21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-1.2.3

MARS ENTRY VEHICLE AERODYNAMIC FLIGHT MEASUREMENTS

Blanchard R. C., Wilmoth R. G., Moss J. N.
NASA langley Research Center, USA

Keywords: mars, entry vehicle, aerodynamic, flight measurements

Entry flight measurements of the aerodynamic coefficients from the Viking 1 and Pathfinder Mars missions have been extracted and analyzed. Both missions use a spherically blunted 70 deg. half-angle cone entry vehicle and traverse all speed regimes from free molecule flow down to zero velocity on the planet's surface. The emphasis in this report is on the aerodynamic characteristics experienced by blunt-body vehicles as they make the transition from free-molecule flow to continuum conditions. Flight measurements of normal-to-axial force coefficient are shown for both missions. Measurements of these ratios come directly from accelerometers and do not require knowledge of the atmospheric density. To accurately simulate the aerodynamics in the hypersonic transitional flow regime, the direct simulation Monte Carlo (DSMC) method is used for most of the transitional regime and the Navier-Stokes continuum formulation is used at the less rarefied conditions. DSMC simulations are compared with flight aerodynamic coefficient ratio data in the rarefied-flow regime with good agreement. The Viking 1 flight measured drag coefficient is also presented and combined with DSMC simulations to provide a complete hypersonic to free molecule flow drag profile. Using flight acceleration measurements and code generated aerodynamics, the Pathfinder atmospheric density profile is calculated and compared to Viking 1 measured densities. Viking 1 results are slightly larger than the recent Pathfinder density data in the rarefied-flow regime, as expected due to diurnal effects, but are in excellent agreement at lower altitudes where atmospheric mixing occurs.

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