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The problem of optimal synthesis of a nonlinear system's control law parameters of satellite attitude control under constraints is considered. The maximum stability degree of a system is considered as an optimality criterion. The reaction wheels' control moments and angular velocities achievable within the drives' physical characteristics are considered as constraints. A linear model of the system converted from the original nonlinear model was used to solve the problem. The decomposition method, based on the transition from real time to relative time, is used to separate the tasks of optimality criterion maximization and constraints consideration. A method of synthesizing the optimal form of system transient process according to the maximum stability degree criterion is developed. An analytical method for determining the optimal values of control law parameters is proposed, based on the structural features of the linear differential equations system. A method that takes into account constraints on control moments and angular velocities of reaction wheels, based on transition scale from relative time to real time and its calculation algorithm, ensuring that conditions of all constraints are met, is developed. An example of solving the problem of optimal system synthesis is considered. The results demonstrate the effectiveness and simplicity of the proposed methods and algorithm for targeted selection of a system's technical characteristics, taking into account constraints on reaction wheels' maximum angular velocities and control moments values. [ABSTRACT FROM AUTHOR]

A closed-loop integrated model including micro-vibration disturbance, dynamic characteristics of satellite, optical system of star sensor and attitude control algorithm is established. The control torque error caused by additional disturbance torque and the star sensor imaging error caused by structural resonance is fully integrated analyzed, which are firstly presented into the attitude control system (ACS). Steady-state and transient response analyses are completed to evaluate the impact of such two errors on performances of (ACS). Steady-state response results show that the effect of control torque error appears in lower frequency band with a peak of 6.784E-8″ at 53 Hz, while influence of star sensor imaging error on attitude determination mainly concentrates in high frequency band with maximum response of 0.4101″ at 315 Hz. Transient response results show that the two errors will not significantly affect control indicators such as rise time, overshoot and peak time. The results indicate that the influence of star sensor imaging error is non-negligible for satellite ACS which required milli-arc-second attitude control accuracy. According to the analytical results, traditional analysis only on payload optical axis cannot reveal the whole impact of micro vibration on LOS error, the two errors of micro-vibration introduced to ACS in this work must be considered for the development of spacecraft with 0.1″ pointing accuracy. • A closed-loop integrated model and attitude control algorithm is established. • ACS offset caused by control torque error and star sensor imaging error induced by micro vibration are presented. • The two errors significantly affect control indicators under steady-state response condition. • Control torque error appears in lower frequency band with small magnitude. • Star sensor imaging error mainly concentrates in high frequency band with considerable magnitude. [ABSTRACT FROM AUTHOR]

The problem of optimal synthesis of a nonlinear system’s control law parameters of satellite attitude control under constraints is considered. The maximum stability degree of a system is considered as an optimality criterion. The reaction wheels’ control moments and angular velocities achievable within the drives’ physical characteristics are considered as constraints. A linear model of the system converted from the original nonlinear model was used to solve the problem. The decomposition method, based on the transition from real time to relative time, is used to separate the tasks of optimality criterion maximization and constraints consideration. A method of synthesizing the optimal form of system transient process according to the maximum stability degree criterion is developed. An analytical method for determining the optimal values of control law parameters is proposed, based on the structural features of the linear differential equations system. A method that takes into account constraints on control moments and angular velocities of reaction wheels, based on transition scale from relative time to real time and its calculation algorithm, ensuring that conditions of all constraints are met, is developed. An example of solving the problem of optimal system synthesis is considered. The results demonstrate the effectiveness and simplicity of the proposed methods and algorithm for targeted selection of a system’s technical characteristics, taking into account constraints on reaction wheels’ maximum angular velocities and control moments values.

A review of advanced fault detection and diagnosis (FDD) techniques in attitude control systems (ACSs) of spacecraft is presented. In the first part of the paper, several types of ACS failure scenarios with their practical solutions are presented. Next, the existing approaches to FDD are considered and classified based on different criteria, including applications and design techniques. The literature of this part showed that to enhance ACS operational safety, predictability of failure of an ACS and/or of its components as well as reducing the possibility of failure occurrence is imperative. In addition, fast FDD of various kinds of failures is necessary to guarantee the required reliability of an ACS. The second part of this study highlights challenges involved with different FDD approaches, emphasizing their practical applicability. Current research gaps in FDD techniques such as insensitive residual signal, process monitoring methods, accurate plant model design, easy-to-use software development, FDD tuning process, dealing with noisy sensor measurements, time taken for fault management, the sensitivity of FDD system to faults, and FDD robustness are further elaborated on. Subsequently, the state-of-the-art FDD and its future needs are reflected on. The results of this study could direct spacecraft manufacturers and ACS providers to focus on future needs and improve ground testing for enhanced operational reliability and redundancy. [ABSTRACT FROM AUTHOR]

