The US Defense Research Advanced Projects Agency (DARPA) is pioneering a project to extend drone flight times significantly by using wireless energy transfer, which has significant implications for drone technology and base logistics.
This month, Defense One reported that DARPA is funding Raytheon with US$10 million to develop energy “webs” that could keep drones in the air indefinitely. According to Defense One, the POWER program by DARPA is looking to create a new possibility for designing platforms that don’t rely on the amount of fuel they carry for their capabilities.
It says the two-year contract will enable Raytheon to create an airborne relay design to enable “webs” capable of harvesting, transmitting, and redirecting optical beams. The source notes that these “webs” will transfer energy from ground sources to high altitudes for the precision and long-range operation of unmanned systems, sensors, and effectors.
Defense One notes that the idea of wireless power transfer dates back to Nikola Tesla’s 19th-century experiments with power transmission via radio frequency resonance through coils over short distances. It says early research by the National Aeronautics and Space Administration (NASA) and others aimed to power things with microwave energy, but the helicopter had to be relatively close to the power source.
The source says that in April last year, researchers with the Naval Research Lab beamed 1.6 kilowatts of power over 1 kilometer at the US Army Research Field in Blossom Point, Maryland. In contrast, it says DARPA’s POWER effort calls for lasers, which promise to deliver more energy with a narrower beam.
It says the concept is crucial because it allows for persistent and distributed assets in an anti-access/area denial (A2/AD) environment, protecting assets and balancing against long-range precision fires. However, the source notes that it also raises concerns about aerial occupation.
Using lasers for energy transmission may still be in its infancy, but it has profound military implications.
Wireless power
In an October 2022 article, DARPA said current military platforms requiring long range, endurance, or significant weapons capability must be large enough to carry substantial stores of liquid fuel to complete their mission. However, it said wireless power transforms these platforms into conduits, giving small, inexpensive platforms capabilities such as unlimited range and endurance.
DARPA has identified an issue with the efficiency of converting waves to electricity and back in a multi-hop network, leading to significant losses. It says each conversion is relatively inefficient, and multiplying that effect over a chain is impractical.
Nevertheless, the US is continuing to work on the technology to harness the military advantages it brings. In June 2022, The Warzone reported that DARPA was looking to outfit aerial tankers as “airborne energy wells” to recharge battery-powered drones. The Warzone says DARPA seeks defense-industry feedback on equipping the US Air Force’s existing KC-135 and KC-46 tankers with an underwing energy-beaming pod.
The source notes that such a pod should be capable of generating a 100-kilowatt continuous-wave laser with a thermal control unit that integrates the laser pod into the tanker with a nearly hemispherical field of coverage.
The Warzone notes that the project aims to address the endurance problems associated with battery-powered drones by enabling them to recharge their batteries in flight.
It says the proposed airborne energy well won’t recharge larger drones in the short term. Still, it says larger and more complex designs will likely be battery-powered over time, adding impetus to the development of in-flight recharging technology.
Quiet flight
Also, it adds that while battery-powered drones can be very quiet, their limited endurance makes building larger designs unfeasible.
Despite that challenge, the US Intelligence Advanced Research Projects Activity’s Great Horned Owl program envisages fully electronically powered quiet flight for the next generation of high-end intelligence, surveillance, and reconnaissance (ISR) drones operating in heavily defended airspace.
IARPA says the program focuses on fuel-to-electricity, combining an advanced internal combustion engine, an alternator/generator, and electricity-to-thrust devices using innovative motor propulsion systems.
It is plausible that IARPA’s Great Horned Owl program could incorporate DARPA’s POWER technology at some stage in its development, eventually producing entirely battery-powered prototypes that can be recharged in flight.
Beyond drones, the technology behind DARPA’s POWER project could be used to power remote military outposts.
In an October 2022 article for Popular Mechanics, Kyle Mizokami notes that a military power plant could generate electricity and covert it into a laser beam, aim it at a relay drone, which would then beam the laser to other drones down the line until the last drone aims the beam at a military outpost which then converts the laser into electricity.
Mizokami notes that such technology would eliminate the need for slow and vulnerable fuel convoys and generators to convert diesel into electricity, power hybrid or electric military vehicles, and improve the quality of life in those outposts by eliminating diesel fumes. Such a technology may plausibly be applied in the Pacific as the US looks to increase the number of its island bases to bolster its military presence against China.
Stars and Stripes reported in August that the US aims to reactivate its disused World War II airbases in the Pacific to disperse its forces to avoid getting destroyed on the ground by a pre-emptive missile strike. Stars and Stripes said the number of US Pacific airbases will increase over a 10-to-15-year period but did not mention how many airbases the US could operate from.
Not to be left behind, China has its take on laser energy transmission. In January, Asia Times reported that Chinese researchers at Northwestern Polytechnic University (NPU) fitted drones with photoelectric conversion modules that could convert light into electricity, enabling high-powered laser beams to power the drones remotely while in flight.
NPU’s School of Artificial Intelligence team conducted a drone experiment combining autonomous charging with intelligent signal transmission and processing technology.
The NPU team encountered several challenges in their experiment, such as tracking the drones in the air, laser distortion, and laser safety concerns. However, they overcame these by using intelligent algorithms that could track airborne drones, adaptive beam-shaping technology, and a protection algorithm that adjusts laser intensity to safe levels if an obstacle is detected.