Uncertainty Quantification Applied to the Analysis and Design of Hypersonic Inflatable Atmospheric Decelerators for Spacecraft Re-Entry

NASA continues to bridge the gap between current metric-ton class robotic missions and large robotic and human explorations missions with 20-50 metric-ton payloads. Hypersonic Inflatable Aerodynamic Decelerators (HIADs) have been shown to be a viable candidate to replace the traditional rigid aeroshell and provide advantages such as high altitude deceleration for pin point landing, increased entry, descent, and landing times, and increased payload capability with mass and space savings of the stowed configuration. Accurate numerical modeling of such complex systems is significantly important in obtaining robust and reliable designs of a HIAD. The primary objective of the research undertaken with this fellowship was to investigate the uncertainty for the multidisciplinary analysis of the HIAD subject to uncertainty sources in the high-fidelity computational models used and inherent variations in the operating conditions (environments). Efficient stochastic expansion response surface methods were implemented to obtain the uncertainty in the performance metrics of interest associated with the hypersonic flow field, fluid-structure interaction, and the flexible thermal protection system response of the HIAD. A global nonlinear sensitivity analysis was applied to identify key uncertainty sources which contribute to the performance metric uncertainty. The performance metric uncertainty and key uncertainty sources were analyzed and reported to provide information in improving the robustness and reliability of the HIAD design. In order to achieve the primary objective the research undertaken under the fellowship, three annual goals were outlined to investigate the uncertainty of HIAD at the subsystem level. In the first year, demonstration and implementation of an efficient uncertainty quantification (UQ) approach with an efficient stochastic response surface approach for the high-fidelity numerical modeling of hypersonic flow simulations of a fixed aeroshell of HIAD scale was completed. The results identified and showed a small fraction of the large number of aleatory and epistemic uncertain parameters were significant in influencing the aerodynamic heating magnitudes and uncertainties. Uncertain parameters were also identified that influenced the surface pressure and shear stress of the HIAD aeroshell. In the second year, uncertainty analysis of a deformable HIAD, accounting for the interaction between the hypersonic flowfield and the inflatable structure in the presence of material stiffness, inflation pressure, and surface pressure and shear stress uncertainties, was completed. Significant flowfield uncertain variables from the first year were included in this analysis. Additional uncertain parameters in the structural model were introduced to obtain the uncertainty in the HIAD deformation and resulting surface conditions. The uncertainty results identified the structural component uncertainties that drive the deflection uncertainty and how shape deformation contributed to the resulting surface condition uncertainties. The third year focused on the thermal protection system (TPS) component of the HIAD. A detailed uncertainty analysis was conducted on the TPS thermal response in the presence of external pressure and aerodynamic heating uncertainties. The important factors that drive the pressure and aerodynamic heating uncertainties from the first year were retained, and additional uncertain parameters in the thermal protection system thermal response model, such as material thermal properties, decomposition phenomena, and layup thicknesses, were introduced to obtain the TPS bondline temperature uncertainty. Global nonlinear sensitivity analysis was performed to reduce the dimension of the complete set of uncertain variables. Uncertainty of the bondline temperature was obtained with the reduced set of important uncertain variables. The TPS bondline temperature uncertainty and sensitivities provided information for future studies in improving the robustness and reliability of the flexible TPS.