A Technique to Predict Clefting of Lobed Super-Pressure Balloons

Lobed super-pressure balloons have shown a tendency to deploy into unexpected asymmetric shapes, hence their design has to strike a balance between the lowest stresses achieved by increasing lobing and the risk of incomplete deployment. This paper proposes a computational clefting test that can be applied to any given balloon design. The test consists in setting up the balloon in its symmetrically inflated configuration, then breaking the symmetry of this shape by artificially introducing a clefting imperfection, and finally determining the equilibrium shape of the balloon. Wrinkling of the balloon film and frictionless contact are included in the computation. The clefting test is applied successfully to three 27 m diameter super-pressure balloons that have been tested indoors by NASA, of which one had remained clefted when it was inflated and the other two had deployed completely.