Recovering unmanned undersea vehicles with a homing and docking sonar

There is a great deal of interest in deploying and recovering an unmanned undersea vehicle (UUV) with a submarine or a surface ship. This paper describes a homing and docking sonar (HDS) that was developed for a 21-inch diameter UUV and host platform. The system consists of two transducer disks, the first mounted on the host platform and the second mounted on the UUV. Each disk is divided into four quadrants with the four quads projecting in a summed configuration and receiving as four separate signal channels. The four-channel received signals are processed separately to facilitate the measurement of bearing and elevation angles. The HDS system is designed to support the acoustic transfer of telemetry data as well as provide the homing and docking functionality. The HDS operates as follows: (1) The HDS disk on the platform transmits a short pulse; (2) the HDS disk on the UUV receives the pulse and transmits a reply pulse; and (3) the HDS disk on the platform receives this pulse and transmits a second reply pulse. Based on these three pulses, the platform HDS estimates range, azimuth, and elevation to the UUV. The HDS on the UUV estimates range to the platform, as well as the orientation of the UUV relative to the direction vector to the platform disk. This epoch of three pulses is sent every 3 to 5 seconds as the UUV swims toward a capture cone on the platform. The UUV steers itself to the maximum response axis (MRA) of the platform disk using angles measured by the platform. (This angle data is sent to the UUV over the HDS or via a separate acoustic communication link.) The angles measured on the UUV are used to align the UUV with the platform disk MRA. Range measurements are provided to the UUV's on-board guidance algorithm. Successful docking of the UUV was first achieved during at-sea testing in April 2005. The HDS system has demonstrated near theoretical angle accuracies of less than 0.25 degree and range accuracy of less than 6 inches for UUV/platform separations of more than 500 feet.