Three-Dimensional Guidance with Terminal Time Constraints for Wide Launch Envelops

This paper proposes a three-dimensional, nonlinear guidance strategy for terminal-time-constrained interception of a nonmaneuvering target. The restrictive assumption of decoupling the three-dimensional interceptor–target engagement into two separate mutually orthogonal planes is relaxed. The guidance commands are derived using sliding mode control, with a time-to-go estimate that accounts for interceptor’s heading angle errors. It is shown that even for arbitrarily wide launch envelops, interception is guaranteed at a prespecified desired impact time. Further, a weighted control allocation technique is presented to allocate suitable lateral accelerations along the pitch and the yaw directions. Finally, numerical simulations, including extensive Monte Carlo assessments, are carried out with constant speed as well as two different realistic interceptor models that consider time-varying speed owing to aerodynamic parameter variations. Guidance strategy is shown to be effective in the presence of noisy measurements, uncertainties, and system lag. The performance of the proposed strategy is shown to be superior compared with an existing one.