Satellite Attitude Dynamics Research Articles

High-Accuracy, Vision-Based Attitude Estimation System for Air-Bearing Spacecraft Simulators

Air-bearing platforms for simulating the attitude dynamics of satellites require highly accurate ground truth systems. Commercial off-the-shelf motion-capture systems are used for this scope, although they are complex and expensive. This paper shows a novel and versatile method to estimate the attitude of rotational air-bearing platforms using a monocular camera and sets of fiducial LED markers. The work proposes a geometry-based, iterative algorithm that is significantly more accurate than other literature methods that involve solving the perspective-n-point problem. Additionally, autocalibration procedures to perform a preliminary estimation of the system parameters are shown. The developed methodology is deployed onto a Raspberry Pi 4 microcomputer and tested with an array of LEDs soldered on a custom printed circuit board. Data obtained with this setup are compared against simulations of the system to determine and validate its performance. The hardware setup is also validated against independent inclinometric and gyroscope sensor measurements. Simulation and test results show expected 1-sigma accuracies of 12 arcs and 37 arcs for about- and cross-boresight rotations of the platform, respectively, and average latency times of 6 ms.

Detection and Analysis of Anomalous Behavior in On-Orbit Satellites Using AI Algorithms

The increasing deployment of satellites for essential applications necessitates robust anomaly detection to maintain their operational integrity. Traditional methods, which depend on manual monitoring and predefined thresholds, often prove inadequate in the complex space environment. This paper investigates the application of Artificial Intelligence (AI) algorithms to improve the detection and analysis of anomalous behavior in on-orbit satellites. AI, especially through machine learning (ML) and deep learning (DL), provides advanced capabilities for processing extensive telemetry data and identifying intricate patterns. By leveraging historical data, AI systems can establish normal operational parameters and detect deviations indicating potential anomalies. Techniques such as supervised and unsupervised learning are employed to develop models with high predictive accuracy. Furthermore, AI facilitates root cause analysis by correlating anomalies with operational conditions or external factors, enabling effective corrective measures. The integration of AI also promotes autonomous satellite operations, which are crucial for deep-space missions. This advancement enhances satellite reliability and safety, supporting sustainable and progressive space exploration. In this research, machine learning algorithms were employed to develop the proposed anomaly detection system. The system aims to detect subtle failures in the spacecraft’s attitude dynamics system, particularly in the reaction wheel subsystem, by learning solely from the spacecraft's nominal behavioral data. The system was developed from a small satellite's attitude dynamics control system, which may exhibit bearing failures in the reaction wheels. Two types of anomaly detection systems were introduced: a two-sided learning anomaly detection system and a one-sided learning anomaly detection system. For this study, a two-sided learning anomaly detection system was developed using the Logistic Regression (LR) method. This provided a foundation for the training process using a machine learning approach. By learning from both nominal and failure behaviors of the satellite, the system was designed to detect small reaction wheel friction failures effectively.

Estimation of satellite attitude dynamics and external torques via mixed Kalman/H-infinity filter under inertia uncertainties

Estimation of satellite attitude dynamics and external torques via mixed Kalman/H-infinity filter under inertia uncertainties

Variable-structure PD controller for satellite attitude: Stability analysis and design for optimal performance

A novel variable structure controller is investigated for satellite attitude control. This novel controller does not lead to a sliding mode, which avoids the chattering problem, making it suitable for practical implementation. Detailed formulation of the controller is presented along with analytical stability analysis for a second order system. The system having this nonlinear controller is homogeneous, which leads to a similar response at large and small deviations from the equilibrium. A procedure for tuning homogeneous controllers for all initial conditions is proposed. A detailed model of the satellite attitude dynamics, actuator dynamics, and delays in the system is utilized to optimize controller gains numerically. A comparative analysis shows the superiority of the proposed controller over a conventional PID controller in terms of better transients and lower energy consumption.

Uncertain optimal attitude control for space power satellite based on interval Riccati equation with non-probabilistic time-dependent reliability

Considering the multi-source uncertainties and disturbances in the attitude dynamics of space power satellite (SPS), an interval dynamic model of SPS is proposed based on the non-probabilistic theory, which is controlled by a novel uncertainty-based linear–quadratic regulator (LQR) method with time-dependent reliability. Based on the interval analysis method, an interval time-varying attitude dynamic model of SPS for sun-pointing is established considering the uncertain inertia and initial states as unknown-but-bounded parameters. Feedforward and feedback controllers are designed to offset the disturbance and control attitude, respectively. An interval Riccati equation-based optimal control method is proposed to develop a novel uncertainty-based LQR method. Non-probabilistic time-dependent reliability is constituted based on the interval process and first passage theory to assess attitude states. An uncertain multi-objective optimization of attitude control with reliability constraints is proposed to realize the uncertain LQR method. Verified by a numerical example of SPS, the proposed method takes only 0.6‰∼0.8‰ time consumption of 10,000 Monte Carlo simulations while maintaining a certain accuracy.

