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Model-based FDIR and Fault Accommodation for a Rendezvous Mission around the Mars Planet: the Mars Sample Return Case
Abstract
The research work presented in the paper addresses the design of a model-based fault diagnosis and fault recovery system for any faults occurring in the actuator and sensor units of the chaser spacecraft of the ESA Mars Sample Return (MSR) mission. Key features of the proposed method are the use of a parity space and covariance-based strategy with jointly a H∞ observer for fault diagnosis of sensor faults, a H∞/H- filter for robust fault detection of actuator faults and a bank of unknown input observers jointly used with a dot product of vectors strategy for actuator faults. For fault accommodation, a ”retreat” FDIR strategy scheduled by the FDI unit, is retained. The proposed FDIR architecture obeys to a hierarchical one and fits the industrial requirements. Especially, it is compliant with the Aurora avionics architecture. A simulation campaign, based on a nonlinear high-fidelity simulator developed by GMV space and Thales Alenia Space industries, is conducted under highly realistic conditions.
... Such a solution requires obviously a (reliable) fault diagnosis unit, so that the control allocation algorithm is aware about the faulty thrusters. The interested reader can refer to [33,22,37,65,34,35] for the development of model-based diagnosis solutions applied to real space missions. 4 This FTC strategy is used in [15] with a time-varying terminal SMC approach and in [28] in cooperation with an adaptive integral SMC technique. ...
... Numerical value of the main characteristics of the chaser spacecraft (derived from the Microscope satellite [33], and the spacecraft involved in the ESA's Mars Sample Return [37,34] and e.Deorbit [7,10,35] ...
... This property directly follows from the CA's characteristics described in Section 4.4. Then, with (31), (36), (37) and under Assumption 2, it can be verified that (23) and (24) can be rewritten: These equations are nothing else than the dynamics to be controlled by the GSTA controller. ...
This paper addresses the design of a sliding mode fault-tolerant control scheme for a particular class of actuator faults, for Rendezvous space missions with a passive target. The technique is based on a Super-Twisting controller, scheduled by a fault estimator. The core element of the proposed design technique is that it is based on the Dual-Quaternion formalism that enables to take into account the coupling between relative position and attitude motions. It is proved that the control law converges to the sliding surface in finite time. Stability on it is too proved by means of the Lyapunov theory. Finally, simulations results from a high-fidelity simulator that considers solar arrays flexible modes, propellant sloshing, and the most dimensioning space disturbances (i.e. gravity gradient, magnetic field, solar pressure, and aerodynamic drag), demonstrate the potential of the proposed solution.
... Such a solution requires obviously a (reliable) fault diagnosis unit, so that the control allocation algorithm is aware about the faulty thrusters. The interested reader can refer to [33,22,37,65,34,35] for the development of modelbased diagnosis solutions applied to real space missions 4 . This FTC strategy is used in [15] with a time-varying terminal SMC approach and in [28] in cooperation with an adaptive integral SMC technique. ...
... This property directly follows from the CA's characteristics described in Section 4.4. Then, with (31), (36), (37) and under assumption 2, it can be verified that (23) and (24) can be rewritten:ω (c) ...
... Such a solution requires obviously a (reliable) fault diagnosis unit, so that the control allocation algorithm is aware about the faulty thrusters. The interested reader can refer to [33,22,37,65,34,35] for the development of modelbased diagnosis solutions applied to real space missions 4 . This FTC strategy is used in [15] with a time-varying terminal SMC approach and in [28] in cooperation with an adaptive integral SMC technique. ...
... This property directly follows from the CA's characteristics described in Section 4.4. Then, with (31), (36), (37) and under assumption 2, it can be verified that (23) and (24) can be rewritten:ω (c) ...
The goal pursued by this article, is to evaluate the potential of sliding-mode control and estimation techniques, to address fault tolerance against a large class of actuator faults, including loss of controllability of the faulty actuator, for autonomous rendezvous between a chaser spacecraft and a passive spacecraft on a circular orbit. The proposed solution is based on the dual quaternion formalism, to describe in a single equation, rotational and translational spacecraft dynamics, solar array flexible modes, propellant sloshing, the most dimensioning space disturbances, and their coupling. Such a modelling formalism enables to propose a six degree-of-freedom fault tolerant control architecture, which relies on the generalized super-twisting control algorithm nested with a nonlinear fault estimator. An anti-windup strategy based on polytope algebra is applied to the control algorithm, to prevent instability due to actuator saturation when faults occur. Asymptotic stability of the proposed fault-tolerant control scheme is formally proved with respect to a wide variety of faults, providing that the first derivatives of the fault estimation error versus time and the sliding surface, are bounded. Intensive simulations from a functional engineering simulator that accurately simulates the rendezvous mission, are presented in the paper, as well as capture-oriented criteria. The presented results demonstrate that the proposed fault-tolerant solution is able to cover any kind of thruster faults, including total loss of controllability of the faulty thruster, as well as solar array flexible modes, propellant sloshing, gravity gradient, the second zonal harmonic, atmospheric drag and magnetic disturbances.
