by Imran H. Khan

Confluence of efficient solar cells, electric motors, energy harvesting techniques,composite materials, dense and sophisticated avionics is creating opportunities to develop Unattended Unmanned Aircraft Systems (UUAS). The first wave of UASs have enabled many applications that were unachievable with manned systems. As it turned out many of the UASs required more manpower on the ground than manned systems. There are still many more applications that become physically and economically viable if the humans are completely taken out of the loop.  This requires that the system be smart enough to take into account all eventualities, and have the ability to harvest energy from natural sources.

Two class of UUASs have recently evolved to offer applications requiring nearly indefinite operations.

Flying Fish

The first type consists of UUAS capable of prolonged operation on the ocean. University of Michigan investigators have developed two models of what they call Flying Fish. They were funded in part by DARPA to create a platform that could be used for persistent ocean surveillance. The mission required the vehicle to autonomously maintain a physical presence in a predefined watch-circle in the open ocean via continuous self-managed drift-and-flight sequences subject to environmental disturbances. They have been designed for unattended always-on operation, demonstrating safe and autonomous flight to and from the water’s surface. Flying Fish is the first UUAS to operate in and over water with energy harvesting. One of the most distinguishing features of the second-generation Flying Fish is its waterproof solar energy harvesting system with an array of solar-cells on the main wing and high-efficiency load-maintenance and charging circuitry. As an ocean observation platform Flying Fish has the unique ability to abandon a drifting loiter-strategy to intercept or chase entities at airborne speeds that exceed all large surface and sub-surface craft. Specific applications for Flying Fish might include oil-spill or algae bloom identification or boundary tracking, water-quality sampling, or acting as periodic communication relay to submerged assets.  Flying Fish has accomplished fully-autonomous watch circle maintenance in the open ocean (Monterey Bay) and in a local Michigan lake (Douglas Lake).

The second class of UUAS operates on the other extreme of the atmospheric envelope. They are designed to fly nearly perpetually,  operating at altitudes above 60,000 feet. These machines have very large wing spans and the ability to continuously fly through the night, using energy harvested during the day. Because of the high operating altitude they are guaranteed availability of daily sunlight.


The first such UUAS is Zephyr from Qinteq. It achieved an altitude of over 70,00o ft during a fourteen day flight. Launched by hand, the aircraft flies by day on solar power delivered by amorphous silicon solar arrays that cover the aircraft’s wings and are no thicker than sheets of paper. These are supplied by Uni-Solar, the world’s largest producer of flexible solar panels. The solar arrays are also used to recharge the lithium-sulfur batteries that are used to power the aircraft by night and supplied by Sion Power Inc, a leading developer of  high energy rechargeable battery technology. Together they provide an extremely high power to weight ratio on a continuous day/night cycle, thereby delivering persistent on station capabilities. The target goal for production quality aircraft is three months of uninterrupted flight.


SolarEagle by Boeing is the other UUAS that is being designed to fly for five years. It will be able to carry a 100o pound payload with 5 kwatts of power at heights between60,000 and 90,000 feet. At these heights it would contend with some of the roles being currently being performed by satellites. During testing, the SolarEagle demonstrator will remain in the upper atmosphere for 30 days, harvesting solar energy during the day that will be stored in fuel cells and used to provide power through the night. The aircraft will have highly efficient electric motors and propellers and a high-aspect-ratio, 400-foot wing for increased solar power and aerodynamic performance. Key suppliers for the program include Versa Power Systems and QinetiQ.


These platforms are going to open up new opportunities for developing applications that leverage the low cost and persistent availability of flying platforms at different heights. Some of these would be replacing the current applications of surveillance and communications being performed for a limited dwell times but at a higher cost.  For commercial applications to gain widespread adoption it is important to create a comprehensive strategy for safely and fully integrating UAS into the national airspace system over both rural and urban regions. Once this is in place, it will be possible to treat UAS based application as an on demand service. A mind set change similar to that the software development underwent with the advent of viewing software as service.

These type of UASs will eventually meld into the fabric of our society in an ecologically responsible manner.  They will provide persistent monitoring of resources and at the same time increasing the availability of communications around the globe.  The video above  shows some curious dolphins attracted to the Flying Fish UAS because of its non threatening size and lack of noise.

The UUAS niche is still in its infancy and wide open both from technology and business perspective. The core technologies needed in terms of efficient solar cell, battery technology, flight management systems and composites will preclude dominant players from staking the grounds for quite sometime to come. In some ways this technology can further the democratization of technology, as the impact would be spread over a large number of consumers. This is the time for small players in the UAS arena to think big.


I would like to thank Dr. Ella Atkins for providing me information about the Flying Fish.

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