Modern airships brace for space odyssey

Airships are dusty relics of aviation history. Lighter-thanair vehicles conjure images of the Hindenburg, in its glory and destruction, and the Goodyear Blimp, a floating billboard that barely resembles its powerful predecessors. But now engineers are designing sleek new airships that could streak past layers of cloud and chart a course through the thin, icy air of the stratosphere, 65,000 feet above the ground — twice the usual altitude of a jetliner.

Steered by scientists below, these aerodynamic balloons might be equipped with onboard telescopes that peer into distant galaxies or gather oceanic data along a coastline. “Stratospheric airships could give us spacelike conditions from a spacelike platform, but without the spacelike costs,” said Sarah Miller, an astrophysicist at the University of California, Irvine.

High-altitude airships are still in their relative infancy. None has ever flown at 65,000 feet for longer than eight hours. But a recent study from the Keck Institute for Space Studies at Caltech suggests that a more capable airship may not be far-off. And NASA is expected to sponsor a contest to build better airships, breathing new life — and funding — into the idea. These airships would not be the first vehicles to venture into the stratosphere, of course.

Rockets and satellites routinely whiz past 65,000 feet into earth orbit and beyond, and weather balloons already bob about in the upper reaches of the atmosphere. “Balloons have been around for 200 years, so everybody thinks, well, gosh, it’s such old technology, how hard can it be?” said Steve Smith, an aerospace engineer who in 2005 designed one of the first successful stratospheric airships. “That’s the farthest thing from the truth.” Unlike free-flying weather balloons, a blimp can be actively maneuvered, providing the control necessary to carry out advanced missions with expensive equipment. But that maneuverability is compromised the moment it begins to lose its aerodynamic shape.

For that reason, airship design is a balancing act. During the day, the helium inside the balloon warms and expands; at night, it contracts as the temperature drops. “That’s the real technical challenge,” Smith said. “You want enough gas in there so that it won’t collapse at night, and strong materials so it won’t burst during the day.” This problem is compounded in a stratospheric airship, which must maintain its aerodynamic shape as it ascends through rapid temperature and pressure changes between layers of the atmosphere.

For Mr. Smith’s first successful stratospheric airship, the Hi- Sentinel 20, he chose a milky white polyester fabric that was tear-resistant and highly flexible. The United States Army commissioned test flights of the Hi-Sentinel 20 to determine whether blimps could hoist communications satellites above enemy territory. The airship took off from New Mexico in 2005 and remained aloft only about eight hours, but it proved that an unmanned blimp could be steered through the stratosphere by a team of engineers on the ground.

Other test ships — the Hi-Sentinel 50 and the Hi-Sentinel 80 — were also successful. But the Army’s interest waned with the end of the Iraq war, leaving Mr. Smith and his team short on funds. In search of a new market, he approached scientists with his promise of an inexpensive aircraft that could carry remote-controlled telescopes above the clouds.

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