Direct simulation Monte Carlo (DSMC) simulations are performed for the Apollo capsule in the hypersonic low-density transitional ow regime. The focus is on ow conditions similar to that experienced by the Apollo 6 Command Module during the high altitude portion of its reentry. Results for aerodynamic forces and moments are presented that demonstrate their sensitivity to rarefaction that is, for free molecular to continuum conditions. Also, aerodynamic data are presented that shows their sensitivity to a range of reentry velocity, encompasing conditions that include reentry from low Earth orbit, lunar return, and Mars return velocities (7.7 to 15 km/s). The rare ed results are anchored in the continuum regime with data from Navier-Stokes simulations.

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An experimental study of underexpanded and highly underexpanded axisymmetric nitrogen free jets seeded with 0.5% nitric oxide (NO) and issuing from a sonic orifice was conducted at NASA Langley Research Center. Reynolds numbers based on nozzle exit conditions ranged from 770 to 35,700, and nozzle exit-to-ambient jet pressure ratios ranged from 2 to 35. These flows were non-intrusively visualized with a spatial resolution of approximately 0.14 mm x 0.14 mm x 1 mm thick and a temporal resolution of 1µs using planar laser-induced fluorescence (

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