Controller design challenges for waterjet propelled unmanned surface vehicles with uncertain drag and mass properties

The issues affecting low-level controller design for a wave-adaptive modular class of unmanned surface vehicles (USVs) are presented in the context of supporting the autonomous launch and recovery (ALR) of an Autonomous Underwater Vehicle (AUV) aboard an USV. The ALR of an AUV presents a challenging control problem because control parameters are chosen based on the dynamics of the vehicle, which can change abruptly and significantly when an AUV is jettisoned or docked. Tight control of the vehicle state is required to conduct an underway recovery, with looser requirements for the launch. Knowledge of the vehicle response is important for control system design. A simulation, based on physical modeling and experimental results, was developed to support the design of a low level controller. A cascaded proportional derivative (PD) controller has been implemented in simulation and tested for two dissimilar reference speeds and two payload conditions. The simulation results suggest that an adaptive controller may be necessary to overcome the time-varying nature of USV dynamics during an ALR mission.