Wireless Power Network Could Maintain Drone Air Dominance for Years

Currently, drones run out of power after days, hour or minutes. If there was wireless power beaming then electrically powered drones could stay flying over a battlefield indefinitely. Years of flight could become possible. Swarms of drones would be have the power to stay over entire states or countries indefinitely. The multi-year electrical drones could also act as ultra-low flying alternatives to satellites.

RTX (Raytheon) Corporation has received $10 million for the two year DARPA wireless energy relay program. The goal of the POWER program is to design and demonstrate airborne optical energy relays. The principal technical challenges will be to develop and demonstrate a payload capable of redirecting optical energy transmissions, correcting wavefronts to maximize beam quality at each relay, and selectively harvesting energy for platform power. Energy will be shifted in a matter of seconds or minutes, enabling them to pivot capability near instantaneously without reconfiguring supply lines.

1) 200 km transmission range (measured between ground sites)
2) 10kW of laser energy delivered to the final ground node if using the 50kW source laser (assuming 50% conversion efficiency this equates to the program goal of 5kW of electric power, ground receiver or measurement device will be provided by the government team)
3) Transmission through 3 airborne relay nodes
4) At least 1kW of throttlable energy harvesting simultaneously at each of the three airborne nodes.

The designs will be subject to the following constraints:
1) All system apertures less than 1 meter diameter
2) Demonstration system compatible with existing airframes
3) Compatible with operations at high altitude (60kft or higher) to minimize atmospheric losses.

DARPA selected RTX Corporation, Draper, and BEAM Co to design prototype lop wireless optical power relays. The Persistent Optical Wireless Energy Relay (POWER) program, aimed at revolutionizing energy distribution through airborne wireless power transfer.

The optical energy relays designed in POWER’s phase one will be demonstrated on the ground.

In the second phase, they will be demonstrated in pods carried by existing aircraft.

Power beaming will enable smaller, less expensive future aircraft since fuel storage and engine volume could be dramatically reduced. This will be explored through conceptual designs in phase one. Eventually these new, small, distributed platforms could provide cost-effective aircraft with unlimited range and endurance to support military missions. Each relay design will be evaluated based on accurate and efficient energy redirection, wavefront correction for high beam quality, and throttleable energy harvesting.

In the third and final phase of the program, the relays will be demonstrated through an airborne optical pathway that aims to deliver 10 kilowatts of optical energy to a ground receiver that is 200 kilometers away from the ground source laser.

The first phase will include benchtop demonstrations of critical technologies and is expected to last 20 months with potential for a three-month option of additional risk reduction efforts. The second phase will involve an open solicitation in early 2025 and will focus on integration of the relay technologies onto an existing platform for a low-power, airborne demonstration.

High-altitude, long-endurance RQ-4 Global Hawk drones will be used for the airborne relay demos.

The RQ-4 Global Hawk has:
A 44-foot-long airframe
A wingspan of more than 116 feet
A height of 15 feet
A gross takeoff weight of 26,750 pounds
A 1,500-pound payload capability
A single Rolls-Royce AE3007H turbofan engine

The US Air Force has 21 RQ-4 Global Hawk Block 30 drones. The Air Force also has three Block 20 drones that have been modified to the EQ-4B Battlefield Airborne Communications Node variant. The RQ-4 Global Hawk is the largest military UAV in the United States. It has a wingspan of just over 130 feet, a length of 47.6 feet, and a cruise speed of 400 miles (640 km) per hour. It can fly for about 36 hours.

Drones will operate at or around 60,000 feet to minimize atmospheric losses and enhance relay survivability. Efficient and precise redirection is necessary to avoid platform thermal challenges and to ensure the relayed beam effectively illuminates the desired target. To account for degradation of beam quality as the beam transits atmospheric disturbances, the relay must be able to correct the optical wavefront as needed to achieve system efficiency goals. Finally, the relays must be able to selectively harvest energy from the optical beam to provide on-board auxiliary power and thereby demonstrate necessary characteristics for future indefinitely persistent relay platforms.

Here is a 46 page report on the DARPA plans.

Wireless power is a key to unlocking novel platforms and capabilities, and to revolutionizing flexible effects delivery. The optical relays aimed for development via the POWER program are a critical hardware component for optical power beaming links. Relays more generally are a necessary component for creating flexible, scalable networks. Other power transfer modalities such as radio frequency or acoustic waves are suitable in other environments and are the focus of ongoing DARPA research that may lead to future programs, but are beyond the scope of POWER. Ultimately, more dynamic energy transport should be expanded to air, space, maritime, land, and undersea domains for maximum impact. Each effort within the Energy Web Dominance portfolio, such as POWER, focuses on key enabling technologies to continue to mature towards this larger vision.

DARPA envisions that the final (Phase 3) demonstration will be conducted at White Sands Missile Range (WSMR) utilizing the High Energy Laser Systems Test Facility (HELSTF). The HELSTF facility will provide substantial controlled airspace as well as a beam director and highpower laser suitable for demonstrating the POWER program goals. The program goals and expected efficiencies are baselined off the currently available HELSTF 50kW class laser. The beam director provides at least a 60 cm transmit aperture with adaptive optics for compensation of atmospheric conditions on the initial ground-to-air link. This provides the capability to select beam spot size (focus) at the first aerial node. The facility is expected to have more than one option for the laser at the time of the Phase 3 demonstration, with wavelengths in the range of 1.03um to 1.08um. Other alternatives for beam directors may be available as well.

Performers will be expected to coordinate with HELSTF for use of the optimum laser and beam director combination and to coordinate laser safety considerations for the demonstration. Other laser sources and beam directors may be proposed; but the proposal must substantiate a clear demonstration plan that fits within the POWER timeline. Representative and scalable risk mitigation demonstrations prior to Phase 3 are expected. The specifics of those risk mitigation demonstrations should be addressed in the proposal and will be evaluated by the government to
assess the adequacy of the risk reduction steps for the proposed design.

Along with utilization of the HELSTF facility, DARPA anticipates that the baseline platform for the final demonstration will be the RQ-4 Global Hawk. The wing pylons of the Global Hawks have a max weight of ~ 500 lb. (dependent on CG) and max payload diameter of 30” to avoid ground impact. Additionally, the Global Hawks have a number of internal payload bays; the largest, lower-facing bay can hold 700 lbs. Proposals that deviate from the provided host platform are acceptable but will need to provide an executable alternative demo plan. A layout and table of volumes for the internal bays on the Global Hawk are provided below