... In [10,11], the classical SIMPLEX-based CA algorithm is changed by the Nonlinear Inverse Pseudo Control (NIPC) solution to improve the FTC performances of the terminal rendezvous phase of the Mars Sample Return mission. An alternative solution can also be found in [12,13] by acting at the guidance level. The FTC strategy consists of the following principle: if the chaser is outside the so-called approach corridor or/and with an attitude outside of a pre-defined threshold, then a switch on a healthy redundant thruster set is made and a "retreat" maneuver is engaged. ...
... Note that the spacecraft possesses 24 thrusters of 22N to control both attitude and position motions. Let us introduce the thruster influence coefficients defining how each thruster affect each component of u in (1), i.e.[12,16], a useful model of the thruster management unit has been considered here. It consists of the the left pseudo-inverse of matrices. ...
The design of a model-based Fault Tolerant Control (FTC) strategy based on Virtual Actuators (VA) in a built-in Guidance, Navigation and Control (GNC) setup is addressed for the e.Deorbit space mission. This mission, initiated by the European Space Agency (ESA), aims at removing a large defunct satellite from Earth orbit: ENVISAT. The goal of this paper is to promote academic solutions to add fault tolerance capacities against thruster faults without any change or new tuning of the already in-place GNC solution. The validation of the proposed FTC solution is assessed by a simulation campaign based on a high-fidelity nonlinear industrial simulator.
... Second, the duration of entry is short and the corresponding state variables change rapidly. Therefore, in order to ensure the reliability and security of the entry GNC system, the autonomous technologies, including real-time online fault diagnosis, are really needed (Li et al., 2014;Henry et al., 2016). ...
... Fault tolerant control were developed to ensure the adaptively compensate for the malfunction or failure of controller, in order to maintain the stability of the system and the basic performance of a class of control methods (Mahmoud et al., 2003). Therefore, fault tolerant control can provide certain 'self-repairing' capability in the event of serious fault for safe flight control systems (Henry et al., 2016). The design of FTC generally falls into two categories: passive and active FTC. ...
The capability of autonomous fault detection and reconstruction is essential for future manned Mars exploration missions. Considering actuator failures and atmosphere uncertainties, we present a new active fault-tolerant control algorithm for Mars entry by use of neural network and structure adaptive model inversion. First, the online BP neural network is adopted to conduct the fault detection and isolation. Second, based on the structure adaptive model inversion, an adaptive neural network PID controller is developed for Mars entry fault-tolerant control. The normal PID controller will be automatically switched into neural network PID controller when an actuator fault is detected. Therefore, the error between the reference model and the output of the attitude control system would be adjusted to ensure the dynamic property of the entry vehicle. Finally, the effectiveness of the algorithm developed in this paper is confirmed by computer simulation. Nomenclature D C = Coefficient of Drag 0 r = Martian Radius, m L C = Coefficient of Lift ref S = Reference Area of Entry Vehicle, 2 m D = Drag Acceleration, 2 m s v= Velocity of Entry Vehicle, m s m g = Mars Gravity Acceleration, 2 m s = Flight Path Angle, rad h = Altitude, m = Longitude, rad s h = Constant Scale height, m = Latitude, rad L = Lift Acceleration, 2 m s = Density of Mars Atmosphere, 3 kg m ref l =Length of Entry Vehicle, m 0 = Density of Mars Atmosphere on Surface, 3 kg m m =Mass of Entry Vehicle, kg = Bank Angle, rad r = Distance from Martian Center to Entry Vehicles, m = Heading Angle, rad
... Therefore, landers will probably occur fault which leads to the safety problem of landers. 6,7 Reviewing the past 46 Mars exploration missions since 1960, only eight landing missions were successfully achieved due to the strong impact of disturbance and fault during the Mars landing process. 8,9 Overall, improving the precision and reliability of Mars landers is a key issue that needs to be addressed. ...
As a class of autonomous deep-space exploration robots, Mars lander is simultaneously affected by wind disturbance and actuator fault, which hinders precise landing on Mars. In this article, we propose a composite guidance approach by combining disturbance observer and iterative learning observer together. The Mars wind disturbance is dealt by the disturbance observer providing wind estimation which is rejected through feed-forward channel. Meanwhile, the iterative learning observer is used to estimate the deficiency of actuators. The proposed guidance scheme ensures not only the precision but also the reliability of the Mars guidance system. The stability of the closed-loop system is analyzed. Simulations made in different situations demonstrate the performance of the proposed approach.
The increasing complexity of deep space missions introduces significant challenges in maintaining spacecraft health, particularly in the propulsion systems, due to the inherent communication delays with Earth. This research proposes a novel framework for the autonomous, data-driven fault diagnosis of spacecraft propulsion systems. Leveraging data generated from a spacecraft propulsion system simulation model. The study addresses the limitations imposed by computational resources and sensor installation constraints through Sequential Forward Selection (SFS) for optimized sensor placement and feature selection. The framework's effectiveness is demonstrated through implementation on a microcomputer, showing promising results in terms of diagnostic accuracy and processing speed, thus highlighting its potential for onboard spacecraft application. This study not only advances the autonomous capabilities of spacecraft in deep space but also contributes to the broader field of Prognostics and Health Management (PHM) by providing a scalable, efficient approach to fault diagnosis in critical spacecraft systems. The proposed framework demonstrates a promising approach to optimizing diagnostic tasks for spacecraft systems. However, the trade-offs observed necessitate a careful consideration of task-specific requirements and the potential need for adjustments to maintain a high level of accuracy alongside computational efficiency.
