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fork(2) [soylentnews.org] writes:

      Conventional balloons, called "zero-pressure" balloons have been used for years to study phenomena as diverse as atmospheric chemistry and cozmic microwave background. But they don't last long. During the daytime, sunlight heats and expands the helium. At night, the contracting helium requires that the balloon must drop ballast to avoid drifting too low. Zero-pressure balloons can only achieve long flights during summertime near the poles, when constant daylight allows them to stay afloat for weeks at a time.

      As an alternative, the helium in "superpressure balloons" is pressurized. Because their volume doesn't change as they're headed/cooled, they can remain at a constant altitude.

      On May 17, NASA launched a monster superpressure balloon from Wanaka, New Zealand. From an article by Patrick Monahan in Science [sciencemag.org]:

The latest and largest pressurized balloon to be launched by NASA has set a record for endurance: the longest midlatitude flight by a large scientific balloon. Packing 532,000 cubic meters of helium and measuring 114 meters in diameter, the balloon circled the Southern Hemisphere for 46 days, lofting a gamma ray telescope to the edges of space. Nightly dips in altitude forced a premature end to the voyage yesterday, but the flight still marks a milestone in NASA's efforts to develop so-called superpressure balloons as a low-cost alternative to satellites.

      [...]

      Yesterday, NASA brought the balloon down near the coast of Peru, 32 kilometers north of the town of Camana. Plans are already underway to retrieve the balloon and its payload from the mountainous area. Careful study of the balloon may help NASA avoid the same altitude dips in future flights. Still, the wayward balloon hauled in some novel astrophysical data. It carried the Compton Spectrometer and Imager (COSI), a gamma ray telescope that aims primarily to probe how elements are forged in supernovae. COSI observed the gamma rays emitted by radioactive nuclei in the supernova debris, and may be able to measure their polarization -- observations that are hard to make from the poles because of background gamma radiation from cosmic rays channeled toward the poles by Earth's magnetic field.

      NASA decided to end the balloon's flight yesterday (July 4) because of problems.

The balloon’s flight path during the long austral nights and short days was as erratic as a zero-pressure balloon's: It dipped as much as 10 kilometers nightly from its cruising altitude of about 33 kilometers, possibly because of a helium leak that later closed back up. And rather than circling the Southern Ocean for 100 days as intended, the balloon veered off over the South Pacific after just one circumnavigation, having slipped out of the winter cyclone winds that circle Antarctica. "Mother Nature is in charge of our business," says NASA Balloon Program Office Chief Debora Fairbrother in Wallops Island, Virginia. "She truly has been exercising her rights."

      [...]

      Still, NASA has a full slate of superpressure balloon missions lined up in the coming years, studying phenomena ranging from dark matter to cosmic rays. As more superpressure balloon projects produce useful data, says Eliot Young, a planetary scientist at the Southwest Research Institute in San Antonio, Texas, "everyone is going to realize it’s a great opportunity."

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