A proposed improved balloon system for carrying scientific instruments in the stratosphere would include a lightweight, ambient-pressure helium balloon and a vented infrared Montgolfiere (see figure). [An infrared Montgolfiere is an ambient-pressure warm-air balloon, named after the familiar fire-heated hot-air balloons invented by the Montgolfier brothers. An infrared Montgolfiere is heated primarily by the Sun during the day, and/or by infrared radiation from relatively warm surface of the Earth at night.] The system would feature controllability of altitude for taking scientific data, landing, or taking advantage of favorable winds for relocation. The system would be designed for long life, but would weigh less (and therefore cost less) than do previously developed long-life balloon systems.
The advantages of the proposed system are best understood in the context of two prior classes of long-life, high-altitude balloons. One prior class is that of helium superpressure balloons, in which pressures above ambient are maintained in order to maintain constant densities and thus constant altitudes. The other prior class is that of infrared Montgolfieres (used by themselves, rather than in combination with ambient-pressure helium balloons according to the present proposal). Superpressure balloons must be strong, and thus heavy, to maintain their interior pressures above ambient. Montgolfieres are not as efficient as helium balloons are and hence must be very large, and correspondingly heavy. A Montgolfiere by itself floats higher during the day than during the night, and thus is not well suited for observations for which altitude control is required. Altitude control for helium balloons has been effected by partial venting of helium (for descent) or dropping of ballast (for ascent), but these releases entail a tradeoff between controllability and longevity.
In the proposed system, there would be no deliberate venting of helium or release of ballast. The ambient-pressure helium balloon would provide most of the lift during the day. The infrared Montgolfiere could be used to make up for the small decrease in buoyancy caused by nighttime cooling of the helium balloon, or to increase altitude. A vent in the top of the infrared Montgolfiere could be used to vary the buoyancy.
Masses and sizes of a conventional superpressure helium balloon and of the balloons in the proposed system have been calculated for a payload mass of 500 kg at the altitude where the ambient pressure is 0.01 bar (1 kPa). The total mass of the proposed system was found to lie between one-fifth and one-third of that of the superpressure helium balloon, the exact value depending on specific design parameters. Because the construction of an ambient-pressure balloon is much easier than is that of a superpressure balloon, the cost of the proposed system should be even lower than that indicated by the ratio of masses.
This work was done by Jack Jones of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at ">www.nasatech.com/tsp under the Physical Sciences category.
This Brief includes a Technical Support Package (TSP).
Long-Life Stratospheric Balloon System with Altitude Control
(reference NPO-20742) is currently available for download from the TSP library.
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