DARPA advanced attack sub technologies program

Darpa Looks at New Technologies for Next-Generation Attack Submarine
Aviation Week & Space Technology
01/30/2006, page 519

Ramon Lopez
Washington

Pentagon's R&D agency drives technology to cut the price of submarines

Printed headline: Run Silent, Run Cheap

With the cost of a single Virginia-class attack submarine approaching $2.5 billion, efforts to find lower-cost technologies are becoming a fiscal imperative for the cash-strapped Pentagon. And that's precisely what lies at the heart of a futuristic project that could yield a radically new submarine design.

The Defense Advanced Research Projects Agency (Darpa) and the U.S. Navy are spending $100.7 million in the next four years on Tango Bravo, an effort that might someday lead to the production of a new attack submarine. Tango Bravo, a term taken from Navy slang for "technology barrier," is intended to produce a design that provides all the capabilities of Virginia-class boats at half their size and cost. If the effort is successful, submarines utilizing the design would not only be much less expensive to build and maintain, but highly adaptable and capable of operating in both deep ocean and littoral or coastal waters, the latter a focus of evolving Navy strategy.

The ambitious effort has all the elements of a classic Darpa program: challenge, risk and a high payoff. But don't call it a new class of submarines, at least not yet. Officials insist that Tango Bravo is just a demonstration of nascent technologies and doesn't include plans to develop an actual craft. The program instead seeks to evaluate certain technologies to determine whether they can meet stringent submarine performance requirements while reducing ship-acquisition and life-cycle costs.

Yet Tango Bravo, if it matures beyond the drawing board, could bring fundamental changes to U.S. submarines, some of which would be revolutionary, according to advocates.

Khine Latt, Darpa's program manager for Tango Bravo, says the agency's goal during this phase of the project is to demonstrate concepts focused on the current operational environment. "Our challenge is to define the demonstration parameters so that the science and technology unknowns are adequately characterized while, at the same time, balancing resources against the breadth and scale of the demonstrations," she says.

Submarine missions and designs are evolving. One example is the conversion of ballistic missile submarines to carry guided missiles and serve special ops platforms.Credit: ELECTRIC BOAT

As originally conceived in 2004, Tango Bravo was to concentrate on five areas considered major technology barriers for a next-generation submarine design. These are: shaftless propulsion; an external weapons-launch system; an electric actuation system; hull-adaptable sonar arrays, and an automated attack center.

In June 2005, Darpa awarded nearly $36 million in contracts for five technology demonstrations, which cover only three of the five technical areas. Because of a funding shortfall, hull-adaptable sonar and a revamped automated attack center have dropped off the radar screen for now.

The two discarded technical areas were, like the others, aimed at lowering costs while increasing operational capabilities. For example, the demonstration of a prototype sonar array adaptable to a variety of hull shapes would in theory provide significantly better detection and tracking performance than current Virginia-class hull-mounted arrays, at half the cost. Likewise, the automatic attack center was expected to yield savings by demonstrating a capability to operate with eight officers and enlisted personnel at battle stations, down from 17 required on the Virginia-class (SSN-774). This would be possible through replacement of current-generation sonar, fire-control and tactical data-display systems, allowing one sailor to do work that now requires two.

Darpa solicited bids and received proposals for all five technology areas, but made what it calls a "best value" judgment. That meant channeling money for contracts to three of the five areas. At this point, there are no plans to go beyond these three technologies, the agency says.

Darpa decided to go with the technical areas where it could get the most bang for its buck. "Tango Bravo is funding research in three of the five areas, because resolution of these technology issues would most impact the early phase of submarine concept development and design," says Latt.

The proposed Tango Bravo sub would be half the size and cost of a Virginia-class submarine.Credit: ELECTRIC BOAT

The three technical areas will proceed according to schedule. The Tango Bravo program is structured into multiple phases over the next three years, and technologies that advance through all phases will continue to follow-on development or design efforts beginning in 2009.

The first area, shaftless propulsion (i.e., propulsive systems that do not require a shaft to penetrate the pressure hull) would provide Virginia-class speed--more than 25 kt.--and not less than 50% of the displacement of the Navy's newest attack sub, or approximately 7,800 tons.

Two defense contractors were selected to develop shaftless submarine propulsion, providing for reduced arrangement complexity and lower costs. General Dynamics Electric Boat of Groton, Conn., received $6.3 million while DRS of Parsippany, N.J., was awarded $5 million. Each contract covers 12 months of R&D, mostly involving computer simulations and analyses. The second phase, set to last 18 months, will involve component development, while phase three, also 18 months, is to include demonstrations of large-scale prototypes.

Shaftless propulsion would be a major cost-saving. Both Electric Boat and DRS are evaluating approaches to replacing a mechanical shaft with large permanent magnetic motors mounted outside the pressure hull.

Neither Latt nor her deputy, U.S. Navy Capt. Jerry Burroughs, is willing to divulge details regarding the competing shaftless-propulsion concepts, citing the competitive environment and proprietary technologies.

Electric Boat officials are equally tight-lipped, declining to even confirm the use of permanent magnetic motors. Franz Edson, director of submarine concept formation and payload integration, says phase-one work "will involve performance prediction and a significant number of trade studies," leading to selection of "appropriate technologies and further development."