The nonlinear model predictive control (MPC) approach is used to control the coupled translational‐rotational motion of an all‐thruster spacecraft when one of the actuators fails. In order to model the dynamical response of the spacecraft in MPC, instead of direct integration, a neural network (NN) model is utilized. This model is built of a static NN, followed by a dynamic NN. The static NN is used to find the changes of the mapping of “the demanded forces to the thrusters” and “the real torques/forces produced by the remaining thrusters” after the failure occurrence through online training. In this manner, the effect of failed thruster on the dynamics can be found and the need for conventional and separate “fault detection and isolation” in previous works is eliminated. The dynamic NN is used to replicate the dynamical equations of the spacecraft excluding the effects of the mapping of thrusters demand to the real generated force and torque. Using updated model of the spacecraft through the learning capability of the NNs, the nonlinear MPC is able to compensate the failure of the thruster with the help of the remaining active thrusters. Through numerical simulations, it is shown that in the presence of thruster failure(s) this approach can effectively control the spacecraft with the remaining actuators.
The presented work is a result of a research collaboration between European Space Agency, Thales Alenia Space and IMS Laboratory with the aim of promoting fault-tolerant control strategies to advance spacecraft autonomy. A multiple observer based scheme is proposed jointly with an online constrained allocation algorithm to detect, isolate and accommodate a single thruster fault affecting the propulsion system of an autonomous spacecraft. Robust residual generator with enhanced robustness to time delays induced by the propulsion drive electronics and uncertainties on thruster rise times is used for fault detection purposes. A decision test on the residual of the fault detector triggers a bank of nonlinear unknown input observers which is in charge of confining the fault to a subset of possible faults. The faulty thruster isolation is achieved by matching the residual and the thruster force directions using the direction cosine approach. Finally, the fault is accommodated by redistributing the desired forces and torques among the remaining (healthy) thrusters and closing the isolated thruster. Simulation results from the "high-fidelity" industrial simulator, provided by Thales Alenia Space, demonstrate the fault-tolerance capabilities of the proposed scheme.
This paper presents the design process and evaluation of a fault detection and isolation (FDI) filter for the provision of health monitoring capabilities on the Hopper reusable launch vehicle (RLV) during a period of the re-entry. A high fidelity nonlinear model of the Hopper RLV is employed, with NDI control providing a robust vehicle response during unfaulted vehicle operation. Two fault scenarios are considered; faults in the rudder actuator and sideslip sensor. A robust FDI filter design procedure is developed based on H-infinity FDI theory. Scheduling of designed LTI filters is employed to overcome the inherent variation in the vehicle's dynamical characteristics during re-entry. A key feature of the developed design process is that FDI filters are designed in open-loop, despite the vehicle dynamics being unstable. Monte-Carlo analysis performed using nonlinear simulations demonstrates the robustness and effectiveness of the proposed FDI approach.
In this paper, the problem of Nonlinear Unknown Input Observer (NUIO) based Fault Detection and Isolation (FDI) scheme design for a class of nonlinear Lipschitz systems is studied. The proposed FDI method is applied to detect, isolate and accommodate thruster faults of an autonomous spacecraft involved in the rendezvous phase of the Mars Sample Return (MSR) mission. Considered fault scenarios represent fully closed thruster and thruster efficiency loss. The FDI scheme consists of a bank of NUIOs with adjustable error dynamics, a robust fault detector that is based on judiciously chosen frame and an isolation logic. The bank of observers is in charge of confining the fault to a subset of possible faults and the isolation logic makes the final decision about the faulty thruster index. Finally, a thruster fault is accommodated by re-Allocating the desired forces and torques among the remaining healthy thrusters and closing the associated thruster valve. Monte Carlo results from 'high-fidelity' MSR industrial simulator demonstrate that the proposed fault tolerant strategy is able to accommodate thruster faults that may have effect on the final rendezvous criteria.
This paper deals with performance and reliability evaluation of a fault diagnosis scheme based on two distinct models to detect and isolate a single thruster fault affecting a chasing spacecraft during rendezvous with a passive target in a circular orbit. The analysis is conducted in the frame of a terminal rendezvous sequence of the Mars Sample Return mission. A complete description of a robust residual generation design approach based on eigenstructure assignment is presented. Unknown time-varying delays, induced by the thruster drive electronics and uncertainties on thruster rise times, are considered as unknown inputs. Particular novelty of the work is a new method for estimating the unknown input directions used to enhance the robustness properties of the diagnosis scheme. Monte Carlo results from a high-fidelity industrial simulator and carefully selected performance and reliability indices allows us to evaluate the effectiveness of both schemes. The obtained results reveal that the proposed fault diagnosis scheme based on a position model is a justified competitor to the conventionally used attitude model-based scheme.
Two robust fault detection schemes are presented to detect faults affecting the thrust system of the chaser spacecraft involved in the rendezvous phase of the Mars Sample Return (MSR) mission. The idea of both proposed methods is to transform the unstructured uncertainty caused by the electronic induced delays into unknown inputs and decouple them by means of an eigenstructure assignment (EA) technique. The first method utilizes a Cayley-Hamilton theorem based transformation whereas the second relies on a first-order Padé approximation of the time delay. The performances of the proposed schemes are compared by a sensitivity/robustness analysis campaign of 4240 runs within the “high-fidelity” industrial simulator provided by Thales Alenia Space.
