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Feasibility of underactuated formation reconfiguration in elliptic orbits without radial or in-track thrust is investigated in this paper. For either underactuated case, by using a linear time-varying dynamical model of spacecraft formation, controllability and feasibility analyses are conducted, based on which the preconditions on reconfigurable formations are then derived. With the inherent coupling of system dynamics, the reduced-order sliding mode control technique is employed to design a closed-loop underactuated controller for either case. To ensure the stability of the closed-loop system, the conditions imposed on the controller parameters are derived, and the parameter adaptation laws are then solved analytically. Meanwhile, the explicit relationships between the steady accuracies of system states and the controller parameters are obtained via a Lyapunov-based approach. Numerical examples are simulated in a J2-perturbed environment to validate the theoretical analyses. The results indicate that by using the proposed control schemes, underactuated reconfiguration in elliptic orbits is still feasible even in the absence of radial or in-track thrust and in the presence of unmatched disturbances. [ABSTRACT FROM AUTHOR]

The hub-spoke tethered formation system (HS-TFS) is attractive in many space applications, such as multi-point measurements, providing flexible frame for solar sail and other membrane or net structures. To utilize the specific advantages of the system, such as reduction of fuel consumption, promotion of the formation stability, the HS-TFS is usually designed as a rotating system. However, the rotating motion will increase the complexity of the formation control of the HS-TFS. In this paper, the formation control of the rotating HS-TFS is investigated. First, an analytical model based on several reasonable assumptions is introduced to describe the dynamics of the rotating HS-TFS. Based on this model, two coordinated formation control strategies are proposed and described in detail, in which the tension forces of the tethers, propulsions of the sub-spacecraft, and the torque of the master-spacecraft are used as control inputs. Then a closed-loop control system is constructed to validate the proposed coordinated formation control strategies. Finally detailed numerical simulations are implemented based on the closed-loop control system. The simulation results show that the proposed coordinated control strategies are capable of assigning the operating time of the torque of the masterspacecraft and improving the efficiency of the formation control of the rotating HS-TFS. [ABSTRACT FROM AUTHOR]

An adaptive fuzzy second-order terminal sliding mode control scheme is developed to solve the problem of rigid spacecraft attitude maneuver in which the external disturbances and uncertain inertia parameters as well as actuator faults are explicitly taken into account. The proposed controller incorporates a second-order terminal sliding mode to obtain finite time convergent performance as well as chattering elimination, meanwhile the fuzzy logical system is implemented to estimate the system uncertainties of the rigid spacecraft. Lyapunov stability analysis shows that the designed control algorithm guarantees the practical finite time stability of the attitude maneuver errors with great robustness to system uncertainties and actuator faults. Numerical simulations are also presented that not only highlights closed-loop performance benefits from the proposed control algorithm, but also illustrates its effectiveness in the presence of disturbances and uncertainties when compared with classic finite time sliding mode control schemes for spacecraft attitude maneuver control. [ABSTRACT FROM AUTHOR]

The problem of relative motion control of spacecraft rendezvous process on elliptical orbit is considered in this paper. Due to the presence of nonlinear dynamics and external disturbances, two robust controllers are developed based on sliding mode control theory. The first one is an optimal sliding mode controller; in which optimal control theory is used to reduce the tracking error and fuel cost, and then integral sliding mode control technique is applied to robustify optimal controller. The other controller is a backstepping sliding mode one that is developed based on nonlinear dynamics of spacecraft rendezvous; having applied the backstepping method to synthesis the tracking errors and Lyapunov functions, a sliding mode controller is developed to guarantee the Lyapunov stability, handling of all nonlinearities, robustness against uncertainties as well as tracking the desired position. It is assumed that the chaser and target spacecraft are in a low Earth orbit and subject to the perturbing effects of J2 and atmospheric drag. In addition, two fault tolerant scenarios, i.e. thruster degradation and short thruster failure are also considered to verify the robustness and efficacy of the control approaches. Simulation results confirm the effectiveness of the proposed controllers in reaching to the desired position in case of actuator fault-free and fault tolerant situations. [ABSTRACT FROM AUTHOR]

A neural network Hamilton–Jacobi–Bellman (HJB) approach is introduced to deal with the spacecraft rendezvous problem with target spacecraft in arbitrary elliptical orbit. The Lawden equations are utilized to describe the relative motion of two spacecrafts. A generalized non-quadratic functional is introduced to describe constrained control. An approximate solution to the value function of the HJB equation corresponding to constrained controls is obtained by solving for a sequence of cost functions satisfying a sequence of Lyapunov equations. An inverse optimal controller is introduced to design the initial stabilizing admissible control for successive approximation. Furthermore, an optimal control law is obtained to stabilize the closed-loop system under constrained controls, and the spacecraft rendezvous mission can be accomplished with the nearly optimal controller. In comparison with the existing quadratic-regulation-based approaches used to deal with the rendezvous problem, which requires the value function of the nonlinear differential equations, the optimization factor and constrained control are taken into consideration simultaneously, and an approximate optimal constrained state feedback controller has been tuned a priori off-line. Stability analysis as well as simulation results are provided to illustrate the effectiveness of the presented approach. [ABSTRACT FROM AUTHOR]

