(American Institute of Aeronautics and Astronautics, 2018-01)
Hart, Kenneth A.; Simonis, Kyle R.; Steinfeldt, Bradley A.; Braun, Robert D.
Aerodynamic forces and moments are significant perturbations on low-Earth-orbiting objects, second in magnitude to the nonspherical gravity field. Traditionally, the aerodynamic perturbations are calculated using a direct simulation Monte Carlo method. Under certain assumptions, these forces and moments can be described analytically via free-molecular flow theory. Using symbolic manipulation techniques, exact expressions for the free-molecular aerodynamics of analytic shapes can be derived. In this investigation, analytic expressions for the aerodynamic force and moment coefficients of primitive and composite parametric surfaces are derived, then validated against industry-standard direct simulation Monte Carlo techniques. A framework for the rapid and accurate calculation of free-molecular aerodynamics of composite geometries based on superposition is described. This framework is applied to axisymmetric composite geometries. Results within 6% of direct simulation Monte Carlo calculations are obtained in 0.05% of the time. The analytic aerodynamics models enable rapid trajectory and uncertainty propagation for low-Earth-orbiting objects. A case study on aerodynamic perturbations of a low-Earth-orbit nanosatellite is included to demonstrate application of these analytic models. The case study shows that these derived analytical free-molecular aerodynamics produce results that are applicable to inclusion in rapid trajectory propagation tools for orbit prediction and conceptual mission design.
Item Description: Analytic hypersonic rarefied aerodynamics paper published in the Journal of Spacecraft in Rockets, with primary application being resident space objects in low-Earth orbit. Supplemental CDF file contains equations that would not fit in full paper.
(Georgia Institute of Technology, 2014-06)
Ginn, Jason M.; Clark, Ian G.; Braun, Robert D.
The dynamic stability and equilibrium conditions of a parachute are studied using a six degree of freedom dynamic model that includes apparent inertia effects. Existing parachute dynamic models are discussed and the selection of a relevant model is shown. The chosen dynamic model that incorporates apparent inertia is summarized and used for analysis. The
moments on the parachute system caused by the apparent inertia term are shown to affect
both the equilibrium point and the stability of the system. The adjustment to equilibrium is observed and discussed. A small disturbance stability analysis is performed to give a stability criterion in terms of the slope of the tangential aerodynamic force. The dynamic
modes, pitching and coning, are discussed. Computational integration of the equations of
motion is used to validate the small disturbance analysis as well as to show the effects of
large disturbances.