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This paper proposed a neural network approximation-based backstepping sliding mode control approach (NN-BSMC) to address the problem of attitude tracking control for spacecraft in the presence of inertial uncertainties, external disturbances and input saturation. First, the attitude dynamics model of the spacecraft is presented, and the error dynamics model with input saturation is derived. Second, a control scheme using sliding mode control (SMC) and backstepping technique is proposed to guarantee the robustness against the dynamics uncertainty and deal with the effect of input saturation. Under this framework, a neural network (NN) approximator is developed to online estimate the dynamics uncertainty of the spacecraft. Adaptive laws are designed to update the NN weight and estimate the unknown bound of approximation error. The control law does not require the prior knowledge about the bounds on the uncertainty and can provide complete compensation for the uncertainty. Moreover, a Lyapunov-based approach is employed to prove the global stability of the closed-loop system and the asymptotical convergence of the attitude tracking errors. Finally, numerical simulations are carried out to demonstrate the effectiveness and robustness of the proposed controllers. Contrasting simulation results indicate that the neural network backstepping sliding mode controller reduces the chattering effectively and has better performance against the sliding mode controller.

In this paper, the problem of capture area determination for space debris removal is investigated. A new method to calculate the capture area based on the reachable domain approach is proposed. The capture area refers to the intersections of the debris orbit and maneuvering coverage of the capture unit. A large number of capture units are initially deployed on a cleaner platform, which is assumed to move on a circular orbit and provide on-orbit secondary launch for the capture units. First, the highly nonlinear equations for the boundary of capture area are formulated. Second, the evaluation criteria of capture area existence are established. Two cases corresponding to the maximum value of the geocentric distance difference are analyzed. Furthermore, a computation algorithm to calculate the boundary points of the capture area is proposed. An optimization method is employed to solve the highly nonlinear equations instead of the conventional Newton iteration method. The simulation results show that the calculated capture area coincides exactly with the actual intersections of the capture unit’s maneuvering coverage and the debris orbit, demonstrating the effectiveness and accuracy of the proposed method.

A new bionic space debris removal device, inspired by the spider predation, is designed in this paper, which consists of flexible webs, central hub, traction mass and rotating mechanism. Firstly, the concept of bionic space debris removal and corresponding system design are described in detail. Secondly, the dynamic models of spin deployment and collision are derived and foumulated respectively. Thirdly, a finite element analysis is presented to simulate the dynamic characteristics of the spinning webs deployment process. In addition, a finite element model of the webs is developed for structural modal analysis. Finally, a number of collision simulation analysis are carried out using finite element method and propagation of small disturbances along the tether are demonstrated via numerical simulations. The simulation results effectively reflect that the motion characteristics of the large deformation and large displacement in the process of capturing the target. Furthermore, it show that the proposed novel bionic flexible web can meet design requirements for a space debris removal system.

The stratospheric airship provides a unique and promising aerostatic platform for broad applications, which requires fast and robust positioning control to support these tasks. A finite time control scheme is proposed to address the problem of positioning control for stratospheric airships subject to dynamics uncertainty. A nonsingular terminal sliding mode controller is designed for positioning control, which overcomes the problem of asymptotical convergence of sliding mode control and the singularity problem of terminal sliding mode control. Under the framework of nonsingular terminal sliding mode control, a fuzzy logic system is employed to approximate the uncertain dynamics of the stratospheric airship, and the fuzzy logic system approximation-based finite time sliding mode controller is designed. The finite-time convergence of positioning errors and the stability of the closed loop system are guaranteed by Lyapunov theory. Finally, the effectiveness and performances of the proposed controller are demonstrated through experimental simulations. Contrasting simulation results illustrate that the proposed controller decreases chattering effectively and ensures faster convergence compared to sliding mode controller.

