Sliding-Mode Impact Time Guidance Law Design for Various Target Motions

In this paper, two kinds of sliding-mode guidance laws with impact time constraint are proposed for intercepting various target motions, including nonmaneuvering and maneuvering targets. To achieve the desired impact time, the line-of-sight (LOS) dynamics is controlled to track a novel time-varying LOS profile created by the LOS rate-shaping approach. Unlike the existing LOS rate-shaping approaches that transform the equations of motion with the downrange variable as the independent variable, no such manipulation is necessary in this technique by virtue of a polynomial LOS profile in time. To nullify the LOS tracking error, the terminal sliding-mode technique is used to obtain a finite time convergent guidance law against nonmaneuvering targets, and it is combined with the inertial-delay control to derive an ultimately bounded guidance law against maneuvering targets. Furthermore, fast online determination of the single tuning parameter involved in the LOS profile is provided via a systematic parameter selection methodology. This technique is user/designer-friendly in that it does not involve the error-prone estimates of time-to-go and predictive interception point. Numerical simulations under time-varying velocities and various target maneuvers are conducted to validate the effectiveness and robustness of the proposed guidance law.