Navy moving out on unmanned underwater vehicle development

Feb. 1, 2001
As leaders of the U.S. Navy look to the first two decades of the 21st Century, they project a world in which their submarine fleet is decreasingly required to counter a major blue-water threat and increasingly likely to operate close to shore to support land- and air-warfare operations.

By J.R. Wilson

U.S. Navy submarines in the future will carry torpedo-sized unmanned underwater vehicles such as the one in the artist's rendering above. These autonomous vehicles will do jobs like reconnaissance, mine detection, and extending the range of sensor systems.
Click here to enlarge image

Washington — As leaders of the U.S. Navy look to the first two decades of the 21st Century, they project a world in which their submarine fleet is decreasingly required to counter a major blue-water threat and increasingly likely to operate close to shore to support land- and air-warfare operations.

As a result, Navy leaders are turning to their submarines for coastal or "littoral" applications. This inevitably means expanding the capabilities of U.S. submarine forces.

One emphasis in this effort centers on the development of unmanned undersea vehicles (UUVs), also sometimes referred to as autonomous underwater vehicles (AUVs). These are untethered vehicles, roughly the size of modern torpedoes and launched from submarine torpedo tubes, and extend the submarine's sensor range by as far as several miles.

"That has clearly been a focus of what we're doing right now," says Rear Adm. Charles B. Young, commander of the U.S. Naval Undersea Warfare Center in Newport, R.I., and deputy commander for undersea technology at Naval Sea Systems Command in Arlington, Va.

"We have been working on several small UUV systems to do things such as look at environmental and meteorological events and report those back," Young says. "We've looked at them as sensor nodes to communicate with each other and pass information."

Navy submarine leaders published a report last year called 'Submarine Roads Ahead' that envisions submarine systems through 2020. "In that context offboard sensors and vehicles play a heavy role," Young says. "Stealth will be an important component to keep our knowledge of the battlespace available to the theater and national commanders."

Offboard sensors mounted on UUVs are expected to provide mine detection — with some UUVs also possibly tailored for mine destruction — along with acoustic parameters, seismic events, and a host of other information useful to naval movements and missions.

Not all UUVs are "swimmers", however. At the Naval Post Graduate School Center for AUV Research in Monterey, Calif., Navy leaders also are paying attention also to "crawling" devices that could work in the surf at depths of 10 feet or less as well as move onto shore if necessary. These could accomplish such missions as detecting — and possibly destroying — mines intended to thwart a seaborne invasion.

Clearing mines

"Trying to get mines identified and cleared from 40 feet through the surf zone and onto the beach is a very important mission," says Center director Anthony J. Healey. "We have a reconnaissance phase that sweeps the area with sonar to bring up images of mine-like objects. Then we use another vehicle to bring back video of any suspect objects. You could possibly have one vehicle do both tasks, but not always."

The Navy already has developed vehicles to deal with water from 40 to 300 feet deep, which have different sensors, Healey explains "One vehicle can't do it all," he says. "We have to have a bag of tools, then make those tools work."

The technological challenges that untethered devices pose range from communications to navigation to command and control to power. Eliminating the tether means the submarine and UUV computers cannot talk directly through the water, which also means the UUV must store all sensory data. Both require more sophisticated computers aboard the UUV than a tethered vehicle would require. A tether also provides virtually unlimited power; without it, range and time on station are severely limited.

On the other hand, untethered vehicles have enormous advantages over their tethered brethren that must operate in the vicinity of surface ships or submarines. A tether, for example, always must be kept taut to keep it from dragging on the bottom.

Current technology requires UUVs to extend an antenna above the water's surface to obtain signals from Global Positioning System (GPS) satellites as well as to send and receive messages, including new mission information. This dependence on surfaced antennas may change, however. Researchers are looking into more direct communications, including classified research into the use of underwater lasers.

