Observability-Aided Target Interception Using Bearing-Only Measurements via Cooperative Estimation

Interception missions using passive seekers depend on estimating relative range from noisy bearing-only measurements. In GPS-denied environments, terminal guidance requirements such as achieving a negative relative range rate and zero line-of-sight (LOS) rate may induce unobservable conditions near interception, leading to estimator divergence and increased miss distance. This work addresses the resulting conflict by introducing a cooperative surveillance agent to provide geometric diversity. For the pursuer–surveillance–target system, we develop a relative-state estimator using only inter-agent bearing measurements and design the surveillance-agent guidance law based on an Observability-Gramian-derived metric embedded within a Model Predictive Control (MPC) framework. Monte Carlo simulations show that the proposed approach maintains consistent average Normalized Estimation Error Squared (NEES) performance, reduces estimation uncertainty during terminal engagement, and enables successful target interception compared to baseline scenarios without surveillance support.