Zephyr solar plane set for record endurance flight
A UK unmanned solar-powered plane will attempt to set a remarkable new endurance record in the coming days.
The Zephyr vehicle will launch from a military range in the US and try to fly non-stop, day and night, for two weeks.
Developed by the British defence and research company Qinetiq, the project has already flown continuous missions up to 83 hours.
But this latest venture, if successful, should prove that the robotic solar plane concept has finally come of age.
This type of vehicle, which can circle over a particular area for extended periods, is expected to have a wide range of applications in the future.
The military will want to use them as reconnaissance and communications platforms. Civilian and scientific programmes will equip them with small payloads for Earth observation duties.
"We now have an aircraft that we believe is capable of actually fulfilling missions for the military or the civil user," Jon Saltmarsh, Qinetiq's Zephyr project manager, told BBC News.
"We would offer it as a service. We would provide a 'hook in the sky' that you could put a payload on to, and we will guarantee to keep it up there 24 hours a day for a couple of months."
During the day, Zephyr uses its state-of-the-art solar cells spread across its wings to recharge high-power lithium-sulphur batteries and drive two propellers. At night, the energy stored in the batteries is sufficient to maintain Zephyr in the sky.
The latest test will take place at the US Army's Yuma Proving Ground in Arizona, where Qinetiq set an unofficial endurance record of 82 hours and 37 minutes in 2008.
The latest version of Zephyr is now 50% bigger than its predecessors.
The updated vehicle has a wingspan of 22.5m, and features a new wingtip and tail design that dramatically improve aero performance.
It also has a wider configuration near the main body to accommodate more equipment. In addition, the team has upgraded the avionics and power management systems on board.
The presence at Yuma of the Federation Aeronautique Internationale (FAI), the world air sports federation, will make any endurance mark set by Zephyr "official".
Previous flights have been conducted in the absence of the FAI, meaning the current recognised mark for endurance held by a robotic plane is only 30 hours, 24 minutes. This was set by the US robot Global Hawk.
The 50kg Zephyr will probably climb to about 40,000ft on its first day, and then try to maintain 60,000ft thereafter. It is likely to lose about 20,000ft each night.
The bigger size of the vehicle means it now takes five individuals to launch the vehicle, as opposed to the three previously.
"The team runs gently into the wind until it wafts out of their hands. It's a very effective and reliable process, it's cheap and it works," said Mr Saltmarsh.
The unique selling point of solar UAVs will be their persistence over a location. Low-Earth orbiting satellites come and go in a swift pass overhead, and the bigger drones now operated by the military still need to return to base at regular intervals for refuelling.
Solar UAVs can be left in the sky, their operation maintained by an autopilot.
The Qinetiq team has watched with interest the development of the Swiss Solar Impulse project which recently performed the first day-night flight of a manned sun-powered aeroplane.
"All this is proving that the time for solar aircraft has come," said Mr Saltmarsh.