Direct adaptive control of spacecraft near asteroids

An orbit–attitude, direct model reference adaptive control methodology is developed and applied to spacecraft trajectory tracking in the vicinity of asteroid with dynamical coupling. The asteroid gravitational field is modeled using a polyhedral gravity model, and the asteroid is assumed to be rotating. Orbit–attitude dynamical coupling due to solar radiation pressure and gravity gradient is implemented. Spacecraft and asteroid parameters such as mass, inertia, and gravitational field are assumed to be unknown. A direct adaptive controller with e modification is implemented to track hovering and orbital trajectories in the vicinity of the asteroid. The direct model reference adaptive controller does not require parameter estimation and is robust to model and disturbance uncertainties. The controller is designed separately for orbit and attitude case. A Lyapunov analysis is presented to prove the asymptotic stability of the orbit–attitude adaptive control system. A numerical simulation for asteroid Kleopatra is presented with orbital and hovering tracking maneuvers. The results show that the adaptive controller is able to successfully track trajectories in the vicinity of the asteroid without assuming system parameters.