altitude as it has no further buoyancy. This altitude stability exists only as long as the balloon is in the fully inflated or "taut" state. Once the balloon starts descending (due to loss of hydrogen by diffusion or by other loss) it becomes flabby and is no longer stable. It will continue descending until corrective action is taken or until it reaches the earth.
The altitude control is to be used is the ballast valve. When correctly set it will determine the lower limit of the balloon's oscillation as it would release a free flowing liquid ballast from a reservoir whenever the balloon descends a short distance below a preset altitude.
To test this tentative solution to the basic problem, intermediate sizes of balloon made of suitable fabric or films are needed in addition to the altitude controls.
Balloons
Balloon manufacturers and fabricators of plastic films were contacted to locate a suitable balloon material. The following materials were suggested:
Material
Advantages
Disadvantages
Disposition
Plastic Film
Polyethylene
Good low temperature properties (Gen.Mills desires to fabricate Picard's balloons from this).
Low tensile strength, Milky-translucent, Medium permeability.
10 ea. 15 ft. balloons being fabricated from it.
Saran
Transparent, low permeability, high tensile strength.
Tears easily, fair low temperature properties (?), weak at seams if heat sealed.
5 large balloons being fabricated.
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