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Wireless energy transfer for UAVs

Wed, 05/05/2010 - 8:34am
Jason Lomberg, Technical Editor

Lasers have been described as the “holy grail” of weapons—who wouldn't want to be like Luke Skywalker? But while researchers have pondered everything from “pain rays” to the “Zeus” anti-IED system, the folks over at LaserMotive are pushing something else entirely—power beaming for UAVs.

Power beaming is nothing new, nor is the overall concept of wireless energy transfer. The popular consumer product, Powermat, operates through electromagnetic induction. But power beaming has never been attempted on so large a scale. In the white paper, “Laser Power for UAVs,” LaserMotive discusses the technology and potential applications.

The main problem with UAVs, as LaserMotive sees it, is their limited range. The Predator and Reaper UAVs can loiter for up to 40 and 42 hours, respectively (though endurance nosedives when fully-loaded). The Boeing Condor set the record for fuel-based UAVs at 80 hours. Electric-based platforms have very limited range, and solar-powered UAVs are fragile and expensive. Thus, LaserMotive poses the question: what if we could have robust, high-performance UAVs that never needed to land?

Their solution is a series of laser power links, strategically-placed, enabling extended or even indefinite flight time. As seen in the diagram, the laser transmitter converts power from a primary source into a monochromatic (single-wavelength) beam of light. A receiver on the UAV converts the laser light back to electrical power. Within the receiver are specialized photovoltaic cells matched to the laser wavelength or beam intensity. Similar to hybrid autos (especially the “extended range” Chevy Volt), an on-board storage device is required.

Schematic diagram of power beaming to UAV

The company foresees three potential applications:

1) A stationary observing platform for long-duration ISR (Intelligence, Surveillance, and Reconnaisance).
2) Extended or multi-mission applications.
3) Unlimited Patrol

#1 and #3 are fairly similar. For an “unlimited patrol,” missions would be conducted within 10 miles (to an altitude of one mile) of a laser refueling station. For “extended” missions, UAVs would loiter over a target and periodically return to the nearest beaming station to “refuel.” On-board batteries would extend the range, and with periodic refueling, UAVs could theoretically remain airborne indefinitely. The “beaming stations” could even be mobile.

Of paramount importance is the efficiency of the photovoltaic or laser cells in the UAV receiver. Solar cells are, at best, 20% efficient. LaserMotive doesn’t say, but it hints at efficiencies from 20-25%. Ultimately, the most viable application might be #2—extending the range of existing UAVs by placing beaming stations along their flight path. Otherwise, the UAVs are restricted to recon, as we can’t “beam up" weapons.

LaserMotive claims the technology already exists, and a prototype could be ready within 18-24 months. A system of their design already won the 2009 NASA Centennial Challenge for Beamed Power. I’ll be very interested to see how this develops.

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