  This article presents a path-following control law for autonomous orbital
maintenance of small body missions. The control law is robust, stable, and
capable of controlling only the orbital geometry, allowing the spacecraft to
operate with idle-thruster periods. It is entirely analytical and suitable for
real-time operations. The control law is inspired by the two-body problem and
uses sliding mode control theory to ensure robustness against bounded
disturbances. Practical considerations, such as measurement noise, thruster
limitations, and hysteresis-based control switching, are taken into account.
The proposed control law is demonstrated and validated through several
examples, including orbit-keeping around the asteroid Bennu, showing its
feasibility and efficiency for small body missions. The results indicate that
the control law can achieve precise and safe orbit maintenance with minimal
fuel consumption, making it a valuable asset for autonomous space missions.
