Finite-Time Controller for Flexible Satellite Attitude Fast and Large-Angle Maneuver

In order to deal with the fast, large-angle attitude maneuver with flexible appendages, a finite-time attitude controller is proposed in this paper. The finite-time sliding mode is constructed by implementing the dynamic sliding mode method; the sliding mode parameter is constructed to be time-varying; hence, the system could have a better convergence rate. The updated law of the sliding mode parameter is designed, and the performance of the standard sliding mode is largely improved; meanwhile, the inherent robustness could be maintained. In order to ensure the system’s state could converge along the proposed sliding mode, a finite-time controller is designed, and an auxiliary term is designed to deal with the torque caused by flexible vibration; hence, the vibration caused by flexible appendages could be suppressed. System stability is analyzed by the Lyapunov method, and the superiority of the proposed controller is demonstrated by numerical simulation.

Structured H∞ Control for Spacecraft with Flexible Appendages

Spacecraft with large flexible appendages are characterized by multiple system modes. They suffer from inherent low-frequency disturbances in the operating environment that consequently result in considerable interference in the operational performance of the system. It is required that the control design ensures the system’s high pointing precision, and it is also necessary to suppress low-frequency resonant interference as well as take into account multiple performance criteria such as attitude stability and bandwidth constraints. Aiming at the comprehensive control problem of this kind of flexible spacecraft, we propose a control strategy using a structured H-infinity controller with low complexity that was designed to meet the multiple performance requirements, so as to reduce the project cost and implementation difficulty. According to the specific resonant mode of the system, the design strategy of adding an internal mode controller, a trap filter, and a series PID controller to the structured controller is proposed, so as to achieve the comprehensive control goals through cooperative control of multiple control modules. A spacecraft with flexible appendages (solar array) is presented as an illustrative example in which a weighted function was designed for each performance requirement of the system (namely robustness, stability, bandwidth limit, etc.), and a structured comprehensive performance matrix with multiple performance weights and decoupled outputs was constructed. A structured H-infinity controller meeting the comprehensive performance requirements is given, which provides a structured integrated control method with low complexity for large flexible systems that is convenient for engineering practice, and provides a theoretical basis and reference examples for structured H-infinity control. The simulation results show that the proposed controller gives better control performance compared with the traditional H-infinity one, and can successfully suppress the vibration of large flexible appendages at 0.12 Hz and 0.66 Hz.

General Planar Motion Modeling and Control of a Smart Rigid-Flexible Satellite Considering Large Deformations

In this paper, the motion of a smart rigid-flexible satellite by considering large deformations for its flexible appendages in general planar motion is modeled. Therefore, the satellite can experience translational and rotational motions also its flexible appendages can vibrate arbitrarily in the motion plane. Two control forces perpendicular to each other and one control torque are responsible for controlling the motion of the satellite on the desired trajectories. Also, piezoelectric actuators and sensors suppress vibrations and estimate the transverse displacement of the satellite's flexible appendages, respectively. The coupled ordinary-partial differential equations of motion, equations of the sensors, and boundary conditions of the system are obtained using extended Hamilton's principle. Then, these equations are discretized using the Galerkin method. The discretized equations of motion are a set of coupled nonlinear ordinary differential equations due to the consideration of the large rotation angle of the satellite and large deformations for its flexible appendages. Adaptive super-twisting global nonlinear sliding mode controller is designed to satisfy the control objectives including position and attitude control, as well as suppressing vibrations of the flexible appendages in the presence of uncertainties and external disturbances. Eventually, numerical simulations are presented to illustrate the effectiveness of the proposed controller.

Configuration optimization of photogrammetry system based on spectral radius for on-orbit measurement

Non-contact optical measurement is a potential approach to on-orbit vibration measurement for flexible appendages, providing dynamic information for spacecraft control system. Binocular photogrammetry system is a practical configuration to achieve this measurement. In this paper, optimization approach and strategy for configuration parameters of this system are raised. Measurement matrix is specially defined to obtain the objective function for the optimization. Successive linear programming algorithm is used for optimization iteration. Transient responses of flexible appendages calculated by finite element model and corresponding images generated by OpenGL help to achieve this simulation-based optimization. The feasibility and effectiveness of the optimization are verified both by numerical study and experiment. Error analysis of the optimal system reveals great improvement in accuracy and robustness after optimization. This optimization is a promising approach to designing the configuration of binocular photogrammetry system and helping to achieve reliable on-orbit dynamic measurement results.

Large-scale flexible spacecraft mass properties determination using torque-generating control

It is necessary to determine the mass properties of an on-orbit large-scale flexible spacecraft in order to achieve high-precision attitude control. The mass properties of the spacecraft include the inertia, the center of mass, and the mass. Research in this area had been mostly focused on rigid spacecrafts. The coupling between the rigid body of the spacecraft and the large flexible appendages on it, however, could have significant effect on the mass properties determination. This article proposes a momentum conservation–based determination method that takes into consideration the rigid–flexible coupling factors of large-scale flexible spacecrafts. First, a control method is designed to ensure that the spacecraft stays motionless after the motivation incurred for mass properties determination. Second, an inertia matrix determination method is developed using a Kalman filter, in which the coupling factors are added in the amendment procedure. Third, the Kalman filter with input is applied in the determination of the center of mass: on the one hand, this method can use one the accelerometer placed at the flexible appendages, if the deformation can be measured; on the other side, the method can use three accelerometers placed at three orthogonal points of the rigid part of the spacecraft, when the deformation cannot be measured. Finally, the mass can be gained by estimating the center of mass twice. Simulations were carried out on a large-scale rigid–flexible coupling spacecraft. The results demonstrated that the determination errors in all cases are less than 10%, which meet the engineering requirements.

Soft Matter Emerging Investigators Issue 2021 - "Propulsion of an elastic filament in a shear-thinning fluid at low Reynolds numbers"

Some micro-organisms and artificial micro-swimmers propel at low Reynolds numbers (Re) via the interaction of their flexible appendages with the surrounding fluid. While their locomotion have been extensively studied with...

Robust H∞ Control for the Spacecraft with Flexible Appendages

Aiming at the oscillation suppression of spacecraft with large flexible appendages, we propose a control strategy using H∞ control. The weighting functions are designed for the specific flexible modes of the spacecraft and the frequency of harmonic interference in its operating environment. Taking into account the structural uncertainty of systematic modeling and the comprehensive performance requirements of system bandwidth constraint and attitude stability, the H∞ comprehensive performance matrix is constructed. A space telescope with a large flexible solar array is presented as an illustrative example, and a control design that meets the requirement for pointing accuracy is proposed. The simulation results show that the designed controller satisfies the requirements of attitude stability and high pointing accuracy and has effectively suppressed the disturbance of endemic frequency. The design scheme and selection method of the weight function shown in this paper can be a reference for the controller design for oscillation suppression of this type of spacecraft with flexible structures.