ESA GNC Conference Papers Repository

Close proximity operations including descent and landing are some of the most critical phases for sample return missions, typically characterised by very challenging propellant consumption requirements. While common descent strategies involve an extended period of forced controlled motion, either by translating to the surface from a close hovering station-keeping point or by starting the descent from a distant Quasi-Satellite Orbit, significant fuel savings could be achieved by further exploiting the natural dynamics in the vicinity of the target. However, a common characteristic of the gravitational environments around asteroids and small bodies is that they are both highly perturbed and essentially poorly known, calling for the development of reliable autonomous guidance, navigation and robust control strategies. After introducing the complex dynamics environment considered for the study and describing the specific challenges associated with the descent and landing on small bodies, this paper will address the design of propellant efficient landing trajectories, including novel approaches using results from dynamical systems theory. Reference trajectories will be presented and compared to more classical strategies. Confronted to the reality of a highly perturbed and unknown dynamics environment, the second part of the paper will present the results of innovative nonlinear and robust closed-loop guidance and control schemes, again systematically benchmarked against state-of-practice algorithms. The paper will focus on Phobos as a strategic and archetypal study case, illustrating the implications of the proposed strategies on the system design and operations for a future interplanetary Sample Return mission.