Advances in unmanned underwater vehicles (UUVs) are providing government agencies and commercial organizations with new capabilities across a variety of mission requirements. However, many underwater vehicles only address specific criteria or support well-defined (and limited) niches. As an example, the Naval Sea Systems Command’s (NAVSEA) Littoral Battlespace Sensing (LBS) system includes the LBS-G long-endurance glider to collect oceanographic data, but also needs the LBS-AUV for military applications.
Requirements for Littoral Areas
The total U.S. shoreline is 95,471 miles according to the National Oceanic and Atmospheric Administration (NOAA), which is nearly the same distance as circling the equator four times. America’s diverse shoreline includes busy ports, towering bridges carrying commuters, powerful rivers, and various estuaries. Despite these geographical differences along the coastline, UUVs and related underwater systems all require the following capabilities to be effective in shallow water missions:
- High maneuverability (to navigate around piers, bridges, oil rigs, etc.);
- Payload flexibility and capacity (to transport and use sonar for example);
- Near real-time data acquisition and/or transmission;
- Portability (easy to transport and deploy rapidly);
- Intuitive operator controls.
Typical operations in these shoreline areas include:
- Bathymetry studies;
- Contraband detection;
- Environmental monitoring;
- Harbor/port security;
- Search and rescue;
- Ship inspection;
- Submerged infrastructure inspection.
Reverse Engineering 20 Million Years of Evolution
The U.S. Department of Homeland Security (DHS) Science & Technology Directorate (S&T) sponsored Boston Engineering to develop a UUV to strengthen the capability to search, inspect, and operate in harsh environments and constricted underwater areas. The Bluefin Tuna, and other pelagic fishes like it, exhibit remarkable swimming performance in all areas: high-speed burst swimming (30-50 knots), high maneuverability (180 degree turns in a single body length), and efficiency (routinely migrate for long distances to 25,000 miles). Boston Engineering’s BIOSwimmer UUV is based on this model to deliver a unique and tactically-relevant intersection of speed, maneuverability, and endurance.
Most of the tuna’s propulsive motion is concentrated in the rear third of its body. This means that the forward two-thirds of the body is rigid, creating significant payload area (BIOSwimmer can carry about 700 in3 and 23 lbs. of dry payload). BIOSwimmer has a propeller thruster on a flexible tail, giving the vehicle a turning radius of less than one meter. The UUV’s propulsion technology also enables BIOSwimmer to approach an object closely and to hold its position while sensors collect data. The five-foot long UUV can be launched quickly and can operate at depths of 0.5 meters to 100 meters.
The BIOSwimmer includes a tow-body-based antenna that operators can use to communicate with the UUV while it is underwater. If the antenna is removed, the BIOSwimmer can collect and store data while it is underwater, and download its results after the mission.
Alternatives for Shallow Water Missions
In addition to UUVs, the most common maritime robotics used in littoral waters are remotely operated vehicles (ROVs) and autonomous unmanned vehicles (AUVs). Here’s an overview of their capabilities in this environment.
ROVs are controlled by operators via cables connected from a control panel to the ROV. However, the cables (tethers) are susceptible to getting entangled in underwater plant growth, debris, and other obstacles that are more likely in challenging environments. ROVs can include a video camera, lights, and sonar systems. Common uses include identifying objects in submerged hazardous areas, conducting research, and safeguarding harbors via operations such as vessel hull inspections.
Torpedo-shaped AUVs such as Hydroid’s REMUS 100 and Bluefin Robotics’ Bluefin-12 have been used to conduct wide area surveys by scanning back and forth in a “lawn mower” pattern underwater. While this may be suitable for covering large areas of water, such vehicles can have some difficulty turning in tight areas, which can become a severe limitation when navigating objects in shallow waters or adjusting its operational swimming patterns for other missions. Holding position relative to a diver is also very difficult with these systems.