A sliding mode (SM) re-entry control system is proposed for an assured crew re-entry vehicle (ACRV). The vehicle has a low lift/drag ratio (0.3). The trajectory controller drives the ACRV in a predefined track. The reference vectors for the attitude controller are generated by the trajectory controller and navigation system. The feedback SM controller is designed to accommodate the structural parametric uncertainties and environmental disturbances. The SM controller is optimized by both the genetic algorithm (GA) and the simulated annealing (SA) methods. A comparative study is done between both optimization methods and the efficiency of the SA method is proved. The system is subjected to a sensitivity study in terms of various thrust torque profiles. A robustness check is done by changing the system parameters. A pulse width pulse frequency (PWPF) modulator modulates the output torque dictated by the attitude controller. The simulation results demonstrate the proposed method's effectiveness in achieving the various required parameters. [ABSTRACT FROM AUTHOR]

This study proposes a combined fault diagnosis scheme based on a recurrent neural network (RNN) and an H− observer for satellite attitude control systems (ACSs) in the presence of model uncertainties, external disturbances, and measurement noise. The ACS is decoupled into multiple independent channels, such that the residuals generated by the observers respond to the corresponding faults. A novel multilayer adaptive Gaussian recurrent neural network (MAGRNN) structure is developed as an approximator to estimate the lumped disturbance; a robust term is introduced to improve accuracy. Considering the actuator fault in the finite frequency domain and the fault-sensitive index, a set of H− unknown input observers (UIOs) is designed using the output of the MAGRNN-based approximator as compensation. The existence conditions of the approximator and observer are proposed and proved. The fault diagnosis results for three cases verify that the proposed method can be used for small fault detection and isolation. [ABSTRACT FROM AUTHOR]

This work is focused on the calibration of magnetometers for the attitude control system of the SamSat-ION university nanosatellite. A calibration methodology is proposed to take into account the temperature drift of the sensors readings. Measurements are carried out in twelve static positions, with sequential cooling and heating in the temperature range from –10 to +50°С, and are used to calculate the estimates of the temperature dependences of the bias, scale factor, and nonorthogonalities of the magnetometer axes. The main results of the ground tests of the SamSat-ION onboard systems obtained in accordance with the proposed methodology are discussed. The operability of the onboard systems during and after calibration under temperature variations (rise and drop) has been confirmed. Taking into account the found parameters, affected by various temperature gradients, decreases the measurement error about twelve-fold, which makes it possible to ensure reliable operation of the attitude control and stabilization system of nanosatellites that include magnetometers. [ABSTRACT FROM AUTHOR]

This study aims to analyze the nonlinear dynamics of a satellite attitude control system equipped with reaction wheels and a PD controller. Based on the angular momentum conservation theorem for a closed mechanical system, the nonlinear equations of the attitude control system dynamics are presented as a linear system of differential equations with time-varying parameters. The asymptotic properties of the angular momentum of a mechanical system including a satellite and reaction wheels as rigid bodies are investigated. A relation has been established between the dynamic parameters of the attitude control system and the initial value of the angular momentum of the satellite. The issue of asymptotic stability for differential equations with time-varying parameters is simplified to the asymptotic stability problem for the ultimate homogeneous system of linear differential equations with constant elements. The dependencies of the dynamic parameters of the attitude control system on the constant parameters of this ultimate system of linear differential equations, as well as the initial values of the satellite's angular momentum, enable us to apply proven and effective engineering methods. These methods are used not only for analyzing the stability of the control system but also for synthesizing the parameters of the control law based on the quality requirements of transient processes such as the stability margin, responsiveness, oscillation, transient time, and overshoot. In this case, the calculation of the control law parameters will be grounded in exact equations, not on approximate equations of the control system dynamics obtained by linearization. [ABSTRACT FROM AUTHOR]

ObjectiveIn order to improve the attitude control performance of a remote operated vehicle (ROV) in complex underwater environments, the attitude control of ROV with multi-motor coordinated propulsion is studied. MethodsFirst, for the structure and algorithm of the multi-motor system, a deviation coupling structure based on a PID speed compensator and a new non-singular terminal sliding mode control (SMC) algorithm are respectively proposed, and a novel ROV attitude control method based on multi-motor cooperative propulsion is designed. The kinematic and dynamic model of an ROV is then established, the thrust analysis of the thruster group is carried out, and the decoupling simplified ROV dynamic model is developed. Finally, the ROV sliding mode attitude controller is designed. ResultsThe simulation results show that the structure and algorithm proposed in this paper improve the anti-interference, synchronization and rapid response capabilities of the multi-motor system, thereby enhancing the stability and robustness of the ROV attitude control system. ConclusionThis method can provide a new solution for ROV attitude control.

