A novel partial space elevator for cargo transportation is proposed with a conceptual design of an electrodynamic tether to provide clean and propellant-free driving force for climbing motions and to control the coupled attitude motions of tethers. The nonlinear dynamics and control of the upward and downward cargo transportation problems are addressed for the novel elevator. Based on an assumption of a 2-piece dumbbell model, a 3-dimensional dynamic model of the system is established by involving the coupling motions between the electrodynamic forces, tether tension, and tether attitude motions. Accounting for the complicated dynamics and system constraints, a nonlinear model predictive controller is proposed to achieve the stable cargo transportations by adjusting the tether current and tension. Finally, 2 numerical simulations are given to validate the novel design and to verify the effectiveness of the controller. The simulation results manifest that the appealing clean technology is feasible to long space cargo transportations without the requirements of chemical propellant and additional thrusters.

This study focuses on stabilizing the libration dynamics of an electrodynamic tether system (EDTS) using generalized torques induced by the Lorentz force. In contrast to existing numerical optimization methods, a novel analytical feedback control law is developed to stabilize the in-plane and out-of-plane motions of a tether by modulating the electric current only. The saturation constraint on the current is accounted for by adding an auxiliary dynamic system to the EDTS. To enhance the robustness of the proposed controller, multiple perturbations of the orbital dynamics, modeling uncertainties, and external disturbances are approximated using a neural network in which the weighting matrix and approximation error are estimated simultaneously, such that these perturbations are well compensated for during the control design of the EDTS. Furthermore, a dynamically scaled generalized inverse is utilized to address the singular matrix in the control law. The closed-loop system is proven to be ultimately bounded based on Lyapunov stability theory. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed analytical control law.

This paper presents a disturbance observer-based linear quadratic Gaussian (LQG) control strategy to stabilize the flexible spacecraft considering the vibration suppression of flexible appendages using an orthogonal cluster of magnetically suspended reaction sphere actuators. The nonlinear dynamic equation of a flexible satellite is given and then linearized using the Jacobian method to get a linear state-space model. The dynamic equation of the reaction sphere actuators is derived by considering 2 virtual gimbals. A new steering law is designed to produce the tilt angle commands of orthogonal reaction sphere actuators. The proposed disturbance observer-based LQG considers process disturbances and measurement noises, and performs a trade-off search between control efforts and regulation performance. Numerical simulations are performed to evaluate the proposed strategies for an attitude stabilization scenario, and the results illustrate that the disturbances are effectively mitigated.

A group of cooperative agents can finish complicated missions that are difficult for a large machine. In the past two decades, spacecraft attitude coordination has attracted significant research attention owing to its wide potential applications. This paper presents a survey of recent research progress on the spacecraft attitude consensus problem, paying particular attention to the papers published in major aerospace, dynamics, automation, and robotics journals since 2015. Attitude consensus concepts for centralized, decentralized, and distributed cases are reviewed. This overview summarizes results on system dynamics and consensus algorithms based on frequently used attitude representations, such as Euler angles, modified Rodrigues parameters, unit quaternions, and rotation matrices. Studies conducted under complicated operating conditions are also covered. Experimental results on attitude consensus are discussed. In the final section, the main conclusions are drawn and several potential research directions are provided.

This paper presents a solution to the leaderless consensus of multiple spacecraft on $SO(3)$ under a connected undirected graph. An algorithm is proposed to generate an undirected tree graph from a connected undirected communication topology. A distributed observer is designed to estimate the desired attitude and angular velocity for each spacecraft under the generated tree graph. An adaptive controller with a general connected undirected graph is developed to complete the synchronization task. Cases with zero and nonzero final angular velocities are considered. Theoretical proofs and numerical simulations are presented to demonstrate the effectiveness of the proposed controllers.