Satellite Attitude Control Using Double-Gimbal Variable-Speed Control Moment Gyro with Unbalanced Rotor

Attitude dynamics of a rigid satellite actuated using a double-gimbal variable-speed control moment gyro (DGVSCMG) with an unbalanced rotor is derived in the framework of geometric mechanics. The proposed formulation accounts for dynamics of the gimbal motors and the rotor motor for finding the required motor torque to actuate the satellite along with the DGVSCMG for achieving high-precision attitude control. The satellite attitude control is accomplished using a proposed cascaded adaptive fixed-time sliding mode control to ensure bounded finite-time convergence. A sliding manifold is also designed to ensure convergence of gimbals angular rates to the desired values. Actuator saturation, system uncertainties such as intrinsic disturbance torques due to the gimbals and rotor bearing friction, extrinsic disturbances due to the environmental factors, and uncertainty in inertia of the satellite bus are accounted for designing the controller. Lyapunov stability analysis is carried out to prove bounded finite-time stability of the proposed system. Simulation results are presented to substantiate the claim made assuming the rigid satellite to be equipped with only one DGVSCMG.

Attitude dynamics of satellites with variable shape mechanisms using atmospheric drag torque and gravity gradient torque

Disturbance torques, such as atmospheric drag torque and gravity gradient torque, have always been an issue in attitude control for satellites in low Earth orbit. Although attitude control systems using disturbance torques has been studied with various methods, most previous research has focused on attitude control using aerodynamic stability to remove disturbances. We propose a new attitude control system that actively uses disturbance torque. This system controls the attitude using disturbance torques by changing the equilibrium point of the attitude motion by changing the shape of the satellite. We formulate the attitude dynamics of a variable-shape satellite as a preliminary study. This paper shows that the satellite attitude can be adjusted by varying the equilibrium point of attitude motion by changing the satellite shape. Also, we investigate the stability around the equilibrium point for each shape, and the results show the distribution of the stability index and the equilibrium point for each shape. Finally, we show that the attitude asymptotically converges to an equilibrium point by using the variable shape function and magnetic control.

Adaptive chaos synchronization of an attitude control of satellite: A backstepping based sliding mode approach

This paper uses adaptive backstepping sliding mode control to synchronize two satellite attitude dynamics with perturbing torques. The external perturbing torques induce chaotic motion with no control inputs. The proposed control system uses Lyapunov theory and Barbalat's Lemma to guarantee the asymptotic stability of the controlled system. Simulation results confirm the effectiveness of the proposed design.

Chaotic pitch motion of an aerodynamically stabilized magnetic satellite in polar orbits

The paper is devoted to the chaotic attitude dynamics of magnetic satellites with stabilizing panels. The pitch motion under the gravitational and restoring aerodynamic torques and small perturbations, namely, the magnetic torque and the aerodynamic damping, is considered. On the example of a CubeSat having an aerodynamic instability, it is demonstrated that the unperturbed phase space evolves with orbital altitude both quantitatively and qualitatively, forming different sets of homoclinic and heteroclinic trajectories. The Melnikov method is used to find the combinations of system parameters resulting in regular and chaotic motions. The occurrence of chaos is verified by means of Poincaré sections.

Orbit–attitude dynamics and control of spacecraft hovering over a captured asteroid in the earth–moon system

Orbit–attitude dynamics and control of spacecraft hovering over a captured asteroid in the earth–moon system

Attitude estimation and control based on modified unscented Kalman filter for gyro-less satellite with faulty sensors

A modified unscented Kalman filter is presented to estimate the quaternion parameters as well as the angular velocities of a rigid gyro-less satellite under faulty sensor conditions. The task is carried out using the Sun sensor and magnetometers as attitude sensors with bounded noise and unknown fault(s). Following the presentation of the satellite attitude dynamics and filtering formulations, a new fault detection and isolation algorithm is proposed. The latter is based on a modified unscented Kalman filter structure for improved fault detection, sensor isolation, and attitude control (AC). A Backtracking Search Algorithm (BSA) is also used to design and optimize the PID controller gains, as well as to optimize sensor installation orientation for residual signal decoupling. In this regard, the paper presents and proves a theory that describes how the proposed optimization process for sensor installation can analytically decouple the faulty orientation signal from the healthy ones. A comparison of attitude and angular velocity estimation approaches using the standard Kalman, extended Kalman, and a proposed modified unscented Kalman filter is also provided. The results show that the proposed filter performs significantly better in closed-loop AC systems and copes adequately with sensor faults.

