Deployment Analysis of Pneumatic Envelopes Including Ascending Balloons and Inflatable Aerodynamic Decelerators

For functional reasons, many structures, such as large high-altitude scientific balloons or inflatable aerodynamic decelerators, are rotationally symmetric. Under certain loading conditions, a stress analysis of the complete structure can be facilitated by restricting the analysis to a fundamental section with appropriate boundary conditions. Using the analytical results for the fundamental section and the symmetry of the complete structure, one can obtain an analysis of the complete structure. Because the number of degrees of freedom in a fundamental section is significantly less than the number of degrees of freedom in the complete structure, the time to compute the stress distribution is significantly reduced. However, even though the complete structure with the symmetry condition is a stable local minimum, it need not be stable within the class of feasible configurations without the symmetry condition. This could occur if the theoretical boundary conditions imposed to calculate the fundamental section are not natural boundary conditions of the complete structure. Compliant inflatable membranes that rely on differential pressure to maintain the desired symmetric equilibrium shape can be susceptible to this circumstance. To illustrate this phenomenon and to demonstrate how stability and deployability are intertwined, we consider two structures: a pumpkin-shaped superpressure balloon and a tension-cone inflatable aerodynamic decelerator. Using the instance when an axisymmetric state changes from stable to unstable, we are able to estimate the minimum deployment pressure in an ascending pumpkin balloon and the torus collapse pressure in a tension-cone inflatable aerodynamic decelerator. In both cases, good correlation is found between analytical predictions and available experimental data. [PUBLISHER ABSTRACT]