Guidance, Navigation and Control System Design of Envisat Active Debris Removal

Space debris is becoming one of the major risks to be suffered by operating and future space missions. Recent studies show that the number of potentially hazardous uncontrolled orbital bodies is growing with time, increasing the probability of impact with operational satellites. To counteract this problem, several studies are being suggested to remove these dangerous objects from space. Among these, ESA proposed the e.Deorbit mission, whose objective would be the capture, detumbling and deorbit of the large inoperative satellite Envisat. However, the final deorbit phase encompasses a set of challenges and issues that are still to be tackled. The present thesis provides an approach for the guidance, navigation and control system design that solves those challenges and that can safely and robustly remove the spacecraft from orbit. For this purpose, the latest configuration of a rigid stack composed by Envisat and the chaser spacecraft is considered, in which it is deorbited using a series of perigee lowering maneuvers using a single main engine. The work proposes a guidance algorithm that can autonomously deorbit the stack using a pseudo-mean anomaly as control variable and the Linear Tangent Guidance concept for the final targeting. This algorithm is shown to robustly deorbit the stack regardless of its initial position in its orbit or of the initial mass of the target spacecraft within the specified uncertainty. Secondly, the work proposes a MEKF navigation filter based on the navigation sensors which are proposed for the chaser as of the latest configuration. Finally, a control law utilizing the INDI controller principles is suggested as a robust solution to the uncertainty in the inertia of the target spacecraft. It is shown that this controller behaves robustly against mismatches on the dynamic model. The complete integrated solution is then analyzed, exhibiting a promising behavior towards the correct active debris removal, and future investigation is encouraged. The work presented lays the foundations for the GNC design on a challenging yet necessary line of technological development towards the deorbit of large space debris for a more sustainable space environment.