Formation-Keeping Strategies At The Earth-Moon L4 Triangular Libration Point

This thesis examines the use of thrusters and solar sails for spacecraft formation keeping control at the Earth-Moon L4 point. Particular emphasis was placed on the study of underactuated control, in which fewer control inputs than the system's degrees of freedom are available. A linear LQR control scheme, an integral augmented sliding mode controller and a bang-bang controller were applied to the dynamic spacecraft system. The nonlinear controllers produced errors falling with tighter tolerances than the linear controllers in the perturbed environment. Performing similarly well as the underactuated thrusters system was the solar-sails-controlled spacecraft formation using a bang-bang controller. This shows that solar sails could be a viable propellantless technique for relative control. A linear control technique was able to bound errors to within a couple of hundred metres, using a hybrid propulsion system. Of the cases studied, only the fully-actuated thrusters-based system was able to explicitly track a circular trajectory, but had [Delta]V requirement of more than 100 times greater than that needed for tracking the natural, elliptical trajectory.

Formation-Keeping Strategies At The Earth-Moon L4 Triangular Libration Point

This thesis examines the use of thrusters and solar sails for spacecraft formation keeping control at the Earth-Moon L4 point. Particular emphasis was placed on the study of underactuated control, in which fewer control inputs than the system's degrees of freedom are available. A linear LQR control scheme, an integral augmented sliding mode controller and a bang-bang controller were applied to the dynamic spacecraft system. The nonlinear controllers produced errors falling with tighter tolerances than the linear controllers in the perturbed environment. Performing similarly well as the underactuated thrusters system was the solar-sails-controlled spacecraft formation using a bang-bang controller. This shows that solar sails could be a viable propellantless technique for relative control. A linear control technique was able to bound errors to within a couple of hundred metres, using a hybrid propulsion system. Of the cases studied, only the fully-actuated thrusters-based system was able to explicitly track a circular trajectory, but had [Delta]V requirement of more than 100 times greater than that needed for tracking the natural, elliptical trajectory.

Optimized formation control of multi-agent system using PSO algorithm

<p>Formation Control (FC) is an important application for Multi-agent Systems (MASs) in coordinated control and especially for Unmanned Aerial Vehicle (UAV) which are widely used nowadays in military and civil sections. FC is mostly applied in conjunction with consensus algorithm. In this paper, a framework for an implementation of consensus FC that involves the decentralized type of network control is considered in order to achieve formation keeping, where the control of each vehicle is calculated dependent upon locally existed facts. The dynamic behavior of each vehicle agent is governed by its second-order dynamic model, and the networked mobile vehicle system is modeled by a directed graph. Then, Particle Swarm Optimization (PSO) is implemented for speeding up the convergence to the desired geometrical shape. Acceleration of the network while approaching the coveted shape is achieved and omissions of undesired swing that transpires through the acceleration is examined. The merits and effectiveness of the applied approach are demonstrated using two different examples.</p>

Loosely displaced formation-keeping control for satellite swarm with continuous low-thrust

Aiming at a long-term formation-keeping problem for the satellite swarm, the concept of a loosely displaced formation is proposed in this article. On this basis, a continuous low-thrust control strategy for maintaining the loosely displaced formation is designed. The control objective is to reduce more fuel consumption during the formation-keeping. For achieving that, we proposed a forward-feedback control strategy by using pseudo-spectral method and sliding mode theory. To be specific, the control strategy includes two parts: a forward control and a feedback control. For the forward control, a numerical optimization with the Legendre pseudo-spectral method is attempted to convert the optimal control problem into a nonlinear programming problem and fuel consumption is selected as the optimization index. For stability issue, the feedback control via adaptive finite-time sliding mode theory is introduced as an additional control component. Finally, the numerical results demonstrate that propellant mass is effectively saved as well as the formation can be tracked accurately with this control strategy proposed in this article.