Robotic vehicles taking up positions under the sea

Propelled by the US Navy, autonomous underwater vehicles (AUVs) are beginning to make their mark in applications that range from mine clearing to antisubmarine warfare. A number of AUV startup companies have spun off from the academic and oceanographic institutions where they were established and are now producing the vehicles in small quantities.

Among the military applications that the navy has identified for AUVs are intelligence, surveillance, and reconnaissance; mine countermeasures; antisubmarine warfare; inspection and identification; oceanography; payload delivery; and time-critical strikes. Commercial applications include underwater surveys, fisheries research, search and recovery, wreck and navigational hazard mapping, and water profile sampling.

According to the 2011 Pentagon report Targeting U.S. Technologies: A Trend Analysis of Reporting from Defense Industry, the AUV market will grow exponentially by 2020, with roughly 1400 AUVs expected to be built worldwide over the next decade. Global expenditures on AUVs between 2010 and 2019 are projected to total $2.3 billion. The report warned that US AUV technology is being coveted and targeted by Asian Pacific countries. Some nations in that region have stepped up efforts to acquire the US technology—which is subject to export controls—by trying to penetrate the companies’ computer networks, by having individuals seek employment with cleared contractors, and by other methods.

“We’re seeing an explosion of undersea vehicles in mine countermeasures [MCMs],” declared William Burke, deputy chief of naval operations for warfare systems. Deployed from combat ships, aircraft, or other platforms, AUVs “get the man out of the minefield” and improve the efficiency of mine clearing, Burke added.

Frank Herr, director of the Office of Naval Research’s (ONR’s) ocean battlespace sensing department, says the navy believes that compared with standard methodologies, autonomous vehicles can greatly increase the rate at which mines are cleared. Researchers have developed unmanned surface vehicles that can deploy AUVs, and underwater vehicles are being used to scan the sea floor and rapidly identify mines. Herr says the ONR is exploring multiple approaches for developing AUVs that can neutralize mines. One requirement, he notes, will be for an inexpensive AUV, since neutralizing a mine is likely to destroy the vehicle.

Adapting AUVs to MCMs originated in the mid 1990s, says Christopher von Alt, president of AUV manufacturer Hydroid. In the 1990s, while at Woods Hole Oceanographic Institution (WHOI), he codeveloped a small AUV for oceanographic research with support from the National Oceanic and Atmospheric Administration (NOAA). The Naval Special Warfare Command, home to the SEALs, was then looking for shallow-water MCMs to support amphibious landings. At the time, he says, the only tool the SEALs had for mine detection was a “long rope with a carefully spaced string of knots that were used to separate a platoon of divers as they swam parallel to the beach searching for mines.”

Von Alt says the ONR funded his proposal to use a sidescan sonar that can efficiently create an image of large areas of sea floor and to mount it on a WHOI-developed AUV known as the remote environmental monitoring unit system (REMUS). The technology was successfully demonstrated on the 36-kg AUV in 1997. When Hydroid was spun off from WHOI and opened its doors in 2001, the SEALs ordered 17 of the REMUS 100 AUVs. A similar vehicle was used to sweep the Iraqi port of Umm Qasr for mines in advance of a humanitarian ship docking there. Another was used by NOAA to ensure that shipping lanes were unobstructed after two hurricanes lashed Galveston, Texas, in 2008.

The larger, 326-kg REMUS 600 was then developed at WHOI with ONR funding. Originally built to support research on synthetic aperture sonar, it can operate in water up to 1500 meters deep.

Currently the navy has 60 REMUS 100s in service for MCMs in very shallow-water environments. Three REMUS 600s are in service in support of the navy’s Middle East and East Africa operations. Three more are due to arrive there next month, and an additional three are expected in February. The mine warfare version of the navy’s multimission littoral combat ship will be equipped with AUVs beginning in fiscal year 2017, says Herr.