Edson calls the work "revolutionary," not so much because of the technologies associated with shaftless propulsion, but with what it can do for submarines in general, like the impact on volume. He claims Electric Boat has a strong technical solution. "I am optimistic, but not naive [enough] to think this is a walk in the park."

DRS was more open to discussing its approach to designing and developing a shaftless propulsor. The company claims it is a unique solution, based on next-generation permanent magnetic motor and electric-drive technologies, that will reduce size and free up space for a submarine's payload.

This design will also drive down costs, according to Ed Bartlett, president of DRS Power Systems. "The most precious and expensive real estate in a submarine is inside the pressure hull," he says. "By moving things outside the hull, we can reduce the cost of the ship."

As the follow-on to the Seawolf, the Virginia-class craft (shown with mini-sub) was supposed to be more affordable and adaptable to post-Cold War missions.Credit: ELECTRIC BOAT

DRS's technical approach builds on work it completed for the U.S. Navy on the next-generation DD(X) destroyer. The company built an engineering development model employing permanent magnetic motors for the main propulsion, but a test failure led to a five-month schedule delay. The technical glitch was resolved, but not before the Navy switched to induction motors for the ship.

Bartlett says DRS has a wealth of knowledge regarding commercial versions of permanent magnetic motors, and has been delivering production motors for oil drilling and mass transit systems for more than a decade. The company's first submarine application for permanent magnetic motors is dubbed "Speed," for shaftless propulsion with external electric drive. "Speed takes everything we learned on DD(X) and moves it outside the hull," says Bartlett.

"Shaftless propulsion is revolutionary because it is the fusion of every technology discipline in ship design, from naval architecture to mechanical engineering, to motor and electronics design and engineering," Bartlett says. "We are designing a machine that merges the propulsor, the motor and the drive system."

Bartlett lauds permanent magnetic motor technology, saying it offers simplicity, reliability and low-cost operation. "The difficulty is in coming up with the right design rules and machine interactions," he notes.

Permanent magnetic motors are made possible by the availability of low-cost, high-quality magnets and insulated-gate bipolar transistor switches, which are huge, fast-switching semiconductors.

Tango Bravo research to date is "encouraging," says Bartlett. "I'm extremely confident. Our early test results give us a lot of faith that we are going down the right path and will be able to achieve our technical goals. We believe that at the end we will have learned enough to start a design and build one for a submarine."

Work is also proceeding on the second area, the external-launch system. General Dynamics, recipient of a $10-million, 18-month first-phase contract for system design, will develop and demonstrate a system capable of firing Mk. 48 torpedoes. Northrop Grumman Newport News received an equal amount for similar research. The second phase of that effort, demonstrator development, will also last 18 months, and involves fabrication of a full-scale demonstrator and fixed-launcher demonstrations. The third phase, involving submarine integration and at-sea demonstrations, will last for 12 months.

External weapons stow-and-launch capability holds out considerable promise for reducing the price of a submarine by making the pressure hull smaller. But some consider this technology barrier as hard a nut to crack as shaftless propulsion.

USS Jimmy Carter (SSN-23), the third and final Seawolf-class nuclear-powered attack submarine, was commissioned in 2005.Credit: ELECTRIC BOAT

Darpa's Latt says the U.S. Navy has never before mounted and fired torpedoes from outside a submarine's pressure hull. The Navy's Burroughs notes that continual exposure to seawater could severely degrade the reliability of torpedoes.

Pat Bevins, who runs Electric Boat's project management and concept formulation for Tango Bravo, says the Navy and Electric Boat have flirted with eliminating the torpedo room since the 1990s. "That's what Tango Bravo is all about: to develop technologies that might allow us to put the weapons external of the pressure hull."

He says an attack submarine's external weapons-launch system might include several torpedoes grouped together in a faired assembly that's attached to the outside of a submarine but embedded in the ship's hull line. "We would protect the torpedoes from the elements, providing a benign environment up to the point of launch," Bevins says.

To prove the concept, Electric Boat will demonstrate a canister-launch system; a single-weapon launcher that will test launch forces in a static mode while measuring the acoustics. "I rate our chances for success as good, not excellent," he concedes. "This is a tough technical problem. But if we succeed, there would be a huge benefit in reducing the cost of the ship."

The third technical area is evaluating the potential of electric actuation to replace hydraulic, pneumatic and mechanical controls in driving ship-control surfaces. For this, Electric Boat received a third Tango Bravo contract. The $4.7-million, 18-month phase-one award is for the development and demonstration of a radically reduced ship infrastructure concept that uses electric actuation in place of hydraulic and mechanical actuation of control surfaces, including the rudder and stern and bow planes. A follow-on R&D effort will cover another 18 months.

Electric Boat's Edson, who has spent the past 26 years devising advanced technologies for warships, is optimistic about the potential of Tango Bravo. But his optimism doesn't mean Tango Bravo will make it into the ocean anytime soon. As skeptics point out, a department barely able to afford its current class of submarines isn't likely to jump on board plans to fund a full-scale prototype, particularly with an ongoing war in Iraq that has little use for submarines.

But if the Pentagon does decide to go that route, industry, at least, is cautiously optimistic.

"These [technologies] are not pie-in-the-sky, gee-whiz kinds of things," Edson insists. "They are real, of tremendous benefit and I think achievable with the right engineering talent."

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