Microscope is a satellite due to be launched in March 2008 (Microscope is undertaken jointly by the Centre National d'Etudes Spatiales, France, the ESA, the Office National d'Etude et de Recherche en Aerospatial, France, and the Cote d'Azur Observatory, France). It has the mission of testing the equivalence principle, which postulates the equality between gravitational mass and inertial mass. This paper addresses the fault diagnosis task of the Microscope thrusters. The faulty situations correspond to thrusters blocking themselves and/or closing when in operation. Two model-based diagnosis schemes based on H-infinity/H- filters are proposed and compared with each other in terms of performances and complexity. Nonlinear simulations show that both schemes are able to detect and isolate faults, despite the presence of measurement noises, measurement delays, sensor misalignment phenomena, and disturbances (i.e., third-body disturbances, J(2) disturbances, atmospheric drag, and solar radiation pressure).
The problem of active fault-tolerant control with reconfiguration mechanism for uncertain linear systems with external disturbances is addressed applying the supervisory control approach. A key feature of the proposed approach is establishment of a set of conditions providing mutual performance in the sense of taking into account the interaction of the fault detection, isolation, and accommodation subsystems in order to achieve global fault-tolerance performance with guaranteed global stability. The efficiency of the approach is demonstrated in an example of computer simulation for a flight system benchmark. Copyright © 2012 John Wiley & Sons, Ltd.
Even though spacecraft are carefully designed and tested to meet their mission lifetime, many suffer unrecoverable on-orbit failures very early. Other spacecraft, despite severe failures, are able to exceed their expected lifetime when effective failure recovery procedures are applied. In 2005, a study of on-orbit spacecraft failures was undertaken which resulted in identifying 156 failures occurring from 1980 to 2005 on civil and military spacecraft. These failures were analyzed to compare different spacecraft subsystems and estimate their impact on the mission. Although there is no perfect system that could prevent any failure, the lessons learned from the past years show that adequate testing, redundancy and flexibility are the keys to a reliable spacecraft failure recovery system.
Supervisory fault tolerant control with integrated fault detection and isolation: A switched system approach
This paper focuses on supervisory fault tolerant control design for a class of systems with faults ranging over a finite cover. The proposed framework is based on a switched system approach, and relies on a supervisory switching within a family of pre-computed candidate controllers without individual fault detection and isolation schemes. Each fault set can be accommodated either by one candidate controller or by a set of controllers under an appropriate switching law. Two aircraft examples are included to illustrate the efficiency of the proposed method.
In this paper, a general approach is presented to design robust fault detection and isolation (FDI) filters for LTI uncertain systems under feedback control. A two-step design procedure is proposed to derive non-conservative robust FDI filters. The first step consists of designing an optimal FDI filter that maximizes fault sensitivity performance and simultaneously minimizes the influence of unknown inputs, for a large class of model perturbations. The design problem is formulated so that all free parameters are optimized via Linear Matrix Inequality techniques. The second step consists of a systematic post-design analysis procedure. A test is proposed to check if all FDI objectives are achieved for all specified model perturbations. The problem is formulated using an appropriate performance index over a specified frequency range. The solution is based on the generalized structured singular value. Finally, experimental results from a pilot laboratory system are presented to demonstrate the effectiveness of the proposed method.
A procedure to calculate the margin of safety of a thruster system is presented. The margin of safety is the excess control authority of a thruster system available to overcome the worst case disturbances and is based on calculating the minimum control authority of the thruster system normalized by the worst case disturbances. Various controllers are presented for both one-sided and two-sided thrusters and their minimum control authorities are compared. Finally, a procedure to optimize a thruster system configuration in the sense of maximizing the margin of safety is presented and applied to the design of a thruster system for the Quick STEP spacecraft, an orbiting gravitational physics experiment. The techniques presented in this article are generally applicable to many other multi-degree of freedom actuation systems like the primary flight control effectors on a highly maneuverable aircraft for example.
The research work presented in this paper addresses the design and validation of a robust model-based fault diagnosis system to detect and isolate any thruster fault occurring in the thruster-based propulsion system of the chaser spacecraft during rendezvous on a circular orbit around the Mars planet. The REFERENCE mission is the ESA Mars Sample Return (MSR) mission. Key features of the proposed method are the use of a Hi/H∞ filter for robust fault detection and a bank of unknown input observers jointly used with a dot product of vectors strategy for fault isolation. Robust performance over a large range of uncertainties (a total of 36 uncertainties is considered) is formally demonstrated through the μ3 formalism.
Fault monitoring is a vital part of every satellite mission. Especially for rendezvous scenarios a reliable and fast actuator fault detection is indispensable to avoid collision between both spacecraft. To reduce expensive monitoring hardware, a model-based thruster fault approach, only depending on a rate sensor is developed. It is able to reliably detected thruster stuck closed, thruster stuck open and leaking thruster faults in short time. Monte Carlo results produced in a complete satellite simulator are presented to show fault detection and isolation performance of the proposed algorithms.
