Taking Unmanned Underwater Vehicles to the Next Level of Performance

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A Knifefish unmanned undersea vehicle (UUV) training model undergoes crane operations aboard the Military Sealift Command expeditionary fast transport vessel USNS Spearhead. (U.S. Navy photo by Master-at-Arms 1st Class Alexander Knapp)

The Unmanned Aerial Vehicle (UAV) is one of the most transformational military innovations of the past few decades. These crewless aircraft that are used in both kinetic strikes and ISR missions have revolutionized the way military missions are conducted – making it possible to fly difficult, dangerous missions without any risk to American warfighters.

Since their emergence, UAVs – or drones, as they’re most commonly known – have taken on an increasingly important role in the air domain. Today, the U.S. Department of Defense (DoD) owns and operates more than 11,000 autonomous aircraft, using them for countless missions in our most recent military operations.

The ability of UAVs to carry out missions without American casualties has resulted in the DoD looking to create other autonomous vehicles for other domains. This has led to the development of Unmanned Underwater Vehicles (UUVs) and Unmanned Surface Vehicles (USVs) for the sea domain, and the military’s ongoing development of the Optionally Manned Fighting Vehicle (OMFV) for the land domain.

Currently, Collins, along with the U.S. Navy, is demonstrating a 42-kWh fuel cell system under the ONR LEUVP FNC program…The result will be an increase in mission duration, search area coverage, and rate of transit to target – as well as…logistics and availability improvements …

While the OMFV is still in development, UUVs and USVs are currently being tested and evaluated for use in missions. Unfortunately, the widespread adoption of USV and UUV has run into a significant problem – mission endurance.

Li-ion is trying…but can’t cut it
The current, typical USVs and UUVs utilize lithium-ion (Li-ion) batteries for power. These batteries are responsible not just for overall vehicle power, but for its propulsion, as well. Unfortunately, there have been numerous stories of UUVs that have struggled to get the mission endurance they need to perform in their environment. In fact, there have been instances of UUVs that have been unable to make forward progress when facing swift currents.

But that’s not the only challenge that Li-ion batteries present to the DoD. Anyone that can remember back five or six years may recollect seeing stories about certain cell phones and tablets that had a problem with their lithium batteries.

This is far from the only instance where Li-ion batteries in consumer products have sparked problems. In February of this year, Li-ion batteries in electric cars onboard the cargo ship, Felicity Ace, caught fire. According to a Reuters article about the fire, the Li-ion batteries created additional challenges because “…the blaze require[d] specialist equipment to extinguish.”

The fact remains, Li-ion battery technology raises considerable concerns about safety. In the unlikely event that a Li-ion battery was to catch fire, it’s incredibly difficult to extinguish or control. When you consider that the eventual goal of many UUVs would be to store and launch them from submarines, a Li-ion battery explosion could be catastrophic.

…UUVs and USVs are currently being tested and evaluated for use in missions. Unfortunately, the widespread adoption of USV and UUV has run into a significant problem – mission endurance.

These safety and reliability challenges with Li-ion batteries have already caused problems for the DoD. In 2008, the U.S. Special Operations Command’s (SOCOM) submersible Advanced Seal Delivery System (ASDS-1) returned to port in Pearl Harbor for maintenance and charging when it caught fire. The vehicle burned for six hours and was so badly damaged that an estimated 32 months and $237 Million would be needed to repair it.

And if the mission endurance and safety issues weren’t enough, there’s also the challenge of recharging. Today, recharging the Li-ion battery for a UUV or USV is a slow process that can take hours – impacting the readiness of the vehicles and keeping them out of the fight for long periods of time.

The alternative to recharging is to keep spare batteries onboard military vessels so that they can quickly be swapped out, but that involves keeping even more potentially combustible batteries on hand, increasing the likelihood of a fire. The lithium batteries have to be stored in a specially designed “battery locker” of considerable size and weight. The locker takes up valuable space aboard ships, submarines, and land vehicles.

Between the safety concerns, mission endurance challenges, and refueling shortfalls, it’s clear that Li-ion technology is not the answer for USV and UUV. But what alternatives exist?

Fuel cells address common Li-ion concerns
Fuel cell systems that are now under development can improve mission endurance while also offering gains in safety and logistics costs. Fuel cells increase vehicle availability by eliminating the long lithium battery recharging process – replacing it with fuel cell refueling that takes the same time as refilling a car with gasoline.

Additionally, these fuel cell systems do not need a locker or in that case any storage. Since there are no spare batteries to transport, they take up zero space and add no weight to already weighed-down sailors, airmen, and soldiers.

Currently, Collins, along with the U.S. Navy, is demonstrating a 42-kWh fuel cell system under the ONR Long Endurance Undersea Vehicle Propulsion (LEUVP) Future Naval Capability (FNC) program. This LEUVP system is designed to seamlessly replace the UUV lithium-ion battery energy section in the PMS 406 Knifefish 21-inch diameter UUV.

The Collins UUV fuel cell is directly targeted to increase the Knifefish’s operational effectiveness. The result will be an increase in mission duration, search area coverage, and rate of transit to target—as well as the logistics and availability improvements mentioned.

A key challenge to fleet adoption is also being worked on simultaneously by Collins and ONR. Fuel cells need to be refueled either on land, dockside, or underway by a ship at sea.

Today, recharging the Li-ion battery for a UUV or USV is a slow process that can take hours – impacting the readiness of the vehicles and keeping them out of the fight for long periods of time.

Working with the Office of Naval Research (ONR), Collins Aerospace is developing an on-demand system for refueling USV and UUV fuel cells. The system – known as the Refueling and Servicing Package (RASP) – can be deployed in a standard ISO container for use on a Navy LCS platform or dockside.

Using just distilled water and the ship’s power, the RASP can refuel the hydrogen tank, refill Liquid Oxygen (LOX) tanks, remove product water, refill distilled water, and charge the emergency battery. The successful adoption of the LEUVP fuel cell system requires a safe and effective refueling and sustainment capability, which RASP will provide.

Working collaboratively, Collins and the U.S. Navy are on the path to make fuel cells for unmanned vehicles a reality. Improvements in mission reach, vehicle availability, time on target, and safety can be realized with fuel cells.

To learn more about Collins Aerospace, CLICK HERE. To read more about PEM Fuel Cell Mission Endurance System, CLICK HERE.