This paper proposed a fuzzy logic system approximation-based sliding mode control approach via backstepping technique (FLS-BSMC) to address the problem of positioning control for stratospheric satellites subject to dynamics uncertainty and input constraints. First, the positioning problem for stratospheric satellite is formulated. Second, the control design using sliding mode control via backstepping technique is demonstrated. Under this framework, an approximator based on fuzzy logic system (FLS) is designed to estimate the uncertain dynamics of the stratospheric satellite, and an adaptive law is designed to update the weight of the FLS. Moreover, boundness of all the signals of the closed-loop system is proven by using Lyapunov stability theorem. Finally, Compared experiment simulations of positioning control with and without input constraints are given to illustrate the effectiveness of the designed controller.

In view of the growing threat of space debris and the limitation of current debris removal method. A novel conceptual solution for multiple space debris removal is proposed, and a low-cost and miniaturized removal system is designed in this paper. And the structural composition of this removal system is designed and the space debris removal process is introduced, the system can be divided into two components including satellite platform and many mission CubeSats. The mission CubeSats can be re-launched into the transfer orbits of different space debris through a push-launch method, and the fuel consumptions on the removal mission for three space debris, using the proposed multiple removal system and traditional removal system are calculated and compared. The compared results demonstrated that the proposed solution for multiple space debris removal and the designed removal system can decrease the fuel consumptions effectively.

The robotic airships provide potential aerial platforms for various applications and require robust trajectory tracking to support these tasks. A time-specified nonsingular terminal sliding mode control (TS-NTSMC) scheme is proposed to address the problem of trajectory tracking for robotic airships, which can avoid the singularity problem and specify the convergence time of terminal sliding mode control. First, the problem of trajectory tracking of robotic airships is formulated. Second, a nonsingular terminal sliding manifold consisting of pre-specified nonlinear functions is proposed, and the TS-NTSMC law is designed for trajectory tracking. Time-specified convergence and stability of the closed-loop system can be guaranteed by Lyapunov theory. Finally, compared experimental simulations are given to illustrate the advantages of TS-NTSMC against NTSMC.

The robotic airship provides a unique aerostatic platform for various applications, and these applications require high-precise trajectory tracking. However, it is a challenging problem due to nonlinearity and uncertainty of airship dynamics. This paper proposes an adaptive backstepping neural network control (ABNNC) approach to address this problem. First, the kinematics model and dynamics model of the robotic airship are presented. Second, the control problem of trajectory tracking is formulated, and a trajectory controller is designed using backstepping approach. A radial basis function neural network (RBFNN) is employed to approximate the uncertain dynamics model of the airship, and an adaptive law is designed to update the NN weight in the processing of approximation. The ultimate boundedness of the tracking errors are proven based on the Lyapunov theory. Finally, simulations are presented to illustrate the effectiveness and high precision of the designed controller.

This paper investigates the collision-free distributed coordination control of six-DOF spacecraft formation flying. Dual quaternions are used to develop the kinematic and dynamic models of relative translational and rotational motion between spacecraft. By assuming that the reference relative orbit and attitude information is only available to a subset of members in formation, an observer is introduced to estimate the reference information in finite time. With the estimates provided by the observer, a sliding mode controller is then designed for the coordination of six-DOF formation flying. Meanwhile, the artificial potential function method is employed to design evasive maneuvers in case of any collisions during orbital maneuvering. The overall stability of the closed-loop system is guaranteed by a Lyapunov-based method. The feasibility of the proposed control scheme is then demonstrated by a typical formation reconfiguration mission in a low Earth orbit environment.

Compressive sensing (CS) theory provides a framework for signal reconstruction using a sub-Nyquist sampling rate. CS theory enables the reconstruction of a signal that is sparse or compressible from a small set of measurements. The current CS application in optical field mainly focuses on reconstructing the original image using optimization algorithms and conducts data processing in full-dimensional image, which cannot reduce the data processing rate. This study is based on the spatial sparsity of star image and proposes a new compressive measurement and reconstruction method that extracts the star feature from compressive data and directly reconstructs it to the original image for attitude determination. A pixel-based folding model that preserves the star feature and enables feature reconstruction is presented to encode the original pixel location into the superposed space. A feature reconstruction method is then proposed to extract the star centroid by compensating distortions and to decode the centroid without reconstructing the whole image, which reduces the sampling rate and data processing rate at the same time. The statistical results investigate the proportion of star distortion and false matching results, which verifies the correctness of the proposed method. The results also verify the robustness of the proposed method to a great extent and demonstrate that its performance can be improved by sufficient measurement in noise cases. Moreover, the result on real star images significantly ensures the correct star centroid estimation for attitude determination and confirms the feasibility of applying the proposed method in a star tracker.

