Improved Fixed-Time Convergence Guidance Scheme Design and Its Application to Missile

This study presents a fixed-time convergence guidance scheme for impact time and angle control.First,two improved fixed-time stable systems are presented,which have smaller initial control command and better terminal convergence.16 An improved fixed-time extended state observer is proposed to provide accurate estimation of system states and disturbance,which effectively solves peaking value problem.Furthermore,an improved fixed-time sliding mode controller is derived,which avoids the singular problem and achieves faster convergence rate with smaller initial control command.Second,a new guidance scheme with impact angle and impact time constraints is proposed for intercepting a stationary target.By introducing a virtual target,the guidance process is divided into two stages.The proposed fixed-time controller is employed in the first stage.The method with a virtual leader ensures that the missile intercept the virtual target with desired line-of-sight angles at a specific time.By using the proportional navigation guidance law,the missile keeps travelling with desired flight-path angles to hit the real target in the second stage,17 so as to achieve the impact time and angle control.Finally,the feasibility and effectiveness of the proposed guidance scheme in different engagement scenarios are verified by numerical simulations with comparisons.