Fault-Tolerant Attitude Control for Flexible Spacecraft Without Angular Velocity Magnitude Measurement

Aiming at the attitude control problem of flexible spacecraft, an improved sliding mode controller is presented. First of all, the dynamics equation and the kinematics equation described by error quaternion and error angular velocity are studied, which avoid the non-single question of the end attitude. What’s more, according to the mathematical model of flexible spacecraft attitude system, the sliding mode controller is designed by the Lyapunov approach. Finally, in order to reduce the chattering of variable structure control for flexible spacecraft attitude, the smoother “arc tan function” is used to replace the sign function to reduce the chattering. And optimization to reduce the maximum control torque required by the system, which can avoid the vibration of flexible appendages. Simulation results show that the proposed control scheme can effectively achieve the spacecraft attitude control. Besides, On account of this, we can find that it can eliminate the chattering of traditional sliding mode control and keep good robustness. Keywords-flexible spacecraft; error quaternion; sliding mode control; Chattering reduction

Investigations of an integrated angular velocity measurement and attitude control system for spacecraft using magnetically suspended double-gimbal CMGs


 
 
 This paper presents an adaptive fault-tolerant control (FTC) scheme for leader-follower consensus control of uncertain mobile agents with actuator faults. A local FTC component is designed for each agent in the distributed system by using local measurements and certain information exchanged between neighboring agents. Each local FTC component consists of a fault detection module and a reconfigurable controller module comprised of a baseline controller and an adaptive fault-tolerant controller activated after fault detection. Under certain assumptions, the closed-loop system stability and leader-follower consensus properties of the distributed system are rigorously established. A simulation example is used to illustrate the effectiveness of the FTC method.
 
 

In this paper, a passive fault tolerant attitude control is investigated for a nano-satellite with three magnetorquers and one reaction wheel in the presence of actuator constraints, external disturbances, and partial loss of actuator effectiveness as unknown actuator faults. For this purpose, a variable structure control approach is employed due to its ability to deal with the partial loss of actuator effectiveness and adjusting the maximum amplitude of the control signal by a control gain. A modified sliding variable is designed based on angular velocity and attitude errors with an adaptive parameter coefficient. The dynamics equation of the adaptive parameter is extracted during the stability proof of the closed-loop system. Changing the value of this parameter changes the effect intensity of the quaternion errors on the sliding variable and causes the attitude errors to maintain within a limited range. Applying this parameter to the modified sliding variable makes the controller perform well even if the adaptive parameter is significantly reduced. Furthermore, directly using the adaptive parameter in the structure of control law makes the controller generate a chattering-free torque. Comparing the simulation results with the results of two variable structure control methods designed in previous articles shows that its performance in attitude tracking commands has improved. In addition, Monte Carlo simulations with random actuator faults are performed to show the robustness of the proposed controller in the presence of actuator constraints and external disturbances.

The unknown disturbances and the changing uncertainties bring difficulties for designing a stable attitude controller for UAV. In this paper, a novel adaptive fault-tolerant attitude control approach is designed based on the long short-term memory (LSTM) network for the fixed-wing UAV subject to the high dynamic disturbances and actuator faults. Firstly, the high dynamic disturbances can be compensated by the adaptive laws. Meanwhile, the actuator faults can be handled by the proposed adaptive fault-tolerant control (AFTC) scheme. Moreover, the LSTM network is introduced to approximate the unknown and time-accumulating nonlinearities. With the introduction of the one-to-one nonlinear mapping (NM), the output constraints in the control system can be guaranteed. Additionally, it can be demonstrated that the boundness of all the signals can be assured. At last, numerical simulation results are provided to illustrate the effectiveness of the proposed method.

