Observer-based guidance law against maneuvering targets without line-of-sight angular rate information

This paper presents a robust observer-based finite-time convergent guidance law to intercept maneuvering targets. To avoid the undesired chattering phenomenon existing in classical sliding mode control, the adaptive super-twisting algorithm is first introduced to design a robust guidance law to drive the line-of-sight (LOS) angular rates to a small region around the origin in finite time. The important feature of the proposed adaptation algorithm is in nonoverestimating the values of the guidance law gains, which is achieved by using a 'detector' scheme in the updating law. Moreover, with the proposed adaptive law, the presented guidance law requires no information on target maneuvers. Since the LOS angular rate is difficult for a pursuer to measure accurately for some seekers, a novel adaptive super-twisting observer is proposed to estimate it and a composite guidance law is then synthesized. Detailed finite-time stability analysis and comparison results with other guidance laws demonstrate the superiority of the proposed formulation.