Bearings-Only Information Based Guidance Law for Trajectory Shaping Applications

Abstract

Munitions like projectiles and artillery mortars follow ballistic trajectory to hit the target. However, unguided munitions may miss the target due to external disturbances or errors in aerodynamic modeling. A guided trajectory that mimics the ballistic one efficiently utilizes the gravity and augments it with terminal accuracy.

The first part of this thesis proposes a novel bearings-only information based guidance law for mimicking short range surface-to-surface ballistic trajectories. Analysis of the ideal ballistic trajectory is carried out and closed-form expressions are derived for the projectile heading error (difference between the instantaneous heading angle and the line-of-sight angle to the impact point) and its derivative. Satisfying the launch angle, the terminal angle of approach, and the initial heading error rate of the ballistic trajectory, a guidance law is designed using bearings only-information of the impact point. Further analysis is carried out evaluating the variation in guidance gains, capturability, and the boundedness of the terminal lateral acceleration. Simulation results show the efficacy of the proposed guidance method in mimicking short range ballistic trajectories.

Maintaining seeker lock-on to the target is a primary requirement for any prospective missile guidance law. Shaping a trajectory to satisfy a terminal impact angle becomes challenging, particularly for a missile seeker with a narrow field-of-view (FOV). The second part of this thesis analyzes the proposed mimicking guidance law for the specific application of achieving a desired impact angle without violating seeker’s field-of-view. The guidance gains are obtained by imposing a desired impact angle and the seeker’s look-angle constraint. Considering different impact angles and seeker’s field-of-view limits, simulations are performed with different launch angles using the kinematic vehicle model and a realistic model with given thrust and aerodynamic characteristics.