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This article proposes barrier Lyapunov function-based guidance strategies to achieve target interception, by a seeker-equipped interceptor having a limited field-of-view (FOV), at a prespecified impact time. A novel approach to respect the FOV constraint, using the conditions on time-to-go of the engagement, is first proposed. Guidance commands are then derived to steer the course of the interceptor in a way so as to adhere to the necessary conditions. Guidance strategy is first derived for 3-D engagements, and then, the same for planar scenarios is presented as a special case. The set of achievable impact times for given initial conditions, while satisfying FOV constraints, is first obtained, and then, a way to expand the achievable range of impact time is suggested using a two-stage approach. The behavior of lead angle is analyzed, and it is shown that guidance commands remain nonsingular and converge to zero near interception. Simulations are shown to validate the efficacy of proposed methods for various initial engagement geometries. [ABSTRACT FROM AUTHOR]

This paper proposes predefined-time convergent guidance schemes that can drive the pursuer on a collision course corresponding to the target interception from a pre-specified impact direction, irrespective of initial engagement geometries. The target interception at the desired impact angle is first transformed into a problem of controlling the line-of-sight angle and its rate. Then, guidance commands are derived using sliding mode control (SMC) to ensure the convergence of corresponding errors to zero within a predefined time. A nonlinear disturbance observer is used to estimate the target's maneuver, and the estimation error is treated as an uncertainty while rejecting its effect by virtue of SMC. Guidance commands are also derived for the case where the target maneuver is completely unknown except for its upper bound. It was shown that the gain could be selected based on the maximum bound on target maneuver to enforce sliding mode on the chosen surface, and thus guarantees target interception at a pre-specified impact angle, provided the closing speed of the engagement is positive. Owing to the use of a nonlinear framework while deriving pursuer guidance commands, the proposed guidance strategies remain valid even for engagements with large initial deviations where schemes based on linearized dynamics may fail or have degraded performance. The efficacy of the proposed guidance methods is validated through simulations for the pursuers having constant speed and time-varying speed, for various engagement geometries. The results of proposed strategies are compared with those of existing guidance and shown to be superior. [ABSTRACT FROM AUTHOR]

In this paper, cooperative guidance strategies for the survival of cooperating team of two unmanned aerial vehicles (UAVs) against two attackers are proposed. The guidance schemes are designed under the assumptions that each UAV is being pursued by one attacker without cooperation with other attacker. The guidance schemes are designed to combat attackers guided either by proportional navigation (PN) or augmented PN guidance methodologies. The attackers are lured onto a collision course with each other such that intra-attacker interception is achieved before the target UAVs are captured. Sliding mode control techniques are employed to satisfy the sufficiency conditions for the survival within a finite time. Due to the nonlinear framework used for guidance design, the proposed strategies remain effective even for the engagements with large heading angle errors. Numerical simulations are presented to demonstrate the effectiveness of the proposed guidance strategies under various engagement geometries. [ABSTRACT FROM AUTHOR]

In this article, a sliding mode control–based nonlinear guidance scheme for controlling both impact angle and impact time simultaneously is proposed. The problem of impact angle control is first transformed to that of controlling line-of-sight angle and its rate, while the requirement of impact time is achieved by tracking the desired time-to-go. The chosen time-to-go estimate accounts for the curvature required to meet the impact angle requirements toward the target interception. In order to satisfy both of these terminal constraints, the sliding surface is defined as a combination of impact time error and the variable pertaining to the errors in line-of-sight angle and its rate, with appropriate gains assigned to them. The interceptor first performs necessary maneuvers to meet the impact time requirements and then steers its course to achieve the target interception at a desired impact angle. The guidance law is initially derived using nonlinear engagement kinematics against stationary targets and then extended to cater to constant velocity targets using the concept of predicted interception point. Numerical simulations are performed to validate the efficacy of the proposed guidance scheme for various initial engagement geometries. The performance of the proposed guidance scheme is also compared with those of the existing guidance laws and shown to be superior. [ABSTRACT FROM AUTHOR]

