Sunday, August 26, 2012

Wireless Energy Transmission: Powering Future Naval Drones

Unmanned aerial systems have delivered affordable intelligence, surveillance, and reconnaissance (ISR) capabilities to smaller naval vessels that were previously unique to much larger platforms. In the past decade, small tactical unmanned aerial systems (STUAS) have enabled ground and sea forces operating in the Philippines, Southwest Asia, and Africa to see over the next ridgeline or island, well beyond their line of sight. The introduction of wireless power transmission will add yet another capability to the utility of these naval drones.

Lockheeed Martin Skunkworks and Kent, Washington-based company Lasermotive recently demonstrated the ability to recharge the batteries of small, electrically-powered unmanned aircraft in-flight, radically extending the endurance of these tactical drones. In July 2012, a Stalker UAV powered by laser transmission flew for 48 hours in a wind tunnel. As a point of comparison, the normal endurance of this drone is only 2 hours, a difference of 2400%. Follow on tests occurred in the desert, under less simulated conditions.

Laser power beaming works much like solar power in that a high intensity laser is aimed at specialized photovoltaic cells which convert the light to electricity. The laser is steered by a beam director controlled by a tracking system and can be mounted on land, a ship, or even another aircraft. Ironically, the U.S. Navy’s pursuit of directed energy weapons to counter enemy unmanned vehicles may evolve one day into a capability to power its own drones. In 2010 the Navy demonstrated the Laser Weapons System (LaWS) at sea, an array of six 5.5-kW industrial fiber lasers on the former USS Paul Foster test ship. Another laser system was tested in August 2012 on the destroyer USS Dewey. Lasers do have drawbacks for this application. First, they are limited to line-of-site, but range can be extended via airborne mirror relays. The effectiveness of lasers can also be disturbed by atmospheric interference, especially at sea level. The Navy is working on technologies to mitigate these propagation issues.

However, lasers aren’t the only means by which future naval drones could be powered. Nikola Tesla first tested wireless electrical transmission using electromagnetic energy in the late Nineteenth Century. Today, while numerous start-up companies are working to commercialize “WiTricity”or “WiPower,” the Navy’s nearly ubiquitous AN/SPY-1 phased-array radar offers another possibility for wirelessly powering naval drones. By steering individual beams, the radar could potentially serve as an afloat recharging station for passing drones.

Currently, only smaller drones such as the Stalker and AeroVironment Puma are electrically powered. But given this new technology, larger UAVs including the Scan Eagle could be modified from internal combustion engines to work via wireless power transmission. The operational possibilities offered by wirelessly powering drones are extensive. A laser-equipped surface vessel of any size transiting a strait or other chokepoint could continuously power a STUAS, greatly increasing its sensor range and enhancing its awareness of other surface contacts. Other naval UAVs could be sea-launched then “refueled” by orbiting laser aircraft or ground stations to conduct long duration over-land ISR.

Even farther into the future, wireless energy transmission will power naval drone swarms. Someday, large groups of unmanned air or surface vehicles mimicking natural formations of birds or schools of fish will operate autonomously to collect intelligence, attack enemy ships, and any other number of missions. To date, drone swarm technology has been simulated using small quadrotors, which are limited by payload, extremely short flight time and range. Though in October 2010, LaserMotive powered an electric quadrotor drone for over 12 hours, proving that longer duration drone swarms powered remotely from afloat or ashore are possible.

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