GUIDANCE LAW EVALUATION FOR MISSILE GUIDANCE SYSTEMS

In missile guidance system, to reduce the interception “miss distance,” it is important to choose a suitable guidance law and navigation constant. This paper investigates and compares the system behavior of guidance laws under different navigation constants. Based on use of the adjoint technique, miss distance sensitivity analyses which consider the system noise, target step maneuver, initial heading error and system parameters for different guidance laws and navigation constants are presented. Based on these analyses, some suggestions for choosing a suitable guidance law and navigation constant are given for the design of missile guidance systems. Also, a suggestion for the optimal escape time for pilots of fighter planes is given.     

Inspection of an underwater structure using point‐cloud SLAM with an AUV and a laser scanner

This paper presents experimental results using a newly developed 3D underwater laser scanner mounted on an autonomous underwater vehicle (AUV) for real‐time simultaneous localization and mapping (SLAM). The algorithm consists of registering point clouds using a dual step procedure. First, a feature‐based coarse alignment is performed, which is then refined using iterative closest point. The robot position is estimated using an extended Kalman filter (EKF) that fuses the data coming from navigation sensors of the AUV. Moreover, the pose from where each point cloud was collected is also stored in the pose‐based EKF‐SLAM state vector. The results of the registration algorithm are used as constraint observations among the different poses within the state vector, solving the full‐SLAM problem. The method is demonstrated using the Girona 500 AUV, equipped with a laser scanner and inspecting a 3D sub‐sea infrastructure inside a water tank. Our results prove that it is possible to limit the navigation drift and deliver a consistent high‐accuracy 3D map of the inspected object.     

An All-Aspect Near-Optimal Guidance Law

In this paper, a new guidancelaw known as the all-aspect proportional navigation (AAPN) guidancelaw is formulated. AAPN is a modification of traditional proportionalnavigation, with an additional term added to improve performanceat large heading error angles. The missile guidance problem isfirst formulated as an optimal control problem and solved usinga combined genetic algorithm-shooting method. The problem isrepeatedly solved at various heading error angles. By employingChebychev polynomial fitting, we can then determine the parametersof the AAPN. Subsequently, AAPN is compared against the proportionalnavigation guidance law as well as the optimal solution. Theresults clearly show that AAPN outperforms PN at large headingerror angles. Also, its performance is only slightly inferiorto the optimal solution.     

Differential evolution based 3-D guidance law for a realistic interceptor model

This paper presents a novel, soft computing based solution to a complex optimal control or dynamic optimization problem that requires the solution to be available in real-time. The complexities in this problem of optimal guidance of interceptors launched with high initial heading errors include the more involved physics of a three dimensional missile–target engagement, and those posed by the assumption of a realistic dynamic model such as time-varying missile speed, thrust, drag and mass, besides gravity, and upper bound on the lateral acceleration. The classic, pure proportional navigation law is augmented with a polynomial function of the heading error, and the values of the coefficients of the polynomial are determined using differential evolution (DE). The performance of the proposed DE enhanced guidance law is compared against the existing conventional laws in the literature, on the criteria of time and energy optimality, peak lateral acceleration demanded, terminal speed and robustness to unanticipated target maneuvers, to illustrate the superiority of the proposed law.     

An online-implementable differential evolution tuned all-aspect guidance law

This paper proposes a differential evolution based method of improving the performance of conventional guidance laws at high heading errors, without resorting to techniques from optimal control theory, which are complicated and suffer from several limitations. The basic guidance law is augmented with a term that is a polynomial function of the heading error. The values of the coefficients of the polynomial are found by applying the differential evolution algorithm. The results are compared with the basic guidance law, and the all-aspect proportional navigation laws in the literature. A scheme for online implementation of the proposed law for application in practice is also given.     

Development of guidance laws for a variable-speed missile

The most used guidance law for short-range homing missiles is proportional navigation (PN). In PN, the acceleration command is proportional to the line-of-sight (LOS) angular velocity. Indeed, if a missile and a target move on a collision course with constant speeds, the LOS rate is zero. The speed of a highly maneuverable modem missile varies considerably during flight. The performance of PN is far from being satisfactory in that case.In this article we analyze the collision course for a variable-speed missile and define a guidance law that steers the heading of the missile to the collision course. We develop guidance laws based on optimal control and differential game formulations, and note that both optimal laws coincide with the Guidance to Collision law at impact. The performance improvement of the missile using the new guidance law as compared to PN is demonstrated.Recommended by A.W. Merz     

A time differences of arrival‐based homing strategy for autonomous underwater vehicles

