Charu Chawla

Partial Integrated Guidance and Control of Interceptors for High-Speed Ballistic Targets

A new partial integrated guidance and control design approach is proposed in this paper, which combines the benefits of both integrated guidance and control as well as the conventional guidance and control design philosophies. The proposed technique essentially operates in a two-loop structure. In the outer loop, an optimal guidance problem is formulated considering the nonlinear six degrees-of-freedom equation of motion of the interceptor. From this loop, the required pitch and yaw rates are generated by solving a nonlinear suboptimal guidance formulation in a computationally efficient manner while simultaneously assuring roll stabilization. Next, the inner loop tracks these outer loop body rate commands. This manipulation of the six degrees-of-freedom dynamics in both loops preserves the inherent time scale separation property between the translational and rotational dynamics, while retaining the philosophy of integrated guidance and control design as well. Because of this, the tuning process is quite straightforward and nontedious as well. Extensive six degrees-of-freedom simulations studies have been carried out, considering three-dimensional engagement geometry, to demonstrate the effectiveness of the proposed new design approach engaging high-speed ballistic targets. A variety of comparison studies have also been carried out to demonstrate the effectiveness of the proposed approach.

Robust Partial Integrated Guidance and Control of Interceptors in Terminal Phase

Integrated guidance and control (IGC) algorithms proposed in the recent literature do not exploit the inherent time scale separation property that exists in aerospace vehicles between rotational and translational motions. Since the amount of body rates needed is explicitly not available in an IGC approach, the design tuning becomes very difficult. Consequently, unless the design is done in an extremely careful manner, this approach may lead to instability of rotational dynamics. To overcome this difficulty, a new time scale separated partial integrated guidance and control design is proposed in this paper. In this design, an outer loop optimal control formulation is solved in a computationally efficient manner using a recently-developed model predictive spread control philosophy. It directly generates the commanded pitch and yaw rates, from an outer loop (formulated in the framework of optimal control theory), whereas the commanded roll rate is generated from a roll stabilization loop. The inner loop tracks the outer loop commands using a nonlinear Dynamic inversion philosophy. In both the loops Six-degree of freedom (Six-DOF) interceptor model is used directly. This intelligent manipulation preserves the inherent time scale separation property between the translational and rotational dynamics, while preserving the benefits of the IGC philosophy. Comparative Six-DOF simulation studies of proposed partial integrated guidance and control (PIGC) scheme with an existing SDRE based one-loop IGC design as well as with a conventional three-loop design shows that the proposed PIGC scheme outperforms both of them. Moreover, to address the problem of modeling inaccuracy, a neuro-adaptive design is augmented to dynamic inversion technique in the inner loop. Numerical results indicate that the proposed approach leads to good performance robustness.

Neuro-Adaptive Augmented Dynamic Inversion Based PIGC Design for Reactive Obstacle Avoidance of UAVs

In this paper, the problem of reactive obstacle avoidance is addressed by an innovative partial integrated guidance and control (PIGC) approach using the Six-DOF model of real UAV unlike the kinematic models used in the existing literatures. The guidance strategy uses the collision cone approach to predict any possible collision with the obstacle and computes an alternate aiming direction for the vehicle to avoid the obstacle. The reactive nature of the avoidance problem within the available time window demands simultaneous reaction from the guidance and control loop structures of the system i.e, in the IGC framework (executes in single loop). However, such quick maneuvers causes the faster dynamics of the system to go unstable due to inherent separation between the faster and slower dynamics. On the contrary, in the conventional design (executes in three loops), the settling time of the response of different loops will not be able to match with the stringent time-to-go window for obstacle avoidance. Such tracking delays will affects the system performance adversely. However, in the PIGC framework, it overcomes the disadvantage of both the IGC design and the conventional design. PIGC approach executes the avoidance maneuver in two loops. In the outer loop, the vehicle guidance strategy attempts to reorient the velocity vector of the vehicle along the aiming point within a fraction of the available time-to-go. The outer loop generates the body angular rates which are tracked by the inner loop to generate the necessary control surface deflections. Control surface deflections are realized by the vehicle through the first order actuator dynamics. A controller for the first order actuator model is proposed in order to reduce the actuator delay. Every loop of the PIGC technique uses nonlinear dynamic inversion technique which has critical issues like sensitiveness to the modeling inaccuracies of the plant model. To make it robust against the parameter inaccuracies of the system, it is reinforced with the neuro-adaptive design. In NA design, weight update rule based on Lyapunov theory provides online training of the weights. To enhance fast and stable training of the weights, preflight maneuvers are proposed. Preflight maneuvers provides stabilized pre-trained weights which prevents any misapprehensions in the obstacle avoidance scenario. Simulation studies have been executed with different number and size of the obstacles. NA augmented PIGC design is validated with different levels of uncertainties in the plant model. Various comparative study shows that the NA augmented PIGC design is quite effective in avoiding collisions in different scenarios. Since the NDI technique involved in the PIGC design gives a closed loop solution and does not operate with iterative steps, therefore the reactive obstacle avoidance is achieved in a computationally efficient manner.