The influence of Earth's gravity and lunar-solar disturbances can cause a geostationary satellite to deviate from its intended position. To counteract this, periodic stationkeeping maneuvers are necessary. These maneuvers depend on the attitude control system to maintain stability and ensure the satellite's antenna remains directed towards the Earth station, ensuring mission services. This paper presents a design contribution to the attitude control system of a geostationary satellite, specifically during north-south station-keeping maneuvers. To effectively manage the satellite's position within a designated station-keeping box and control its attitude in three axes, a minimum of six 10 N chemical thrusters is required. The thruster configuration is designed to calculate torque parameters by considering the thrust vector, satellite mass, and the forces and moments acting upon them. The satellite model used in this study includes a rigid satellite dynamics model, perturbation model, PD controller, pseudo-rate modulator, and logic thruster selector. Once the system design is complete, numerical simulations can validate its performance and effectiveness. The simulation results confirm that all requirements have been met and the station-keeping design has been successfully implemented. [ABSTRACT FROM AUTHOR]

This study aims to analyze the nonlinear dynamics of a satellite attitude control system equipped with reaction wheels and a PD controller. Based on the angular momentum conservation theorem for a closed mechanical system, the nonlinear equations of the attitude control system dynamics are presented as a linear system of differential equations with time-varying parameters. The asymptotic properties of the angular momentum of a mechanical system including a satellite and reaction wheels as rigid bodies are investigated. A relation has been established between the dynamic parameters of the attitude control system and the initial value of the angular momentum of the satellite. The issue of asymptotic stability for differential equations with time-varying parameters is simplified to the asymptotic stability problem for the ultimate homogeneous system of linear differential equations with constant elements. The dependencies of the dynamic parameters of the attitude control system on the constant parameters of this ultimate system of linear differential equations, as well as the initial values of the satellite’s angular momentum, enable us to apply proven and effective engineering methods. These methods are used not only for analyzing the stability of the control system but also for synthesizing the parameters of the control law based on the quality requirements of transient processes such as the stability margin, responsiveness, oscillation, transient time, and overshoot. In this case, the calculation of the control law parameters will be grounded in exact equations, not on approximate equations of the control system dynamics obtained by linearization.

Many satellites are required to be pointed at a target with high accuracy, a task which can in some scenarios be either better or only performed using thrusters. Control algorithms are well studied for solving this problem around a single axis using on/off thrusters, but not for cases where significant inter-axis coupling is present in the moment of inertia or thruster torque matrices, as is often the case when using commercial-off-the-shelf components in nanosatellites. This work proposes a linear programming-based method for applying single-axis phase plane control techniques in a multi-axis environment, while minimizing fuel usage and obeying constraints on minimum impulse bit and pointing accuracy. A multi-axis extension of a feedback pulse-width pulse-frequency modulation scheme is also developed. Simulations are performed where these methods are compared to existing multi-axis control techniques in the presence of realistic disturbances and non-ideal thruster behaviour. [ABSTRACT FROM AUTHOR]

Aerodynamics of two capsules of different conception both equipped with aerodynamic control surfaces has been compared at high-altitude Earth reentry path. The capsules are comparable in size but completely different in shape and, hence, in the aerodynamic behavior. The capsules are: 1) a circular cylinder provided with four flapped fins (finned cylinder), 2) a capsule, here tagged as Reentry Space Vehicle (RSV), very similar in shape and dimensions to the Intermediate eXperimental Vehicle. The study was carried out computationally in hypersonic, rarefied flow in terms of aerodynamic global coefficients (lift, drag, moments, etc.) computed by a three-dimensional direct simulation Monte Carlo code at the altitudes of 100 and 120 km, in the interval of angles of attack 0-50 deg and with flap angles of 0 and 20 deg. Computations verified that while RSV exerts a stronger aerodynamic force for the reduction of the capsule reentry velocity, the finned cylinder is better in terms of the attitude control capability. In fact, equilibrium of the finned cylinder is stable at zero angle of attack at the two altitudes, whereas the angle of attack of stable equilibrium of RSV changes with altitude. Hence, RSV needs to be provided with an active attitude control system. [ABSTRACT FROM AUTHOR]

