Modeling and Control of Docking/Grasping system for a small spacecraft

Recently, the use of microsatellites, e.g. CubeSat, has increased due to technology miniaturisation. The combination of several microsatellites allows to design large spacecrafts considering a modular approach and reducing costs. Moreover, in case of a component failure, the modularity makes it possible to replace a single spacecraft instead of repairing a larger one. The most critical phase in this concept is the contact among the microsatellites, which is required to be accurate and at low speed, in order to prevent any potential damage. Magnets may reduce design complexity and docking phase during the final approach manoeuvre. The objective of this thesis is the design of a simulator for small satellites docking considering magnets application. Simulation study is carried out in MATLAB/Simulink environment. Magnets with low magnetization are considered such to not interfere with the correct functioning of magnetometers. Moreover, spacecraft attitude is assumed to be stable during the approach manoeuvre in order to have not interaction between magnets and Earth's magnetic field. Position control during the final approach is regulated by an LQR controller, while attitude is regulated by a PD controller. First, the results show that, minimizing the speed in proximity of the docking phase, the magnets are sufficient to operate autonomously the docking manoeuvre. Moreover, the speed reached at the contact point can be easily managed by commonly used materials. After the contact, impact disturbances are considered in the combined system stabilization. The assembled satellite is controlled by the same attitude and position controllers designed for the single spacecraft. These achievements open to the possibility to build simple models to study spacecraft assembly and multiple-docking applications.