The problem of positioning control for an autonomous airship in the presence of model uncertainties and external disturbances is addressed in the paper. First, the “ZY-1” autonomous airship is introduced and a dynamics model of the airship is presented. Second, a backstepping sliding-mode control approach is proposed to develop the positioning controller. The backstepping controller is designed recursively by selecting some appropriate functions of state variables as pseudocontrol inputs for lower-dimension subsystems of the overall system based on a Lyapunov function, which provides the flexibility to treat nonlinear terms and guarantee the stability of a closed-loop system. Furthermore, the backstepping control combined with the sliding-mode control is proposed to assure the robustness against parametric uncertainties and external disturbances. The stability of the closed-loop controller is proven via the Lyapunov stability theorem. Finally, simulation results illustrate the effectiveness and robustness...

This paper addresses the problem of attitude regulation for unmanned quadrotors with parametric uncertainties and external disturbances. A novel adaptive fuzzy gain-scheduling sliding mode control (AFGS-SMC) approach is proposed for attitude regulation of unmanned quadrotors. First, the kinematics model and dynamics model of attitude motion are derived, and the problem of attitude regulation is formulated. Second, a sliding mode controller is designed to regulate the attitude motion for its invariant properties to parametric uncertainties and external disturbances. The global stability and error convergence of the closed-loop system are proven by using the Lyapunov stability theorem. In order to reduce the chattering induced by continual switching control of SMC, the fuzzy logic system (FLS) is employed to design the AFGS-SMC, in which the control gains related to sign function are scheduled adaptively according to fuzzy rules, with sliding surface and its differential as FLS inputs and control gains as FLS outputs. Finally, the effectiveness and robustness of the proposed control approach are demonstrated via simulation results.

This paper proposes a neural network approximation-based nonsingular terminal sliding mode control (NN-NTSMC) approach to address the problem of trajectory tracking for robotic airships. First, dynamics model of an airship and control problem of trajectory tracking are formulated. Second, a nonsingular terminal sliding mode controller (NTSMC) combined with neural network (NN) approximation is designed to track the commanded trajectory. Finally, the effectiveness and robustness of the designed controller are illustrated through simulation results. Simulation results indicate that NN-NTSMC reduces chattering effectively and ensures faster convergence and better tacking precision against linear hyperplane-based sliding mode control (LSMC).

The multi-objective optimization of multiple geostationary spacecraft refuelling is investigated in this article. A servicing spacecraft (SSc) and a propellant depot (PD), both parked initially in geostationary Earth orbit (GEO), are utilized to refuel multiple GEO targets of known propellant demand. The capacitated SSc is expected to rendezvous with fuel-deficient GEO targets or the PD for the purpose of refuelling or getting refuelled. The multiple geostationary spacecraft refuelling problem is treated as a multi-variable combinatorial optimization problem with the principal objective of minimizing the propellant consumption and the mission duration. A two-level optimization model is built, and the design variables are the refuelling order X, the refuelling time T and the binary decision variable S. The non-dominated sorting genetic algorithm is employed to solve the up-level optimization problem. For the low-level optimization, an exact algorithm is proposed. Finally, numerical simulations are ...

In this paper, the problem of attitude tracking control for clean platform, with no prior knowledge about the bounds of the parametric uncertainties and external disturbances, in the process of space debris removal is investigated. We proposed a robust adaptive control strategy, which is based on the coupling of the fuzzy logic system (FLS) with sliding mode control (SMC). First, a desired attitude solution model for the space debris removal is developed, and the error attitude dynamics equation of clean platform is formulated. Second, a sliding mode controller is designed due to its appreciable features to the uncertainties and disturbances. On this basis, a FLS is employed to approximate the unknown system functions, and the approximation errors are eliminated using adaptive algorithm. Meanwhile, the control gains of the switching control, being constant in the conventional SMC approach, are adjusted adaptively by fuzzy logic inference techniques in order to reduce the chattering phenomenon. The global stability of the closed-loop system is proven by the Lyapunov stability theorem. Finally, detailed numerical simulations are carried out to verify the robustness and effectiveness of the proposed adaptive fuzzy sliding mode control (AFSMC) approach. The simulation results show that the proposed AFSMC approach can ensure that the spacecraft exactly tracking the desired attitude in presence of inertial uncertainties and external disturbances and effectively reduce the chattering against to the conventional SMC approach.

