  We investigate the autonomous control of gravity-assist hyperbolic
trajectories using a path following control law based on sliding mode control
theory. This control strategy ensures robustness to bounded disturbances. Monte
Carlo simulations in the environments of Titan and Enceladus, considering
significant insertion errors on the order of 50 km, demonstrate the
effectiveness of the proposed approach. The Enceladus example showcases the
applicability of the control strategy for close flybys of asteroids and small
moons during scientific observations. It successfully stabilizes the orbital
geometry within a short time span, avoiding collisions and enabling a close
approach to Enceladus' surface with a separation distance of 10 km.
Furthermore, we explore its application in a Jovian tour, considering a more
complex N-body problem. Results indicate that the control system, while unable
to guarantee a complete tour, plays a crucial role in ensuring precise
trajectory control during flybys. In such cases, the vehicle guidance system
requires higher precision than what can be achieved with a patched conics
model. These findings demonstrate the effectiveness of the proposed control
strategy for gravity-assist maneuvers and highlight its potential for various
space exploration missions involving close encounters with celestial bodies.
