Satellites do that now from what is called geostationary orbit, 22,000 miles above Earth. At that altitude, the satellites’ orbit matches the speed of Earth’s rotation. (At a lower altitude, the satellite would orbit faster.) Satellites maintain their orbit around Earth through a balance of two opposing effects: Earth’s gravity and centrifugal force. An airship would balance the force of gravity with aerodynamic lift, buoyancy, or a combination of the two; it could provide 24-hour coverage of a single section of ground but, at an altitude of only 11 miles, with a much closer view than a satellite offers.
New technologies may finally bring the stratosphere within reach. To go to that altitude, airships would need to carry so much helium they’d have to be gigantic; one concept under study by the Pentagon’s Defense Advanced Research Projects Agency could hold a 15-story building. The resulting design challenge sounds like a logic problem: “If you’re bigger, you have more drag, and if you have more drag, you need more propulsion, and if you need more propulsion, you need more energy,” says Ron Browning, director of marketing at Lockheed Martin Defense and Surveillance Systems in Akron, Ohio, a rubber manufacturing center with a long history of balloon and airship fabrication.
Lockheed Martin’s Akron unit might have been a shoo-in to crack the stratosphere were it not for a matter of money. In 2005, the U.S. Missile Defense Agency awarded Lockheed $149 million for construction of a 400-foot-long prototype called the High Altitude Airship. By 2009 a demonstration version was to fly to 60,000 feet and carry a 500-pound payload. An operational version would carry thousands of pounds of sensors to spot hard-to-find cruise missiles.
This year, the Missile Defense Agency announced that budget cuts required it to “eliminate funding for the High Altitude Airship” beyond fiscal year 2007. Lockheed managers are now lobbying members of Congress to restore funding. “We don’t think this program is going to be a dead end,” Browning says. “There are too many positives with it.”
A key to the High Altitude Airship is the hull material. It has to be light so it doesn’t drag the ship down, but it also must be strong to handle the pressure of the helium. (At 60,000 feet, the density of the air is only six percent what it is at sea level, and that low pressure would produce enormous helium expansion.) And because the goal is “persistent” coverage for weeks on end, the material can’t be porous or the helium would escape.
At stratospheric altitudes, there is less wind, but keeping the airship in place will still require a propulsion system. Standard engines are no good because as they burned fuel, the craft would get lighter and slowly rise until the expanding helium split its seams.
Though the prototype will use lithium ion batteries, Lockheed decided that the operational ship should run on solar power. The top and sides of the craft would be covered with photovoltaic cells to convert sunlight into electricity. Extra energy would be stored during the day to keep the craft’s two propellers churning at night.
“The challenge is getting through that first diurnal cycle,” Browning says. “That has not been accomplished before.”
O Mighty ISIS
Under a research effort called ISIS (Integrated Sensor Is Structure), engineers at DARPA hope to build a stratospheric airship containing a giant radar antenna. The antenna will double as the interior support structure—a weight-saving design. “We’re really a radar program,” says electrical engineer Tim Clark, DARPA’s ISIS program manager. “The platform just turned out to be a stratospheric airship. And that’s because we wanted big antennas. You can’t get much more surface area than a stratospheric airship.”
The bigger the antenna, the more detail it can see. “If the wind blows a tree and it sways, you’ve got to be able to separate out the tree movements from a vehicle’s movement,” explains Clark. “It’s easier to do if your resolution on the ground or near the ground is small. You have [fewer] things competing.” The 17,200-square-foot antenna would park itself over areas of interest and transmit and receive radar signals that enable it to spot moving trucks, cars, airplanes, and cruise missiles.
Northrop Grumman Electronic Systems of Baltimore, Maryland, and Lockheed Martin’s fabled Skunk Works unit in Palmdale, California, are working on competing ISIS architectures. Lockheed’s Akron unit is developing the lightweight hull materials. If the technology passes a series of reviews, DARPA will shoot for a flight in 2010 or 2011.
21st Century Sampsons
An airship is built to generate lift. Could that lift be harnessed to haul heavy equipment?
Other air freighters have limitations: Cargo planes need runways, and helicopters are expensive—$25,000 an hour or more. And even the most powerful lifter, Russia’s Mil Mi-26 helicopter (see “We Haul It All,” June/July 2006), has limits: Its maximum payload capacity is 30.5 tons, whereas oil companies need to lift objects weighing up to 40 tons.
What makes using an airship as a hauler tricky is that when the craft drops off its load, the sudden loss of weight would make it shoot up in the air, in turn making the helium inside expand until it blew the hull apart. Keeping tons of ballast—dead weight—on hand to counteract the bounce is an “incredibly awkward” solution, Hokan Colting says.