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[This digested article by Edward J. Walsh is reprinted by special permuszon from the Armed Forces JOURNAL International/February 1990.)

The Defense Advanced Research Projects Agency (DARPA) will begin tests in March of two prototype unmanned undersea vehicles (UUVs). The tests are expected to demonstrate the feasibility of a UUV design that could be used for a variety of classified, “high priority” naval missions.

Unlike several other autonomous undersea vehicles, the UUV is planned as a tactical system that would be deployed from submarines, surface ships, and beaches. A Tentative Operational Requirement for a UUV has been approved. A third prototype will be delivered for testing in mid-1991.

The UUV was one of the first prototype programs undertaken by DARPA to “stimulate a greater emphasis on prototyping” of systems before they transition to the Services for full-scale developmenl Captain Edward Craig, director of deep submergence systems in the Office of the Chief of Naval Operations, said the program entails putting together some prototypes of a “back of the envelope” concept to see if proven technologies can be integrated “If it works when we put it in the water, we can develop it for specific missions.”

The technologies being incorporated into the UUV have never before been employed as they will be in this Undersea Vehicle. The program is expected to transition to the Navy in about three years.

The UUV prototype, which is 36 feet long and 44 inches in diameter, is considered a “large” UUV. It is similar in size to a Mobile Undersea Test vehicle that began operational testing off San Diego in late 1988.

Rear Admiral Thomas W. Evans, deputy chief engineer of the Navy and director of advanced submarine R&D at Naval Sea Systems Command said “the Navy would prefer to reduce the size of UUVs as much as possible by using advanced technology to cut the size and weight of the sensors and computers, and most importantly by reducing the size of the power sources needed to drive the UUV.”

Evans is directing the transition of a LOS ANGELES-class attack submarine, the USS MEMPffiS (SSN-691 ), from the tactical submarine fleet to a role as the Navy’s at-sea test-bed for advanced submarine technology, including launch and recovery of both large and small UUVs.

The UUV prototype program is expected to demonstrate the capability to perform certain naval missions from an autonomous, unmanned vehicle that would be equipped with advanced acoustic detection, communications, and signal and data processing systems. UUV mission software, which will direct the vehicle on such missions as mine detection, undersea surveillance and communications, is expected to use “artificial intelligence” algorithms that function akin to human thought processes. Three mission packages will be prototyped: a tactical acoustic system; a mine search system; and a remote surveillance system.

Draper Labs, under a contract with DARPA, has completed’ assembly of the first UUV prototype and is continuing work on the second. The hull will be built of titanium, a material that provides a much higher strength-to-weight ratio than steel. Pressure testing of the first hull was performed in late December 1989.

An internal pressure hull will house the UUV mission payload, which will occupy a five-foot-long section, and the batteries, which will be located in two 52-inch compartments. System sensors will be housed in the forward six-foot compartment. Vehicle electronics will be located in a 52-inch midsection.

The propulsion system, consisting of a 12-horsepower electric motor, and a motor controller, will occupy the aft 12 feet of the vehicle. The motor is built to operate when completely flooded with seawater. Bearings are fabricated with a special non-corrosive alloy, and the copper windings that carry power to the motor are impervious to wear. During normal operations, the internal volume of the motor is filled with oil in order to equalize pressure between the inside and outside of the motor, permitting use of a thinner and lighter “soft” housing, instead of a traditional, bulkier housing. The small motor — 10 inches wide by 20 inches in diameter – achieves an extremely high degree of power density by use of samarium cobalt or “rare earth” magnets mounted in the rotor shaft.

Draper Lab’s approach to the UUV design is based on a need to make it fully “fault tolerant.” Since no man is in the loop, the UUV must be highly reliable and able to operate despite computer hardware failures. The vehicle will employ three fully redundant computer (fault-tolerant) processors. The processors employ a “voting” approach to UUV system management. All operational programs – those that control guidance, navigation, and mechanical subsystems such as ballast pumps – are run by alJ three computers, which must “agree” on how the subsystems are controlled. If only two agree, the ship is operated in a degraded mode.

Mission packages eventually will also be run on the Draper Lab’s processors, although mission contractors are being required to provide computer hardware.

Specific mission plans remain classified. However, the UUV mission concept is basically the same as that of unmanned aerial vehicles being developed by the Services.

Although the program is “looking at the submarine side, UUVs can be launched from surface ships or ships of opportunity.” It is conceivable that UUVs could be dropped from aircraft or helicopters.

UUVs equipped with tactical acoustic systems, if assigned to such missions as reconnaissance, surveillance, and target acquisition, presumably would be used for detection and tracking of hostile submarines and surface ships. Acoustic elements will likely include a sophisticated active sonar to detect quieter Soviet submarines.

The tactical acoustic system software will be integrated with the UUV following the operational testing that begins next month. Prior to delivery to the San Diego test site, mission software will run on a high-fidelity, real-time simulator at Draper Labs. Physical integration of the mission package into the UUV prototypes, actual testing, and test support will be performed. The acoustic system package will transition from DARPA to the Navy in mid-1991.

Development of the mine search system mission package calls for mission software to be written by Lockheed. Raytheon will provide accessory acoustic components, such as depth sounders and altitude monitors. Bell Labs will furnish a fiber-optic communications link, required for transmission of “supervisory” commands from a “host’ platform such as a submarine or surface ship to the UUV mission processor. The link must be ultra-thin to minimize drag when spooled out over thousands of yards and requires a tether management system with sensor and software.

The remote surveillance system mission-architecture operational requirement will “require a substantial sensor payload oriented to ASW.” DARPA expects to complete development of the mission specification. Operational testing of this system aboard the UUV prototypes will be conducted from mid-1992 through mid-1993.

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