Masses of long-life, high-altitude balloons could be decreased substantially.
An improved, lightweight design has been proposed for super-pressure balloons used to carry scientific instruments at high altitudes in the atmosphere of Earth for times as long as 100 days. [A super- pressure balloon is one in which the pressure of the buoyant gas (typically, helium) is kept somewhat above ambient pressure in order to maintain approximately constant density and thereby regulate the altitude.] The proposed design, called "meshed pumpkin," incorporates the basic concept of the pumpkin design, which is so named because of its appearance (see figure). The pumpkin design entails less weight than does a spherical design, and the meshed-pumpkin design would reduce weight further.
The basic idea of the meshed-pumpkin design is to reinforce the membrane of a pumpkin balloon by attaching a strong, lightweight fabric mesh to its outer surface. The reinforcement would make it possible to reduce the membrane mass to one-third or less of that of the basic pumpkin design while retaining sufficient strength to enable the balloon to remain at approximately constant altitude for months.
For example, the pumpkin balloon shown in the figure is made from a complex composite of polyester fabric, adhesive, polyethylene terephthalate film, and polyethylene film. The balloon has an areal mass density of 62 g/m2 and a total mass of 2,800 kg. The balloon can carry a payload of 1,600 kg at an altitude of 33 km. One corresponding meshed-pumpkin design calls for reinforcement of the membrane with a 1-by-1-in. (2.54-by-2.54-cm) mesh of polybenzoxazole scrim fiber of 25 denier (a lineal mass density of about 2.8 mg/m). With this reinforcement, the complex composite membrane could be replaced by a simple polyethylene film 0.5 mil (12.7 μm) thick, reducing the mass of the balloon to <400 kg. The mesh would provide a strength of 400 N/m, giving a factor of safety of 5, relative to the strength required for a pumpkin balloon with a bulge radius of 8 m.
This work was done by Jack Jones and Andre Yavrouian of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Materials category.
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Refer to NPO-21139, volume and number of this NASA Tech Briefs issue, and the page number.
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Meshed-Pumpkin Super-Pressure Balloon Design (reference NPO-21139) is currently available for download from the TSP library.
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