Coupled orbit-attitude dynamics and trajectory tracking control for spacecraft electromagnetic docking

In this paper, the simplified electromagnetic force/torque model and coupled orbit-attitude dynamics modeling in spacecraft electromagnetic docking are investigated, and an improved sliding mode control scheme based on planned trajectory is proposed. In this scenario, the docking two spacecraft are equipped with four energized solenoids with iron cores fixed in the body frame, and small-angle hypothesis is used to derive the simplified electromagnetic force/torque model, based on which the coupled orbit-attitude dynamics equation is established. With trajectory planning of relative orbit and attitude, where the tracking process of coupled orbit-attitude is divided into three successive parts with predefined time using three characteristic time instants, a sliding mode control strategy is proposed to solve the tracking problem. Simulation results illustrate the simplification rationality of electromagnetic force/torque model, and the good tracking performance of coupled orbit-attitude tracking controller at predefined time.

Observer-based robust actuator fault isolation and identification for microsatellite attitude control systems

Purpose The purpose of this paper is to accomplish robust actuator fault isolation and identification for microsatellite attitude control systems (ACSs) subject to a series of space disturbance torques and gyro drifts. Design/methodology/approach For the satellite attitude dynamics with Lipschitz constraint, a multi-objective nonlinear unknown input observer (NUIO) is explored to accomplish robust actuator fault isolation based on a synthesis of Hinf techniques and regional pole assignment technique. Subsequently, a novel disturbance-decoupling learning observer (D2LO) is proposed to identify the isolated actuator fault accurately. Additionally, the design of the NUIO and the D2LO are reformulated into convex optimization problems involving linear matrix inequalities (LMIs), which can be readily solved using standard LMI tools. Findings The simulation studies on a microsatellite example are performed to prove the effectiveness and applicability of the proposed robust actuator fault isolation and identification methodologies. Practical implications This research includes implications for the enhancement of reliability and safety of on-orbit microsatellites. Originality/value This study proposes novel NUIO-based robust fault isolation and D2LO-based robust fault identification methodologies for spacecraft ACSs subject to a series of space disturbance torques and gyro drifts.

Floquet modes and stability analysis of periodic orbit-attitude solutions along Earth\u2013Moon halo orbits

Future space programmes pose some interesting research problems in the field of non-Keplerian dynamics, being the Moon and the cislunar space central in the proposed roadmap for the future space exploration. In these regards, the deployment of a cislunar space station on a non-Keplerian orbit in the lunar vicinity is a fundamental milestone to be achieved. The paper investigates the natural orbit-attitude dynamics and the attitude stabilisation of coupled motions for extended bodies in the Earth–Moon system. The discussion is carried out analysing the phase space of natural dynamics, constituted by both the orbital and the rotational periodic motions of a spacecraft in cislunar orbits. Floquet theory is applied to periodic orbit-attitude solutions in lunar proximity, to characterise their attitude stability properties and their attitude manifolds, which are discussed and analysed focusing on their dynamical features applicable to cislunar environment. Attitude stabilisation methods are proposed and developed, with particular attention to spin-stabilised solutions. Periodic orbit-attitude dynamics are studied to highlight possible favourable conditions that may be exploited to host a cislunar space station with a simplified control action. The focus of the analysis is dedicated to halo orbits and near-rectilinear halo orbit in the circular restricted three-body problem Earth–Moon system.

Full attitude state reconstruction of tumbling space debris TOPEX/Poseidon via light-curve inversion with Quanta Photogrammetry

The tumbling motion of defunct satellite TOPEX/Poseidon (T/P) is governed by the μ-scale Solar Radiation Pressure (SRP) torque that spun up the satellite from the initial, nadir-pointing to the current fast spinning state [1]. In this paper, we advance the methods of Quanta Photogrammetry (QPM) in an effort to determine satellite attitude parameters – the inertial orientation of the body angular momentum vector L, the rotational phase and rate as well as the object pole coordinates with respect to L; the determined pole offset is 3.52°. The presented data support the hypothesis that the full characteristics of the satellite attitude dynamics can be obtained from a single radiant photogram measured by the photon-counting system of the Graz Satellite Laser Ranging (SLR) Observatory during an overhead pass.The analysis of the observed radiant signature of T/P gives the elevation angle of the normal vector to the solar array front surface at −1.7°, RMS = 0.63°, in the spacecraft body-centered reference frame. This information, along with the pole position, is used to model the SRP forces and torques on the satellite and determine the T/P moment of inertia I=69728,σI=75.2[kgm2], by best-fitting long-term spin simulation to the observed trend.

Fast real-time SDRE controllers using neural networks

This paper describes the implementation of fast state-dependent Riccati equation (SDRE) control algorithms through the use of shallow and deep artificial neural networks (ANN). Several ANNs are trained to replicate an SDRE controller developed for a satellite attitude dynamics simulator (SADS) to display the technique’s efficacy. The neural controllers have reduced computational complexity compared with the original SDRE controller, allowing its execution at a significantly higher rate. One of the neural controllers was validated using the SADS in a practical experiment. The experimental results indicate that the training error is sufficiently small for the neural controller to perform equivalently to the original SDRE controller.

