Integral Line-of-Sight Guidance of Underwater Vehicles Without Neutral Buoyancy*

:This paper analyzes an integral line-of-sight guidance law applied to an underac-tuated underwater vehicle. The vehicle is rigorously modeled in 5 degrees of freedom using physical principles, and it is taken into account that the vehicle is not necessarily neutrally buoyant. The closed-loop dynamics of the cross-track error are analyzed using nonlinear cascaded systems theory, and are shown to achieve uniform semiglobal exponential stability. Hence, the integral line-of-sight guidance law compensates for the lack of neutral buoyancy, and it is no longer necessary to assume that the vehicle is perfectly ballasted. The exponential convergence properties of the guidance law are demonstrated in simulations of an autonomous underwater vehicle.