This paper deals with the reliability and performance evaluation of two methods for FDI of on-board sensors and thrusters for attitude control of the Mars Express (MEX) orbiter spacecraft. The study makes use of a detailed non-linear simulation of the MEX, and the FDI performance is evaluated subject to disturbance signals, model uncertainty and measurement noise processes. The two methods are based on robust dynamic observers or filters, used as estimators, which generate the FDI residual signals. When organised into an estimator bank excellent fault isolation properties are achieved upon suitable design. Carefully selected performance criteria indices are used together with Monte Carlo robustness tuning and performance evaluation. These constitute the FDI design methodology, realising a reliability approach for real application of FDI in future spacecraft.
This paper presents research activities conjointly led by EADS Astrium Satellites and the European Space Agency on innovative and robust health monitoring system for the next generation of spacecraft. Two robust FDI schemes are presented to detect and isolate faults affecting the micro-Newton colloidal thrust system of the LISA Pathfinder spacecraft. The first FDI strategy is based on a bank of eight H∞H- residual generators designed according to the Generalized Observer Strategy whereas the second strategy consists of Kalman-based projected observers. The efficiency of the proposed FDI techniques is assessed through non linear simulations performed under realistic conditions (physical parameter uncertainties, disturbances, measurement noises, measurement delays, thruster jet misalignment,...). The results are quite encouraging, illustrate the effectiveness of the proposed techniques and suggest that the solutions could be practical viable candidates.
This paper deals with the design of a robust and reliable model-based Fault Detection and Isolation (FDI) strategy for the next generation of spacecraft. The work draws expertise from actions undertaken within research activities led by EADS Astrium Satellites on innovative and robust health monitoring techniques applied to the LISA Pathfinder spacecraft. In this work, a robust FDI scheme is proposed to detect and isolate faults affecting the micro-Newton colloidal thrust system; a key technology to be tested during the LISA Pathfinder experiment mission. The FDI strategy is based on previous work and consists of a bank of eight robust H ∞/H - residual generators. The design stage is followed by a μ-based post-analysis procedure both to conclude about the FDI robust performances and to determine the worst combination of uncertain parameters leading to the FDI performances degradation. The efficiency of the proposed FDI technique is assessed through nonlinear simulations performed under realistic operational conditions (physical uncertain- ties, disturbances, measurement noises, measurement delays, thruster jet misalignment,...) and considering system-oriented and FDI performance indicators. The results are quite encouraging, illustrate the effectiveness of the proposed technique, and suggest that the solution could be a practical viable candidate for future space programs. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
A most critical and important issue surrounding the design of automatic control systems with the successively increasing complexity is guaranteeing a high system performance over a wide operating range and meeting the requirements on system reliability and dependability. As one of the key technologies for the problem solutions, advanced fault detection and identification (FDI) technology is receiving considerable attention. The objective of this book is to introduce basic model-based FDI schemes, advanced analysis and design algorithms and the needed mathematical and control theory tools at a level for graduate students and researchers as well as for engineers. © 2008 Springer-Verlag Berlin Heidelberg. All rights are reserved.
This paper presents the design of a gain scheduled fault detection and isolation (FDI) filter for the Hopper reusable launch vehicle (RLV). The fault scenario is that of faults in the vehicle's rudder actuator and sideslip sensor during a focused 90 second period of the reentry. Both of the considered faults strongly affect the lateral response of the vehicle, making simultaneous FDI difficult. A dynamically stable model of the Hopper RLV is considered and FDI filter design is performed on linearised models of the vehicle trimmed about the reentry trajectory. H-infinity theory is employed for the FDI filter synthesis, with a set of LTI FDI filters designed at the trim points and then scheduled to form the gain scheduled FDI filter. The effectiveness of the LTI point-design filters and the gain-scheduled filter are determined by simulation using a tightly gain-scheduled model of the linearised vehicle's open-loop response that captures the strongly parameter varying vehicle behaviour as it tracks the re-entry trajectory. The advantages of using gain-scheduled FDI filters for FDI on RLVs are highlighted via the simulations.
This paper describes high-fidelity simulation testing of some of the more popular advanced control allocation techniques integrated with two separate dynamic inversion control laws. The allocation methods include variations of quadratic programming, linear programming, direct allocation, cascaded generalized inverse, and weighted pseudo-inverse. Results are presented for single and multi-axis pitch and roll maneuvers with and without actuator failures. A velocity vector roll is also considered for the no failure case. Results show that a robust control law can mask differences in the various control allocation routines and lead to similar performance from both optimal and sub-optimal allocation methods. Furthermore, the current results illustrate that the closed-loop performance does not directly follow from the openloop measures that are widely used in the literature.
Fault-tolerant Control Systems reports the development of fault diagnosis and fault-tolerant control (FTC) methods with their application to real plants. After an introduction to fault diagnosis and FTC, a chapter on actuators and sensors in systems with varying degrees of nonlinearity leads to three chapters in which the design of FTC systems is given thorough coverage for real applications: (i) a winding machine typifying a subsystem in various sheet and film processes; (ii) a hydraulic three-tank system representative of those used widely in chemical plants; and (iii) an active suspension system demonstrating application in whole large-scale systems by splitting into subsystems.Actuator and sensor faults are accommodated within the control-law design and the integration of fault diagnosis models in the FTC systems described. Commentary is given on the recent results presented. Critical failures â the loss of system observability from total loss of a sensor and of controllability from complete loss of an actuator â are considered. Linearized systems around an operating point and nonlinear systems are discussed and illustrated. A complete simulation platform of the three-tank system, in closed-loop, with or without actuator and sensor faults, is provided for the use of the reader via download from www.springer.com/978-1-84882-652-6.With its emphasis on real application, Fault-tolerant Control Systems makes an important contribution to the literature on FTC and will be of significant assistance to practicing control engineers with problems of this nature to solve. The book will also be of use to academic researchers and graduate students interested in FTC, bringing to their attention the need to adapt their methods for implementation and suggesting ways in which this can be done.
