Thermal Analysis and Testing of Candidate Materials for PAIDAE Inflatable Aeroshell

The Program to Advance Inflatable-Decelerators for Atmospheric Entry (PAIDAE) is a NASA Langley Research Center project whose purpose is to conduct the research, ground testing, and analysis necessary to mature the Inflatable Aerodynamic Decelerator (IAD) technology. Inflatable, or otherwise deployable, aeroshells offer the promise of achieving larger aeroshell surface areas for entry vehicles than attainable without deployment. With the larger surface area comes the ability to decelerate high-mass entry vehicles at relatively low ballistic coefficients. However, for an aeroshell to perform even at the low ballistic coefficients attainable with deployable aeroshells, the aeroshell requires a flexible thermal protection system (TPS) capable of surviving reasonably high heat flux and durable enough to survive the rigors of construction handling, high density packing, deployment, aerodynamic loading, and aerothermal heating. One goal of PAIDAE is to develop a TPS that meets these requirements. In support of this goal, testing of candidate multi-material layups for use as flexible thermal protection systems for inflatable aeroshells was undertaken. Multi-material layups, or coupons, were tested in Langley’s 8-foot High Temperature Tunnel (8'HTT) in order to replicate conditions that are representative of conditions seen in entry simulation analyses of inflatable aeroshell concepts. Coupons are composed of three layers: outer fabrics, insulators, and gas barrier materials. Testing consisted of 6 – 12 coupons being installed on a test sled and the sled being injected into Mach 6 flow for 90 – 100 seconds. The heat flux to which each coupon was exposed was driven by its location on the sled, the total angle-of-attack of the sled, and the facility settings during testing. The test setup allowed for coupons to be tested at discrete heat fluxes of 6W/cm², 11W/cm², and 20W/cm². Thermal analysis of the candidate coupons was performed in order to establish predictions of material response and failure criteria, and to keep barrier layer materials from reaching critical temperature limits during 8’HTT operations and thermal soak. This paper focuses on the thermal analysis, and how the analysis compares to sample coupon test data. This paper will present details of the thermal analysis performed, and provides an overview of the experimental setup, including sled and coupon configuration, 8'HTT conditions, and results.