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Naval Systems: Future Shipboard Power – The Debate Intensifies

By Ed Walsh

The test, which evolved from a joint effort by the Office of Naval Research (ONR) and the Defense Advanced Research Projects Agency that began in 1993, sets the stage for the early1998 start to develop a 1,000-hp motor powered by superconducting magnets. The Annapolis performance is especially significant because the superconducting wires were new high-temperature magnets, meaning that they functioned at minus 321° Fahrenheit (F.), which requires considerably less equipment than the older-technology low-temperature superconductors, which operate at around minus 450° F.

Navy labs also have introduced a sturdy mechanical refrigerator, weighing as little as 40 pounds, that is capable of cooling both high- and low-temperature superconductors without using cryogens. The refrigerator, along with a compressor about the size of a file cabinet, replaces the cumbersome cooling equipment needed to accommodate cryogens such as liquid nitrogen and makes superconductors for ships distinctly conceivable.

Superconducting technology is being put through its paces at NSWC/Dahlgren's Coastal Systems Center, Panama City, Florida, where an advanced lightweight influence sweep system (ALISS) is being tested at sea. The system, developed under a joint Navy-Army advanced concept technology demonstration sponsored by the ONR, uses the older low-temperature superconductor technology, but provides the capability to sweep for influence mines at any speed the craft that carries it can muster—up to about 35 knots for Navy landing craft, air cushion (LCACs).

More breakthroughs with superconductors are likely to come sooner, not later. Furthermore, the excitement about superconductors comes at a time when the Navy is moving toward adopting a more mature power technology, referred to as permanent magnet motors (PMMs), for future ships. A Naval Sea Systems Command (NavSea) integrated product team in late October briefed both the Chief of Naval Operations' Technology Ship Characteristics Improvement Panel (TSCIP) and the flag-level SCIP on a range of future ship-design concepts. One of those, referred to as the "common all-electric ship," would study technologies that could benefit both surface vessels and submarines, assuming the right budget tradeoffs were made. For power generation, the NavSea team endorsed PMMs, along the lines of axial and radial PMMs developed by Kaman Electromagnetics and Newport News Shipbuilding in the early 1990s. Most Navy power-systems officials believe that permanent magnet motors will be selected as the future baseline power source for the Navy's integrated power system, presently being developed by NavSea.

The integrated power system is under contract to Lockheed Martin's Ocean, Radar, and Sensor Systems Division. System components, including a current-technology electric motor and generator, both subcontracted to Cegelec, and power-conversion modules being built by Power Paragon, are scheduled for delivery to NSWC/Carderock's Ship Systems Engineering Site in Philadelphia between March and July. Testing will continue through mid-1999. The system development leaves opportunities for inserting future power technologies, probably the PMMs. Supporters of superconductors still point out, however, that superconductors generate power indefinitely and are easier to regulate.

Permanent magnet motors offer significant advantages in power density over conventional-induction motors, and thus can be only about one-third the size of conventional motors, a benefit reflected throughout the power plant design. Such motors conceivably could be sited outside the hull; they already are being used in ferries, icebreakers, and tankers.

Supporters of superconductors point out that superconductors can generate power indefinitely, and are easier to regulate. Program officials suggest that a strategy for looking more closely at the advantages of superconductors "still has to be worked out."

Meanwhile, NSWC/Carderock also has started a three-phase effort to look at prototype ship-service generators powered by fuel cells. Several contract awards are imminent (one already is in place with Energy Research Corporation). Fuel cells, based on proton-membrane, phosphoric-cid, and molten-carbonate designs, are highly reliable and almost pollution-free. The technology already is used widely by commercial utilities, but has been difficult to design for the confined space available on Navy ships.

The confluence of steps forward on power-systems technologies comes at an eventful time for the surface fleet, as it begins this March to award early study contracts to industry for the next-generation DD-21 land-attack destroyer. The contractor teams are expected to jump into the debate with their own power-generation ideas. The DD-21 program manager does not necessarily have to buy the Navy-developed integrated power system. Whatever he decides, however, the debate over how to add power to the all-electric ship vision will only get more intense.

 

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