Particle Image Velocimetry (PIV) technology, oil flow visualization and Nanoparticle-based Planar Laser Scattering (NPLS) technology are used to investigate the turbulent boundary layer (BL) of a sonic jet injected into a supersonic flow at Ma=2.95. Instantaneous and averaged NPLS images display detailed structures of the bow shock, the horseshoe vortex, separation zones and the collision shock. Root Mean Square (RMS) values of flow quantities calculated from NPLS images and PIV data reveal that turbulent fluctuations are suppressed downstream of the horseshoe separation zone in the jet lateral region and a 33%-35% reduction of the density fluctuation magnitude across the boundary layer is observed, while it is enhanced in the jet wake by 34%-50%. Further away from the wall, the influences of the λ shock system, the expansion process, and the reflected shock on turbulence intensity and velocities of the crossflow BL is weakened. A three-dimensional schematic diagram of the interaction between the sonic jet and the turbulent BL is presented, explaining the formation of the turbulence decay zone in the jet lateral region.

The aerodynamic shape of a stratospheric airship is closely to its aerodynamic drag and propulsion energy consumption. The physalia physalis, which has unique characteristics of cystic shape and flow resistance, provides important bionic inspirations for aerodynamic shape design of the stratospheric airships. This paper proposed a bionic methodology for aerodynamic shape design inspired by the physalia physalis. First, the morphological characteristics of the physalia physalis is investigated via image processing, and its profile is obtained using edge detection. Second, the aerodynamic shape of the stratospheric airship is designed via “morphological imitation”, and the profile of the airship hull is described by function curves. Finally, the computational mesh model of the stratospheric airship is developed, and the drag coefficients, lift coefficients and lift-drag ratio are obtained by computation studies, respectively. Computation results demonstrate that the designed stratospheric airship has better aerodynamic performances than the conventional stratospheric airship.

Aiming at the problem of the space flexible webs collision during the space capture process, the general method of collision detection was given based on the nonlinear finite element method, and the collision dynamic model of the space flexible webs and target was established. In order to verify the versatility of the space flexible webs structure in different capture scenarios, the target capture position and attitude were changed respectively, and different capture scenarios were established to simulate and analyze the working conditions by using the finite element software. The results showed that the target position and attitude during the collision impact process is the key of the results of the flexible webs capture mission, which can provide some reference for the structural design and on-orbit task planning of the space flexible webs system.

The simulation turntable is an important device for the hardware-in-the-loop simulation of satellites or other spacecraft. It can simulate the movement attitude of the spacecraft in space such as roll, pitch, and yaw, and is widely applied in electromagnetic countermeasure, space shooting and other fields. This paper takes the on-orbit service spacecraft as the research object, studies the coordinate system transformation and implementation problems of ground simulation of spacecraft attitude based on the five-axis turntable, designs the coordinate system conversion process and verifies the effectiveness of the conversion process. The coordinate system conversion method studied in this paper can effectively realize the ground simulation of spacecraft attitude on the five-axis turntable, providing theoretical guidance and effective methods for solving the problems of attitude simulation in on-orbit service tasks, having more important guiding values for simulating experiments in the field of aerospace engineering such as rendezvous and docking.

