Attitude stability of blunt-body capsules in hypersonic rarefied regime

To assess the attitude stability of blunt-body reentry capsules in the hypersonic rarefied flight regime, a systematic numerical procedure has been developed and applied practically to the asteroid sample return capsule. The low-density flows around the capsule are solved by the direct simulation Monte Carlo (DSMC) method in the three-dimensional geometry to determine the low-density aerodynamic coefficients. The overall aerodynamic coefficients are defined by an empirical bridging formula from the results of the DSMC analysis and the continuum coefficients obtained by the modified Newtonian method. By the use of these overall coefficients, the six-degree-of-freedom dynamics of the capsule is analyzed along the reentry trajectory. It is shown that the static instability about the pitching axis occurs in the low-density environments when the center of gravity is located in the rear part of the capsule. However, the pitching motion is found to be stabilized safely by initiation of the spin around the capsule axis at appropriate frequencies.