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The article is devoted to the development and application of control moment gyroscopes used for active triaxial attitude control of spacecraft. These gyroscopes belong to the class of inertial actuators, which also includes flywheel control motors, gyro dampers, and passive gyrostabilizers. A distinctive feature of control moment gyroscopes (CMG) is the presence of special drives that control the rotation of the gyroscope relative to its suspension axes. By regulating the speed of this rotation, the drive creates the required control moment. The paper describes the main development stages of Russian CMG and systems based on them, the features of their design and architecture, application issues and development trends. [ABSTRACT FROM AUTHOR]

An active attitude control system using a novel six-layer electromagnetic embedded printed magnetorquer for a 3-U nanosatellite is presented in this paper. The proposed design was optimized in terms of size, dissipated power, torque produced, and generated magnetic dipole moment. The designed printed magnetorquer is the optimum choice for a 3-U small-satellite attitude stabilization in terms of reconfigurability, modularity, lower space occupation, low mass, and lower cost. The printed magnetorquer was designed and analyzed for a 3-U nanosatellite with CubeSat standard dimensions of 10×10×30 cm3. The design was implemented with commercial off-the-shelf (COTS) high-performance microdevices that are reliable and easily accessible for reducing procurement cost. The printed magnetorquer was embedded in internal layers of a printed circuit board (PCB) that does not require additional space on the satellite. Time-varying rotational analyses were performed for various coil arrangements to test the rotation times for spin-stabilized 3-U nanosatellites. Thermal analysis of the 3-U nanosatellite was done to sustain thermal operation and satisfy the feasibility requirements of the system. Essential performance parameters like magnetic moment generated, resultant torque, and power dissipation were examined for comparison with the existing commercial state of the art. The proposed printed magnetorquer with more configurability (2×3 , 3×2 , 1×18 , 18×1 , 9×2 , 6×3 hybrid) features provides versatility to the design aspects by changing the configuration through the onboard computer according to mission needs. [ABSTRACT FROM AUTHOR]

The thruster fault diagnosis problem of the satellite attitude control system is investigated in this article. This challenging problem is first changed into the binary image classification issue. A deep learning based data-driven fault diagnosis approach is then presented. It benefits from this approach that the stuck-open and the stuck-close faults of thruster are detected, diagnosed, and located online with high accuracy. The proposed method is purely data-driven and directly implemented by using raw measurement data only. It is independent of the dynamics of the thruster and the mathematical model of the satellite attitude control system. The effectiveness of the proposed approach is finally demonstrated on a satellite example. [ABSTRACT FROM AUTHOR]

In this article, a L1 neural network adaptive fault-tolerant controller is exploited for an unmanned aerial vehicle attitude control system in presence of nonlinear uncertainties, such as system uncertainties, external disturbances, and actuator faults. A nonlinear dynamic inversion controller with sliding mode control law is designed as the outer-loop controller to track the attitude angles quickly and accurately which reduces dependence on model accuracy. A L1 neural network adaptive controller of the inner loop is introduced to compensate the nonlinear uncertainties and have a good attitude tracking. The radial basis function neural network technique is introduced to approximate a lumped nonlinear uncertainty and guarantee the stability and transient performance of the closed-loop system, instead of converting it to a half-time linear system by the parametric linearization method. Simulation results demonstrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

Digital twin has become a critical technical solution for satellite in-orbit service and maintenance. The majority of existing research in this field has focused on constructing system-level digital twins, with various typical applications that primarily describe the operating condition of satellite subsystems. However, achieving a more meticulous portrayal of in-orbit satellites necessitates the inclusion of physical field information, e.g., the temperature field serves as a fundamental basis for characterizing the thermodynamic state and plays a crucial role in precise thermal management of a satellite. The main challenge for realizing thorough state detection and real-time response lies in the cross-level model fusion of system simulation and physical field calculation. To overcome this problem, this paper proposes a Hybrid Digital Twin (HDT) framework that seamlessly integrates the digital twin at the system-level with its physical field-level counterpart, enabling a comprehensive and detailed representation of modeling objects. Specifically, at the physical field-level, deep learning methods are utilized to construct an accurate surrogate model, offering a lightweight, computationally efficient and accelerated execution alternative to the Finite Element Analysis models. At the system-level, multi-domain unified modeling technology is employed to ensure both efficiency and accuracy of coupling simulation. Moreover, a co-simulation approach is developed on the basis of the Functional Mock-up Interface, overcoming the bottleneck of cross-level information interaction and computing time synchronization. The practical utility of the proposed framework is verified by a real-world engineering problem, i.e., satellite temperature field perception and attitude control in the context of the harsh space environment. Whole process engineering experiments demonstrate the effectiveness of the HDT, with mean absolute errors below 1 K for temperature field reconstruction and within 1° for attitude control. [ABSTRACT FROM AUTHOR]

