The shadowy X-37B, the Air Force’s unmanned, reusable spacecraft, is set to launch for its sixth flight on May 16 from Cape Canaveral Air Force Station, Florida. While most of the payloads set for the flight are standard fare for space experiments, at least the ones that are disclosed, one of them has immense potential implications for the future of remote power generation and especially long-endurance unmanned aircraft propulsion.
The X-37B’s upcoming mission is known as both Orbital Test Vehicle-6 (OTV-6) and U.S. Space Force-7 (USSF-7). It will carry out missions that will assess the effects of cosmic radiation and other “space effects” on plant seeds and various material samples. According to a Space Force press release, which went out on May 6, another payload aboard the X-37B will be an experimental system designed by the Naval Research Laboratory that is capable of capturing solar power and beaming that energy back to Earth in the form of microwaves.
While the press releases of the Department of Defense and the Space Force are scant on details, the Naval Research Laboratory’s head of beamed power has explicitly stated in the past that this system has enormous implications when it comes to long-endurance unmanned aerial vehicles (UAVs). In addition, it could allow satellites to provide reliable power anywhere on the planet or even to spacecraft or other satellites in orbit.
The U.S. Naval Research Laboratory (NRL) has been promoting similar-sounding technologies over the last year. In October 2019, the NRL conducted a three-day long demonstration of the Navy’s latest power-beaming capabilities at the Naval Surface Warfare Center in Bethesda, Maryland. In the demonstration, the NRL transmitted a completely silent, invisible beam of 2-kilowatt laser power over 300 meters through the air over attendees’ heads. The demonstration was meant to showcase the safety and technological readiness of this utterly transformative concept.
As far as the aforementioned applications of this capability, research or military outposts in remote locations would no longer have to rely on low-power solar systems or haul heavy generators and large amounts of fuel, but instead could bring a rectifying antenna, or rectenna, to capture energy in the form of microwaves beamed from satellites overhead. In addition, areas ravaged by natural disasters could use the system to generate electricity to aid in reconstruction efforts long before traditional electrical infrastructure is rebuilt. It could even power autonomous ships at sea.
Dr. Paul Jaffe, an electronics engineer with the U.S. Naval Research Laboratory who is leading the NRL’s research into power beaming, says that the technology will open up entirely new frontiers in terms of long-endurance unmanned aircraft. “If you have an electric drone that can fly more than an hour, you’re doing pretty well,” Jaffe said. “If we had a way to keep those drones and UAVs flying indefinitely, that would have really far-reaching implications. With power beaming, we have a path toward being able to do that.” The Navy was granted a patent for a similar system in 2016 invented by Jaffe.
Beamed Power Aircraft
Using lasers to beam power to small UAVs has been a subject of research for some time. The U.S. Air Force began testing lasers as a source of propulsion for small “lightcraft” as early as the 1980s and managed to get small cone-shaped craft to fly hundreds of feet in the air propelled only by laser beams. This new concept is different, though, in that the beamed power UAVs the Navy envisions will feature traditional propulsion systems (such as rotors or propellers) and instead have rectennas that capture the energy from directed energy beams to constantly replenish their electrical power reserves.
In 2011, NASA’s Glenn Research Center published research on laser power-beaming systems with funding from the Air Force Research Laboratory’s Revolutionary Munitions Directorate at Eglin Air Force Base in order to examine “long-range optical ‘refueling’ of electric platforms such as micro unmanned aerial vehicles (MUAV)”. Also in 2011, a RAND Corporation study conducted on behalf of the Air Force found that while the concept of laser-beamed power is sound, atmospheric interference from clouds could pose limitations on flight paths and ceilings.
DARPA held a power beaming roundtable in 2015 which featured representatives from top defense contractors, research universities, and various DoD-operated laboratories. In 2018, DARPA demonstrated its latest laser-powered aircraft, the Silent Falcon, which the project lead Joseph A. Abate says was meant to “demonstrate that remote electric refueling of DoD systems via high energy laser power beaming to extend mission operation time in contested and remote environments.”
While lasers have been examined for their use in beaming power to UAVs, these have typically involved ground-based or possibly airborne lasers to beam power. Placing the source of power generation and transmission in space is a new take on this concept, offering superior lines of sight and a continuous, renewable source of energy via the sun.
Still, low earth orbit satellites circle the planet at incredibly high speeds and their maneuverability is limited, so there will be limitations to the Navy’s latest beamed power system, but as a proof of concept, it is essential. A constellation of satellites would likely be necessary to have a truly 24/7 supply of power, enabling UAVs to be ‘passed’ from satellite to satellite for continuous or tightly scheduled recharging. The same can be said for any receiver applications on the planet’s surface.
Beamed Power And The Future of UAVs
In 2014, the superintendent of the Naval Research Laboratory’s Plasma Physics Division Thomas Mehlhorn published a paper in IEEE Transactions on Plasma Sciences which offered an overview of plasma physics and pulsed power as they relate to national security. The article spans a wide variety of topics including nuclear weapons, inertial confinement fusion, and high-energy laser weapons. In the paper, Mehlhorn also touches upon the Navy’s beamed power UAV research at the time, writing that the continuous flight times offered by beamed power systems could change surveillance, reconnaissance, and communications gateway/relay missions forever:
“Building upon the concept of scalability, rather than using a laser beam to kill a UAV, they began to pursue the idea of beaming power to a UAV to allow continuous flight, with potential application to both surveillance [Intelligence, Surveillance, and Reconnaissance (ISR)] and countermeasure missions. The team has pursued this idea using NRL applied research funds with the vision that long-range laser power beaming to UAVs could allow for long-duration flights with reduced manpower requirements for many Navy and DoD missions, including off-board decoys, persistent surveillance, and communication relays.”
According to an October 2019 Navy.mil press release, the Navy’s beamed power system has also been endorsed by the Marines, Army, and Air Force and is expected to throughout the Department of Defense in the near future. The extent to which such systems have already been tested or deployed is unclear, although the Department of Energy has explored the concept of beaming microwaves from space since at least 2014. Doing the same from the ground, within line of sight of the aircraft, which can still be dozens or even hundreds of miles away depending on the altitudes involved, is such an easier task that it would be a bit puzzling if the technology isn’t already under development, or even possibly in some sort of clandestine operational state.
Doing so from another aircraft is also clearly an objective based on the existing literature and would help mitigate the line of sight limitations with ground-based power beaming stations, but would sacrifice endurance and simplicity. In the 2011 RAND study cited above, the authors write that possibilities for beamed power applications include “ultra-high-altitude observation stations or communication relays and flocks of high-altitude sensor probes powered remotely from a large aircraft ‘mother ship.'”
Meanwhile, the China Academy of Space Technology claimed to already be testing such a system in 2019 and said that a fully-functional Chinese microwave beaming power station in space could be deployed by 2050.
As you can probably tell at this point, this technology has massive implications not only for the future of UAVs, but for all of mankind. Such a system could be used to keep UAVs in the air for very long periods of time to replace cell towers or communications satellites in the event of a crisis in a region or even for normal operations of increasingly complex communications networks. Unlike a tethered aerostat, these UAVs would require far less infrastructure, could be moved around at will for optimum coverage, and could land quickly for servicing. They could even deploy dozens of miles, or even further, away from their base stations. With a space-based power source, they could fly anywhere on earth. Obviously, the implications for overhead surveillance are equally impactful.
So, while the X-37B’s latest mission details seem neat on a scientific level, the reality is the microwave system it is testing could change the game for many military-related applications and could actually open the door for near-continuous unmanned flight throughout the atmosphere.
Contact the editor: Tyler@thedrive.com