The LENS XX Expansion Tunnel was designed and constructed by CUBRC to provide a research and testing capability to investigate real gas, shock layer chemistry, viscous interaction and ablation effects on the performance of hypervelocity vehicles. LENS XX generates clean uncontaminated high enthalpy flows at velocities up to 35,000 ft/sec to simulate re-entry into Earth and other planetary atmospheres. Unique experimental studies have been conducted to evaluate the aerothermal and real gas chemistry effects which control heat shield performance both in Earth and Martian environments. LENS XX has also been used by NASA to obtain detailed spectrographic measurements in clean air for its planetary entry program. As part of this testing, unique studies have also been conducted to evaluate catalytic heating effects on different surface coatings, and to determine the effects of flow chemistry on boundary layer transition at re-entry velocities. Testing programs have been conducted to examine the combined effects of viscous/inviscid interaction and flow chemistry on the performance characteristics of maneuverable re-entry vehicles. Recently, LENS XX has been used in the performance of major fundamental experimental research programs, coupled with Computational Fluid Dynamics (CFD) modeling, to evaluate and improve the models of air chemistry employed in the most advanced computer codes. These new algorithms are used to model complex regions of shock wave boundary layer interaction in hypervelocity flow at re-entry velocities.