Waves apply significant forces to small boats, in particular when such vessels are moving at a high speed in severe sea conditions. In addition, small high-speed boats run the risk of diving with the bow into the next wave crest during operations in the wavelengths and wave speeds that are typical for shallow water. In order to mitigate the issues of autonomous navigation in rough water, a hybrid controller called POSTMAN combines the concept of POS (point of sail) tack planning from the sailing domain with a standard PID (proportional- integral-derivative) controller that implements reliable target reaching for the motorized small boat control task.
This is an embedded, adaptive software controller that uses look-ahead sensing in a closed loop method to perform path planning for safer navigation in rough waters. State-of-the-art controllers for small boats are based on complex models of the vessel’s kinematics and dynamics. They enable the vessel to follow preplanned paths accurately and can theoretically control all of the small boat’s six degrees of freedom. However, the problems of bow diving and other undesirable incidents are not addressed, and it is questionable if a six- DOF controller with basically a single actuator is possible at all. POSTMAN builds an adaptive capability into the controller based on sensed wave characteristics.
This software will bring a much-needed capability to unmanned small boats moving at high speeds. Previously, this class of boat was limited to wave heights of less than one meter in the sea states in which it could operate. POSTMAN is a major advance in autonomous safety for small maritime craft.
This work was done by Terrance L. Huntsberger of Caltech and Felix Reinhart of the Research Institute for Cognition and Robotics for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
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NPO-47986
This Brief includes a Technical Support Package (TSP).
POSTMAN: Point of Sail Tacking for Maritime Autonomous Navigation
(reference NPO-47986) is currently available for download from the TSP library.
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Overview
The document presents the Technical Support Package for POSTMAN (Point of Sail Tacking for Maritime Autonomous Navigation), developed by NASA's Jet Propulsion Laboratory (JPL). It addresses the challenges faced by small high-speed boats operating in rough sea conditions, particularly the phenomenon known as "bow diving," where the bow of the boat dives into the next wave crest. This issue can lead to reduced speed, capsizing, and potential damage to the vessel's hull and sensors. The document notes that bow diving is influenced by various factors and lacks a comprehensive design solution to prevent it entirely.
To tackle these challenges, the POSTMAN system employs a hybrid control approach that combines sailing techniques with advanced control algorithms. The system integrates a Point of Sail (POS) tack planning method with a Proportional-Integral-Derivative (PID) controller, enabling the vessel to navigate effectively while considering wave dynamics. The POS is defined as the difference between the target direction (TD) and the main wave direction (MWD), which is determined through stereo and radar sensory analysis.
The document outlines the operational framework of the hybrid controller, where macro-navigation is managed by the tack planner based on wave and target direction information, while micro-navigation is handled by the PID controller to ensure accurate target reaching. This dual approach aims to enhance the vessel's performance in challenging maritime environments.
Additionally, the document references simulations conducted with a small unmanned surface vehicle (USSV) operating at 50% throttle in varying wave heights, corresponding to sea states 0 through 4. These simulations help validate the effectiveness of the POSTMAN system in real-world conditions.
Overall, the Technical Support Package emphasizes the importance of innovative control strategies in improving the safety and efficiency of autonomous maritime navigation. It highlights the ongoing research and development efforts at JPL to address the complexities of navigating small boats in adverse sea conditions, ultimately contributing to advancements in maritime technology with broader applications.