This paper presents a scheme for fault detection and isolation (FDI) of on-board gyroscope sensors and thrusters for spacecraft attitude control, based on the example of the Mars Express (MEX) satellite. The main contribution of the paper is related to the design and the optimization of an FDI procedure based on robust observers or filters, used as estimators, which generate the FDI residual signals. When organized into an estimator bank, excellent fault isolation properties are achieved upon suitable design. The residual evaluation relies on decision logic, whose thresholds are properly selected and specified. The FDI strategy is applied to the non-linear simulation of the MEX system, and the FDI performance is evaluated subject to disturbance signals, model uncertainty, and measurement noise processes. The robustness and reliability properties of the robust residual generators are investigated and verified in simulation by selecting suitable performance criteria together with Monte Carlo analysis. The results obtained highlight a good trade-off between solution complexity and achieved performances. Comparisons with the existing fault diagnosis algorithms implemented on board the MEX spacecraft are finally reported. The proposed FDI design methodology constitutes a reliability approach for real application of FDI in future spacecraft.
This paper presents the design and implementation of a model predictive control (MPC) system to guide and control a chasing spacecraft during rendezvous with a passive target spacecraft in an elliptical or circular orbit, from the point of target detection all the way to capture. To achieve an efficient system design, the rendezvous manoeuvre has been partitioned into three main phases based on the range of operation, plus a collision-avoidance manoeuvre to be used in event of a fault. Each has its own associated MPC controller. Linear time-varying models are used to enable trajectory predictions in elliptical orbits, whilst a variable prediction horizon is used to achieve finite-time completion of manoeuvres, and a 1-norm cost on velocity change minimises propellant consumption. Constraints are imposed to ensure that trajectories do not collide with the target. A key feature of the design is the implementation of non-convex constraints as switched convex constraints, enabling the use of convex linear and quadratic programming. The system is implemented using commercial-off-the-shelf tools with deployment using automatic code generation in mind, and validated by closed-loop simulation. A significant reduction in total propellant consumption in comparison with a baseline benchmark solution is observed.
The control algorithm hierarchy of motion control for over-actuated mechanical systems with a redundant set of effectors and actuators commonly includes three levels. First, a high-level motion control algorithm commands a vector of virtual control efforts (i.e. forces and moments) in order to meet the overall motion control objectives. Second, a control allocation algorithm coordinates the different effectors such that they together produce the desired virtual control efforts, if possible. Third, low-level control algorithms may be used to control each individual effector via its actuators. Control allocation offers the advantage of a modular design where the high-level motion control algorithm can be designed without detailed knowledge about the effectors and actuators. Important issues such as input saturation and rate constraints, actuator and effector fault tolerance, and meeting secondary objectives such as power efficiency and tear-and-wear minimization are handled within the control allocation algorithm. The objective of the present paper is to survey control allocation algorithms, motivated by the rapidly growing range of applications that have expanded from the aerospace and maritime industries, where control allocation has its roots, to automotive, mechatronics, and other industries. The survey classifies the different algorithms according to two main classes based on the use of linear or nonlinear models, respectively. The presence of physical constraints (e.g input saturation and rate constraints), operational constraints and secondary objectives makes optimization-based design a powerful approach. The simplest formulations allow explicit solutions to be computed using numerical linear algebra in combination with some logic and engineering solutions, while the more challenging formulations with nonlinear models or complex constraints and objectives call for iterative numerical optimization procedures. Experiences using the different methods in aerospace, maritime, automotive and other application areas are discussed. The paper ends with some perspectives on new applications and theoretical challenges.
In this paper, a new method to handle faults for flexible satellite attitude control system during orbit maneuver is investigated. Fault tolerant control based on on-line control allocation is proposed to keep the stability and reliability of the system. First, a robust adaptive controller which considers constrained input and external disturbance is discussed. If faults occur, an on-line control allocation scheme for satellite attitude control system with actuator redundancy is adopted. In this way, fault tolerant control can be realized without reconfiguring the baseline controller. Numerical simulation is given to demonstrate the effectiveness of the methods suggested in this paper.
An eigenstructure assignment-based method for reconfigurable control systems designs is developed. When the dynamics of the process being controlled are changed due to operating condition variations, or system component failures, the proposed method is capable of reconfiguring the control system so that the eigenvalues and eigenvectors of the original closed-loop system are recovered to a maximum extent. If full state feedback is permissible, the method guarantees the stability of the reconfigured system. If only system output is accessible, the method will recover the subsequent dominant eigenvalues and eigenvectors of the original system, and the stability of the reconfigured system will be maintained if a sufficient condition derived herein is satisfied. This condition unveils some intrinsic relationships between the degree of process variations, stability margins of the original system and the stability of the reconfigured system with output feedbacks. The steady-state performance of the original system under step inputs is also recovered via an optimal selection of a closed-loop system input weighting matrix. To illustrate the effectiveness of the proposed reconfigurable control system design technique, an aircraft longitudinal control system is used to demonstrate the reconfiguration procedure.