"The Navy is seriously pursuing the development and use of acoustic modems for underwater communications; the principal is similar to radio modem communications through the air," Healey says. "The technology allows you to communicate vertically through the water column at depths up to 6000 meters [nearly four miles] and even transmit digital data files at a slow data rate. The cone angle on these modems may be 30 to 40 degrees, so at 6,000 meters you have a reasonable surface area in which to operate. You need to apply things like compression technology so you can manage your bandwidth."

Commercial spin-ons

Young says the commercial world has demonstrated tremendous breakthroughs in underwater acoustic technologies the Navy can use with its UUVs.

"We have had some very successful technology programs and are in the process of putting that into our Virginia-class design [for the Navy's newest attack submarine]. The LMRS [long-term mine reconnaissance system] is using some of that technology," Healey says. "We see applications of that even going further in perhaps developing the capability to insert undersea communications nets in which you would have nodes that could be fiber-connected or through buoys or some other mechanism and underwater vehicles would approach those and communicate through acoustic or perhaps laser methods. But we haven't deployed any of those yet."

There has, however, been success in similar efforts with another program, the Remote Environmental Monitoring Units (REMUS). This involves low-cost UUVs designed for coastal monitoring and multiple vehicle survey operations. About a dozen of the 52-inch long, 7.5-inch diameter vehicles have been fielded. During the past three years, they have been able accurately to find and provide the location of objects on the seafloor via sidescan sonar. They use low-cost transponders and home on a 1 meter docking cone, swim in, latch, and make an electrical connection to download data, receive mission reprogramming, and recharge batteries in the open ocean.

These tests also offer possible solutions for shallow-water operations, where Healey says a different scheme is necessary for communications.

"They are limited in range because of acoustic multipath problems, channel fading, and background noise," he says. "We can go horizontal, but the range is limited due to the same issues; technology similar to cellular telephones, using spread spectrum techniques, is being developed to make this work within 4 to 5 kilometers in shallow water."

One such system, the acoustic radio interactive exploration system (ARIES), is designed as a network server vehicle to link several different underwater vehicles. It will collect data from all the vehicles in the network, communicate data among heterogeneous groups of vehicles, and communicate command and control from a surface ship or submarine. ARIES also could redirect vehicles already on station, based on the information they have gathered and transmitted back to their human operators.

On the surface, the vehicle uses GPS for navigation, Healey says. Its underwater navigation involves a 1.2 MHz acoustic Doppler navigator from RD Instruments in San Diego. "That gives us an accuracy close to 1 percent of distance traveled underwater," Healey says. "On the surface, of course, you have sub-meter accuracy with GPS. Long term distances are bounded by the errors on GPS, so you will get within a meter even at distances of 1,000 meters; at 1,000 meters underwater, you would be off about 10 meters," Healey explains.

"We can travel a couple of hours at 3.5 knots; REMUS has better range, going 5 knots for 8 to 12 hours, so they can get out as much as 60 kilometers," Healey says. "That means they can cover quite a bit of the ocean on a hydrographic survey — water depth, current and symmetry measurements, bioluminescence and temperature measurements. An operational system to operate vehicle networks should be able to operate at extended ranges, depending on the application, with a maximum probably similar to that of REMUS."

LMRS (AN/BLQ-11) is the today's only active Navy UUV program, having recently completed critical design review during the engineering and manufacturing development (EMD) phase. Prime contractor Boeing Information & Oceanic Systems in Anaheim, Calif., is building the first system, which will undergo its initial in-water integration test in 2002. Navy acceptance tests are scheduled for 2003, with initial operational capability (IOC) set for September of that year.

"The LMRS prime mission is minefield detection and classification of mines," explains Capt. John Lambert, UUV program manager at the Naval Undersea Warfare Center. "The system consists of two UUVs and equipment aboard the submarine. The concept of operations is to launch one of those UUVs to follow a preprogrammed path searching for mines and mine-like objects. It then returns to the submarine, is recovered, and the data are downloaded and analyzed. While the first UUV is out searching, the second is being programmed for its own mission."

