The unique Zephyr “high-altitude pseudo satellite” (HAPS) is displayed by Airbus Defence & Space again in model form here at the Farnborough International Airshow. The European multinational bought the program in 2013 from UK research group Qinetiq, which developed it right here at Farnborough over the previous 12 years. Sadly, the man behind the concept and its slow but steady progression towards technical maturity won’t be available to explain. Local resident Chris Kelleher died unexpectedly last August, aged 58.
Kelleher also worked on the UK’s Skynet military communications satellites, so he understood the potential for a loitering stratospheric vehicle that could be a low-cost complement or alternative. But while other companies tried to develop high-altitude airships or aircraft powered by other novel means to address this requirement, the 20-strong Zephyr team placed its faith in a very lightweight solar and battery-powered UAV.
They may have chosen the correct path, since the payloads they are targeting are reducing in size year-by-year. Airship designers have struggled to find strong but lightweight envelope materials that can withstand the harsh stratospheric environment, with its very low temperatures, high ozone content and intense ultraviolet radiation. With help from the U.S. government, Aerovironment developed the Global Observer and Boeing the Phantom Eye, both powered by hydrogen fuel cells. But neither has found a customer. Meanwhile, by placing flexible silicon solar arrays on a carbon fiber airframe, and adding the latest lithium-sulfur batteries, the Zephyr team has achieved unprecedented endurance and control.
The program has steadily progressed through a series of increasingly ambitious demonstrations, helped by some funding from the U.S. and UK militaries. Wingspans have doubled from the initial 12 meters (39.4 feet) in 2003, while weights have quadrupled. In July 2008, the Zephyr 6 reached over 60,000 feet and flew for 82 hours from the Yuma Proving Grounds in Arizona, controlled from a line-of-sight ground station and carrying a 2-kg (4.4-pound) communications payload. Two years later, the team was back in Arizona with the larger Zephyr 7, to make a record-breaking 14-day flight that was validated by observers from the Fédération Aéronautique Internationale.
But the most significant demonstrations took place in 2014. An 11-day flight was launched from British-controlled Ascension Island in the South Atlantic during the low-sunlight conditions of the southern hemisphere winter. This explored the ability of the Licerian battery packs provided by Sion Power to store enough solar energy to power the Zephyr through the long hours of darkness, without significant loss of altitude. This was also the first flight controlled by a satcom datalink.
There was also a flight in 2014 from Dubai that explored the Zephyr’s integration into civilian airspace. The UAV was equipped with Mode S ADS-B so that it could report ascending through a “bubble” of airspace that other traffic could avoid. The Zephyr takes up to 12 hours to reach its operating altitude above the jetstream. It has almost no ground speed when flying into wind. When on station at 65,000 feet or above, it loiters by GPS control. It is hand-launched by a five-man ground crew, and recovered by belly-landing.
The UK Ministry of Defence has kept faith with the Zephyr, despite a crash during the 2014 deployment to the southern hemisphere. It has given Airbus D&S a $14 million (£10.6 million) contract to provide two larger UAVs for an operational concept demonstration next year. Designated Zephyr 8, they will have 50 percent more battery power than the Zephyr 7 on display here—which has now been retired. They will have a wingspan of 25 meters (82 feet), weigh 55 kg (121 pounds) and offer a payload of 5 kg (11 pounds).
“These British-designed unmanned aircraft will fly at the edge of the Earth’s atmosphere and allow us to observe our adversaries for weeks, providing critical intelligence for our forces,” said a British defense minister. The UK is believed to be most interested in using the Zephyr for supporting its special forces, with payloads such small video cameras, SIGINT (signals intelligence) sensors, and covert communications.
According to Airbus D&S head of unmanned system Jana Rosenmann, the Zephyr has “enormous commercial potential, especially for internet connectivity.” Facebook and Google think the same, and have both bought small start-up companies working on larger, solar-powered HAPS. But the European aerospace giant believes it is on the best development path. The various Zephyr demonstrations to date have logged more than 900 hours.
Airbus D&S has also suggested environmental monitoring, direct broadcast TV and radio, and narrowband mobile communications as other applications. It is, of course, a very “green machine.” Before buying the program, Airbus D&S did five years of research on how a HAPS could complement the company’s own satellite offerings through what was then the Astrium subsidiary of EADS. One of the biggest advantages is the ability to bring a HAPS back to earth to change out or update payloads.
The Zephyr 7 on display here has achieved a type certification from the UK Military Aviation Authority (MAA). But Rosenmann acknowledged that civilian certification is still a challenge. So is “the market price point, which is strongly linked to battery development,” she continued. The company is aiming for an endurance of several months aloft.
Airbus D&S is now developing a larger version that would weigh up to 140 kg (309 pounds) and carry a payload of 20 kg (44 pounds) on a 33-meter (108-foot) wingspan. It is designated Zephyr T because it has twin tails to support the additional weight. The Zephyr 8 for next year’s UK-funded demonstration has been redesignated Zephyr S (for single tail).