Tubulars Gore Tetroon Model

A Tetroon is an equilateral tetrahedron balloon made up of four equilateral (60°) triangles.  The payload is suspended from one corner so that the center of the opposite face becomes the top of the balloon.

A tetrahedron is formed by flattening a cylinder and sealing off the two ends skewed at right angles to each other if the distance from one corner of the flattened cylinder to the center of the opposite end is identical to the width of the flattened cylinder and that center point is used as the starting point of that end seal.  The two seals and the four vertexes formed by the edges of the triangles between the ends of the seals are all equal and form the six corner edges of the tetrahedron.

When a tetrahedron is inflated with a lifting gas it will form a crude teardrop (with three corner poking out from the top surface.)   It is then termed a Tetroon.  If a tetroon is pressurized it approximates a sphere with four conical corners in bas relief.  The volume of a pressurized tetroon actually approaches that of the sphere fabricated from the same amount of material.  On initial investigation, the advantage of fabrication from one straight sided piece of material with no tailoring or curved seams is readily apparent.

Note that in the picture above, the material web used to fabricated this tetroon is an inflated tube. It is all one tube.  See that on the exposed surfaces the tubing is up and down, while on the hidden surfaces it runs across.  The original flattened cylinder described above is formed by a spiral of flat tubing, much like the strip of pasteboard used to form a core for a roll of paper towels.   After the one long spiral seal and the two closing end seals are completed the tubing is inflated to form the corrugated tubular gore conformation.

For the eXtreme Altitude Project (XAP) the tubing will be fabricated to the appropriate diameter so that it just lifts its own weight when filled at sea level with helium.  That requires a tube of only a few inches in diameter.  The maximum allowable size of such a balloon system is that which only creates a pressure head in the tubing at the top of the balloon which the tubing can withstand.  (The pressure head is caused by the barometric pressure differential in the atmosphere and is highest at launch.)

A Metalized Mylar Tetroon Partially Inflated