Use of Shuttle Orbiter aerodynamic data to validate accomodation coefficient models

Knowledge of the free-molecule flow regime is important in order to determine precise satellite orbits and to find the bridging function between continuum flow and free-molecule flow for use in the development of single-stage-to-orbit vehicles. For this thesis, two variable accommodation coefficient models were integrated into the computer program used to calculate the aerodynamic forces present on a body, and the results were compared with measured values from the Space Shuttle Orbiter. It was concluded that although the diffuse method under-predicts the aerodynamic lift present on the Orbiter in low-earth orbit, the variable accommodation coefficient models vastly over-predict the amount of lift present. This difference is attributed to the fact that the tiles on the Orbiter are non-engineering surfaces. Also, unlike predictions using the variable models, lift-to-drag ratio predictions using the diffuse model were very sensitive to wall temperature and atmospheric temperature and composition. It is recommended that experiments be performed in orbit, coupled with direct measurements of atmospheric conditions, to produce real data that could be used to improve the mathematical models