A new sensor‐based homing integrated guidance and control law is presented to drive an underactuated autonomous underwater vehicle (AUV) toward a fixed target, in 3‐D, using the information provided by an ultra‐short baseline (USBL) positioning system. The guidance and control law is first derived at a kinematic level, expressed on the space of the time differences of arrival (TDOAs), as directly measured by the USBL sensor, and assuming the plane wave approximation. Afterwards, the control law is extended for the dynamics of an underactuated AUV resorting to backstepping techniques. The proposed Lyapunov‐based control law yields almost global asymptotic stability (AGAS) in the absence of external disturbances and is further extended, keeping the same properties, to the case where known ocean currents affect the motion of the vehicle. Simulations are presented and discussed that illustrate the performance and behavior of the overall closed‐loop system in the presence of realistic sensor measurements and actuator saturation. Copyright © 2009 John Wiley & Sons, Ltd.     

Underwater docking of an under-actuated autonomous underwater vehicle: system design and control implementation

Underwater docking greatly facilitates and extends operation of an autonomous underwater vehicle (AUV) without the support of a surface vessel. Robust and accurate control is critically important for docking an AUV into a small underwater funnel-type dock station. In this paper, a docking system with an under-actuated AUV is presented, with special attention paid to control algorithm design and implementation. For an under-actuated AUV, the cross-track error can be controlled only via vehicle heading modulation, so both the cross-track error and heading error have to be constrained to achieve successful docking operations, while the control problem can be even more complicated in practical scenarios with the presence of unknown ocean currents. To cope with the above issues, a control scheme of a three-hierarchy structure of control loops is developed, which has been embedded with online current estimator/compensator and effective control parameter tuning. The current estimator can evaluate both horizontal and vertical current velocity components, based only on the measurement of AUV’s velocity relative to the ground; in contrast, most existing methods use the measurements of both AUV’s velocities respectively relative to the ground and the water column. In addition to numerical simulation, the proposed docking scheme is fully implemented in a prototype AUV using MOOS-IvP architecture. Simulation results show that the current estimator/compensator works well even in the presence of lateral current disturbance. Finally, a series of sea trials are conducted to validate the current estimator/compensator and the whole docking system. The sea trial results show that our control methods can drive the AUV into the dock station effectively and robustly.     

Three-dimensional optimal path planning for waypoint guidance of an autonomous underwater vehicle

In this paper, optimal three-dimensional paths are generated offline for waypoint guidance of a miniature Autonomous Underwater Vehicle (AUV). Having the starting point, the destination point, and the position and dimension of the obstacles, the AUV is intended to systematically plan an optimal path toward the target. The path is defined as a set of waypoints to be passed by the vehicle. Four criteria are considered for evaluation of an optimal path; they are “total length of path”, “margin of safety”, “smoothness of the planar motion” and “gradient of diving”. A set of Pareto-optimal solutions is found where each solution represents an optimal feasible path that cannot be outrun by any other path considering all four criteria. Then, a proposed three-dimensional guidance system is used for guidance of the AUV through selected optimal paths. This system is inspired from the Line-of-Sight (LOS) guidance strategy; the idea is to select the desired depth, presumed proportional to the horizontal distance of the AUV and the target. To develop this guidance strategy, the dynamic modeling of this novel miniature AUV is also derived. The simulation results show that this guidance system efficiently guides the AUV through the optimal paths.     

Aiming point guidance law for air-to-air missiles

A new aiming point guidance (APG) law is presented which generates a missile turn rate command proportional to the heading error, that is defined as the angle between the current missile heading and predicted aiming point. The target under consideration is assumed to be manoeuvring with constant longitudinal and/or lateral accelerations, and the missile dynamics are modelled as an acceleration-limited first-order lag point mass. The aiming point is calculated based on current intercept geometry and target velocity and position. Time-to-go, a key factor for successful interception, is estimated by a time-to-go predictor. With the heading error defined as stated above, the guidance law can guide the missile into the collision course in the early stage of the engagement. As a consequence, the later part of the missile trajectory tends to be a straight line, provided that the target maintains its current status. The performance of the proposed APG is evaluated by simulation and is compared with the proportional navigation guidance (PNG) and Kim's prediction guidance (PRG) law (Kim 1985). Numerical simulations show that APG is superior to PNG and PRG in both intercept time and miss distance     

基于移动长基线的多AUV 协同导航

基于扩展卡尔曼滤波（EKF）理论研究了多AUV 协同导航定位的移动长基线算法．移动长基线多AUV 协同导航结构中,主AUV 内部装备高精度导航设备,从AUV 内部装备低精度导航设备,外部均装备水声装置测量 相对位置关系,利用移动长基线算法融合内部和外部传感器信息,实时获取从AUV 的位置信息．建立了协同导航 系统数学模型,设计了EKF 协同导航算法,在各种测试情况下通过仿真验证了所推导的分析结果,对EKF 和几何 解方程算法的导航效果进行了比较．研究结果表明,以主AUV 作为移动的长基线节点时,通过EKF 算法可以显著 提高群体的导航定位精度．     

