Unknown Inertia Parameters Research Articles

Chebyshev neural network-based attitude-tracking control for rigid spacecraft with finite-time convergence

In this paper, the problem of finite-time attitude-tracking control for a rigid spacecraft is addressed. Uncertainties including unknown inertial parameters, external disturbances, actuator failures and saturation constraints are considered. Firstly, a smooth function which is different from the common saturation treatment is presented to deal with the actuator constraints. Secondly, a fast non-singular terminal sliding mode (FNTSM) manifold composed of tracking errors is constructed. To estimate the unknown function in the sliding surface derivative, Chebyshev neural network (CNN) is introduced and thus the strict assumptions on uncertainties in many related works are abolished. By designing the CNN adaptive laws, a new fault-tolerant control scheme is proposed such that the attitude tracking can be achieved within a limited time interval. Compared with the existing CNN-based achievements with finite-time convergence, the approximation errors are proved to be finite-time stable instead of uniformly ultimately bounded (UUB). Finally, simulation experiments are conducted to demonstrate the satisfactory tracking performance of the attitude controller.

Minimum-Learning-Parameter-Based Fault-Tolerant Control for Spacecraft Rendezvous With Unknown Inertial Parameters

In this paper, robust control strategies are explored to solve the problem of rendezvous maneuver for rigid spacecraft exposed to the external disturbance, actuator faults and unknown inertial parameters. To pursue the control objective, two adaptive controllers are constructed via the sliding mode control (SMC) technology. Firstly, a basic control scheme is designed in the event of unknown inertial parameters and external disturbance, where the Minimum-learning-parameter (MLP) algorithm is adopted for approximating the unknown system dynamics. Though effective, the basic controller is not applicable in the actuator fault scenarios. Considering this drawback, adaptive laws are designed in the second controller to tackling the actuator faults. It is illustrated that the proposed controllers will endow tracking errors with asymptotic stability and strong robustness to actuator faults. Finally, the effectiveness of the control strategies is verified by numerical simulations.

Finite‐time attitude‐tracking control for rigid spacecraft with actuator failures and saturation constraints

SummaryIn this article, the problem of finite‐time attitude‐tracking control for rigid spacecraft is addressed. Uncertainties caused by external disturbances, unknown inertial matrix, actuator failures, and saturation constraints are tackled simultaneously. First, a smooth function that is more qualified to approximate the standard saturation characteristics is presented to deal with the actuator saturation constraints. Second, a fast nonsingular terminal sliding mode (FNTSM) manifold is constructed as a foundation of controllers design. By incorporating the fuzzy logic system into FNTSM technique, a less demanding solution of coping with model uncertainties is provided because the requirement of a prior knowledge of unknown inertial parameters and external disturbances in many existing achievements is removed. To reduce the number of parameters to be estimated, the norm approximation approach is exploited. Subsequently, an antichattering attitude controller is presented such that all the tracking errors converge into arbitrary small domains around the origin in finite time. The result is further extended to obtain a fault‐tolerant controller against completely failed actuators. Finally, numerical simulation is conducted to verify the effectiveness of the proposed control scheme and comparison with relevant literature demonstrates its high performance. Furthermore, an experiment for the large satellite Hubble Space Telescope is carried out to validate the practical feasibility.

Adaptive Saturated Neural Network Tracking Control of Spacecraft: Theory and Experimentation

An adaptive saturated neural network (NN) controller is developed for 6 degree-of-freedom (6DOF) spacecraft tracking, and its hardware-in-the-loop experimental validation is tested on the ground-based test facility. To overcome the dynamics uncertainties and prevent the large control saturation caused by the large tracking error at the beginning operation, a saturated radial basis function neural network (RBFNN) is introduced in the controller design, where the approximate error is counteracted by an adaptive continuous robust term. In addition, an auxiliary dynamical system is employed to compensate for the control saturation. It is proved that the ultimate boundedness of the closed-loop system is achieved. Besides, the proposed controller is implemented into a testbed facility to show the final operational reliability via hardware-in-the-loop experiments, where the experimental scenario describes that the simulator is tracking a planar trajectory while synchronizing its attitude with the desired angle. Experimental results illustrate that the proposed controller ensures that the simulator can track a preassigned trajectory with robustness to unknown inertial parameters and disturbances.

