INFLUENCE OF SONIC-LINE LOCATION ON MARS PATHFINDER PROBE AEROTHERMODYNAMICS

Flowfield solutions over the Mars Pathfinder Probe spanning the trajec tory through the Martian atmosphere at angles of attack from 9 to 11 d eg are obtained. Aerodynamic coefficients derived from these solutions reveal two regions where the derivative of pitching moment with respe ct to angle of attack is positive at small angles of attack, The behav ior is associated with the movement of the sonic line between the blun ted 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 firs t occurs as the shock layer gas chemistry evolves from highly nonequil ibrium to near equilibrium, above approximately 6.5 km/s and 40-km alt itude, causing the effective specific heat ratio to decrease. The tran slation next occurs in an equilibrium Row regime as velocities decreas e through 3.5 km/s and the specific heat ratio increases again with de creasing 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 n ose to the aft shoulder of the blunt cone.