Unmanned Underwater Vehicles: Is Bigger Better?

The U.S. Navy has many mundane, messy and perilous underwater missions that are better performed unmanned vehicles. When considering the right vehicle for the mission, size does matter.

Unmanned Underwater Vehicles (UUVs) are classified into three basic size categories: man-portable, lightweight, and large displacement based on size (as measured by displacement) and endurance. The Navy considers vehicles that are larger in diameter than the standard submarine 21-inch torpedo tube as "large displacement" UUVs.

In his 2016 posture statement to Congress, Secretary of the Navy Ray Mabus said that Autonomous Undersea Vehicles (AUV) are a key component of the Navy's effort to expand undersea superiority AUVs are conducting sea sensing and mine countermeasure tasks today with human-in-the-loop supervision.

"By removing the need for environmental control systems - things like oxygen generation, G-force limitations, we can develop platforms that stretch the bounds of our imagination. Endurance is another important advantage unmanned technology brings to the fight. Our UUVs need to be able to stay out for months at a time, allowing them to observe large areas for prolonged periods, without interruption and without degradation," Mabus said. "While nominal force structure requirements for FY25 have not been determined, the Navy is committed to growing both the size and composition of the AUV force. In the near-term, AUVs present an opportunity to increase undersea superiority and offset the efforts of our adversaries," he said. "LDUUV will be launched from a variety of platforms, including both surface ships and submarines. The craft's missions will include ISR, acoustic surveillance, ASW, mine countermeasures, and offensive operations."

The LDUUV differs from other unmanned underwater vehicles built or evaluated by the Navy in that its large displacement allows for greater energy capacity to support increased persistence. "The greater energy capacity extends the reach of Navy UUVs," said Naval Sea Systems Command (NAVSEA) spokesman Dale Eng.

According to Eng, the LDUUV is planned as an unmanned undersea vehicle to conduct "dull, dirty, dangerous, and otherwise impossible" missions relative to manned platforms. The LDUUV will not only extend the mission capability of its host platform, but it will also allow the host to conduct concurrent operations due to its significant persistence-measured in weeks instead of hours. "As a result, the LDUUV effectively acts as a force multiplier. In addition, the LDUUV will support advances in technology and future payloads (such as advanced ISR capabilities, deployable payloads, and advanced, longer duration energy sources) via its modular open architecture."

The LDUUV program will design and build a modular, reconfigurable Unmanned Undersea Vehicle (UUV) with Open Architecture (OA) software (SW) focused on introducing a new class (large displacement) of UUVs to the Navy to provide increased endurance, payload hosting, and delivery capability. The LDUUV will be modular in design and include hotel functionality (guidance and control, navigation, autonomy, situational awareness, core communications, and power distribution), energy and power, propulsion and maneuvering, mission sensors (payloads), and communications links.

"It is intended that modules will have well defined interfaces for the purposes of implementing cost-effective upgrades in future increments to leverage advances in technology," said Eng.

The Naval Undersea Warfare Center (NUWC) Newport Division will serve as lead system integrator. "We anticipate releasing additional opportunities in the future to industry to support LDUUV Prototype fabrication," said Eng. "Testing will be conducted by the government. Specific details such as testing location are still under review."

The effort is projected to include industry, academia and governmental field activities. NUWC Newport Division will release LDUUV-related opportunities for industry under FBO announcements, Eng says.

Innovative Naval Prototype

The Navy's "program of record" LDUUV is different than the Office of Naval Research Large Displacement Unmanned Underwater Vehicle Innovative Naval Prototype (LDUUV-INP) experimental UUV. "The LDUUV-INP advances the state of energy, autonomy, and endurance technologies in a large UUV format," said Eng. "Technologies developed under the ONR LDUUV-INP have informed, and will continue to inform the Navy LDUUV associated program of record. Further LDUUV-INP advances will enable future missions envisioned for this system."