The LMRS currently is designed with two sonar sensors — one that looks forward and the other that looks to the side. The forward looker detects any mine-like objects, then does a quick sort of its database according to size to further determine if it is a potential mine. The sidelooking sonar then takes more detailed imagery of the body that has been detected.

"We don't currently have an ability to do this kind of search without alerting potential adversaries to what we're doing," Lambert says. "What we have now are either airborne or surface systems and as soon as those assets show up on the scene, a potential adversary knows what we're doing, probably in advance of the arrival of other forces. With this system, we can detect the mines without being seen, then clear them immediately before the other forces arrive. Another possibility is we just don't operate there. We also can find the holes in their defenses and exploit them."

COTS components

As with most new military systems, LMRS makes extensive use of commercial-off-the-shelf (COTS) components. "We're using COTS computers fitting into backplanes, trying to get as close to state-of-the-art as we can. We also have a technology refresh plan and when it makes sense to upgrade, we will do so to have the best value insertion of available technology," Lambert says. "The whole system is modular and open, so when it makes sense to make these insertions into the vehicles, we can. The same is true of the processors that remain aboard the submarine." The LMRS is built in the same shape as weapons that go aboard the submarine so it can be dropped in as needed and removed when not., he says.

The program is funded for nine systems that will go aboard fast attack submarines, including the new Virginia class. A four-person cadre handles systems operation (one chief petty officer and three petty officers) that will be permanently assigned to the system rather than to any one submarine.

Cadre members will be responsible for loading the system aboard the submarine; preparing for launch; programming for mission, launch and recovery; downloading mission data; and analyzing it using the submarine's computers. The LMRS system elements that remain aboard the sub also come in torpedo-shaped containers with drop-down panels. All elements fit in standard weapons and use standard weapons handling equipment and personnel.

The target cost will be $15 million to $18 million for each production system, which consists of two vehicles, all of the shipboard mission computers, all of the hardware required to launch and recover — including robotic arm and spider and winch within the launch tube — spare batteries, transport van, and monitoring subsystems.

"This is going to be the Navy's first deployed clandestine mine-reconnaissance system, which brings a big new capability to our operating forces," Lambert says.

Yet LMRS is not the only one on the drawing board. "There are two major technology processes we're engaged in to look to the future," Lambert says. "The future naval capabilities process looks at various sensor packages and propulsion and energy for future missions. The other is the submarine technology insertion process, whereby we look at more near-term needs — 2010-2015 — to make sure we're making investments in the right technologies submarine-force wide."

Young says the future potential for UUVs covers a wide range of missions, both defensive and offensive — and includes some undersea versions of concepts also under consideration in the air.

"We have had a great deal of experience with UUVs with bombs on them — smart torpedoes. But an undersea version of a UCAV [unmanned combat air vehicle] is certainly something we are looking at and considering, although we do not have any specific programs for that," he says.

Deployable systems

Another concept under study at the Naval Undersea Warfare Center is Manta, a conceptual submarine-borne UUV system that can be deployed at long distances. With their advanced payloads, Manta vehicles could gather intelligence, perform tactical oceanography, and/or anti-submarine warfare missions.

According to Young, the Manta vision calls for:

  • multi-mission capability;
  • seamless integration of several different Manta vehicles into future submarine and surface ship platforms;
  • unmanned vehicles that operate autonomously for long time periods in shallow-water dynamic environments;
  • the capability to carry sensors to perform anti-submarine warfare, surveillance, and tactical oceanography missions;
  • full connectivity to the battle group above surface and through water communications; and
  • weapons and counter-measure deployment capabilities.

"We could see if a cascading effect from the submarine platform is a concept of operations we should look at," Young says. "We take a big sub into an area and coming off it would be either a manned or unmanned smaller sub, which could be armed or not and could carry not only torpedo-like weapons but also other weapons; some directed energy weapons might be useful as we develop that technology. From that vehicle, there could be another cascade of smaller vehicles."

Another technology under investigation is the use of gravity sensors for navigation. Prototypes of those have been developed, but they are not part of any current development program in the U.S. Navy, which may be waiting for expressed commercial interest to spur their development as a COTS component.