The robotic airship is a unique and promising light-than-air platform, which has attracted worldwide developing interests for its broad applications. This article addresses the control problem of trajectory tracking for robotic airships. A neural network fuzzy sliding mode controller is proposed to steer a robotic airship along a referenced trajectory precisely. First, the dynamics model of a robotic airship is presented, and the problem of trajectory tracking is formulated. Second, a sliding mode controller is designed to track a time-varying trajectory. The neural network is employed to approximate the uncertain model of the airship, with the tracking error and its derivatives and the trajectory and its derivatives as neural network inputs and the approximation of the uncertain model as neural network output. And a fuzzy logic system is adopted to reduce the chattering results from the sliding mode controller. The control gains are tuned synchronously with the sliding surface according to fuzzy rules, with switching sliding surface as fuzzy logic inputs and control gains as fuzzy logic outputs. The stability and convergence of the closed-loop controller are proven using the Lyapunov stability theorem. Finally, the effectiveness and robustness of the proposed controller are demonstrated via simulation results. Contrasting simulation results indicate that the neural network fuzzy sliding mode controller reduces the chattering effectively and has better performance against the sliding mode controller.

This article proposed a novel control approach for trajectory tracking of robotic airships. First, the nonlinear dynamics model of a robotic airship is derived and formulated. Second, a sliding mode controller is designed to track the commanded trajectory for its robustness against parametric variations and external disturbances. To address the chattering problem results from the sliding mode controller, a radial basis function neural network is adopted to construct the neural network self-gain-scheduling sliding mode controller in which the control gains are scheduled synchronously with the sliding surface via radial basis function neural network according to the learning algorithm, with switching sliding surface and its differential as radial basis function neural network inputs and control gains as radial basis function neural network outputs. In addition, the stability and convergence of the closed-loop controller are proven using the Lyapunov stability theorem. Finally, the effectiveness and robustness of the proposed controller are demonstrated via numerical simulations. Contrasting simulation results indicate that the neural network self-gain-scheduling sliding mode controller attenuates the chattering effectively and has better performance against the sliding mode controller.

This paper proposes a fuzzy gain scheduling backstepping sliding mode control (FGS-BSMC) approach for a class of uncertain strict-feedback nonlinear system. First, system description and problem formulation is given. Second, the FGS-BSMC is proposed to design the controller for the strict-feedback nonlinear system. A sliding mode control (SMC) is employed to construct the backstepping sliding mode control (BSMC) approach for design flexibility of backstepping control and robustness of SMC. In order to decrease chattering result from SMC, a fuzzy logic system (FLS) is designed to construct the FGS-SMC, in which the gain of sign function can be scheduled adaptively according to the fuzzy rules. Finally, a verification example is given to demonstrate the effectiveness the proposed FGS-BSMC. Simulation results illustrate that the FGS-BSMC decreases chattering effectively and has better control performance against BSMC.

In this article, a new manoeuvring strategy for the multiple geosynchronous satellites inspection problem is proposed. In contrast to previous research, it can be used to visit multiple geosynchronous satellites orbiting in different orbital planes in an economical way. In the proposed mission scenario, several chasers are initially placed in an equatorial high eccentric orbit. Two orbital manoeuvres are exerted at perigee to adjust the apogee of the chaser for every inspection. Subsequently, the targets will be visited when they fly through the ascending or descending nodes of their orbits. Based on the proposed strategy, a two-level optimization approach is developed to optimize visitation order and time regarding fuel consumption. Meanwhile, the manoeuvre velocity and time are determined. Finally, the proposed method is applied to several numerical test cases to demonstrate its validity for mission planning optimization for the visual inspection of multiple geosynchronous satellites.

This paper addresses the positioning problem of an unmanned airship in the presence of parametric uncertainties and external disturbances. A sliding mode controller (SMC) based on fuzzy approximati...

This paper presents a novel approach for station-keeping control of a stratospheric airship platform in the presence of parametric uncertainty and external disturbance. First, conceptual design of the stratospheric airship platform is introduced, including the target mission, configuration, energy sources, propeller and payload. Second, the dynamics model of the airship platform is presented, and the mathematical model of its horizontal motion is derived. Third, a fuzzy adaptive backstepping control approach is proposed to develop the station-keeping control system for the simplified horizontal motion. The backstepping controller is designed assuming that the airship model is accurately known, and a fuzzy adaptive algorithm is used to approximate the uncertainty of the airship model. The stability of the closed-loop control system is proven via the Lyapunov theorem. Finally, simulation results illustrate the effectiveness and robustness of the proposed control approach.