ONR has long been involved in undersea technology and the development of underwater vehicles, including LDUUVs. According to Chief of Naval Research Rear Adm. Mat Winter, ONR's Innovative Naval Prototype LDUUV program will design and build five LDUUVs: two preliminary designs, two pier-to-pier vehicles, and one submarine compatible vehicle. "The program is developing energy, autonomy and core systems to operate in a complex ocean environment near harbors, shorelines, and other high traffic locations. Goals include doubling air-independent UUV energy density, using open architecture to lower cost, and enabling pier to pier autonomy in over-the-horizon operations. Achieving these goals will reduce platform vulnerability and extend the Navy's reach into denied areas. ONR is developing a long endurance, fuel cell-based power plant to be incorporated into LDUUV prototypes. A long endurance mission demonstration is scheduled in FY 2016."

Critical to the success of LDUUV is the energy source. "The Navy is reviewing multiple energy sources to include Silver-Zinc batteries, Lithium-Ion batteries, PEM (or Proton Exchange Membrane) fuel cells, solid oxide fuel cells, and various metal burner advanced energy systems such as aluminum combustors," Eng says. "Each energy source under review will be considered based on its energy density, safety, and procurement and life cycle cost."

Eng Chief of Naval Research the Navy plans to utilize multiple host platforms for LDUUV in support of worldwide operations. This includes surface ships such as LCS, and submarines (both SSGNs and Virginia class SSNs) via Large Ocean Interfaces (LOIs) such as the extended Dry Dock Shelter (DDS) and the Universal Launch and Recovery Module (ULRM). The Navy plans to utilize dedicated and specifically trained Sailors from an unmanned undersea vehicle detachment (Det. UUV) at Commander, Submarine Development Squadron 5 located at Bangor, Washington. Eng said the Sailors will be specifically trained to conduct mission planning, and will embark supporting host platforms in support of launch and recovery operations.

In fact, missions for some large unmanned vehicles, like the DARPA ACTAUV and Boeing's Echo Voyager XLDUUV (see story page 22) do begin and end at the pier, instead of being launched or recovered by a host ship.

A great example of a value-added role of a very big system is Theseus (see below), which laid 220 km of cable under Arctic ice a decade ago.

Easier Said Than Done

The promise of modularity and commonality are powerful. A UUV that can perform multiple missions makes sense, but the reality is more difficult. Many systems were rushed to the customer to meet an urgent need, without the benefit of common logistics, or the ability of systems to operate or communicate together. Many proprietary systems can mean that most of them will not truly mature.

"Successful system integration and true modularity don't come from just designing to requirements - they require a different mindset," said Ethan Butler, Director of Strategic Systems at Bluefin Robotics in Quincy, Mass.

"It's vital to be thinking 'modular' from the very beginning, so that when the time comes to adapt to a different mission or payload you don't find yourself fighting against design decisions that only work for one."

Bluefin, which was an MIT spinoff in 1997 and was acquired by General Dynamics Mission Systems earlier this year, has integrated hundreds of different payloads into its vehicles, Butler said.

Butler points out that while the Knifefish mine countermeasures UUV is a highly specialized instantiation of the company's Bluefin 21 vehicle, it was the fundamentally modular design of the parent Bluefin 21 vehicle that made specialization possible. "Our architecture is modular down to the very lowest level so that we don't have to redesign the vehicle for every different mission."

The concept of modularity, and plug-and-play, is not as simple as it sounds, said consultant Mike Good. "We had a lot of people tell us that they had systems that were ready to use 'off the shelf.'

But many weren't at the technical maturity level they claimed," Good said. "These systems have to be tested in a rigorous environment - as a stand-alone system, and then as a system-of-systems (SoS). Integrating multiple systems into a new capability is much harder than most people realize."

Good said we've become used to the idea with our computers and USB connections. "But the simplicity of a USB thumb drive to the user can be misleading with respect to the enormous effort that is behind making it work. As an example, the current USB specification is several hundred pages long and the evolutionary product of over 22 years of work across many industry players," he says. "And that's just the paperwork for the agreed upon interface standard, not the final product itself."

Good, a retired Navy captain and former program manager for LCS mission modules, says that in conversations with OPNAV and Congressional staffs, he's found that the significant effort behind integration is not well understood - and almost always undervalued - which leads to it being under resourced.

"That drives us to 'standalone' capabilities. We don't get the more powerful results we could with integrated ones."

(As published in the May 2016 edition of Marine Technology Reporter)