Adaptive fault-tolerance control based finite-time backstepping for hypersonic flight vehicle with full state constrains

In this paper, a novel adaptive fuzzy fault-tolerant controller is developed for the Hypersonic Flight Vehicle (HFV) in the presence of unknown inertial and aerodynamic parameters. Based on the functional dissolution technique, the longitudinal model of hypersonic vehicle is transformed into velocity subsystem and altitude subsystem. With consideration of full state constraints, the controller is designed based on finite-time stability theory and the barrier Lyapunov functions (BLFs). To deal with the unknown faults, a new robust adaptive distributive law is proposed. In order to avoid the problem of “explosion of complexity” and obtain the finite-time convergence performance, the fuzzy fault-tolerant dynamic surface control (DSC) is designed. Finally, simulation results are provided to verify the effectiveness of the proposed control scheme. It is shown that all the signals in the closed-loop are bounded.

Detumbling of a non-cooperative target with unknown inertial parameters using a space robot

The detumbling of a non-cooperative, tumbling target by a space robot for the purpose of performing on-orbit servicing is a challenging and risky endeavour. The formulation of a detumbling control strategy must respect end-effector force/torque limits of the space robot without prior knowledge of the target’s inertial parameters (mass, inertia tensor, location of center of mass). Prior studies have formulated detumbling strategies with the assumption of accurate knowledge of the target’s inertial parameters. However, obtaining accurate estimates of the target’s inertial parameters is difficult, and parameter uncertainty may lead to instability and violation of the end-effector’s force/torque limits. In this paper, a novel detumbling strategy is presented to detumble targets without prior knowledge of their inertial parameters. Detumbling of the target is achieved by controlling the space robot to follow a reference force/torque that is designed to detumble the target while respecting force/torque limits at the end-effector, without the use of the target’s inertial parameters. To ensure stable detumbling of the target, a robust compensator is designed based on bounds of the target’s unknown inertial parameters. Furthermore, in order to reduce the robust control gains, bounds on the target’s unknown inertial parameters are estimated in real-time once the post-grasping detumbling process starts. Stability proof of the closed-loop system has been provided. Numerical simulations have been conducted, and the results have demonstrated the effectiveness of the proposed method.

Event-triggered adaptive control for attitude tracking of spacecraft

Plug-and-play technology is an important direction for future development of spacecraft and how to design controllers with less communication burden and satisfactory performance is of great importance for plug-and-play spacecraft. Considering attitude tracking of such spacecraft with unknown inertial parameters and unknown disturbances, an event-triggered adaptive backstepping controller is designed in this paper. Particularly, a switching threshold strategy is employed to design the event-triggering mechanism. By introducing a new linear time-varying model, a smooth function, an integrable auxiliary signal and a bound estimation approach, the impacts of the network-induced error and the disturbances are effectively compensated for and Zeno phenomenon is successfully avoided. It is shown that all signals of the closed-loop system are globally uniformly bounded and both the attitude tracking error and the angular velocity tracking error converge to zero. Compared with conventional control schemes, the proposed scheme significantly reduces the communication burden while providing stable and accurate response for attitude maneuvers. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

Adaptive control for spacecraft rendezvous subject to actuator faults and saturations

An adaptive saturated fault-tolerant controller is proposed for a spacecraft rendezvous maneuver with a cooperative target spacecraft. The six-degree-of-freedom (6-DOF) relative dynamics subject to unknown inertial parameters, external disturbances, actuator faults and saturations are formulated in the pursuer's body-fixed frame. To design controller satisfying asymmetric magnitude constraints, a modified smooth hyperbolic tangent function is applied to approximate the non-differentiable saturation function. Based on the augmented system technique, an adaptive fault-tolerant saturated controller is designed for the pursuer by using a Nussbaum function matrix compensating for the nonlinear term arising from the input saturations. In addition, a Levant differentiator is introduced to obtain the derivative of the virtual control in finite time that avoids the complicated calculation. It is proved via Lyapunov stability theory that all the signals in the closed-loop augmented system are bounded and the relative errors asymptotically converge to zero. Numerical simulations are performed to illustrate effectiveness of the proposed controller.