Periodic attitude motions along planar orbits in the elliptic restricted three-body problem

A way to improve the accuracy of the three-body problem model is taking into account the eccentricity of primary attractors. Elliptic Restricted Three-Body Problem (ER3BP) is a model for studying spacecraft trajectory within the three-body problem such that the orbital eccentricity of primaries is reflected in it. As the principal cause of perturbation in the employed dynamical model, the primaries eccentricity changes the structure of orbits compared to the ideal Circular Restricted Three-Body Problem (CR3BP). It also changes the attitude behavior of a spacecraft revolving along periodic orbits in this regime. In this paper, the coupled orbit-attitude dynamics of a spacecraft in the ER3BP are exploited to find precise periodic solutions as the spacecraft is considered to be in planar orbits around Lagrangian points and Distant Retrograde Orbits (DRO). Periodic solutions are repetitious behaviors in which spacecraft whole dynamics are repeated periodically, these periodic behaviors are the main interest of this study because they are beneficial for future mission designs and allow delineation of the system’s governing dynamics. Previous studies laid the foundation for spacecraft stability analysis or studying pitch motion of spacecraft in the ER3BP regime. While in this paper, at first, initial guesses for correction algorithms were derived through verified search methods, then correction algorithms were used to refine calculated orbit-attitude periodic behaviors. Periodic orbits and full periodic solutions are portrayed and compared to previous studies and simpler models. Natural periodic solutions are valuable information eventuate in the longer functional lifetime of spacecraft. Since the problem assumption considered in this paper is much closer to real mission conditions, these results may be the means to use natural bounded motions in the actual operational environment.

Characterisation of 6DOF natural and controlled relative dynamics in cislunar space

At the 50th anniversary of Apollo 11, the Moon is back to the scene of scientific and commercial space exploration interests. During the next decade, the establishment of a Gateway in cislunar non-Keplerian orbits will open the space frontiers to sustainable manned and robotic missions on and around the Moon. Such infrastructure will require several logistic operations for its assembly and maintenance, which lean on rendezvous and docking capabilities. Even if few missions have flown on non-Keplerian orbits, Rendezvous and Docking (RV&D) operations have not been performed but in Low Earth Orbit (LEO). Investigations about 6 Degrees Of Freedom (DOF) relative dynamics in non-Keplerian environment are now mandatory to highlight criticalities in the design of the cislunar gateway and to translate RV&D protocols, consolidated in LEO for the International Space Station (ISS), to the new non-Keplerian environment. In this direction, the paper analyses the 6DOF natural orbit-attitude dynamics within the Circular Restricted Three-Body Problem (CR3BP) framework. A novel perspective of the dynamical structures, constituting 6DOF manifolds, allows to better characterise the natural relative dynamics in proximity of non-Keplerian orbits. The importance of orbit-attitude manifolds exploitation is underlined for designing reliable and efficient rendezvous trajectories, enhanced by natural cislunar dynamics.Then, an ephemeris cislunar dynamical model is exploited to address guidance laws for proximity operations. The control capability is included in the dynamics of a chaser vehicle, which is employed to solve the 6DOF guidance problem in proximity of a target spacecraft. The results obtained with the controlled dynamics are compared to those available thanks to natural motion, discussing the energetic and time costs to complete the manoeuvres. A control parametrisation to solve the optimal energy rendezvous problem is proposed.Finally, a feasible operational rendezvous scenario is discussed about the identified favourable locations along the non-Keplerian orbit to perform complex proximity operations. Significant relations between RV&D time and non-Keplerian orbit’s period are discussed as well.

SVD-Aided EKF with Process Noise Covariance Adaptation Applied to Satellite Attitude Dynamics

SVD-Aided EKF with Process Noise Covariance Adaptation Applied to Satellite Attitude Dynamics

Geometric robust adaptive control for satellite attitude tracking with reaction wheels

This study proposes a new robust adaptive tracking controller for satellite attitude dynamics with reaction wheel assembly. With the attitude kinematics represented by rotation matrix, the attitude control system is formulated to accommodate bounded disturbances and uncertain moment of inertia. The associated error dynamics are developed directly in SO(3) from geometric mechanics. Almost global asymptotic stability is formally proved in the sense of Lyapunov by using the geometry. The proposed controller is then applied to both numerical simulations and hardware experiments. It works well for our own developed spacecraft testbed for three experimental scenarios, even with disturbances/uncertainties caused by offsets of the center of mass and air-bearing. The selection of proportional gain dominantly affects the characteristics of attitude tracking. According to numerical simulations and hardware experiments, the proposed controller performs well, even when the measurement accuracy of angular velocity is low.