Christian Tournes

Autopilot for Missiles Steered by Aerodynamic Lift and Divert Thrusters using Nonlinear Dynamic Sliding Manifolds

A new approach to the design of a kinetic-kill longitudinal autopilot steering the missile trajectory by the combination of aerodynamic lift and divert-thrusters (dual-thrusters control) and with its attitude oriented by attitude-thrusters is presented. The proposed approach may increase the total divert acceleration capability by up to 100%, improving the “end-game” intercept accuracy, when such capability is required. The pitch plane autopilot design is based on second order sliding mode control using nonlinear dynamic sliding manifold technique. A robust, high accuracy tracking of the missile normal acceleration guidance command is achieved in presence of considerable model uncertainties created by the interactions between the airflow and the thrusters jets. Results of the computer simulation demonstrate excellent, robust, high accuracy tracking performance of the proposed design.

Guidance and Autopilot for Missiles Steered by Aerodynamic Lift and Divert Thrusters Using Second Order Sliding Mode Control

A new smooth second-order sliding mode control is proposed and proved for a system driven by uncertain sufficiently smooth disturbances. The main target application of this technique (combined with second order sliding mode control based on a nonlinear dynamic sliding manifold) - the guidance-control of a kinetic-kill missile against targets performing evasive maneuvers with an autopilot steering the missile trajectory by the combination of aerodynamic lift and divert-thrusters (dual-thrusters control) and with its attitude oriented by attitude-thrusters is presented. The proposed approach, being robust to target maneuvers, may increase the total divert acceleration capability by up to 100% improving the “end-game” intercept accuracy, when such capability is required. A robust high accuracy tracking of the missile normal acceleration guidance command is achieved in presence of considerable model uncertainties created by the interactions between the airflow and the thrusters jets. The designed second order sliding mode control-based robust guidance-control system performance is verified via computer simulations.

Nonminimum phase output tracking in dynamic sliding manifolds with application to aircraft control

Output tracking in sliding modes is considered for nonminimum phase nonlinear systems. A sliding mode controller design with a dynamic sliding manifold is developed. The desired linear output tracking is provided in a dynamic sliding manifold. The dynamic sliding mode controller combines features of a conventional sliding mode controller and of a conventional dynamic compensator. It is insensitive to matched nonlinearities and disturbances, and it rejects unmatched disturbances regardless of the nonminimum phase nature of a plant. The approach developed is applied to a sliding mode controller design used to track the angle of attack of aircraft or missiles configured with canards.

Predictive Launcher Guidance using Second Order Sliding Mode Control

A new approach to the design of a simplified predictive launcher-guidance is presented. The first stage open-loop prescribed launcher trajectory is simply defined by a controlled pitch tip-off maneuver. Second and third stage closed loop in-plane guidance is based on the continuous calculation, at each thrusting-time of commanded velocity required to achieve the mission objective; function of the current position. Second and third stage out of plane guidance is based on the dot product of velocity and position errors with the unity vector orthogonal to the desired orbital plane. Corresponding values of second and third stage in-plane terminal semi major axis, eccentricity required to achieve desired circular orbit altitude objectives are calculated off-line for given launch latitude and azimuth angle. The autopilot tracking commanded velocity is based on second order sliding mode control technique that yields continuous controls, and achieves desired error response in finite time. Robust high accuracy launcher guidance is achieved in presence of wind shear at the beginning of the trajectory and considerable uncertainties in the thrust magnitude model. The algorithm was tested on Ariane IV type launcher model. Results of the computer simulation demonstrate excellent robust high accuracy tracking performance of the proposed design. Nomenclature

Automatic Space Rendezvous and Docking using Second Order Sliding Mode Control

This chapter presents a Higher Order Sliding Mode (HOSM) Control for automatic docking between two space vehicles. The problem considered requires controlling the vehicles’ relative position and relative attitude. This type of problem is generally addressed using optimal control techniques that are, unfortunately, not robust. The combination of optimum control and Higher Order Sliding Mode Control provides quasi-optimal robust solutions. Control of attitude includes a receiver vehicle passive mode option where the pursuing vehicle controls the relative attitude using the active pixels of a camera viewing a network of lights placed on the receiving vehicle, which by sharing considerable commonality with manual operations allows possible human involvement in the docking process.

