Not cleared to fly: worries about mid-air collisions keep civilian drones grounded.

Papadales pointed out that passive camera systems, such as Prioria's, use less power than radar systems, but require more computer processing. Additionally, they can't "see" through clouds and are not as accurate as radar.

Northrop Grumman Integrated Systems is tackling the sense-and-avoid issue for larger drones such as the Predator or Global Hawk. The company is working with the Air Force Research Laboratory to demonstrate the feasibility of collision avoidance technologies for both cooperative and non-cooperative traffic, said Robert Miller, director of Northrop future unmanned systems advanced capabilities development. Cooperative aircraft are those that carry a transponder and emit a signal to show their position.

Researchers are combining electro-optical sensors with information from the traffic collision avoidance system (TCAS) to detect cooperative air traffic. TCAS is an airborne alerting system for pilots that uses range and altitude data to detect and avoid collisions. The company is also testing combinations of electro-optical and infrared technologies to detect non-cooperative traffic. Miller noted that one challenge associated with electro-optical sensors is false alarms, but said that Northrop is working to further reduce them.

The Air Force Research Laboratory funds the development efforts, Miller said at the conference.

The Air Force in particular has an interest in solving the sense-and-avoid issue, Papadales said, because it flies long-range missions across the national airspace. The service had to fight to get the Global Hawk approved for flight, he said.

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