶船航向角误差。利用仿真数据对转换模型及误差模型进行了计算验证。结果表明,位置误差满足精度要求。该方法对延拓外测处理时段具有积极意义。     

Sensitivity Considerations in Trajectory Optimization

A technique by which the trajectory optimization problem can be formulated to include the trajectory sensitivity functions in the performance index is presented. It is shown that an explicit steering law, which can be derived for the upper atmospheric flight of a vehicle, is a function of the sensitivity state, adjoint vectors, and the parameters of the chosen trajectory dynamics. The new steering law is compared with the one without sensitivity considerations. A computational method is presented to implement the new steering law.     

多飞行器再入段时间协同弹道规划方法

提出了一种多飞行器再入段时间协同弹道规划方法。首先,在纵向平面内规划满足航程与终端约束的纵向标称轨迹。随后,在采用轨迹跟踪律跟踪纵向标称轨迹的同时,运用考虑初始横侧向状态的多边界航向偏差角走廊策略控制飞行器的横侧向机动,以满足到达时间约束与终端约束,进而实现单枚飞行器到达时间约束下的轨迹规划。在此基础上,完成了飞行器的到达时间分布与飞行能力分析,给出了最小与最大到达时间的分析计算方法,并根据多飞行器协同再入的任务需求完成了协同飞行时间决策。最后,多飞行器协同再入与扰动条件下的仿真结果表明,该方法能够规划出满足到达时间与终端约束的协同再入轨迹,具备良好的计算精度与鲁棒性。     

Optimal guidance of extended trajectory shaping

To control missile＇s miss distance as well as terminal impact angle, by involving the timeto-go-nth power in the cost function, an extended optimal guidance law against a constant maneuvering target or a stationary target is proposed using the linear quadratic optimal control theory.An extended trajectory shaping guidance（ETSG） law is then proposed under the assumption that the missile-target relative velocity is constant and the line of sight angle is small. For a lag-free ETSG system, closed-form solutions for the missile＇s acceleration command are derived by the method of Schwartz inequality and linear simulations are performed to verify the closed-form results. Normalized adjoint systems for miss distance and terminal impact angle error are presented independently for stationary targets and constant maneuvering targets, respectively. Detailed discussions about the terminal misses and impact angle errors induced by terminal impact angle constraint, initial heading error, seeker zero position errors and target maneuvering, are performed.     

求解最优月球软着陆轨道的隐式打靶法

基于间接法思想推导出一种隐式打靶法对月球软着陆轨道优化问题进行了研究。建立月球软着陆轨道归一化系统模型，利用庞特亚金极大值原理将月球软着陆轨道优化问题转化为满足最优必要条件的两点边值问题（TPBVP），采用一种新的时间变量使两点边值问题的终端时刻固定，同时将终端时刻看作状态变量并引入终端时刻的哈密尔顿函数值作为隐式终端条件，提出一种隐式打靶法对含有隐式终端条件的两点边值问题进行迭代求解，从而得出燃料消耗最优的月球软着陆轨道。仿真结果表明，与直接法和混合法相比，隐式打靶法优化精度高，收敛速度快，实现了月球软着陆过程燃料消耗最优。同时应用隐式打靶法求解不同发动机推力值的最优月球软着陆问题，得到燃料消耗最小的最优推重比，可为月面着陆器下降级发动机选型提供参考。     

VTOL Aircraft Control Output Tracking Sensitivity Design

A method is presented for reducing trajectory sensitivity and achieving robust asymptotic tracking for linear feedback systems when there are parameter perturbations and disturbance inputs. The controller consists of a servocompensator containing the modes of the reference signals and disturbance inputs, a stabilizing feedback loop, and a feedforward compensator. Application of the method to the design of a vertical takeoff and landing (VTOL) aircraft flight control system is discussed. The use of a precompensator allows performance maneuvers such that the aircraft tracks desired trajectories and the feedforward and feedback signals aid in reducing the trajectory sensitivity to variations of parameters due to change in airspeed and to wind gust. Simulation results are presented to show the robust tracking, disturbance rejection, and sensitivity reduction capabilities of the flight control system.     

Propagation and System Accuracy Impact of Major Sensor Errors on a Strapdown Aircraft Navigator

A strapdown system is considered as an unaided inertial navigator aboard an aircraft. Presented here are simulation results detailing the propagation of navigation errors (in nautical miles) due to strapdown sensor errors for four trajectories. They indicate the type of performance that can be expected from a strapdown system utilizing good ?off the shelf? gyros and accelerometers, and dramatically illustrate the improvements necessary in these components to obtain navigation performance comparable to that available from a good gimballed inertial system. The total navigation error for each trajectory is broken down to show the contribution from each of the various error sources. This breakdown quickly reveals which are the critical error sources for a given trajectory class, and also points up the relationship that exists between each individual error source, aircraft maneuvers, and the resulting navigation error. Several of the error mechanisms are discussed at length and a set of linearized differential equations which can be used to analyze error propagations is presented. These results should be of particular interest to the system designer who is faced with the problem of specifying the sensor error parameters necessary to meet mission performance requirements. With an analysis similar to the one presented here, but structured around his own expected mission trajectories, the designer should be able to confidently predict system accuracies and intelligently perform tradeoffs on the critical system parameters.     

