Aeroelastic Stability of Thermal Protection System for Inflatable Aerodynamic Decelerator

Abstract

A theoretical aeroelastic stability analysis has been performed on the flexible thermal protection system for an inflatable aerodynamic decelerator. Structural models consist of one or more truncated conical shells of the Donnell type, which may be elastically supported along the middle surface. The aerodynamic model is first-order piston theory. The Lagrangian of the system is formulated in terms of the generalized coordinates for all shell displacements, and the Rayleigh–Ritz method is used to derive the equations of motion. The aeroelastic stability boundaries and mode shapes are found by calculating the eigenvalues and eigenvectors of a large coefficient matrix. When the thermal protection system is approximated as a single conical shell, circumferentially asymmetric coalescence flutter between the second and third axial modes is observed. When many circumferential elastic supports are included, the shell flutters symmetrically in zero circumferential waves, with the first, second, and third axial modes being the most critical. In this case, the flutter boundary, flutter mechanism, and critical modes may change significantly with the addition of structural damping. Aeroelastic models that consider the thermal protection system as multiple interacting shells tend to flutter asymmetrically at high dynamic pressures relative to the single shell models, with higher axial modes being more critical. It is also found that tension applied at the shell edges, orthotropicity, and elastic support stiffness are important parameters that can dramatically affect the shell’s flutter behavior.