Robust finite-time spacecraft attitude control under input saturation

A structurally simple controller is proposed to achieve the finite time attitude stabilization of spacecraft in the presence of external disturbance, input saturation and lack of inertia information. To be specific, considering that the conventional singularity problem arises with the traditional terminal sliding mode surface adopted, a novel time-varying fast terminal sliding mode surface is firstly developed. The proposed time-varying fast terminal sliding mode surface helps to avoid the undesirable phenomenon, and no modified or switched terms is needed. Then a control signal that rigorously obeys a known maximum-torque constraint is introduced. A rigorous analysis of the proposed formulation is provided and finite time convergence of the attitude and angular velocity is guaranteed. Numerical simulation studies are presented to help illustrate the effectiveness of the proposed controller.