A third REMUS, the 6000, was developed after von Alt convinced the Naval Oceanographic Office that deep-sea mapping could be better performed by AUVs than by vehicles being towed at depths of 6000 meters. The drag created by 8 kilometers of cable reduced the speeds of mapping ships to around 1 knot. An AUV capable of operating at such depths triples productivity, von Alt explains. In 2011 nonmilitary REMUS 6000s operated by WHOI located the wreckage of Air France flight 447 in mountainous undersea terrain at a depth of 3500 meters; the plane had crashed off the coast of Brazil in 2009.

Extending the range

At MIT during the 1990s physicist James Bellingham ran an ONR-funded research effort called the Autonomous Ocean Sampling Network and developed a family of AUVs named Odyssey. In 1997 he cofounded the spinoff Bluefin Robotics, which manufactures a line of AUVs that includes an MCM system and a vehicle for inspecting hulls. (The company was acquired by Battelle in 2005.) Bellingham is now at the Monterey Bay Aquarium Research Institute (MBARI), where he has developed a long-range AUV tailored for biological oceanographic research. “It’s fair to say that ONR has been the dominant source of funding for underwater vehicles and has been extremely influential in enabling academic research and enabling the industry,” he says.

The original 110-kg Odyssey vehicle has run missions up to 23 days, compared with the 1-day duration typical for today’s commercially available AUVs. Extending the range by that much required “15 to 20 tricks,” Bellingham says, including a more efficient propulsion system, very-low-power electronics, strategies that shut off power to subsystems when not in use, and the ability to point the AUV up and down by shifting the weight of the batteries rather than adjusting the pitch of the elevators. With low-power mapping sensors now available, the MBARI vehicle could also be adapted for long-duration sea-floor mapping missions, he notes.

The navy is working to develop a large-diameter underwater unmanned vehicle that can operate for periods of up to 70 days. It’s clear that alternative methods of power beyond batteries will be necessary, as will much greater reliability and autonomy than has been achieved, says Herr. The exact missions for the large-diameter vehicle are now being considered in advance of an initial acquisition. But the system will be capable of operating undetected near harbors, shores, and high-surface-traffic locations and presumably would be used for sea-floor mapping in unfriendly areas.

The large-diameter AUV will be powered by a hybrid energy propulsion system, with either fuel cells or a combustion Stirling engine serving as the main power source and computer-controlled lithium-ion batteries supplying backup, Herr says. Both approaches will require that the AUV carry gases under high pressure as fuel.

The slower approach

The development of a different type of AUV, known as a glider, has been funded by the ONR mainly for its application to antisubmarine warfare. Oscillating buoyancy drives the devices through the open ocean. Alternately sinking and rising, the gliders are propelled forward horizontally by their wings. Along their sawtooth paths, the AUVs periodically take temperature and salinity measurements. The thermal stratification of the oceans causes differences in the refraction of sound, a feature that submarines can take advantage of to avoid detection. Conversely, timely information about the ocean’s current thermal map can help in the hunt for enemy subs. Since stratification is continually changing as ocean eddies are created and fade, obtaining a clear picture requires getting lots of real-time measurements.

With the initiation of an autonomous ocean sampling network in 1995, the idea was to enable long-term, inexpensive measurements, says Charles Eriksen, a physical oceanographer at the University of Washington (UW). Eriksen developed the Seaglider, one of three models of gliders that have been manufactured for ONR and nonmilitary users. For the $30 000 that it costs to have a research vessel take measurements for one day, a Seaglider can operate for several months, he says. At about one-half knot, the glider moves just fast enough to maintain effective navigation. The device periodically surfaces, deploys its antenna, fixes its position by GPS, transmits via a satellite link the data it’s collected, and receives new directions. The cycle is repeated for months at a time.

More than 200 Seagliders have been built, and Eriksen estimates that somewhere around 500 gliders of all types have been manufactured. Although that’s significantly larger than the number of prop-driven AUVs, glider production is “woefully short of the numbers needed to really effect significant economies of scale,” he says. In late October, iRobot, the company that manufactured the Seaglider under license from UW, announced it will stop producing them in December; the company cited a lack of profitability and the expected low demand from the military. That means that UW will have to look for a new licensee, Eriksen laments.

For its part, the navy hopes to limit the total number of gliders required by operating moving fleets of them, says Herr. The navy is currently acquiring around 150 gliders.