Numerical Modeling of the 8 Meter Attached Isotensoid Supersonic Inflatable Aerodynamic Decelerator

This paper documents the development and application of numerical modeling techniques for the Exploration-class Supersonic Inflatable Aerodynamic Decelerator, SIAD-E, a component of NASA’s Low Density Supersonic Decelerator (LDSD) project. LDSD is funded by the Space Technology Program through the Technology Demonstration Missions program and is tasked with advancing new deceleration technologies to sufficient readiness levels, enabling them to be infused into potential future robotic and human Mars mission designs. The SIAD-E is an 8 meter diameter isotensoid fabric structure constructed from high tenacity bias braid fabric and inflated by a combination of gas generators and ram air inlets. The isotensoid will be stowed and attached to the outer rim of a typical capsule-like atmospheric entry vehicle, and will inflate high in the Martian atmosphere at velocities 4 times the speed of sound, decelerating the capsule to a speed where it is safe to deploy and inflate a parachute. A key feature of the SIAD-E is that it is an inflatable structure which remains inflated by entrapping gas from the surrounding atmosphere. This aspect of the technology makes it both a mass efficient drag device that can be used with existing launch vehicles and launch vehicle shrouds, and predictably, also a very challenging structure to design and analyze. This paper discusses the use of the commercially available, transient dynamic FEA code LS-DYNA to predict the inflated shape of the structure and the associated design loads. The paper discusses the integration of the LS-DYNA structural code with CFD results from Data Parallel Line Relaxation (DPLR) a NASA fluid mechanics code, to achieve a predictive iterative numerical loop. The combination of LS-DYNA and DPLR was used to predict deformed shapes of the isotensoid at angles of attack, various internal pressures, and the associated fabric loading. In addition, the code pairing was able to highlight areas of the isotensoid surface for optimal placement and sizing of the ram-air inlets; balancing pressure recovery and thermal considerations. This paper documents the processes undertaken to achieve the results as well as the challenges of transferring datasets between codes, between facilities, and the nuances involved with a complex multi-physics application.