26 August 2009—Weather permitting, a new type of aerial robot will take to the skies over Stuttgart, Germany, next week. Looking like something from the Macy’s Thanksgiving Day Parade, the new segmented airship is actually a serious contender for border security, emergency and battlefield communications, and other applications that call for long-duration, high-altitude unmanned aerial vehicles (UAVs).
Unlike dirigibles, blimps, and other aircraft in the ”lighter than air” category, the new airship isn’t piloted or controlled remotely: From takeoff through landing, its flight control is entirely autonomous. No other airship has such a capability, says Bernd Kröplin, a professor of aerospace engineering at the University of Stuttgart and one of the airship’s inventors.
Kröplin says the idea originated from a hallway conversation he had with colleague Frank Epperlein. The two engineers argued over the best type of vehicle for conducting high-altitude, long-duration flights. At the time, they were looking for alternatives to satellites that could provide telecommunications coverage in impoverished areas. ”Epperlein suggested an airship, and I had in my mind an extremely light plane,” Kröplin recalls. ”We started drawing on the wall. From that came the idea.”
Epperlein rushed back to the lab and built a mockup of what they’d discussed: a series of linked balloons that they dubbed an ”AirChain” and later a ”Sky Dragon.” (The commercial product will be known as the Stratellite.) It took the Stuttgart team 15 more years to refine their concept, and they built more than 30 prototypes, flew thousands of test flights, and ran countless computer simulations. In 2002, Kröplin founded TAO Technologies to commercialize the concept, and several years ago, TAO began a joint venture with Sanswire, an aerospace company headquartered in Fort Lauderdale, Fla. (An earlier effort by Sanswire to develop its own long-duration floating telecommunications platform, also known as the Stratellite, failed to launch.)
Along the way the Stuttgart researchers have had to overcome a good deal of skepticism. ”At the beginning, one of my colleagues from flight mechanics told me, ’This will never fly stably. This will never work,’ ” Kröplin says. He wasn’t even sure himself. ”We then started and experimented and tested, and finally we believed it.”
One of the most complex elements of the design, Kröplin says, is the flight control software, which allows the vehicle to ascend and descend on its own, without any intervention from a human pilot. Other airships have rigid frames, which make them both heavy and tricky to maneuver in shifting winds. The Stratellite has no frame, so it’s lightweight and flexible. In videos, its body appears to undulate, like an eel in water. The airship takes just a few hours to inflate and ascend, and it requires no dedicated launch facility or ground control station.
The vehicle’s autonomous operation extends to emergency landings. Early on, German flight authorities informed the team that it needed a way to land the airship safely, even after a system failure. The engineers devised an autonomous, GPS-guided parachute that can land the vehicle with a precision of up to 4 meters. A number of customers are now looking at the landing technology for delivering cargo, among other uses, Kröplin says.
Sanswire-TAO’s ultimate goal is to loft an airship that can ascend to the lower stratosphere, about 18 kilometers up, and fly for weeks or even months at a time, says Dan Erdberg, vice president of operations for Sanswire. The vessel to be tested in Germany next week, the STS-111, is an interim step in that flight plan. It’s designed for altitudes of 4500 to 9000 meters and for missions of up to five days. The current flight-endurance record for a UAV according to the Fédération Aéronautique Internationale is 30 hours, Erdberg notes.
”I think there are many people who still think this is impossible,” Kröplin concedes. ”In the field of flight-vehicle design, there are only a few ideas around, and you get educated in these ideas, and it’s not so easy to switch your brain to a totally different concept. But if we continue to have discussions and tests, eventually we can convince people.”