Trajectory tracking near small bodies using only attitude control

Gravitational orbit–attitude coupling shows a noticeable influence on the motion of a rigid spacecraft in close proximity to small solar system bodies. The gravity gradient moment changes the attitude of the spacecraft, which in turn alters the total gravity force on the spacecraft and has an impact on the orbital motion. In this paper, the polyhedron model of small bodies is adopted and a distributed point-mass model of the spacecraft is developed to reflect this coupling phenomenon more accurately. In particular, taking advantage of the gravitational orbit–attitude coupling, a trajectory tracking scheme for a rigid body using only attitude control is proposed. By changing the attitude of the spacecraft, the gravitational orbit–attitude coupling generates a control force to make the spacecraft track the reference trajectory. This reference trajectory is generated based on a point-mass model. Simulation results in landing and orbiting around asteroid Bennu show the feasibility of this tracking approach. A significant improvement is seen for the coupling-based controlled trajectory over natural motions. The tracking scheme reduces the frequency of orbit control maneuvers and provides a redundant control in the event of thruster failures. This approach can be used as a reference for future small-body missions.