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Ballons may someday collect samples from the surface of Saturn's Titan moon. (NASA)

Floaters

Mars, Venus, Titan - wherever there's air, we can explore by balloon.

His solution, unveiled at an aerospace conference in Washington, D.C., last year, is a two-balloon system. The first would operate near the planet's surface and would look like a cylindrical bellows made of extremely thin sheets of stainless steel "or other suitable alloy," according to Kerzhanovich's paper. The term "metal balloon" might seem an oxymoron, like "jumbo shrimp," but when designing lighter-than-air vehicles for Venus, unconventional thinking is required.

In fact, a corrugated-metal cylinder leans in one corner of the JPL workshop. The bellows is flexible enough that it can be squished like an accordion for storage on the way to Venus, and tough enough that it could survive the clouds of acid. Filled with helium, the thin metal balloon would rise from the surface of Venus, taking photos or carrying a sample container, depending on the mission. When it got above the hot zone, some 10 miles up, it would release a second balloon, which would climb to higher altitudes.

The metal balloon concept isn't quite ready for prime time. For this year's Discovery mission competition, Hall, Kerzhanovich, and colleagues from JPL and the Universities of California, Michigan, and Wisconsin at Madison submitted a more conservative concept. It uses layers of balloons, one tucked inside the other, and operates only in the upper Venusian atmosphere. An entry vehicle would jettison a folded, 17-foot-diameter balloon, which would inflate under a parachute, detach, and begin floating in Venus' upper atmosphere, protected from the acid clouds by a layer of Teflon film. The balloon would last about a month.

The JPL team finished a prototype of this Venus balloon in February, just in time to make the April deadline for Discovery proposals. If the design is selected this fall, the team will get more money to refine their study. Then, if they get the green light for full funding next year-a long shot, admittedly-their projected launch date to Venus would be the autumn of 2013.

Along with the technical details, a scientific paper by Kerzhanovich's Discovery proposal team includes a stirring vision of what their invention might spawn. "In the not-too-distant future, aerial rovers directly descended from the Venus aerostat could be plying the skies above treacherous landscapes and inhospitable depths of a number of worlds across the Solar System.... Such an aerial vehicle funded on a Discovery-class budget would herald a new era in planetary exploration."

The aerobot researchers are well aware that they've got a lot of hard engineering to do first. And there's always that frustrating Catch-22 of the space business: You can't fly until you're proven, and you can't be proven until you fly. But don't cry for Jack Jones, Jeff Hall, and their crew, whether testing prototype airships in Oregon or over a tabletop in California. They'll tell you themselves: It may not be easy to be a balloonist in a world of rockets and wings, but it sure can be fun.

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