Summary: This article is devoted to the problem of attitude control for rigid spacecraft subject to multiple disturbances. Due to the limited communication and storage resource, an event‐triggered anti‐disturbance attitude control approach is proposed for the attitude control system (ACS) with multiple disturbances. Different from some existing event‐triggered attitude control methods, the multiple disturbances are considered and can be divided into an uncertain modeled disturbance and a norm bounded equivalent disturbance. A disturbance observer is designed to estimate the modeled disturbance. Based on the framework of disturbance observer‐based control, the proposed event‐triggered anti‐disturbance controller can guarantee that the ACS converges toward a small invariant set, which successfully avoids continuous communication and Zeno phenomenon. Finally, simulation results are given to demonstrate the efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

At present, the methods based on using linearized dynamical equations are applied for syn- thesis of an attitude control system of a satellite with nonlinear dynamics. Linearized equa- tions describe the satellite dynamics approximately, which is the main their disadvantage. This article shows that basing on the angular momentum theorem, the nonlinear dynamical equations of the satellite attitude control system can be represented in the form of linear differential equations with variable coefficients, which makes it possible to use engineering methods of stability analysis and analysis of transient quality in the process of synthesis of the satellite attitude control system. [ABSTRACT FROM AUTHOR]

The Space Robotics Laboratory (SRL) of Tohoku University and ALE Co., Ltd. have developed a 60-kg-class microsatellite ALE-1, which generates artificial meteors by releasing meteor source pellets towards the Earth. The purpose of this research is to establish a system for ground evaluation and operation training of ALE-1. This satellite requires an accurate orbit and attitude determination technique for operation safety and mission success. A triple redundant system with multiple independent sensors is adopted for ensuring safe operation. A generic ground evaluation system "MEVIμS" is applied to evaluate such a complicated satellite bus system. MEVIμS has a high reliability and flexibility based on the results of its application to past micro-satellite projects. This system contains a satellite simulator with a space dynamics calculator with a high accuracy as well as mathematical models of the space environment and satellite components. A hardware-in-the-loop simulation can be carried out to evaluate the satellite hardware with on-board software by connecting to the simulator virtually. The performance evaluation of the attitude control system and comprehensive mission operational tests were carried out by MEVIμS. The simulation result demonstrated that ALE-1 reached a sufficient level of attitude control accuracy to realize the mission. The result also confirmed that the mission sequence was performed successfully as the mission feasibility and the operation safety were validated. ALE-1 was launched by the fourth Epsilon rocket on January 18, 2019 and initial operation is in progress. Further improvement of the ALE-1 system can be executed by repeated operation training under various conditions to enhance the chance of mission success. [ABSTRACT FROM AUTHOR]

This paper proposes a multiple fault diagnosis (MFD) scheme based on an observer method for satellite attitude control systems (ACSs) subject to nonlinearity and external disturbances of the system. The essential idea is to develop a fault diagnosis scheme and design the corresponding observers for satellite ACSs. The nonlinearity, space external disturbances, sensor uncertainties, and multiple faults problem of the satellite ACS are all taken into account. The proposed MFD scheme is developed at two different levels. First, at the system level, two nonlinear observers based on analytical redundancy are designed for the MFD of the satellite ACS; this level roughly reveals the fault source. Then, at the component level, a bank of sliding mode observers activated by the results of the previous diagnosis is designed to precisely diagnose multiple faults of actuators in the satellite ACS; this level further precisely reveals the fault source. Both the nonlinear observers and the sliding mode observers are confirmed to be asymptotically stable via Lyapunov stability theory. Finally, numerical simulations of a satellite ACS are performed to illustrate the effectiveness of the proposed MFD scheme. [ABSTRACT FROM AUTHOR]