A LTHOUGH the past three decades have witnessed several important developments in attitude stabilization control [1,2], there still remain certain open problems that are of great theoretical and practical interests, such as actuator constraint. Because of physical limitations, typical control actuators (e.g., reaction wheels and thrusters) for attitude control have an upper bound on the torque they can generate. If this issue is not solved during attitude maneuvering, then the attitude system will continue issuing its commands that may no longer be achievable by the satellite, and the required control will quickly saturate actuators. This will subsequently destabilize and even lead to loss of control of the satellite. Therefore, actuator constraint is one key issue that needs to be addressed. At present, a great deal of attention has been focused on the stability analysis and the attitude control design with saturated actuators [3–6]. Another problem that needs to be addressed is fault tolerant control for the attitude system. Any component or system fault can potentially cause a host of economic and safety problems. As a result, online and real-time fault tolerant control (FTC) design for satellites has received considerable attention [7]. Generally speaking, FTC can be classified into two types: passive and active [8]. The passive FTC is designed to be robust to a class of possible faults. It does not require fault detection and diagnosis (FDD) schemes. In an attempt to develop attitude controllers that can accommodate faults, extensive studies on the passive FTC control system for satellites have been performed [9–11]. The active FTC can react to fault events by using a reconfigurationmechanism. The active FTC relies on the availability of an FDD mechanism that gives, in real time, information about the nature and the intensity of the fault. The design of active FTC, especially the fault detection and diagnosis scheme for satellite attitude, has attracted considerable interest [12–14]. Although the methodologies including FDD and control law reconfiguration for the control-type faults of satellite attitude system have been studied extensively (as seen in the preceding references), the problem that is not solved yet is the effective and practical strategies for handling severe failure cases combining with actuators constraint. Lack of such effective FTC strategies may lead to substantial performance deterioration and even the loss of a satellite. The clear knowledge of the link between control reconfiguration and the actuator input constraint is still lacking. Because the control reconfiguration at different time instants with different types of faults has greatly different effects on control actuators saturation, there is no explicit and simple relationship between them, which makes this problem even more difficult. This leads to an important practical problem: how tomake use of the control reconfiguration on available control redundancy. Motivated by this problem, a novel attitude control approach is presented in this paper; an observer-based FDD scheme combining a sliding mode controller by using the estimated information is designed in a framework of active FTC system. The main contribution of this study, relative to otherworks, is that actuator faults, actuator constraints, and external disturbances are simultaneously addressed in an attitude FTC system design.

T HIS Note proposes a new strategy for the design of the attitude determination and control system (ADCS) of reconfigurable spacecraft, with a specific application example to so-called nanosatellites. These spacecraft adhere to the CubeSat standard [1], and the natural discretization of the overall volume into cube units makes them a popular platform for research into spacecraft reconfiguration [2]. The proposed design strategy, called location-scheduled control (LSC), seeks to reduce the development time required for the ADCS of a reconfigurable spacecraft conducting scientific research. In traditional ADCS design, mission science requirements levy pointing requirements onto the ADCS, which drive sensor and actuator selection. Once the ADCS hardware has been chosen, an appropriate control algorithm is selected and tested. In contrast, the location-scheduled approach to ADCS design is a two-phase process. In the first phase, a general purpose self-contained ADCS hardware unit is designed by selecting a suite of sensors and actuators that are appropriate for a class of science missions. Controller gains and ADCS location are then optimized in simulation for a number of generic science payloads, such as those depicted in Fig. 1, in which payload cube (P) layouts dictate possible locations for the ADCS (cubes A or B). In the second phase of the process, one of the previously tested configurations is selected based on the needs of the current science mission. Some amount offine gain tuningwill inevitably be required, but if a member of the catalog of spacecraft configurations satisfies the needs of the science payload, the developer need not return to the first phase of the design process. Although the LSC approach is applicable for many reconfigurable spacecraft, thiswork considers a nanosatellite ADCSdesign problem to demonstrate this methodology. The objective of the design problem is to find the optimal combination of ADCS unit location and control law gainvalues for a nanosatellite performing a detumble maneuver in which the spacecraft has high initial angular velocity and arbitrary initial orientation. Using the CubeSat standard, a 10 10 10 cm cube is designated as one unit of volume (abbreviated 1U), and complete spacecraft are created from these cubes. Traditional CubeSats are typically no larger than 3U in volume, and they have largely been passively controlled via permanent magnets [3,4], gravity gradient booms, or aerodynamic stabilization. This Note focuses on spacecraft that are 6U in volume (as in Fig. 1), with overall dimensions of 10 20 30 cm. This form factor creates greater volume for both complex science payloads and attitude control hardware and is currently under development at NASAAmes Research Center. A nonlinear control law introduced in [5] is used to control the nanosatellite using actuators for which the control authority is restricted by a known upper bound.