Reactive Obstacle Avoidance of UAVs with Dynamic Inversion Based Partial Integrated Guidance and Control

Unlike existing literature on obstacle avoidance of UAVs that mainly propose only guidance techniques (using either kinematic or, at best, point-mass models), an innovative partial integrated guidance and control (PIGC) technique is presented in this paper for reactive obstacle avoidance of UAVs that uses the Six-DOF flight dynamics of the vehicle directly. First, a collision cone approach is used to predict any possible collision with the obstacle and, if necessary, to compute an alternate aiming direction for the vehicle. The vehicle guidance strategy then attempts to quickly align the velocity vector of the vehicle along the aiming point within a fraction of the available time-to-go, which ensures quick reaction leading to safety of the vehicle. The PIGC algorithm presented here essentially has two loops in cascade. In the outer loop (i.e the guidance loop), the velocity vector is aligned with the aiming point by correcting the flight path angles, while simultaneously assuring turn coordination. The outer loop essentially generates the commanded body rates for the inner loop while enforcing the angle corrections through dynamic inversion. In the inner loop (i.e the control loop), these body rates are tracked in a fast dynamic inversion loop by generating the necessary control surface deflections. Simulation studies have been carried out with Six-DOF model of a small real fixed wing UAV with and without actuator model in the system. The comparative study clearly show that the proposed PIGC technique is quite effective in avoiding collisions for both single as well as multiple obstacles.

A nonlinear approach for re-entry guidance of reusable launch vehicles using model predictive static programming

A nonlinear suboptimal guidance scheme is developed for the reentry phase of the reusable launch vehicles. A recently developed methodology, named as model predictive static programming (MPSP), is implemented which combines the philosophies of nonlinear model predictive control theory and approximate dynamic programming. This technique provides a finite time nonlinear suboptimal guidance law which leads to a rapid solution of the guidance history update. It does not have to suffer from computational difficulties and can be implemented online. The system dynamics is propagated through the flight corridor to the end of the reentry phase considering energy as independent variable and angle of attack as the active control variable. All the terminal constraints are satisfied. Among the path constraints, the normal load is found to be very constrictive. Hence, an extra effort has been made to keep the normal load within a specified limit and monitoring its sensitivity to the perturbation.

Partial integrated guidance and control of surface-to-air interceptors for high speed targets

An important limitation of the existing IGC algorithms, is that they do not explicitly exploit the inherent time scale separation that exist in aerospace vehicles between rotational and translational motions and hence can be ineffective. To address this issue, a two-loop partial integrated guidance and control (PIGC) scheme has been proposed in this paper. In this design, the outer loop uses a recently developed, computationally efficient, optimal control formulation named as model predictive static programming. It gives the commanded pitch and yaw rates whereas necessary roll-rate command is generated from a roll-stabilization loop. The inner loop tracks the outer loop commands using the Dynamic inversion philosophy. Uncommonly, Six-Degree of freedom (Six-DOF) model is used directly in both the loops. This intelligent manipulation preserves the inherent time scale separation property between the translational and rotational dynamics, and hence overcomes the deficiency of current IGC designs, while preserving its benefits. Comparative studies of PIGC with one loop IGC and conventional three loop design were carried out for engaging incoming high speed target. Simulation studies demonstrate the usefulness of this method.

Time scale separated nonlinear partial integrated guidance and control of interceptors in the terminal phase

The paper proposes a time scale separated partial integrated guidance and control of an interceptor for engaging high speed targets in the terminal phase. In this two loop design, the outer loop is an optimal control formulation based on nonlinear model predictive spread control philosophies. It gives the commanded pitch and yaw rates whereas necessary roll-rate command is generated from a roll-stabilization loop. The inner loop tracks the outer loop commands using the dynamic inversion philosophy. However, unlike conventional designs, in both the loops the Six degree of freedom (Six-DOF) interceptor model is used directly. This intelligent manipulation preserves the inherent time scale separation property between the translational and rotational dynamics, and hence overcomes the deficiency of current IGC designs, while preserving its benefits. Six-DOF simulation studies have been carried out accounting for three dimensional engagement geometry. Different comparison studies were also conducted to measure the performance of the algorithm.