This paper investigates spacecraft attitude control problem to achieve global fast tracking maneuvers. The concept of state-space form is initially introduced into spacecraft attitude dynamics and kinematics based on the unit quaternion, and then robust finite-time controllers are proposed based on geometric homogeneity and integral sliding mode. Furthermore, gain adaptation laws are employed and developed to eliminate the requirement of boundaries with respect to the lumped uncertainties, while there is no overestimation of the gains. Moreover, global finite-time controllers are designed to get across the singular point caused by the unit quaternion. Finally, simulations are presented to illustrate the effectiveness of the control strategies. [ABSTRACT FROM AUTHOR]

Quasi-periodic orbits in the Earth–Moon system are highly sensitive and even small errors in position and/or velocity have strong influence on the trajectory. These types of trajectories are unstable and must be controlled to maintain the corresponding orbits. This paper investigates the stationkeeping strategy for quasi-periodic orbits near the translunar libration point with full consideration of the contribution from the Sun’s gravity and the Moon’s eccentricity, in which the continuous low-thrust is preformed to enforce the probe following several onboard decided target points on the baseline. A new high-fidelity model is derived to describe motions of the quasi-periodic orbits by using the standard ephemerides. Based on the improved multiple-shooting method and the proposed model, a baseline trajectory is obtained. Then, a new continuous low-thrust-based stationkeeping strategy is proposed. Specifically, by employing Gauss pseudospectral method in the stationkeeping algorithm and by introducing the maximal excursion and fixed time interval, the target points on the baseline trajectory are chosen onboard based on real-time data. Simulation results show that the unstable quasi-periodic orbit can be maintained effectively with the low-energy consumption. [ABSTRACT FROM AUTHOR]

Six degrees of freedom (6DOF) relative motion trajectory tracking control is studied for a chaser spacecraft with parametric uncertainties and external disturbances to approach a tumbling target in deep space. After modeling the nonlinear and coupled relative motion dynamics in the chaser body-fixed frame, reference trajectories of the relative attitude and relative position are designed, then a 6DOF integrated trajectory tracking controller is developed based on a robust adaptive method. Asymptotic stability of the 6DOF closed-loop system is derived within the Lyapunov framework. The performance of proposed controller is demonstrated through a numerical simulation example. [ABSTRACT FROM AUTHOR]

The issue of attitude tracking control with finite-time convergence is investigated for spacecraft in the presence of external disturbance and uncertain actuator configuration as well. More specifically, in view of backstepping technique, the attitude quaternion can firstly track the demanded command in finite time under the virtual control law by introducing a novel terminal sliding manifold. Then, the finite-time convergence to the sliding mode of the angular velocity error will be achieved under the proposed novel finite-time control and a parameter updating law, even under uncertain actuator misalignment. In addition, the finite-time stabilization/convergence of the sliding surface and the spacecraft attitude tracking error have been proved and analyzed using the Lyapunov method theoretically. Finally, numerical simulation results are presented to illustrate the performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

Nowadays, the harmonic drive is widely used as the reducer in the spacecraft manipulator, which may influence the dynamical properties of flexible spacecraft manipulator. The alternative thermal environment makes the spacecraft manipulator to experience periodic heating and cooling in the sunlight and shadow region of the Earth. The analysis of dynamic modeling and motion precision of flexible spacecraft manipulator with harmonic drive, considering the alternate thermal field in orbit is of significant importance for spacecraft manipulator designers in the early stage of design. The thermal load influences the motion precision, which reflects whether the mechanism is performed normally or not. In order to evaluate the loss of motion precision, this paper establishes the dynamical model of spacecraft manipulator with harmonic drive considering the alternate thermal field in orbit. A thermal analysis model of flexible spacecraft manipulator with harmonic drive is developed to characterize the thermal response of the whole spacecraft manipulator system subjected to space heat flux. Two different altitudes including low Earth orbit and geosynchronous Earth orbit are considered. Moreover, the transient temperature fields in different orbits of spacecraft manipulator and the effects of the thermal environment factors on the spacecraft manipulator are investigated. Simulation results reveal the evolution process of the transient temperature field of the spacecraft manipulator system. According to the results, the maximum temperature difference for space manipulator can lead to more severe precision loss compared with the minimum temperature difference. In addition, the vibration frequency of angular velocity error is determined by the maximum thermal heat flux. The proposed method is useful for forecasting the temperature distribution of the spacecraft manipulator system, and will provide meaningful information for performance enhancement of the aerospace facilities. [ABSTRACT FROM AUTHOR]

