Nonlinear Modeling and Initial Condition Estimation for Identifying the Aerothermodynamic Environment of the Space Shuttle Orbiter.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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This report describes improvements made to the data analysis tool HEATEST, used for identification of the reentry aerothermodynamic environment of the Space Shuttle Orbiter. The heating model was changed from a linear perturbation form to that of a piecewise linear interpolation form to account for nonlinear heating rates. Also, a fixed-point initial condition smoother was incorporated to gain better estimates of unknown initial temperatures. Verification of these modifications was accomplished by applications to both simulated and actual flight test data. Simulations of nonlinear heating rates indicated higher than actual coating thickness predictions for the linear perturbation model previously used. Flight results using the improved heating model provided additional verification of a time skew due to nonisothermal wall effects on the OMS pod. Estimation of initial temperatures using the fixed-point initial condition smoother enabled the identification of an unmodeled Mach or Reynolds number effect on the lower surface during the Mach 12 Pushover Pullup maneuver of STS-4.
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