Robust hierarchical sliding mode control for the underactuated tethered system

This paper presents a hierarchical sliding mode control approach for the underactuated tethered system suffering from unknown external disturbances. Taking the three dimensional attitude information of the postcapture combination, the in-plane/out-of-plane angles, and length of the tether into consideration, the dynamics of the tethered system is constructed. Then, based on the dynamics, a hierarchical sliding mode controller is designed and stability of the closed system is guaranteed by rigorous verification. Simulation carried out on the tethered system demonstrates that the proposed control strategy achieves good control efficiencies.