Robust fuzzy 3D path following for autonomous underwater vehicle subject to uncertainties

This paper addresses a three-dimensional (3D) path following control problem for underactuated autonomous underwater vehicle (AUV) subject to both internal and external uncertainties. A two-layered framework synthesizing the 3D guidance law and heuristic fuzzy control is proposed to achieve robust adaptive following along a predefined path. In the first layer, a 3D guidance controller for underactuated AUV is presented to guarantee the stability of path following in the kinematics stage. In the second layer, a heuristic adaptive fuzzy algorithm based on the guidance command and feedback linearization Proportional-Integral-Derivative (PID) controller is developed in the dynamics stage to account for the nonlinear dynamics and system uncertainties, including inaccuracy modelling parameters and time-varying environmental disturbances. Furthermore, the sensitivity analysis of the heuristic fuzzy controller is presented. Against most existing methods for 3D path following, the proposed robust fuzzy control scheme reduces the design and implementation costs of complicated dynamics controller, and relaxes the knowledge of the accuracy dynamics modelling and environmental disturbances. Finally, numerical simulation results validate the effectiveness of the proposed control framework and illustrate the outperformance of the proposed controller as well.     

Teach‐and‐repeat path following for an autonomous underwater vehicle

This paper presents a teach‐and‐repeat path‐following method for an autonomous underwater vehicle (AUV) navigating long distances in environments where external navigation aides are denied. This method utilizes sonar images to construct a series of reference views along a path, stored as a topological map. The AUV can then renavigate along this path, either to return to the start location or to repeat the route. Utilizing unique assumptions about the sonar image‐generation process, this system exhibits robust image‐matching capabilities, providing observations to a discrete Bayesian filter that maintains an estimate of progress along the path. Image‐matching also provides an estimate of offset from the path, allowing the AUV to correct its heading and effectively close the gap. Over a series of field trials, this system demonstrated online control of an AUV in the ocean environment of Holyrood Arm, Newfoundland and Labrador, Canada. The system was implemented on an International Submarine Engineering Ltd. Explorer AUV and performed multiple path completions over both a 1 and 5 km track. These trials illustrated an AUV operating in a fully autonomous mode, in which navigation was driven solely by sensor feedback and adaptive control. Path‐following performance was as desired, with the AUV maintaining close offset to the path.     

Proportional navigation-based collision avoidance for UAVs

A collision avoidance algorithm for unmanned aerial vehicles (UAVs) based on the conventional proportional navigation (PN) guidance law is investigated. The proportional navigation guidance law being applied to a wide range of missile guidance problems is tailored to the collision avoidance of UAVs. This can be accomplished by guiding the relative velocity vector of the aircraft to a vector connecting the current aircraft position to the safety boundary of the target aircraft. Stability of the proposed algorithm is also studied using the circle criterion. The stability condition can be established by choosing the navigation coefficient within a certain bound. The guidance law is extended to 3-dimensional maneuver problems. Inherent simplicity and robustness of the PN guidance law provides satisfactory collision avoidance performance with different initial conditions. Recommended by Editorial Board member Sangdeok Park under the direction of Editor Hyun Seok Yang. This research was performed for the Smart UAV Development Program, one of 21st Century Frontier R&D Programs funded by the Ministry of Science and Technology of Korea. Su-Cheol Han received the B.S. degree from Korea Airforce Academy, Korea, in 1997, and the M.S. degree from Korea Advanced Institute of Science and Technology, Korea, in 2005. At present, he is serving as a pilot in Korea Airforce. His research interests are UAV guidance and control, especially collision avoidance. Hyochoong Bang received the B.S. and M.S. degrees in aeronautical engineering from Seoul National University in 1985 and 1987, respectively. He also received the Ph.D. degree in 1992 from Texas A&M University. From 1992 to 1994, he worked as a Research Assistant Professor at the U.S. Naval Postgraduate School (NPS) conducting spacecraft attitude control research. From 1995 to 1999, he worked for Korea Aerospace Research Institute. Since 2001 he has been a Professor at Korea Advanced Institute of Science and Technology. His current research interest include spacecraft attitude control, spacecraft guidance, UAV guidance and control. Chang-Sun Yoo received the B.S. degree from Korea Aerospace University, Korea, in 1987, the M.S. degree from Korea Advanced Institute of Science and Technology, Korea, in 1991 and the Ph.D. degree from Chungnam National University, Korea, in 2003. Since 1991, he has been a Research Engineer in Korea Aerospace Research Institute, Korea. His research interests are flight simulation, flight control system, inertial and GPS navigation.     

