Rarefied aerodynamics of a deployable re-entry capsule

Several research activities have been already carried out in the field of low-ballistic coefficient re-entry capsules based on deployable umbrella-like aero-shield. The flexible aero-shield, made of ceramic fabrics, acts both as an aero-brake and a Thermal Protection System (TPS), making possible to perform a re-entry from orbital or suborbital conditions with relatively low values of the aero-thermo-dynamic loads. Previous studies have already analyzed Aerodynamics of similar systems, identifying self-stabilizing configurations and creating a preliminary database of force and moment coefficients in different flight regimes. This work is intended to provide a systematic overview of the aerodynamic behavior of a deployable capsule in the rarefied regime, where the differences between the re-entry trajectories from Low-Earth-Orbit and suborbital flight conditions are more evident. Particular focus is given to the longitudinal stability analysis, which demonstrates that, as the continuum hypersonic regime approaches, the capsule could show a stable equilibrium condition in the unfavorable reverse attitude. This unwanted equilibrium condition could be counteracted by moving the center of gravity out of the symmetry axis.