Flexible TPS for Inflatable Atmospheric Decelerators

The High-Temperature Flexible Thermal Protection System (TPS) Testing effort is conducting the research, ground testing, and analysis necessary to mature the Inflatable Aerodynamic Decelerator (IAD) technology. Typically, the entry vehicle aeroshell is limited in size by the launch vehicle shroud. Inflatable aeroshells offer the promise of achieving larger aeroshell surface areas for entry vehicles. This is possible because the aeroshell is compressed and stowed during launch. Therefore, the inflated aeroshell diameter at entry can be many times larger than the launch shroud diameter. A larger surface area, achieved by inflatable aershoshells, allows deceleration of high-mass entry vehicles at relatively low ballistic coefficients. Even at the low ballistic coefficients attainable with deployable aeroshells, the aeroshell requires a flexible TPS capable of surviving relatively 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 the Flexible TPS development effort is to develop and test TPS that meet these requirements. In support of this goal, two series of tests of candidate material layups were conducted in Langley’s 8-foot High Temperature Tunnel (8’HTT)in order to replicate conditions that are representative of conditions seen in entry simulations analyses of inflatable aeroshell concepts. The first test series, conducted in the winter of 2007, utilized readily available tunnel hardware and material combinations and resulted in expanding our understanding of the potential use, and limitations of multi-material layups. In the second test series, conducted during the summer of 2009, only those material layups considered to have a high potential for future application were tested. Reducing the number of test samples and applying lessons learned from the first test series, resulted in a reduced number of failed samples.

TPS sample coupons are composed of three layers: outer fabrics, insulators, and gas barrier materials. Testing consisted of 6 coupons installed on a test sled and the sled being injected into Mach 6.5flow for 90 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, and20W/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 presentation provides and overview of the thermal analysis methodology and results, and a comparison with 8’HTTtest data. This presentation also provides an overview of the experimental setup, including sled and coupon configuration, 8'HTT conditions, and planned Flexible TPS test efforts for Fiscal Years 2010and 2011.