Toward Autonomous Exploration in Confined Underwater Environments

In this field note, we detail the operations and discuss the results of an experiment conducted in the unstructured environment of an underwater cave complex using an autonomous underwater vehicle (AUV). For this experiment, the AUV was equipped with two acoustic sonar sensors to simultaneously map the caves' horizontal and vertical surfaces. Although the caves' spatial complexity required AUV guidance by a diver, this field deployment successfully demonstrates a scan‐matching algorithm in a simultaneous localization and mapping framework that significantly reduces and bounds the localization error for fully autonomous navigation. These methods are generalizable for AUV exploration in confined underwater environments where surfacing or predeployment of localization equipment is not feasible, and they may provide a useful step toward AUV utilization as a response tool in confined underwater disaster areas.     

A Sensor-Based Controller for Homing of Underactuated AUVs

A new sensor-based homing integrated guidance and control law is presented to drive an underactuated autonomous underwater vehicle (AUV) toward a fixed target, in three dimensions, using the information provided by an ultrashort baseline (USBL) positioning system. The guidance and control law is first derived using quaternions to express the vehicle's attitude kinematics, which are directly obtained from the time differences of arrival (TDOA) measured by the USBL sensor. The dynamics are then included resorting to backstepping techniques. The proposed Lyapunov-based control law yields global asymptotic stability in the absence of external disturbances and is further extended, keeping the same properties, to the case where constant known ocean currents affect the dynamics of the vehicle. Finally, a globally exponentially stable nonlinear TDOA and range-based observer is introduced to estimate the ocean current and uniform asymptotic stability is obtained for the overall closed-loop system. Simulations are presented illustrating the performance of the proposed solutions.      

AUV自主导航航位推算算法的分析研究

对AUV (Autonomous Underwater Vehicle)自主导航的航位推算算法做了进一步研究并加以改进，以提高其自主导航精度．然后，利用AUV湖试所获得的数据，对本文提出的修正算法进行了验证．结果表明， AUV的自主导航精度得到很大提高，可以用于修正原来的自主导航算法．     

一种基于深广度权重树模型的局部最优树算法

为了降低用户访问页面的点击次数,提高网站的易用性,给出了一种独特的可以表示页面导航结构的深广度权重树模型,并在不影响导航之间逻辑关系的前提下,提出一种计算权重树的局部最优树算法。通过该算法改变了网站的导航结构,降低了网站总点击次数,继而提高了网站的易用性。实验结果表明该算法是有效的。     

Typhoon at CommsNet13: Experimental experience on AUV navigation and localization

This paper presents two acoustic-based techniques for Autonomous Underwater Vehicle (AUV) navigation within an underwater network of fixed sensors. The proposed algorithms exploit the positioning measurements provided by an Ultra-Short Base Line (USBL) transducer on-board the vehicle to aid the navigation task. In the considered framework the acoustic measurements are embedded in the communication network scheme, causing time-varying delays in ranging with the fixed nodes. The results presented are obtained with post-processing elaborations of the raw experimental data collected during the CommsNet13 campaign, organized and scientifically led by the NATO Science and Technology Organization Centre for Maritime Research and Experimentation (CMRE). The experiment involved several research institutions and included among its objectives the evaluation of on-board acoustic USBL systems for navigation and localization of AUVs. The ISME groups of the Universities of Florence and Pisa jointly participated to the experiment with one Typhoon class vehicle. This is a 300 m depth rated AUV with acoustic communication capabilities originally developed by the two groups for archaeological search in the framework of the THESAURUS project. The CommsNet13 Typhoon, equipped with an acoustic modem/USBL head, navigated within the fixed nodes acoustic network deployed by CMRE. This allows the comparison between inertial navigation, acoustic self-localization and ground truth represented by GPS signals (when the vehicle was at the surface).     

一种考虑洋流影响的AUV组合导航算法

针对由捷联惯导(SINS)、多普勒测速仪(DVL)以及深度传感器组成的自主水下航行器(AUV)组合导航系统,当DVL测量距离无法达到海底的情况下,洋流是该系统主要误差源之一的问题,在SINS/DVL组合导航算法的基础上,提出了一种在原算法中加入洋流信息提高系统导航定位精度的方法,并将以上两种导航算法解算出的AUV位置信息进行仿真对比,仿真结果表明:与未考虑洋流信息的算法相比,加入洋流信息的算法能够有效提高AUV的定位精度。