By Matthew Stock

(Reuters) - An unmanned aircraft system (UAS) developed by engineers from the University of Southampton uses a powered tether to provide unlimited flight time for drones. The developers say it could offer a more cost-effective solution for aerial monitoring and surveillance than other options on the market.

The tethered drone system was a collaboration between the team from Southampton and security firm Cardinal Security, based in Essex, who wanted to build a low-cost observation platform for both military and civilian security operations.

"It's basically a virtual mast, so you could imagine surveillance operations, rescue missions at sea or on land, surveillance of large complexes like nuclear power stations," said Dr Stephen Prior from the University of Southampton.

According to Cardinal Security, the ability to conduct persistent aerial observation has long been sort after by both military and civilian security organizations. Current options include helium balloons, observation masts and free flying multi-rotor drones. But these are each limited by their physical size, height limitation, endurance and stability in strong winds.

"All of the battery-powered multi-rotors suffer from poor endurance, so 20-30 minutes is tops. We can fly, essentially, forever provided we've got fuel in the tank in the fuel generator in the ground station," added Dr Prior, a Reader in unmanned air vehicles at the University of Southampton.

The drone is connected to a mobile ground station via a powered tether. The fuel in the trailer delivers a constant drip feed of electricity to the drone, with a fuel tank capacity big enough to keep it flying for 22 hours -- though it can be topped up to keep the drone airborne indefinitely.

On board the UAV interchangeable pods can host a range of technology; including thermal imaging cameras for search and rescue missions, and high-definition video cameras for aerial surveillance. As well as providing power up to the UAV, the tether brings secure data feeds back to the ground vehicle for viewing, recording and onward transmission.

The developers say that while there are other tethered UAV systems available, their price point makes it a more viable option for companies and emergency responders.

"There are expensive systems out there; very very expensive military systems, so a quarter of a million pounds plus. And we sit somewhere in between that. Our price point is around about 75,000 pounds (GBP) for a complete system solution," said Dr Prior.

"You can hook the trailer up to your 4x4 vehicle and you can drive anywhere you want and get it in the air within a few minutes, and move around to different locations while staying in the air. Or you can come back down to box it up and move to a different location. So it's quite flexible as a system, quite adaptable to the mission scenario and at a good price point that makes it affordable to blue-light services as well as companies that want security," he added.

The system is the only tethered UAV in the UK with permission from the Civil Aviation Authority (CAA) to conduct aerial work up to a height of 122 meters (400 ft).

The team from Southampton and Cardinal Security are now looking to commercialize their proof of concept system, with plans to start low-volume production of the technology later this year.