Unsteady Aerodynamic Modeling of an Atmospheric Entry Vehicles in Subsonic Flow: A Frequency Response Approach

Successful planetary missions often rely on the success of payload delivery through atmospheric entry, descent and landing. The capsules carrying these payloads are typically blunt in shape, designed to withstand and endure the extreme aerodynamic heating environment encountered during entry. However, this design constraint also makes blunt-bodied entry vehicles inherently prone to aerodynamic instability in the low supersonic and subsonic phases of their descent trajectory. There are two unstable scenarios that could happen, either the amplitude of oscillation growth leads to an equilibrium limit cycle amplitude, or the amplitude of oscillation becomes so large that onboard controllers are unable to stabilize the tumbling vehicle. Characterization of dynamic stability is important for the success of planetary missions, and depending on its sensitivity to geometric variables, it is important to model unsteady aerodynamic and pitch damping effects and their responses under these oscillatory conditions.