6-DOF adaptive sliding mode control of probe hovering in the irregular gravity field

This paper presents a 6-DOF control of probe hovering in the irregular gravity field in the asteroid orbital frame. Considering the requirements of the scientific instruments pointing direction and orbit position in practical missions, the coordinate control of relative attitude and orbit between the probe and target asteroid is imperative. First, a 6-DOF dynamic equation is derived taking the irregular gravitation, model and parameter uncertainties, and external disturbance into account. An adaptive sliding mode controller is designed to guarantee the convergence of the state error in the presence of external disturbances and model uncertainties. The closed-loop system is proved to be uniformly asymptotically stable theoretically. 4769 Castalia is chosen as the target asteroid, numerical simulation results demonstrate that the designed control law can perform well for a hovering mission with good control accuracy.