Circular Motion Guidance Law for Coordinated Standoff Tracking of a Moving Target

A guidance law is presented to enable a coordinated standoff tracking of a moving target with multiple fixed-wing unmanned aircraft. The standoff tracking guidance law makes multiple aircraft circle around a moving target while maintaining a specific distance from it with a desired circling rate. The stabilization of a spherical pendulum to a conical motion is applied to the aircraft motion to obtain the standoff tracking guidance commands. The acceleration commands are designed to regulate the position and velocity errors using the Lyapunov stability theory and the backstepping technique. The coordinated standoff tracking with multiple aircraft is achieved by applying the proposed guidance law to a leader-follower formation. The only information transmitted from the leader aircraft to the follower aircraft is the phase angle of the leader. In addition an offset circle is proposed to deal with the aircraft speed limit. Tight phase spacing between the neighboring aircraft is accomplished by tracking the reference position and velocity vectors defined on the offset circle. Numerical simulations and flight tests are performed to verify the effectiveness of the proposed method. Multiple aircraft are successfully guided to a circular motion around the moving target while maintaining tight phase spacing to the neighboring aircraft as well as a desired standoff distance to the target.