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| Because they retain virtually all of their original lifting gas, superpressure balloons will be able to circle the globe for months. |
 Tech Update Archive |
"Superpressure" balloons now being developed by NASA will float several-ton payloads through the stratosphere on missions lasting more than three months.
The high-altitude balloons currently used by scientists, known as zero-pressure balloons, can lift 3-ton instrument packages to about 130,000 ft., but remain aloft for only a few days. They are launched partly inflated and expand as they rise. But after passing through the tropopause, where temperatures drop as low as minus-180�F, they vent most of their gas in the more than 70�F daytime temperature of the stratosphere. When the Sun sets, the remaining gas shrinks. In order to stay aloft, the balloon must drop ballast. As a result, most zero-pressure balloons survive no more than one or two sunsets.
Superpressure balloons are also partially inflated when they leave the Earth. But unlike zero-pressure balloons–which have a venting hole in the bottom–superpressure balloons are completely sealed. This is possible because they are made of highly durable composite plastic and fabric materials that can withstand high internal pressures caused by solar heating. Maintaining helium at a constant volume and density also makes them extremely stable.
"Remaining aloft for months at a time, superpressure balloons will be able to conduct astronomy, particle physics and ozone hole experiments that require both endurance and greater lifting capacity," says Jack Tueller, a balloon project scientist at NASA's Goddard Space Flight Center.
A full-size superpressure-balloon demonstration flight is scheduled for the summer of 1998. The first flight with a working payload could take off in January 2000.