This paper presents a novel fault diagnosis approach in satellite systems for identifying time-varying thruster faults. To overcome the difficulty in identifying time-varying thruster faults by adaptive observers, an iterative learning observer (ILO) is designed to achieve estimation of time-varying faults. The proposed ILO-based fault-identification strategy uses a learning mechanism to perform fault estimation instead of using integrators that are commonly used in classical adaptive observers. The stability of estimation-error dynamics is established and proved. An illustrative example clearly shows that time-varying thruster faults can be accurately identified.
Redundant thrusters are generally used for a reliable attitude control system. Also, redundant thrusters yield a better performance if they are used appropriately. In this paper, the authors propose an efficient redundancy management algorithm to reduce the fuel consumption. The algorithm is based on a linear programming problem which is a constrained optimization problem. For the algorithm, a cost function is defined as a quantity related to the fuel consumption for a maneuver. The independent variables are the thrusters' on-times which are control input variables of a satellite dynamic model. The advantage of the proposed method is verified by numerical examples. The examples show that the proposed method consumes less fuel than an existing method for a given maneuvering command. A sub-optimal algorithm is also discussed for an onboard computation. The proposed algorithm is applied to two maneuvers: move-to-rest and rest-to-rest. This is verified by a numerical simulation.
The performance and computational requirements of optimization methods for control allocation are evaluated. Two control allocation problems are formulated: a direct allocation method that preserves the directionality of the moment and a mixed optimization method that minimizes the error between the desired and the achieved moments as well as the control effort. The constrained optimization problems are transformed into linear programs so that they can be solved using well-tried linear programming techniques such as the simplex algorithm. A variety of techniques that can be applied for the solution of tire control allocation problem in order to accelerate computations are discussed. Performance and computational requirements are evaluated using aircraft models with different numbers of actuators and with different properties. In addition to the two optimization methods, three algorithms with low computational requirements are also implemented for comparison: a redistributed pseudoinverse technique, a quadratic programming algorithm, and a fixed-point method. The major conclusion is that constrained optimization tan be performed with computational requirements that fall within an order of magnitude of those of simpler methods. The performance gains of optimization methods, measured in terms of the error between the desired and achieved moments, are found to be small on the average but sometimes significant. A variety of issues that affect the implementation of the various algorithms in a flight-control system are discussed.
There is an increasing demand for dynamic systems to become safer, more reliable and more economical in operation. This requirement extends beyond the normally accepted safety-critical systems e.g., nuclear reactors, aircraft and many chemical processes, to systems such as autonomous vehicles and some process control systems where the system availability is vital. The field of fault diagnosis for dynamic systems (including fault detection and isolation) has become an important topic of research. Many applications of qualitative and quantitative modelling, statistical processing and neural networks are now being planned and developed in complex engineering systems. Issues of Fault Diagnosis for Dynamic Systems has been prepared by experts in fault detection and isolation (FDI) and fault diagnosis with wide ranging experience.Subjects featured include: - Real plant application studies; - Non-linear observer methods; - Robust approaches to FDI; - The use of parity equations; - Statistical process monitoring; - Qualitative modelling for diagnosis; - Parameter estimation approaches to FDI; - Fault diagnosis for descriptor systems; - FDI in inertial navigation; - Stuctured approaches to FDI; - Change detection methods; - Bio-medical studies. Researchers and industrial experts will appreciate the combination of practical issues and mathematical theory with many examples. Control engineers will profit from the application studies.
In the pseudo-inverse method (PIM) the Frobenius norm based distance between the closed loop model of the faulty system and some reference model is minimized. Stability issues are considered in the Modified PIM (MPIM). This paper proposes to use a set of admissible models, rather than searching for an optimal one which does not provide any stability / adequation guarantee. The approach allows to characterize the set of accommodable faults, and to quantify the robustness of the fault adaptation scheme. Copyright c °2005IFAC.
A new approach for the design of robust H∞ observers for a class of Lipschitz nonlinear systems with time-varying uncertainties is proposed based on linear matrix inequalities (LMIs). The admissible Lipschitz constant of the system and the disturbance attenuation level are maximized simultaneously through convex multiobjective optimization. The resulting H∞ observer guarantees asymptotic stability of the estimation error dynamics and is robust against nonlinear additive uncertainty and time-varying parametric uncertainties. Explicit norm-wise and element-wise bounds on the tolerable nonlinear uncertainty are derived. Also, a new method for the robust output feedback stabilization with H∞ performance for a class of uncertain nonlinear systems is proposed. Our solution is based on a noniterative LMI optimization and is less restrictive than the existing solutions. The bounds on the nonlinear uncertainty and multiobjective optimization obtained for the observer are also applicable to the proposed static output feedback stabilizing controller. Copyright © 2008 John Wiley & Sons, Ltd.