This chapter investigates the dynamics and control problem of Lorentz-augmented spacecraft rendezvous. Previous propellantless rendezvous strategy is developed based on a linearized dynamical model of Lorentz-augmented relative orbital motion. Due to the characteristic of the linearized dynamics, several constraints are imposed on the initial relative position and maneuvering time in this strategy. To get rid of these constraints, nonlinear optimal control schemes for Lorentz spacecraft rendezvous are designed via pseudospectral method in this chapter, based on the nonlinear model of Lorentz-augmented relative motion. In designing the novel rendezvous strategy, two cases with both fixed and free final time are discussed. Also, the effect of J 2 perturbation on optimal rendezvous trajectory is analyzed.

The Lorentz acceleration acting on the Lorentz spacecraft is determined by the local magnetic field and the vehicle’s velocity with respect to the local magnetic field. As derived in the last chapter, both the local magnetic field and the relative velocity are functions of the relative states between spacecraft, that is, relative position and velocity.

Lorentz-augmented spacecraft formation flying (SFF) is one of the most promising applications of Lorentz spacecraft.

Hovering can generally be defined as maintaining a constant position with respect to a target in space. To achieve hovering, a spacecraft thrusts continuously to induce an equilibrium state at a desired position. Due to the constraints on the quantity of propellant onboard, long-time hovering around low-Earth orbits (LEOs) is hardly achievable using traditional chemical propulsion.

Dynamics analysis and controller design of Lorentz-augmented space missions rely highly on the precise modeling of Lorentz-augmented orbital motion. Current models for Lorentz-augmented absolute or relative orbital motion, especially the relative ones, are mostly developed based on the assumption of a nontilted magnetic dipole. However, the Earth’s magnetic dipole is tilted by about 11.3° with respect to the rotation axis of Earth, which is not small enough to be neglected. In view of this fact, this chapter develops dynamical models for Lorentz-augmented absolute and relative orbital motion that explicitly include the dipole tilt angle in both two-body and J 2-perturbed environment.

The stratospheric airship provides a unique and promising platform for broad band telecommunication relay missions, which combine the advantages of both terrestrial and satellite communication. In this paper, the conceptual design, dynamics modeling and attitude control of the stratospheric telecommunication platform are presented. First, the stratospheric telecommunication platform is introduced, including conceptual design, configuration, energy sources, propeller and payload. Second, dynamics model of the platform is derived form the Newton–Euler formulation and the station-keeping attitude control problem is formulated. Then, the adaptive fuzzy sliding mode control scheme is proposed to develop the attitude-tracking control system, with a particular focus on parametric uncertainties and external disturbances. Finally, simulation results verify the effectiveness and robustness of the proposed control scheme. The proposed conceptual design and control scheme provide a promising approach for telecommunication relay missions using the stratospheric station-keeping airship.

The stratosphere airship provides a unique and promising platform for earth observation. Researches on the project design and control scheme for earth observation platforms are still rarely documented. Nonlinear dynamics, model uncertainties, and external disturbances contribute to the difficulty in maneuvering the stratosphere airship. A key technical challenge for the earth observation platform is station keeping, or the ability to remain fixed over a geo-location. This paper investigates the conceptual design, modeling and station-keeping attitude control of the near-space earth observation platform. A conceptual design of the earth observation platform is presented. The dynamics model of the platform is derived from the Newton-Euler formulation, and the station-keeping control system of the platform is formulated. The station-keeping attitude control approach for the platform is proposed. The multi-input multi-output nonlinear control system is decoupled into three single-input single-output linear subsystems via feedback linearization, the attitude controller design is carried out on the new linear systems using terminal sliding mode control, and the global stability of the closed-loop system is proven by using the Lyapunov theorem. The performance of the designed control system is simulated by using the variable step Runge-Kutta integrator. Simulation results show that the control system tracks the commanded attitude with an error of zero, which verify the effectiveness and robustness of the designed control system in the presence of parametric uncertainties. The near-space earth observation platform has several advantages over satellites, such as high resolution, fast to deploy, and convenient to retrieve, and the proposed control scheme provides an effective approach for station-keeping attitude control of the earth observation platform.