Accurate solution of proportional navigation for maneuveringtargets

An accurate solution is presented of the nonlinear differential equations describing motion under proportional navigation when the target is laterally maneuvering. A quasilinearization (QL) approach is used, followed by a perturbation technique to obtain closed-form solutions for trajectory parameters. An explicit expression for the pursuer lateral acceleration is derived and shown to contain contributions due to initial heading error and target maneuver, with a coupling between the two effects. The solution is shown to be a substantial and consistent generalization or an earlier accurate solution for nonmaneuvering targets and also of classical linear solutions for maneuvering targets. The generalized QL solution presented provides very accurate estimates of pursuer lateral acceleration over a much broader range of engagement geometries and target maneuvers than presently available closed-form solutions     

Optimum Steady-State Position and Velocity Estimation Using Noisy Sampled Position Data

The Kalman filtering technique is used to obtain analytical expressions for the optimum position and velocity accuracy that can be achieved in a navigation system that measures position at uniform sampling intervals of T seconds through random noise with an rms value of ?x. A one-dimensional dynamic model, with piecewise-constant acceleration assumed, is used in the analysis, in which analytic expressions for position and velocity accuracy (mean square), before and after observations, are obtained. The errors are maximum immediately before position measurements are made. The maximum position error, however, can be bounded by the inherent sensor error by use of a sufficiently high sampling rate, which depends on the sensor accuracy and acceleration level. The steady-state Kalman filter for realizing the optimum estimates consists of a double integrator, the initial conditions of which are reset at each observation.     

Bias compensation and tracking with monopulse radars in the presence of multi path

The problem of tracking targets in the presence of reflections from sea or ground is addressed. Both types of reflections (specular and diffuse) are considered. Specular reflection causes large peak errors followed by an approximately constant bias in the monopulse ratio, while diffuse reflection has random variations which on the average generate a bias in the monopulse ratio. Expressions for the average error (bias) in the monopulse ratio due to specular and diffuse reflections and the corresponding variance in the presence of noise in the radar channels are derived. A maximum maneuver-based filter and a multiple model estimator are used for tracking. Simulation results for five scenarios, typical of sea skimmers, with Swerling III fluctuating radar cross sections (RCSs) indicate the significance and efficiency of the technique developed in this paper-a 65% reduction of the rms error in the target height estimate.     

Fuzzy adaptive robust control for space robot considering the effect of the gravity

Space robot is assembled and tested in gravity environment, and completes on-orbit service（OOS） in microgravity environment. The kinematic and dynamic characteristic of the robot will change with the variations of gravity in different working condition. Fully considering the change of kinematic and dynamic models caused by the change of gravity environment, a fuzzy adaptive robust control（FARC） strategy which is adaptive to these model variations is put forward for trajectory tracking control of space robot. A fuzzy algorithm is employed to approximate the nonlinear uncertainties in the model, adaptive laws of the parameters are constructed, and the approximation error is compensated by using a robust control algorithm. The stability of the control system is guaranteed based on the Lyapunov theory and the trajectory tracking control simulation is performed. The simulation results are compared with the proportional plus derivative（PD） controller, and the effectiveness to achieve better trajectory tracking performance under different gravity environment without changing the control parameters and the advantage of the proposed controller are verified.     

高超声速滑翔飞行器约束预测校正再入制导

针对大升阻比高超声速滑翔飞行器的再入制导问题,将再入轨迹划分为初始下降段、过渡段和准平衡滑翔段。初始下降段采用定倾侧角飞行,过渡段在最大倾侧角附近飞行,准平衡滑翔段利用数值预测校正方法和准平衡滑翔条件在线设计同时满足过程约束和终端约束的倾侧角制导律。通过标准条件和扰动条件下的仿真结果表明,这种制导律在满足各种约束的条件下,不仅能够达到较高的精度,而且对初始误差具有良好的鲁棒性,能够应付再入时各种不确定性因素的影响。     

Autonomous navigation and guidance for landing on asteroids

This paper presents an autonomous landing navigation and guidance scheme for future asteroid sample return mission. An autonomous navigation scheme based on feature tracking technology is brought out firstly; secondly, desired descent landing trajectories with the initial and terminal constraints are planned in order to achieve arrive-at-time landing on an asteroid; then, two guidance control laws, based on error phase analysis method and PD plus PWPF method respectively, are designed to track reference descent trajectory; finally, the validity of the proposed scheme is confirmed by computer simulation.     