Learning-Based Adaptive Attitude Control of Spacecraft Formation With Guaranteed Prescribed Performance.

This paper investigates a novel leader-following attitude control approach for spacecraft formation under the preassigned two-layer performance with consideration of unknown inertial parameters, external disturbance torque, and unmodeled uncertainty. First, two-layer prescribed performance is preselected for both the attitude angular and angular velocity tracking errors. Subsequently, a distributed two-layer performance controller is devised, which can guarantee that all the involved closed-loop signals are uniformly ultimately bounded. In order to tackle the defect of statically two-layer performance controller, learning-based control strategy is introduced to serve as an adaptive supplementary controller based on adaptive dynamic programming technique. This enhances the adaptiveness of the statically two-layer performance controller with respect to unexpected uncertainty dramatically, without any prior knowledge of the inertial information. Furthermore, by employing the robustly positively invariant theory, the input-to-state stability is rigorously proven under the designed learning-based distributed controller. Finally, two groups of simulation examples are organized to validate the feasibility and effectiveness of the proposed distributed control approach.

Analytical solutions to the matrix inequalities in the ILF control-observer scheme for non-cooperative rendezvous with unknown inertia parameters

ABSTRACTIn this paper, the problem of robust control for non-cooperative rendezvous is investigated based on implicit Lyapunov function (ILF) method. The dynamical model of relative motion between two spacecrafts is established in the body coordinate system of the chaser spacecraft without using the target-orbital information. In view of unknown inertia parameters and external disturbances, an ILF control-observer scheme is introduced, where the ideal controller is first designed and then estimated by the observer. The closed-loop system is proved to be finite-time stable, and the controller and observer gains are, respectively, obtained by solving linear matrix inequalities and parameterised nonlinear matrix inequalities. To reduce the computational burden, analytical solutions to these matrix inequalities are provided. The effectiveness of the theoretical results is demonstrated by simulation examples.

Adaptive Control for Hypersonic Vehicles With Time-Varying Faults

In this paper, a novel adaptive fault-tolerant control (FTC) scheme is proposed for a class of hypersonic flight vehicles (HFVs) with input constraints and unknown inertial and aerodynamic parameters. As an advantage beyond existing adaptive FTC schemes for HFVs, we investigate a more practical and more challenging case that both the elevator and the throttle may suffer from unknown and time-varying faults. By introducing some smooth functions and a linear time-varying model and estimating the bounds of those time-varying uncertainties, the impact of the faults and the input constraints is effectively compensated for and stable altitude and velocity tracking is successfully achieved. Besides, with the aid of the dynamic surface control technique, the proposed scheme is free of the problem of explosion of complexity inherent in traditional backstepping design. Such features result in a simple flight control scheme that can be easily implemented with less computational burden and higher reliability. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

Hardware Simulations of Spacecraft Attitude Synchronization Using Lyapunov-Based Controllers

In the near future, space missions with multiple spacecraft are expected to replace traditional missions with a single large spacecraft. These spacecraft formation flying missions generally require precise knowledge of relative position and attitude between neighboring agents. In this study, among the several challenging issues, we focus on the technique to control spacecraft attitude synchronization in formation. We develop a number of nonlinear control schemes based on the Lyapunov stability theorem and considering special situations: full-state feedback control, full-state feedback control with unknown inertia parameters, and output feedback control without angular velocity measurements. All the proposed controllers offer absolute and relative control using reaction wheel assembly for both regulator and tracking problems. In addition to the numerical simulations, an air-bearing-based hardware-in-the-loop (HIL) system is used to verify the proposed control laws in real-time hardware environments. The pointing errors converge to $$0.5{^{\circ }}$$ with numerical simulations and to $$2{^{\circ }}$$ using the HIL system. Consequently, both numerical and hardware simulations confirm the performance of the spacecraft attitude synchronization algorithms developed in this study.

