By John Rhea
CHARLOTTESVILLE, Va. — Engineers from Litton Marine Systems are blending technologies from two of their ring laser gyro systems into one new model to replace old gyrocompasses on a form, fit, and function basis at lesser cost on U.S. and NATO submarines and surface warships, company officials say.
The new ring-laser-gyro inertial navigation system (INS) from Litton Marine, based in Charlottesville, Va., is known as the WSN-7B.
The new WSN-7B, which blends technologies from the Litton Marine AN/WSN-7 and from two less-accurate export versions, the MK 39 and MK 49, is reducing maintenance costs and enabling Litton Marine to meet the demanding accuracy requirements of the U.S. Navy and the less rigorous specifications permitted for export to other NATO countries.
The new system costs about $300,000, compared with $500,000 for the WSN-7, which has been the traditional mainstay of the Litton line, says Wayne Humphreys, Litton's vice president for government relations. Litton delivered the first WSN-7B in January under a low-rate initial production contract for four systems from the U.S. Naval Sea Systems Command.
The WSN7B is being installed on the attack submarine USS Jimmy Carter (SSN-23) under construction at General Dynamics Electric Boat Corp. in Groton, Conn.
Navy leaders say the plan to backfit this system on submarines and surface ships such as the Oliver Hazard Perry-class guided missile frigate (FFG-7) and mine warfare ships. It will back up the WSN-7 on submarines and be the primary navigation system for the surface ships.
Humphreys claims 80 percent parts commonality among the INS units and sufficient savings on maintenance to pay back their costs in less than four years when they replace traditional spinning-mass INS units.
John Carvil, program manager at the Navy's Space and Naval Warfare Systems Center facility at Little Creek, Va., confirms these savings. He notes that the worst-case cost to repair a spinning-mass electromechanical INS runs more than $100,000. Moreover, he says, the typical submarine experienced three failures a year of its inertial measuring unit. This ate up one-third of a submarine's operational budget, he adds.
Although Carvil refuses to comment on the accuracies of either the U.S. Navy systems or the export versions, he claims that a single, compatible family also cuts costs for training, logistics, and supply support. Other estimates put the accuracy difference between the U.S. Navy's INS units and the export versions at a factor of three.
The adoption of the new family of ring laser gyros logically begins with submarines since they have the most stringent accuracy requirements. Yet Navy leaders want to extend the technology to surface combatants, particularly to guided missile frigates and amphibious assault vessels — and later to the Navy's 12 aircraft carriers.
Officials of the U.S. Coast Guard have adopted the less-accurate MK 39, which Litton introduced in 1997. Coast Guard officials awarded Litton a $5.2 million contract in May to outfit all its 270-foot Famous-class medium-endurance cutters. This project is to be completed within four years in an effort to replace the Coast Guard's spinning-mass gyrocompasses on the cutters.
The ring laser gyros sense a ship's motions and compute its position, velocity, attitude, heading, and rates in digital and analog formats. The data are routed via databuses to the ship's onboard computers, where they are processed.