A way to fly a balloon in and out of the stratosphere
ACCORDING to the old adage, what goes up must come down. But in the case of balloons, the descent sometimes comes sooner than expected. Although helium-filled weather balloons regularly launch instruments high into the stratosphere, at altitudes of 20km (65,000 feet) the air is 15 times less dense, causing the balloons to expand and ultimately burst.
This problem has long vexed the American military, which would like to use lighter-than-air dirigibles as atmospheric satellites, or stratellites. From 20km a blimp would be able to continuously survey an area the size of Texas for months at a time, but in greater detail and at much lower cost than geostationary satellites or those moving in low Earth orbit.
Despite the problems, dirigibles are coming back into service. Global Telesat Corporation, an American supplier of unmanned aerial vehicles, recently purchased its first SkySat. This 38 metre-long remotely operated airship is designed to carry communications and monitoring equipment for intelligence, surveillance and reconnaissance missions. With its familiar cigar-shaped design, however, it will rise only so far—14km, to be precise. And at this altitude ferocious winds require a SkySat to burn through its fuel supply just to stay still. As a result it can remain aloft for only a few days at a time.
The ultimate goal is to find a way to slip above the jet stream and into the virtually windless stratosphere for an even better vantage point, says Dan Erdberg of Sanswire, a Florida company which developed SkySat. Over the years the company has looked at various solutions, and it is now working with Global Telesat to develop a novel, snakelike airship called the STS-111. It is made up of four connected and articulated inflatable sections.