Electrodynamic tether design and control for space debris mitigation

Space debris is posing a threat to future space activities: mitigation of the generation of new debris is crucial. Electrodynamic tether systems can be used in this context to de-orbit quite rapidly satellites at their end of life, effectively reducing the risk of future collisions. They can be integrated in quasi-passive system: the conductive tether, deployed at the satellite end of life, collects electron from Earth ionosphere and re-emits them with a cathode, establishing a current flow thanks to the motional electric field. The generated current, interacting with Earth magnetic field, generates a Lorentz force, which has, by nature, a component opposed to the orbital velocity. The complete system can be very compact before deployment and lighter than classical propulsive alternatives. It can be designed to operate even in case of satellite loss, relaying on the produced current for the generation of the needed power. In this thesis, analysis of the performances and their dependence on design parameters and system configurations is conducted with an accurate simulator: tether flexibility and elasticity are kept into account, as well as thermal effects on the electrical properties. The simulator includes the most accurate environmental models available, among which an ad hoc implementation of a ionospheric electron density model. Real case scenarios are analyzed to understand dependencies on performances and system instabilities. Nature of the instability is studied and possible solutions are investigated. No unique control method has already been individuated as the most feasible and all most promising alternatives are analyzed and compared. The selected control method, which can represent a practical alternative easily implementable in real applications, is analyzed in detail for the first time with an accurate tether model. Particular emphasis is given to the comparison of the approximated and finer versions implemented since the former was never applied before to a flexible tether model and the latter is ad hoc newly introduced formulation of the same concept. Finally control parameters effect on stabilization and performance is studied.