Influence of sonic-line location on Mars Pathfinder Probe aerothermodynamics

Flowfield solutions over the Mars Pathfinder Probe spanning the trajectory through the Martian atmosphere at angles of attack from 0 to 11 deg are obtained. Aerodynamic coefficients derived from these solutions reveal two regions where the derivative of pitching moment with respect to angle of attack is positive at small angles of attack. The behavior is associated with the movement of the sonic line between the blunted nose and the windside shoulder of the 70-deg half-angle cone in a gas with a low effective ratio of specific heats. The translation first occurs as the shock layer gas chemistry evolves from highly nonequilibrium to near equilibrium, above approximately 6.5 km/s and 40-km altitude, causing the effective heat ratio to decrease. The translation next occurs in an equilibrium flow regime as velocities decrease through 3.5 km/s and the specific heat ratio increases again with decreasing enthalpy. Laminar, windside heating levels may decrease with increasing angle of attack resulting from an increase in the effective radius of curvature with sonic line movement from the hemispherical nose to the aft shoulder of the blunt cone.