L+2, an improved line of sight guidance law for UAVs

This paper describes a new guidance law that extends the pursuit guidance law previously developed by Park et. al. Several improvements are presented that allow operation in the real world. A stability analysis accounts for the dynamic response of the bank angle commands which leads to the definition of regions of instability. Another extension accounts for situations where the pursuit aim point is not defined by the previous work. A third extension changes the pursuit distance-to-go from a constant to a constant time-to-go so that the linearized transient response is independent of ground speed. Yet another extension defines a “homing” mode in which the UAV flies to a goal point without a defined path, commonly used as a “return-to-base,” either as a safety measure or as an end-of-mission order. Since there is no constraint that the goal point be stationary, we demonstrate that the new law can be used to follow a moving target whose location is known, such as a mobile ground control station. Simulations with a 6 degree-of-freedom aircraft model demonstrate these features.