Rigid-Body Dynamics in Free-Molecular and Transition Flow

Abstract

Detailed rarefied aerodynamics are usually not coupled with the rigid-body dynamics of spacecraft. In part because of computational constraints, simpler models based upon the ballistic and drag coefficients are employed. Presented is an approach that capitalizes on the availability of ever-increasing computational methods and resources. The feasibility of increasing the fidelity of modeling spacecraft dynamics is explored by coupling rarefied aerodynamics with a rigid-body dynamics model similar to that traditionally used for aircraft in atmospheric flight. Aerodynamic force inputs for an airfoil section in a rarefied flow are provided by analytical equations in the free-molecular regime, and the direct simulation Monte Carlo method in the transition regime. Examples of nonlinear dynamics that cannot be predicted using simpler approaches are presented. The results of this straightforward approach to the coupled-field problem highlight the possibilities for future improvements in drag prediction, control system design, and atmospheric science.