In this paper the problem of designing a robust controller with given structure for a plant describing a drag-free
satellite is addressed. From recent experiences in drag-free control design we first derive an uncertain plant set
representative of many drag-free missions with nonspherical test masses. The design plant is uncertain and a
performance requirement is imposed on the absolute acceleration of the test mass along a measurement axis. The
v-gap metric is first used to derive a simplified uncertain design plant. Then the main performance requirement is
broken down into requirements on the uncertain closed loop behavior of the simplified system. The fulfillment of this
new set of requirements guarantees robust achievement of the overall system goal. Then optimal single-input–singleoutput
controllers are designed that robustly achieve the desired level of performance. The method proposed allows
one to properly account for the uncertainties in the system retaining the decentralized structure of the controller
suggested by the peculiar features of the design plant.
Commercial airplanes are becoming increasingly more sophisticated, placing an increasing burden on pilots to detect and resolve the exhaustive set of possible control effector failures. Automatic techniques are needed to either reconfigure an existing control law or restructure a new control law after failure. A discrete control law has been designed for the longitudinal channel of a mildly statically unstable commercial airplane, to track the glideslope during the approach to landing phase of flight. Single effector failures with time delays for failure detection and identification are analyzed for both the reconfigured and restructured control laws, and results are compared with those from previous research using a statically stable airplane. Strategies considered include reconfiguration and restructuring with new flight conditions. Validation of all cases is made using a 6 DOF nonlinear airplane simulation.
In this paper the design of sliding mode observers for gyro and thruster fault detection and isolation in the Mars Express satellite is presented. The results are part of a project with the goal of examining the potential applicability of the sliding mode observer technique to on-board satellite deployment. A Monte Carlo campaign has been performed to assess the performance and robustness of the sliding mode FDI observers for the rigid satellite model with variations in initial conditions and parametric uncertainty. The results indicate that the observers provide good potential to isolate gyro and thruster faults. No effort were made at this stage to implement a threshold logic, but preliminary implementations are promising.
Future space missions demand high precision control in both angular and linear axes. Therefore propulsion systems providing effort in both axes with a high precision are needed. Microthrusters can satisfy these requirements. These actuators are usually subject to present an allocation problem. Moreover, because of this demand on high precision, the maximal propulsion capacity appears to be critically low, leading to a possible saturation of the actuators. A multi-saturation based model for a highly non-linear allocation function is presented. An anti-windup strategy dealing with the actuator saturation is proposed. Simulations consider a two satellites flight formation scenario. They show the improvement on performance and stability tolerance to off-nominal initial conditions. Simulations are based on a nominal model provided by Thales Alenia Space (TAS).
In this paper, a strategy based on the linear quadratic design, which progressively accommodates the feedback control law, is proposed. It significantly reduces the loss of performance that results from the time delay needed by fault accommodation algorithms to provide a solution. An aircraft example is given to illustrate the efficiency of progressive accommodation.
This paper introduces a procedure for the design of modified linear-quadratic (LQ) state-feedback controls that tolerate actuator outages. The controls improve on the known stability gain-margin properties of the standard LQ regulator by tolerating the insertion of any independent gains from zero to infinity into selected feedback loops. They also guarantee a given performance bound despite the insertion of gains from zero to two into those loops. The reliable LQ design is shown to be equivalent to a standard LQ-optimal design with a modified performance index. Thus, the design procedure is seen as a means of choosing a particular quadratic performance index for which the optimal control will possess the desired reliability properties.
A novel method is presented to synthesize a reliable controller for dynamic systems possessing actuator redundancies. The designed controller will be able to guarantee the stability and to maintain an acceptable performance of the closed-loop system in the event of actuator failures. The method is based on robust pole region assignment techniques with the help of a pre-compensator to modify the dynamic characteristics of the redundant actuator control channels. The effectiveness of this method has been verified on an aircraft bank angle control system design. The results indicate that the proposed scheme is indeed very effective in achieving the closed-loop system integrity in the presence of actuator failures.
A state feedback output tracking adaptive control scheme is developed for plants with actuator failures characterized by the failure pattern that some inputs are stuck at some unknown fixed values at unknown time instants. New controller parametrization and adaptive law are developed under some relaxed system conditions. All closed-loop signals are bounded and the plant output tracks a given reference output asymptotically, despite the uncertainties in actuator failures and plant parameters. Simulation results verify the desired adaptive control system performance in the presence of actuator failures.
In this paper, robust stabilization of a class of linear systems with norm-bounded time-varying uncertainties is considered. It is shown that for this class of uncertain systems quadratic stabilizability via linear control is equivalent to the existence of a positive definite symmetric matrix solution to a (parameter-dependent) Riccati equation. Also, a construction for the stabilizing feedback law is given in terms of the solution to the Riccati equation.
In this paper, a bibliographical review on reconfigurable (active) fault-tolerant control systems (FTCS) is presented. The existing approaches to fault detection and diagnosis (FDD) and fault-tolerant control (FTC) in a general framework of active fault-tolerant control systems (AFTCS) are considered and classified according to different criteria such as design methodologies and applications. A comparison of different approaches is briefly carried out. Focuses in the field on the current research are also addressed with emphasis on the practical application of the techniques. In total, 376 references in the open literature, dating back to 1971, are compiled to provide an overall picture of historical, current, and future developments in this area.