UUV on-board path planning in a dynamic environment for the Manta test vehicle

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Presents recent work in the areas of simulation, mission planning, and mission execution for an unmanned undersea vehicle (UUV). The UUV we consider is the Manta Test Vehicle (MTV), operated by the Naval Undersea Warfare Center (NUWC) in Newport, Rhode Island. A 6-degrees-of-freedom Simulink model of the MTV vehicle dynamics augmented with an autopilot is used to test the algorithms. The on-board mission planner generates reference trajectories for the vehicle to follow, taking into consideration bathymetry data and moving obstacles that are within the forward-looking sonar range. A trajectory consists of a sequence of waypoints and associated headings from the current vehicle location and orientation to the goal. Trajectory generation takes into consideration the dynamic capabilities of the MTV. The D* algorithm - an extension to the Dijkstra shortest-path algorithm which allows efficient re-planning when arc-costs change - is used to generate and maintain a safe trajectory. Trajectory re-planning is triggered when the sonar detects an obstacle in the trajectory currently being followed. A Model Predictive Control (MPC) algorithm is inserted between the D* algorithm and the vehicle inner loop autopilot. The MPC algorithm issues the reference commands to the autopilot to allow the vehicle to follow the planned trajectory. The cost function within the MPC algorithm can be changed depending on the guidance task. The MPC algorithm uses a full nonlinear model of the MTV vehicle to project ahead the output trajectory and employs orthogonal Laguerre polynomials to create basis functions that are used in the synthesis of reference commands to the autopilot. The MPC controller also provides a second layer of obstacle avoidance capability and keeps the vehicle on-track in the presence of a current.