Low-density aerodynamics of the Stardust Sample Return Capsule

The aerodynamics of the Stardust Sample Return Capsule are analyzed in the low density, transitional how regime using free-molecular, direct simulatio n Monte Carlo, Navier-Stokes, and Newtonian methods to provide inputs for c onstructing a transitional flow bridging relation. The accuracy of this bri dging relation in reconstructing the aerodynamic coefficients given by the more exact methods is presented for a range of flight conditions and vehicl e attitudes. There is good agreement between the various prediction methods , and a simple sine-squared bridging relation is shown to provide a reasona bly good description of the axial force, normal force, and pitching moment over a range of Knudsen numbers from 0.001 to 10. The predictions show a st atic instability of the Stardust capsule in the free molecular regime that persists well into the transitional flow. The addition of a thin disk to th e base of the capsule is shown to remove this static instability. However, the extremely high entry velocity of 12.6 km/s for the proposed trajectory introduces difficult design issues for incorporating this disk caused by th e high aerothermal loads that occur even under relatively rarefied conditio ns.