In this article, a nonlinear three-dimensional guidance strategy for multiple identical constant speed interceptors is proposed to capture a stationary target simultaneously. To design this proposed guidance strategy, a proportional navigation based time-to-go estimate, without any small angle assumption, is used. Based on the maximum value of time-to-go estimates of all interceptors, the range error for each interceptors is computed. Sufficiency conditions for simultaneous capture are satisfied by ensuring the range errors and their rates converge to zero for all interceptors. The proposed guidance strategy employs Lyapunov and sliding-mode control-based techniques to achieve these sufficiency conditions. Simulation studies demonstrate that this proposed strategy performs satisfactorily for various geometric engagements and in the presence of a first-order autopilot. [ABSTRACT FROM AUTHOR]

This article proposes a leader–follower cooperative salvo guidance strategy to intercept nonmaneuvering targets by exploiting the advantages of supertwisting sliding mode control. An improved estimate of time-to-go, that does not assume interceptor's small heading angle, is used in the guidance design. This allows the guidance strategy to remain effective even for large initial heading of the interceptor. Under the action of supertwisting control, the error in impact time settles precisely to zero in finite time. The proposed guidance strategy provides robustness against uncertainties and a smooth control signal, along with finite-time convergence of error. The guidance performance has been shown for one-to-one engagement, and in a cooperative framework, to achieve a salvo in a predetermined time. Numerical simulations are presented for various engagement scenarios to aid the analysis, and illustrate the efficacy of the proposed guidance scheme, even under noisy environment. [ABSTRACT FROM AUTHOR]

A cooperative salvo guidance strategy using fixed finite-time consensus is proposed here. The consensus algorithm is based on sliding mode control. The cooperative salvo attack problem is transformed to a consensus problem over a cycle digraph. This aids in designing a guidance strategy through selection of heterogeneous gains. The proposed strategy guarantees convergence to a common impact time for all the interceptors, within a fixed time, from a wide range of initial heading angles. Subsequently, the guidance strategy is extended to cooperatively intercept a constant velocity target. The efficacy of the proposed algorithm is vindicated through simulations on both stationary and constant velocity targets. Numerical simulations are also performed on realistic missile models that account for aerodynamic parameter variations, yielding satisfactory performance. [ABSTRACT FROM AUTHOR]

This paper proposes a guidance strategy, which caters to both impact angle and impact time terminal constraints. This guidance scheme is based on switching between impact time and impact angle guidance laws. Unlike the existing impact time guidance laws, the proposed guidance strategy takes into account the curvature of the trajectory due to requirement of impact angle. The guidance law is derived using sliding mode control theory with the switching surface based on impact time error. The interceptor first corrects its course to nullify the impact time error and then aims to achieve interception with desired impact angle. In order to reduce transitions between the two guidance laws, a novel hysteresis loop is introduced in the switching conditions. The guidance law is initially designed for stationary targets, and later it is extended to constant velocity targets using the notion of predicted interception point. In order to validate the efficacy of the proposed guidance strategy, simulation results are presented with constant as well as realistic time-varying speed interceptor models for different engagement scenarios against stationary and constant velocity targets. The performance of the guidance law is evaluated under noisy measurements and the presence of system lag and its performance is compared with other existing guidance laws. [ABSTRACT FROM AUTHOR]

This paper proposes three-dimensional impact angle control guidance laws based on a sliding mode control technique. Unlike the usual approach of decoupling the engagement dynamics into two mutually orthogonal two-dimensional planes, the guidance laws are derived using coupled engagement dynamics. By using this approach, the control effort required to achieve the objective reduces and the performance of the guidance law is improved. The derivations of guidance laws are done using both conventional as well as nonsingular terminal sliding mode control, which guarantees asymptotic and finite time convergence, respectively, to the desired impact angle. In order to derive the guidance laws, multi-dimensional switching surfaces are used. The stability of the system, with selected switching surfaces, is demonstrated using Lyapunov stability theory. Numerical simulation results are presented to validate the proposed guidance laws for constant speed, as well as a realistic interceptor model with given aerodynamic properties. The simulations show the advantage of using coupled dynamics. The robustness of the proposed guidance laws, with respect to the interceptor’s system lag, is also investigated. [ABSTRACT FROM AUTHOR]

