Electric Drive for DD(X) Sparks Competition Over Exotic Motors

By OTTO KREISHER
Special Correspondent

One of the keys to success in the U.S. Navy’s pursuit of an integrated power system (IPS), or electric drive, for its future surface combatants is development of an electric motor that packs much more power in a much smaller machine than has ever gone to sea.

The motor the Navy selects to drive its new DD(X) destroyers also could be used in the CG(X) cruisers that will follow, and possibly other future naval and commercial vessels.

That potentially lucrative market has triggered a spirited competition among a number of firms that are offering different technologies which are at various stages of maturity but could provide the leap-ahead capabilities the Navy is seeking.

And that is a situation the program officials at Naval Sea Systems Command (NavSea) clearly enjoy. “It’s good for the Navy to have competition,” said Michael Collins, IPS program manager at NavSea.

Northrop Grumman Ship Systems is leading the DD(X) program under a $2.9-billion design and development contract. That includes $275 million for the IPS, an innovation in ship propulsion Navy officials have likened to the jump from sail to steam.

The Navy has used some form of electric drive since 1913, Collins said. What is new about IPS “is the integration of electric propulsion and the electric auxiliaries all into one system,” he said.

In addition to driving the ship, the integrated system will provide electricity for all the current weapons, sensors and other systems and, in the future, for exotic weapons such as magnetic rail guns or lasers. The turbines and generators that will provide the electrical power are well-established technologies.

With IPS, the ship’s engines, or “prime movers,” will no longer be connected to the propellers. Instead, the engines — four marine gas turbines for the DD(X) — will power generators that produce a total of 80 megawatts of electricity — nearly 10 times the electrical power available on today’s Arleigh Burke-class destroyers. That electrical power then will be distributed to most of the ship’s systems and the electric motors that will drive the propellers.

But there is a missing piece to the IPS. To drive the propellers, the Navy needs a 36-megawatt electric motor that is smaller and lighter than any currently powering a vessel.

The Navy needs a motor that provides more power for its size because of its requirement for a top speed of 30 knots or more — well above the speed for commercial vessels. Because so much power is required to hit that increment of speed, “we have nearly twice the propulsion power of a similar size commercial vessel,” Collins said.

“The enabling technology that makes electric drive fit is the high-torque propulsion motor,” said Peter Mongeau, a vice president at DRS Electric Power Technologies, in Parsippany, N.J.

DRS is a leading developer of permanent magnet motors, which use solid blocks of alternating north/south magnets made of a rare earth material called neodymium iron boron attached to the rotor to create a rotating magnetic field in place of the usual wire coils. As a Northrop Grumman subcontractor, DRS is building a 36-megawatt motor that the Navy hopes to use in the first DD(X).

However, because no one has made a permanent magnet motor that powerful, there is no guarantee the DRS machine will be ready for the first ship, said Capt. Charles Goddard, DD(X) program manager. The DRS motor is “our baseline and it’s in the design now and is currently what we plan to use,” he said. “Now we have to prove out the design through the test program.”

The permanent magnet motor is preferred, Goddard said, because it should have “better power density. That means it’s a more compact motor for the same power. It also has the potential to have better noise performance and slightly better efficiency over a range of operations. … But that’s all on paper.”

“We can’t risk the whole ship on a paper motor,” Collins said. Therefore, the Navy is developing a backup motor, he said.

Mongeau concedes that the 36-megawatt motor would be “the world’s biggest permanent magnet motor.” DRS built a 5-megawatt motor, which was tested by the Navy, and other firms have made permanent magnet motors up to 10 megawatts, he said. However, producing a 36-megawatt motor “is not as big a technology jump as the size would indicate,” Mongeau insisted. “These motors scale very well.”

Collins and Goddard agreed that building the more powerful motor is more of an engineering challenge than a technical risk. But, Collins said, “we’re on a pretty tight schedule, so the schedule risk is probably higher than the technical risk.”