Integrated flight control problem on decentralized sliding modes

The paper proposes applying sliding mode stabilization to aircraft flight controls. The nonlinear multiple input, multiple outputs problem of controlling aerodynamic angles, trajectory angles, attitude angles and energy, is addressed by methods of variable structure control. The decentralized algorithm of sliding mode control has been applied to the stabilization of the four following channels: pitch, roll, yaw and energy channels. The output stabilization errors of each channel have the desired response characteristic and are perfectly decoupled from the perturbation of the other channels, and from external perturbations while the results obtained are relative to aircraft configured with conventional nonredundant aerodynamic controls, and with nonorientable engine nozzles, they could be extended easily to redundant controls.<<ETX>>

Phase and Gain Margins with Third Order Sliding Mode Control: An Integrated Guidance Application

Department of Defense Regulation requires designers to evaluate the robustness of their designs using phase and gain margin criteria. Given that such criteria are applicable to linear designs, their inapplicability in their current definition to Higher Order Sliding Mode (HOSM) control designs; non-linear designs techniques in the time domain appeared to constitute a major hindrance to the application of HOSM techniques to aircraft and missiles. This paper illustrates the usage of new phase and gain margin techniques applicable to HOSM designs for providing measures of robustness such designs. The technique consists in replacing the -1 singularity point used with linear designs with describing function based representations of the HOSM controller. It is applied here to general problem of guidance of aerospace vehicles steered with aerodynamic lift that is, to a control problem with relative degree = 3. In the application case we assume the unavailability of attitude measurements. Results show that whether the guidance enforces the collision condition or a proportional integral linear manifold has little effect on the robustness. The concept of practical Relative Degree is introduced and applied instead of the strict definition thereof.

Automatic Docking using Optimal Control and Second Order Sliding Mode Control

This paper is about the application of second order sliding mode control to solving automatic space docking problem. Two problems are considered herein, first the establishment of a close formation by the steering of the last stage thrust engine, and its timely termination and then the docking by itself using centre of gravity and attitude thrusters. The design is based on a combination of second order sliding mode control and minimal time three-level (bang-bang) control techniques. Bang-bang minimal-time optimal control is used to reduce the fuel consumption whereas second order sliding mode control provides required robustness to model uncertainties and considerable simplification of the model used in the design. A continuous (super-twisting) second order sliding mode control is used in controlling of normal and out-of-plane motion, and a pulse width modulation implementation there of is used in the design of the control of longitudinal motion. Computer simulations show that the design achieves excellent performances not withstanding considerable model uncertainties and despite considerable simplification introduced in the model of relative motion used in the control design. Nomenclature (.), (.), (.) x yz ff

Development of a physically based axial compressor model

Aero-engines operate in regimes limited by both rotating stall and surge. The design of controllers allowing to operate close to compressor stability limit and capable of preventing rotating stalls and surge. The Moore-Greitzer cubic model (MG3) [1984, 1986] provides a simplified description of open-loop behavior of an axial compressor. The simple description of the pressure rise in the compressor is not related to the variations of isentropic efficiency and to their causes. In this paper, a dynamic model operating as the MG3 is presented. A velocity triangle model and the modeling of the phenomena causing isentropic losses replace the cubic model. The compressor model while being more complex than the MG3 model is simple enough to be integrated in a control model.

Hypersonic Glider Autopilot Using Adaptive Higher Order Sliding Mode Control with Impulsive Actions

Hypersonic glider designs often exhibit limited control authority and poor transversal stability. Furthermore, the methods used for aerodynamic performance estimation at high flight altitudes and hypersonic speeds are inevitably inaccurate and uncertain. Hypersonic Glider performance could be severely degraded by using traditional control and autopilot techniques that rely on an accurate knowledge of the aerodynamic coefficients. A new autopilot and control approach, presented in this paper, is based on recently developed special Higher Order Sliding Mode Control (HOSMC) algorithms that are mostly based on relative degrees but not on the glider’s mathematical model. Specifically, this autopilot and control approach includes robust continuous aerodynamic control augmented by impulsive reaction control thrusters. Control gain-adaptation allows addressing the vehicle bounded uncertainties and perturbations without overestimating the control gains. The impulsive augmentation of the continuous Higher Order Sliding Mode control provides almost instantaneous convergence thereby mitigating the risk of control loss caused by sideslip angle departures due to poor transversal stability and small lateral control authority. While Higher Order Sliding Mode control algorithms are inherently insensitive to the matched uncertainties and disturbances, the observers embedded in the Continuous Higher Order Sliding Mode Control algorithms reduce the time response of the control compensation. Simulation of a representative hypersonic glider executing normal and bank-to-turn maneuvers and controlled by the studied algorithms demonstrate excellent performance in the presence of significant model uncertainties and perturbations.