The Navy's interest in off-board sensors and payloads was spurred by a 1998 defense task force on the submarine of the future, which criticized the submarine community for not paying enough attention to the front end — sensors and payloads. The Navy signed a memorandum of understating with the Defense Advanced Research Projects Agency (DARPA) in August 1998 to look into those needs.

Phase 1 was an 18-month study and concepts phase, led by DARPA but co-funded by the Navy. Two contracts were let to compete and select two consortia teams.

Lockheed Martin in Manassas, Va led the first team, called Team 2020. Raytheon Naval and Maritime Systems in Portsmouth, R.I, led the second team, called Forward Pass. Each team comprised several defense contractors, but also included academia and some non-traditional contractors. The contracts called for them to investigate new approaches to sensors and payloads for submarines — not only weapons, but also anything that left the boat, whether it returned or not. That included UUVs, unmanned ground vehicles (UGVs), or offboard sensors.

"They had to look at how those payload and sensor concepts would relate to the submarine platform itself — how would you deliver the particular payload or sensor, how would you talk to it and get data from it, and how would it apply in the joint arena in the 2020 timeframe," Young says. "They submitted their final reports in September 2000 and we have started Phase 2 in the Navy labs, where they will take some of those concepts and demo them."

New submarine designs

The consideration of off-board sensors and other payloads also has led the Navy to begin looking at major new designs for submarines themselves. That includes moving some payloads outside the pressure hull to significantly increase each vessel's payload volume.

Young says that is an attractive concept, although it raises significant issues of reliability for something the crew would be unable to access for maintenance while at sea. It also could change the acoustic signature of the host submarine, which could cause serious opposition among submarine crews. Submarines live and die based on their ability to remain silent to even the most sensitive sensors.

Another possible change involves modularity. Current submarine production includes stuffing several sections with equipment, then welding sections together. More advanced modularity concepts would use pre-deployed modules containing missiles, UAVs, UUVs, etc.. Either they would be designed to fit into existing ship designs or new ships would be designed to accept the modules.

The other mode is platform modularity, where the submarine itself is built from self-contained — and interchangeable — pieces. This approach would avoid putting a ship in dry dock for a year to retrofit it with a new sonar system, for example. Instead, the old front-end module could be removed and replaced with a new one containing the advanced technology. That would be done in a matter of weeks, greatly improving force availability.

"We have had the initial concept studies done and have engaged both of our submarine building yards," Young says. "There is work to be done, but we consider the advantages to be so high on the flexibility and adaptability of those that we should pursue it. We think we can do that with our baseline Virginia, so you don't have to start from ground zero of a new ship."

As Navy leaders look to the future of their submarine force, they have defined four strategic concepts. The first is to gain and sustain access for the battle force.

"We see the future requiring a great deal of stealth, operating in the littorals," Young says. "To do that it will have to go offboard and reach far into these ground water areas so we can not only monitor what is going on in the water, but also on shore."

The second is to develop and share knowledge.

"The submarine will be a node in network centric warfare," he says. "We need to be able to know and collect data, process it on board and share it. That requires a lot of computing capability. A piece of that is the undersea connectivity and sensor networks, which may give us the capability to operate with more than one sub in an area with consort ops."

The third concept is to project power with surprise from close in.

"The submarine is not a level of effort platform; it does not carry a huge load of missiles to use for strike, but it does have the capability of carrying and firing those weapons, such as Tomahawks," he says, "so if you have the capability of doing that close in and with surprise, it can aid the battle force. That means getting the right weapons onboard the submarine is important."

The final concept involves weapons of mass destruction counter or deterrence.

"That is going to be the way of the future and we need to have an offensive defense against those, finding out where they are and being able to strike against them," Young says. "In all that, offboard vehicles play a key role for the submarine," Young concludes. "We need the energy force to enable us to get and remain on station, the sensors to do the job and using other offboard vehicles, such as UAVs and UGVs, as an extended network of sensors."

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