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Reduced-order aerodynamic models have been developed for the lift-off phase of NASA’s Space Launch System (SLS), using physics-based modeling technology that serves several purposes. Conventional aerodynamic models establish relationships between operational variables and the forces and moments acting on the airframe—often in the form of response surfaces and “look-up” tables. The physics-based modeling technology provides more information than conventional aerodynamic models: spatially distributed surface properties in addition to integrated forces and moments. The capability enables tighter coupling of the engineering disciplines, integrating aerodynamics, structural dynamics, and flight control at all stages of the system development process. The modeling technology also facilitates accurate and efficient assimilation of heterogeneous data from computational simulations of varying fidelity and computational expense, from ground tests, and from flight tests. The computationally efficient aerodynamic models enable fast-turnaround conceptual design trade studies, flight simulations, and detailed system development with data fusion. Construction of the SLS lift-off aerodynamic model utilized two sets of computational fluid dynamics (CFD) solutions, one based on Reynolds-averaged Navier-Stokes (RANS) simulations and the other on detached eddy simulations (DES). These data were assimilated with wind tunnel measurements of six-degrees-of-freedom forces and moments and surface pressures. The model was evaluated through comparisons between model predictions of forces, moments, and pressures and wind tunnel and CFD values.