We present a novel control approach for trajectory tracking of an autonomous airship. First, the dynamics model and the trajectory control problem of an airship are formulated. Second, the sliding mode control law is designed to track a time-varying reference trajectory. To achieve better control performance, fuzzy adaptive sliding mode control is proposed in which the control gains are tuned according to fuzzy rules, and an adaptation law is used to guarantee that the control gains can compensate for model uncertainties of the airship. The stability of the closed-loop control system is proven via the Lyapunov theorem. Finally, simulation results illustrate the effectiveness and robustness of the proposed control scheme.

An adaptive fuzzy sliding mode control (AFSMC) approach is proposed for a robotic airship. First, the mathematical model of an airship is derived in the form of a nonlinear control system. Second, an AFSMC approach is proposed to design the attitude control system of airship, and the global stability of the closed-loop system is proved by using the Lyapunov stability theorem. Finally, simulation results verify the effectiveness and robustness of the proposed control approach in the presence of model uncertainties and external disturbances.

The attitude control system of an unmanned aerial vehicle (UAV) is a multi-input multi-output, strongly coupled, nonlinear and uncertain system. This study proposes a new attitude control approach for an UAV using the variable structure control theory, with a particular focus on the parameter uncertainty and external disturbance. Firstly, the mathematical model of UAV's attitude motion is derived from the Newton-Euler formulation, including the kinematics and dynamics equations. Then, the attitude controller is designed by use of double loop scheme, the outer loop and the inner loop, which both track the command attitude angles and angular velocities. And a fuzzy system is used to solve the chattering problem. Finally, simulation results demonstrate that the proposed controller accomplished attitude tacking precisely in spite of parameter uncertainty and external disturbance.

A neural-network-based adaptive gain scheduling backstepping sliding mode control (NNAGS-BSMC) approach for a class of uncertain strict-feedback nonlinear system is proposed. First, the control problem of uncertain strict-feedback nonlinear systems is formulated. Second, the detailed design of NNAGSBSMC is described. The sliding mode control (SMC) law is designed to track a referenced output via backstepping technique. To decrease chattering result from SMC, a radial basis function neural network (RBFNN) is employed to construct the NNAGSBSMC to facilitate adaptive gain scheduling, in which the gains are scheduled adaptively via neural network (NN), with sliding surface and its differential as NN inputs and the gains as NN outputs. Finally, the verification example is given to show the effectiveness and robustness of the proposed approach. Contrasting simulation results indicate that the NNAGS-BSMC decreases the chattering effectively and has better control performance against the BSMC.

Near-space autonomous airship represents a unique and promising platform for earth observation and surveillance that involve a long duration airborne presence. In this paper, a six-degrees-of-freedom dynamics model and maneuverability of a near-space earth observation platform are presented. First, the near-space earth observation platform is introduced, including the concept design, configuration, energy sources, propeller and payload. Second, reference frames and motion parameters of the platform are defined, and the kinematics equations describing the platform's dimensional motion are derived. The effects of gravity, buoyancy, added inertia, aerodynamics and thrust on the platform are incorporated into the dynamics analysis, and a dynamics model in vector form of the platform is derived based on Newton-Euler principle. Finally, a simulation program has been developed to implement the dynamics model and applied to analyze the maneuverability of the platform. It is hoped that this work is useful to support the evaluation of maneuverability and the development of control system for the near-space earth observation platform.

The near space autonomous airship represents a unique and promising solution for many applications ranging from surveillance, communication utilities and scientific exploration. In attempt to complete the various missions, the near space airship first requires an accurate control system for autonomous flight. This paper presents an improved sliding mode control method for autonomous flight, considering the characteristics of nonlinearity, strong coupling and uncertainty of an airship. Firstly, the dimensional motion mathematical model of an airship is derived, including kinematics and dynamics equations. Then the controller for autonomous flight is designed by use of an improved variable structure control method, which adopts the boundary layer sliding mode control approach. Finally simulation results illustrate the effectiveness of the proposed method. The proposed control method is robust to parameter uncertainties and external disturbances, and provides an effective approach to design flight control system of a near space airship.