Abstract: In order to improve the estimation accuracy of target's state and to satisfy multi-constraints of intercepting process in the near space, an explicit mid-course guidance law with varying gain against high maneuverable target is designed. Firstly, the dynamic characteristics of the target in the near space was analyzed. Based on it, a geometric prediction method of the target's trajectory is proposed, which approximates the target trajectory to circular arc. Subsequently, the state of target and the interception time-to-go can be more accurately predicted along the arc. Secondly, the explicit guidance law with three-dimensional angular constraints are derived. In order to restrict commanded acceleration within feasible boundaries, a weight function is constructed with respect to dynamic pressure, and is enforced to the performance index function to modulate the guidance gain. Accordingly, the acceleration command can be adjusted to avoid over demanded by the adaptive update of guidance gain as flight altitude increasing. Finally, by combining circle prediction and the explicit guidance law with varying gain, high terminal interception accuracy against high speed maneuverable target is achieved. The simulation results show the proposed method can significantly improve the accuracy of target prediction as well as satisfy the constraints of the terminal impact angle and the available accelerations.

Key words: near space target, midcourse intercept guidance, circular prediction, explicit guidance, varying gain, available acceleration constraint