Robust Command Filtered Adaptive Backstepping Control for a Quadrotor Aircraft

This paper addresses a robust trajectory tracking controller for an underactuated quadrotor with external bounded disturbances and unknown inertia parameters. Different from most of the existing control algorithms, the proposed method does not adopt the dual-loop scheme in which the design is divided into position control and attitude control. Instead, command filter backstepping is employed to design the controller based on the integrated motion model such that the stability can be guaranteed strictly for the flight control system. Furthermore, adaptive compensation and robust compensation are introduced to deal with the uncertainty of the inertia parameters and the external bounded disturbances, respectively. Finally, a similar skew symmetric structure is chosen as the desired structure of the closed-loop system to facilitate the analysis of the stability of the integrated system. Stability and robust performance of the designed controller are verified by Lyapunov stability theorem. Simulations are provided to validate the proposed controller.

Coordinated motion control of a dual-arm space robot with joint-limit avoidance and uncertain inertial parameters

In this article, a new adaptive coordinated motion control approach is introduced for a dual-arm free-floating space robot. This adaptive algorithm is used for the post-capture of a large noncooperative target with joint-limit avoidance and uncertain dynamic parameters. To overcome the problem of dynamics coupling between the space base, its manipulators, and the target, we develop a dual-arm space robotic system. One arm is used to complete the capture task and the other is used to counteract the disturbance to the space base. In this case, a new coordinated motion control law is derived based on reaction null space control. An improved joint-limit avoidance algorithm is implemented for large noncooperative target capture; otherwise, a significant base disturbance may result if the joint-limit constraints are not explicitly considered. Based on momentum conservation, the linear regression form of the estimation problem is obtained, and we further identify the unknown inertial parameters of the target. Finally, the simulation results demonstrate the effectiveness of the proposed algorithm.

Singularity-free adaptive fault-tolerant trajectory tracking controller for VTOL UAVs

ABSTRACTThis paper exploits a singularity-free adaptive fault-tolerant controller for vertical take-off and landing (VTOL) unmanned airborne vehicles (UAVs) to fulfill trajectory tracking manoeuvres, which is robust against parametric uncertainties, actuator faults and unexpected disturbances. Under the hierarchical control framework, the position and attitude loop controls are developed in sequence based on adaptive sliding mode control schemes. Initially, using the saturation property of the hyperbolic tangent function, a position loop controller is synthesised, and a criterion for choosing control parameters is established to guarantee the singularity-free command attitude extraction. Then, in the attitude loop, to avoid singularity which occurs when the pitch reaches , a novel sliding mode surface is introduced, and an attitude control project with the associated initial condition constraint is put forward. In addition, adaptive algorithms are developed to estimate and compensate the uncertainties arising from unknown inertial parameters, thrust and torque faults and undesired disturbances. It is demonstrated in terms of Lyapunov theorem that, with the proposed controller, the closed-loop position and attitude error subsystems of the VTOL UAV are asymptotically stable, respectively. Eventually, simulations validate the tracking performance of the controller.

Robust adaptive spacecraft attitude tracking control based on similar skew-symmetric structure

This paper addresses robust adaptive attitude tracking control for spacecrafts with unknown inertia parameters and bounded external disturbances. The similar skew-symmetric structure is chosen as the desired structure for the closed loop system when there exist no uncertainties. Based on this idea, a backstepping scheme is proposed to design the controller, and adaptive compensation and robust compensation are introduced to deal with the uncertainty of the inertia parameters and the external disturbances respectively. Theoretical analysis shows that fast response and high tracking precision can both be obtained by regulating the related parameters in the proposed controller. Simulation results are provided to demonstrate the effectiveness of the proposed attitude tracking control algorithm.