NavSea wants the bigger DRS motor in place at the Philadelphia Naval Surface Weapons Center so testing can begin by next summer, Goddard said. He expects the Navy to award Northrop the detail design and construction contract for the first ship in March, with a scheduled delivery in 2011.

Mongeau said DRS was well into the detailed design of the bigger motor in June and he was confident it would be ready early next year. He also was confident the DRS motor would be used in the DD(X) ships because it was lighter and more efficient than other contenders.

In case there are problems with the DRS motor, the Navy has a fallback in a 36-megawatt “advanced induction motor,” a relatively safe upgrade to a conventional electric motor, Collins said. The induction motor was built by Alstom, a British firm that produced smaller motors for the Coast Guard icebreaker Healy and the new Lewis & Clark class of supply ships.

A third contender for the Navy’s procurement dollars is an exotic motor being developed by American Superconductor in Westborough, Mass. Chuck Mayer, a company official, said the motor his firm is developing for the Office of Naval Research (ONR) is a better answer to the Navy’s quest for a smaller motor for DD(X).

American Superconductor is working to produce a 36-megawatt motor using high-temperature superconducting technology. In this case, “high temperature” is very much a relative term. Superconduction works on the principle that when most materials are cooled to nearly absolute zero — the temperature at which molecular movement virtually stops — they transmit electrical currents with almost no resistance.

This minimal resistance would allow a 36-megawatt motor to be about one-third the weight of an induction motor and about half that of a permanent magnet machine, Mayer said.

American Superconductor’s “high temperature” motor will work at 30 to 40 degrees above absolute zero on the Kelvin scale, Mayer said. Although that is nearly 400 degrees below zero Fahrenheit, Mayer said that temperature can be produced by commercially available cooling systems used for magnetic resonance imaging machines in hospitals.

That makes the superconductor motor a solid option for DD(X), Mayer said. “I know the permanent magnet is the baseline” motor, but the fact that ONR has awarded $78 million in contracts to produce the superconductor motor “says something about the future,” he added.

American Superconductor built a 5-megawatt motor that is being tested at Florida State University and is developing a 36-megawatt motor Mayer said would be ready for testing in 2006.

Because of that timeline, Collins said, “it’s not really a candidate for the baseline ship. It might be a candidate for an upgrade, if it proves out.”

Although the superconductor motor has the potential to be smaller and lighter than the permanent magnet, Collins said, “permanent magnet motors are a step ahead of this motor,” which is “just now making the jump to the propulsion size.”

But, Mayer said, “we’re very confident that if we had the contract today, we could produce the engine.”

ONR also has awarded contracts to General Atomics in San Diego to develop a direct current (DC) superconducting motor, and to General Dynamics for an “integrated motor propulsor,” in which the propeller is tied directly to the rotor.

General Atomics is testing a 5-megawatt machine it calls the Superconducting DC Homopolar Motor. It operates at a colder temperature than the American Superconductor motor, using cooling technology demonstrated years ago in a proposed Navy minehunting system.

General Atomics business development director Carl Fisher said the firm feels it has resolved some past technical challenges and is looking forward to a new ONR competition for a full-size (36.5-megawatt) DC motor he believes will be even smaller, lighter and quieter than the current alternatives.

Along with the advantages of electric motor technology, the Navy is interested in new propulsion systems that might further advance ship architecture beyond the constraints of conventional drive shafts and propellers.

General Dynamics’ Electric Boat division has developed a Rim-Drive Propulsor (RDP) as an improvement of the external pod motors being used on commercial ships, company officials said. Electric Boat has produced 90-kilowatt and 1.6-megawatt versions of RDPs.

The larger motor is scheduled to be installed on a Navy-provided surface ship test platform in 2006 for trials intended to prove the technology and validate the RDP’s performance.

All of the ONR projects potentially could be used on later versions of DD(X) or other Navy ships, Goddard said.