High Altitude Scientific Balloons

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The materials used to construct modern scientific balloons consist of plastic film and fiber tapes. The plastic film makes up the shell of the balloon while the polyester fiber load tapes provide the strength in the structure and allow it to carry such heavy loads. The polyethylene plastic films range  in thickness from 6 µ to 25 µ with the most common thickness being 20µ (about the same as a sandwich bag).

To fabricate the balloons, layers of film are laid out on a pattern on tables up to 213 m long.  A large scientific balloon can have over 150 gores. The edges of the sheets are sealed together using a specially designed, proprietary heat sealer. Once the sheets are sealed together along the edges of the pattern, they form "gores" and the load tapes are applied to the seals at the edges of the gores.

Using current materials technology, balloon flights are possible in the area below the dashed line on the chart. Small balloons are used to carry light to medium weight payloads to high altitudes. These missions tend to be oriented more toward atmospheric sciences. Hundreds of Aerostar balloons are used each year in the study of the ozone layer at both the northern and southern polar regions to monitor the chemical mechanisms responsible for ozone hole formation each year.

NASA uses Aerostar small balloons for very high altitude wind profile soundings. These balloons carry a GPS sonde to altitudes up to 130,000 feet to obtain wind profiles before a large scientific balloon mission. Plastic balloons reach high altitudes more reliably than rubber weather balloons because the balloon envelope does not stretch as the system ascends. The flaccid balloon is filled with just enough helium to lift the payload and balloon plus about 20% "free lift".  As the balloon ascends, the lifting gas inside – usually helium – expands to inflate the rest of the balloon. The balloon materials do not experience any appreciable stress until the balloon as fully inflated at its peak altitude.

     Small Balloon Accessories

     Small balloons can be flown in two different modes: as sounding balloons, or as
     zero pressure balloons. Sounding balloons ascend until the balloon becomes
     fully inflated and then burst. Zero pressure balloons are equipped with ducts to
     equalize the pressure at the base of the balloon creating a zero pressure
     differential at the bottom of the balloon. At full inflation, the zero pressure balloons
     enter a neutrally buoyant state at a constant altitude.
    
     The zero pressure balloons are used for longer duration flights. Following are
      the suggested and required accessories for the two different types of flights:

     Sounding: No accessories necessary unless a burst panel is desired.

     Burst Panel: A rectangular piece of film that is slightly weaker than the
     surrounding balloon envelope material. It is located at the top of the balloon to
     assure a rapid deflation of the balloon at burst altitude. Balloons without a burst
     panel can deflate more slowly and take longer to reach the ground.

     Zero Pressure: The required accessories are a channel duct and a destruct device

     Channel Duct: A part of the base material in the balloon is left open to the
     atmosphere to allow gas to escape once the balloon is fully inflated. This allows the
     balloon to reach an equilibrium altitude.

     Destruct Device: A rip panel installed at the top of the balloon which is attached
     to a rip chord that passes through the base of the balloon to the payload. As the
     payload is released from the base of the balloon, the rip panel is torn open and
     rapidly deflates the balloon.

     High Altitude Balloon Performance Charts

     I would like more information on High Altitude Research Balloons