Intending to address the issue of sensor fault-tolerant control, a model-free adaptive fault-tolerant constrained control strategy is proposed with virtual sensor technology. The novel introduction of observer-based model-free adaptive control to fault-tolerant control brings benefits to the nonlinear systems with unknown dynamics in the presence of sensor faults. In the design procedures, the dynamic linearization technique is utilized first to establish the equivalent linear model of nonlinear systems. Then, the virtual sensor technology is introduced by designing the novel state-observer-based estimation algorithm to fulfill the data-driven system dynamic and sensor fault modeling. Besides, the broad learning technique is employed with offline training to provide output information for observer-based data-driven modeling under the fault case. Based on the data-driven model, the fault-tolerant constrained control scheme is explored with the anti-windup compensator against input constraints caused by actuator saturation, and the stability analysis is supplied. Finally, the simulations are carried out for both affine and non-affine nonlinear systems to manifest the effectiveness and superiority of the proposed control strategy.

This paper presents a new approach to vibration reduction of flexible spacecraft during attitude control by using pulse width pulse frequency (PWPF) modulator for thruster firing and smart materials for active vibration suppression. The experiment was conducted on the Naval Postgraduate School (NPS)'s Flexible Spacecraft Simulator (FSS), which consists of a central rigid body and an L-shape flexible appendage. A pair of on-off thrusters are used to reorient the FSS. To actively suppress vibrations introduced to the flexible appendage, embedded piezoelectric ceramic patches are used as both sensors and actuators to detect and counter react to the induced vibration. For active vibration suppression using the piezoelectric ceramic patches, Positive Position Feedback (PPF) control targeting at the first two flexible modes of the FSS system is used. Experimental results demonstrate the effectiveness of the control strategy of PWPF modulation for attitude control and PPF for active vibration suppression.

Appointed-time fault-tolerant attitude tracking control of spacecraft with double-level guaranteed performance bounds

This paper addresses the finite-time fault-tolerant attitude stabilization control problem for a rigid spacecraft in the presence of actuator faults or failures, external disturbances, and modeling uncertainties. First, a basic fault-tolerant controller is proposed to accommodate actuator faults or failures and guarantee local finite-time stability. When there is no a priori knowledge of actuator faults, disturbances, and inertia uncertainties, an online adaptive law is proposed to estimate the bounds of these uncertainties, and local finite-time convergence is achieved by an adaptive fault-tolerant controller. In addition, another adaptive fault-tolerant control scheme is derived that explicitly takes into account the actuator saturation. The proposed attitude controller provides fault-tolerant capability despite control input saturation and ensures that attitude and angular velocity converge to a neighborhood of the origin in finite time. Finally, simulation studies are presented to demonstrate the effectiveness of the proposed method.

Adaptive backstepping fault-tolerant control for flexible spacecraft with unknown bounded disturbances and actuator failures

The global adaptive set stabilization problem of the attitude of a rigid spacecraft is addressed in this paper. Two different cases are considered. First, by using adaptive backstepping method, the authors design a global adaptive control law for the attitude control system with unknown inertia matrix such that the attitude and the angular velocities can be globally asymptotically stabilized to a set consisting of two equilibria. And then, based on the obtained backstepping adaptive law, the authors consider the case that the angular velocities are not measurable. By introducing an auxiliary state, a semi-global adaptive set stabilization law without angular velocity measurements is also designed. It is rigorously proved that, for the two cases, both of the closed loop systems satisfy the set stability. The effectiveness of the proposed methods is verified by simulation results.

An integral TSMC-based adaptive fault-tolerant control for quadrotor with external disturbances and parametric uncertainties

This study investigates the robust fault-tolerant attitude control of an orbiting spacecraft with a combination of unknown actuator failure, input saturation and external disturbances. A fault-tolerant control scheme based on variable structure control is developed that is robust to the partial loss of actuator effectiveness, where the actuators experience a reduced actuation but are still active. The results are then extended to the case in which some of the actuators fail completely, although some redundancy in actuation is assumed. In contrast to traditional fault-tolerant control methods, the proposed controller does not require knowledge of the actuator faults and is implemented without explicit fault detection, separation and accommodation processes. Moreover, the designed controller rigorously enforces actuator saturation constraints. The associated stability proof is constructive and develops a candidate Lyapunov function that shows the attitude and the angular velocities converge asymptotically to zero. Simulation studies are used to evaluate the closed-loop performance of the proposed control solution and illustrate its robustness to external disturbances, unknown actuator faults and even input saturation.