In this paper, sliding mode control-based impact time guidance laws are proposed. Even for large heading angle errors and negative initial closing speeds, the desired impact time is achieved by enforcing a sliding mode on a switching surface designed by using the concepts of collision course and estimated time-to-go. Unlike existing guidance laws, the proposed guidance strategy achieves impact time successfully even when the estimated interception time is greater than the desired impact time. Simulation results are also presented. [ABSTRACT FROM AUTHOR]

Guidance laws based on a conventional sliding mode ensures only asymptotic convergence. However, convergence to the desired impact angle within a finite time is important in most practical guidance applications. These finite time convergent guidance laws suffer from singularity leading to control saturation. In this paper, guidance laws to intercept targets at a desired impact angle, from any initial heading angle, without exhibiting any singularity, are presented. The desired impact angle, which is defined in terms of a desired line-of-sight angle, is achieved in finite time by selecting the interceptor's lateral acceleration to enforce nonsingular terminal sliding mode on a switching surface designed using nonlinear engagement dynamics. Numerical simulation results are presented to validate the proposed guidance laws for different initial engagement geometries and impact angles. Although the guidance laws are designed for constant speed interceptors, its robustness against the time-varying speed of interceptors is also evaluated through extensive simulation results. [ABSTRACT FROM AUTHOR]

This paper proposes integrated guidance and control design to intercept a target, which may execute various motions, at a pre-specified time of interception. The problem is addressed considering nonlinear engagement kinematics and the interceptor is steered using the combined effects of canard as well as tail configurations (dual-controlled interceptors). Different formulations of time-to-go, without the restrictive assumption of interceptor's small heading angle, have been used in deriving the guidance commands, allowing the proposed strategy to remain effective over a wide range of impact time values. A weighted effort allocation scheme, in canard and tail deflections, has been proposed to generate the required lateral acceleration. The overall design uses sliding mode control owing to its simplicity of design, while a nonlinear finite-time disturbance observer is used to estimate the target's maneuver. Finally, simulations are presented for various target motions, and time-constrained interception with an impaired actuator is also shown, vindicating the efficacy of the proposed technique. [ABSTRACT FROM AUTHOR]

This paper deals with nonsingular guidance and control design for an interceptor, using a decoupled approach, steered by the combined effects of both canard and tail, to intercept a moving but non-maneuvering target at a time specified a priori. First, interceptor's desired lateral acceleration, consisting of nominal and corrective components, is derived using deviated pursuit guidance. While the nominal component is the pursuit guidance law, the corrective component drives the time-to-go error to zero within a finite-time in an optimal manner. Using a desired error dynamics and a meaningful performance index, the lateral acceleration demand is minimized during the transient phase. With exact knowledge of time-to-go and the consideration of nonlinear kinematic model, the proposed design circumvents the errors arising out of any approximations. Interceptor's canard and tail deflection commands are derived using predefined-time convergent sliding mode control, which allows the autopilot to precisely track the commanded lateral acceleration within a time specified during design. Finally, simulations are presented for various cases to demonstrate the efficacy of the proposed design. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of maximizing the warhead effectiveness, by achieving impact at the structurally vulnerable points of the targets. The impact direction is first defined using target frame, and then a unique relation between the desired impact angles and the desired line-of-sight angles is derived. Using this relation, two nonlinear guidance strategies, based on finite-time sliding mode and optimal control methods, are proposed to achieve interception of maneuvering targets at a pre-specified desired impact orientation. Unlike most of the existing three-dimensional guidance strategies, the proposed guidance strategies are derived without decoupling nonlinear coupled engagement kinematics into two mutually orthogonal planes and performing linearization, thereby avoiding possible performance deterioration for engagement with large heading errors. The performances of proposed guidance strategies are evaluated for various engagement geometries as well as constant speed and different realistic time-varying speed pursuer models subjected to aerodynamics parameter variations, and found to be satisfactory. [ABSTRACT FROM AUTHOR]