Battery-powered unmanned aircraft are all well and good, but batteries need recharging. Solar energy is a good way of recharging them in flight, to extend endurance, but it doesn't work at night. So DARPA has awarded Aurora Flight Sciences a contract to develop an integrated energy scavenging and storage system that works both day and night.
The system could be used to power portable electronics and other unmanned vehicles, but Aurora's focus is on a micro air vehicle it calls the Skate. This is a highly-agile flying-wing MAV designed to be pulled from a backpack, unfolded and launched like a boomerang to fly in confined spaces like city streets and even inside buildings.
Aurora plans to replace the Skate's structure with thin-film lithium batteries formed into the shape of the wing, and covered on its upper surface by solar cells for daytime recharging and on its lower surface with infrared photovoltaic cells for night-time recharging.
The twin-prop Skate uses 40W of power, of which 95% would come from sunlight and only 5% from thermal energy - "but we'll take everything we can get," says principal investigator Phillip Johnson. "It all comes for free. We're not adding anything - we're replacing the existing structure [and battery] with an advanced power system."
Thin-film lithium batteries are used in things like radio-frequency identification tags, and the complete energy scavenging and storage system "will feel like a credit card", he says. The Skate battery will be a thin sandwich of anode, electrolyte and cathode, wrapped in plastic and formed into the shape of the wing.
Aurora's SBIR Phase 1 contract is for a six-month design study "to see if it's doable", Johnson says. If it is, this could lead to a Phase 2 contract to built and fly a MAV with the integrated energy scavenging and storage system. Aurora is also working on a navigation system inspired by bat sonar, so flying by night could become natural for the Skate.