Research on angles-only/SINS/CNS relative position and attitude determination algorithm for a tumbling spacecraft

In this paper, the relative navigation technique of final approach phase for a tumbling target spacecraft is studied and exploited. It is assumed that the tumbling target is in failure or out of control and there is no good a priori rotation rate information. The Euler’s rotational dynamics is used to propagate the target angular velocity, and the unknown inertia parameter circumstance is also considered. The chaser spacecraft is equipped with three strapdown gyros and accelerometers and a star sensor that determine the absolute motion parameters, and an optical camera that measures relative azimuth and elevation angles to the target spacecraft. On the basis of the rotational and translational motions of both spacecrafts, an angles-only/ strapdown inertial navigation system/celestial navigation system navigation filter is designed. Simulation results indicate that the proposed algorithm can accurately estimate the relative position, velocity, and attitude between two spacecrafts and compensate the biases of the gyros and accelerometers.

Passivity-Based Adaptive Finite-Time Trajectory Tracking Control for Spacecraft Proximity Operations

A passivity-based robust adaptive finite-time trajectory tracking control strategy is developed for a pursuer spacecraft proximity to a cooperative target spacecraft in space. The relative position vector between the pursuer and the target is required to direct toward the docking port of the target while the attitude of the two bodies must be synchronized. With the effective reference trajectory, the finite-time control of relative translational and relative rotational motions is finished simultaneously by using a unified passivity-based adaptive control method. Finite-time stability of the closed-loop system for six degree-of-freedom relative motion is proved in spite of the unknown inertial parameters and external disturbances. Numerical simulations including six-degree-of-freedom rigid-body dynamics are performed to demonstrate the effectiveness of the proposed controller.

Multiple-Model Adaptive Control for Spacecraft Under Sign Errors in Actuator Response

This paper addresses the attitude tracking control problem for spacecraft with unknown inertia parameters and sign errors in actuator response that are uncertain in occurring time instants and patterns. Either a software or hardware error may cause actuation sign errors, which may lead spacecraft to fail. A new multiple-model adaptive control scheme is developed to compensate the uncertainties of actuation sign errors and inertia parameters, which ensures the desired system global stability and asymptotic attitude tracking properties. Such a control scheme employs a set of adaptive estimators to generate parameter estimates, estimator states, and estimation errors, in which the uncertainties of inertia parameters are parameterized. Then, a set of control signals are designed by using such estimates and estimation errors, and a switching mechanism is established based on calculating multiple cost functions from the estimation errors to select the most appropriate control signal with the minimum cost function as the applied control signal. Simulation results of an application to a spacecraft model with four reaction wheels and comparison of results with a Nussbaum gain-based control design verify the effectiveness of the proposed control scheme.

6-DOF integrated adaptive backstepping control for spacecraft proximity operations

Relative motion control with 6 degrees of freedom (6 DOF) is investigated for a chaser spacecraft with parametric uncertainties to approach an unknown tumbling space target. Unlike the conventional relative motion model described in the target orbital frame, the relative motion model formulated in the chaser's body-fixed frame can simplify modeling and control design for spacecraft proximity operations, while the chaser's thrust misalignment and the natural couplings between relative translation and relative rotation are considered in the 6-DOF integrated dynamics. After the coupled relative motion dynamics are modeled, a 6-DOF integrated state feedback controller is designed by combining the classical backstepping technique with a simple norm-estimation adaptive method to achieve good control performance and decrease the computational burden. The chaser's and target's unknown inertial parameters, unknown thrust misalignment, and upper bound of unknown disturbances are estimated by online adaptive laws. Ultimately, uniformly bounded convergence of the relative position and relative attitude is proved via Lyapunov analysis. The performance of the proposed controller is demonstrated through numerical simulations.