TSTO运载器一级返场轨迹优化设计与在线生成

对水平起降两级入轨（TSTO）运载器一子级返场轨迹优化和轨迹在线生成问题进行了研究。首先，给出了较独特的一子级再入轨迹设计策略：先给定侧向剖面，再分段优化求解三维轨迹。针对返场过程的大幅转向需求，设计了形式简单的倾侧角-航向角偏差剖面，并定义了具有不同任务的航向转弯段和航向微调段；针对一子级宽速域气动变化显著特点，为避免轨迹跳跃，定义了增高减速段和下降滑翔段，并采用分段优化策略求解三维轨迹。其次，针对分离扰动造成的一子级初始状态偏差，扩展了自适应高维伪谱插值（AMPI）算法的参数空间，并将其应用于返场轨迹在线生成问题。仿真结果表明，设计的倾侧角剖面能够在倾侧角不翻转的前提下调整飞行航向对准着陆场，设计的分段优化策略能够保证高度曲线平稳无跳跃，采用的自适应高维伪谱插值算法能够在分离扰动影响下快速准确地实现在线轨迹生成。     

Low-Sensitivity Design of Optimal Linear Control Systems

The quadratic performance criterion, linear optimal control problem is reformulated to incorporate constraints on trajectory sensitivity. The open-loop solution is obtained for sensitivity functions defined for small plant-parameter variations. This approach has provided a beginning for other attempts to solve the low-sensitivity analytical design problem, as reported in the references.     

飞机着陆导引中的随机最优控制问题

论述了应用随机最优控制理论的基本原理和方法，解决飞机在大气紊流中着陆的控制问题。用协方法分析法，推导出可直接计算机飞机着陆精度的线性离散随机系统的误差方差的传播方程，并进一步分析了滤波灵敏度对飞机着陆控制的影响。     

Docking control for probe-drogue refueling: An additive-state-decomposition-based output feedback iterative learning control method

Designing a controller for the docking maneuver in Probe-Drogue Refueling (PDR) is an important but challenging task, due to the complex system model and the high precision requirement. In order to overcome the disadvantage of only feedback control, a feedforward control scheme known as Iterative Learning Control (ILC) is adopted in this paper. First, Additive State Decomposition (ASD) is used to address the tight coupling of input saturation, nonlinearity and the property of NonMinimum Phase (NMP) by separating these features into two subsystems (a primary system and a secondary system). After system decomposition, an adjoint-type ILC is applied to the Linear Time-Invariant (LTI) primary system with NMP to achieve entire output trajectory tracking, whereas state feedback is used to stabilize the secondary system with input saturation. The two controllers designed for the two subsystems can be combined to achieve the original control goal of the PDR system. Furthermore, to compensate for the receiver-independent uncertainties, a correction action is proposed by using the terminal docking error, which can lead to a smaller docking error at the docking moment. Simulation tests have been carried out to demonstrate the performance of the proposed control method, which has some advantages over the traditional derivative-type ILC and adjoint-type ILC in the docking control of PDR.     

基于阻力加速度倒数剖面的再入轨迹规划与制导方法

针对升力式飞行器再入制导问题,提出了一种基于阻力加速度倒数剖面的在线解析规划与制导方法。首先将过程和终端约束转换成阻力加速度倒数形式的飞行走廊,采用三次样条函数描述倒数剖面。然后通过解析计算航程上下界,利用待飞航程在倒数剖面内的近似线性关系,以满足待飞航程为目标,迭代计算得到阻力加速度倒数剖面;在飞行过程中根据当前状态和实际待飞航程,周期性更新阻力加速度倒数剖面。通过对阻力加速度剖面的跟踪进行纵向制导,解算倾侧角指令;通过倾侧角反向来进行侧向制导,限制航向角偏差。实现了再入轨迹的在线快速生成与更新,并利用阻力加速度动态特性,将其与跟踪制导结合,提出的方法效率高,适应性强,有工程应用的潜力。     

Trajectory Estimation with Multi-range-rate System Based on Sparse Representation and Spline Model Optimization

The classic state methods for trajectory estimation in boost phase with multi-range-rate system include method of point-by-point manner and that of spline-model-based manner. Both are deficient in terms of model-approximation accuracy and systematic error determination thus resulting in the estimation errors well beyond the requirements, especially, concerning the maneuvering trajectory. This article proposes a new high-precision estimation approach based on the residual error analysis. The residual error comprises three components, i. e. systematic error, model truncation error and random error. The approach realizes self-adaptive estimation of systematic errors in measurements following the theory of sparse representation of signals to minimize the low-frequency components of residual errors. By taking median- and high-frequency components as indexes, the spline model-approximation is improved by optimizing node sequence of the spline function and the weight selection for data fusion through iteration. Simulation has validated the performances of the proposed method.