A dynamic control allocation approach is presented to address the attitude stabilization problem of a rigid spacecraft. The approach is developed by using a least-square support vector machine. Actuator uncertainty including misalignment and magnitude deviation is explicitly addressed. A dynamic inverse control law is firstly designed. A least-square support vector machine-based adaptive compensator is then designed to handle actuators uncertainties, external disturbances and unknown moment of inertia. Lyapunov stability analysis shows that the closed-loop attitude system is asymptotically stable. More specifically, constrained quadratic programming-based robust dynamic control allocation is implemented to manage the redundancy actuators. The goal of minimizing the assumption of total energy is achieved. A numerical example is provided to demonstrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

This article investigates the decentralized coordinated control problem for formation flying spacecraft associated with coupled attitude and translational dynamics by probing into local information exchange among spacecraft. A six degree-of-freedom coupled model is established by employing the unified Euler–Lagrange formulations of attitude dynamics and translational dynamics. With the novel use of adaptive control, a six degree-of-freedom continuous robust coordinated controller is proposed in the presence of parametric uncertainty and time-varying disturbances with unknown bounds. Furthermore, it is extended to the case where both of switching topologies and non-constant communication delays exist. The six degree-of-freedom coordinated controller can guarantee formation spacecraft follow a time-varying reference trajectory while aligning their attitudes and keeping some special formation configuration. Numerical simulations demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Closed-form solutions of an optimal impact-angle-control guidance for a first-order lag system are derived. Under the assumptions of a stationary target and a first-order missile with constant speed and small flight path angle, they are obtained by solving a third-order linear time-varying ordinary differential equation. It is shown that the solutions are expressed by combinations of polynomial, logarithmic, and hypergeometric functions. Moreover, terminal misses due to the system lag and homing geometries for zero miss-distance have been studied. Linear and non-linear simulations are performed to verify the proposed results. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of attitude control of a spacecraft when unknown dead zones of unknown bounds exist at the actuators. A robust adaptive controller with parameter update laws are designed for the spacecraft’s attitude and an asymptotically stable tracking performance is mathematically proven based on the proposed design. Numerical simulation results along with the theoretical proof show that the proposed control scheme can successfully stabilize the attitude of the spacecraft with the unknown actuator dead zones. [ABSTRACT FROM PUBLISHER]

In this paper, a fault-tolerant control scheme based on a second-order dynamic terminal sliding mode is proposed for a near-space vehicle attitude dynamical system in the presence of actuator faults, model parameter uncertainties and external disturbances. The principle of the proposed dynamic terminal sliding mode scheme is firstly introduced. Then, a near-space vehicle attitude faulty model with parameter uncertainty is established. Furthermore, two dynamic terminal sliding mode controllers are designed for the inner and outer loops. It is shown that the proposed algorithm can reduce chattering phenomenon and guarantee system stability and asymptotic state tracking. Finally, simulation results are provided to demonstrate the performance of the proposed fault-tolerant control scheme. [ABSTRACT FROM PUBLISHER]

This work mainly explores a quaternion-based output feedback control scheme for the flexible spacecraft attitude tracking problem in which not only the unavailability of the body angular velocity measurements is considered, but also external disturbances and uncertain inertia parameters as well as input constraints are explicitly taken into account. The proposed controller incorporates a pseudo velocity filter to account for the unmeasured angular velocity, and the neural network technique is implemented to approximate the system uncertainties of the flexible spacecraft in the synthesis of the control algorithms. It is shown that this developed control method ensures the uniformly ultimate boundedness of the attitude tracking error and the control input can rigorously enforce actuator magnitude constraints. Numerical simulation results are also presented which not only highlight ensuring closed-loop performance benefits from the control law derived here, but also illustrate its robustness in the face of external disturbances when compared with conventional approaches for spacecraft attitude tracking control. [ABSTRACT FROM AUTHOR]

This paper deals with the attitude control of a rigid spacecraft with two reaction wheels. First, we derive a discontinuous state feedback law based on Lyapunov control. The control input is obtained by multiplying the gradient vector of the Lyapunov function by a matrix that is composed of a symmetric matrix and an asymmetric one. Under this method, when the angular momentum of the system is zero, the desired point is the only stable equilibrium point of the controlled system. Next, we investigate the behavior of the controlled system when the angular momentum of the system is not zero but small. In this case, the system converges to either a limit cycle or an equilibrium point which is not the desired point; however, in both cases, the error in attitude remains small. [ABSTRACT FROM AUTHOR]