Static instability of mars entry vehicles flying at small angle of attack

Three-dimensional Navier-Stokes equations in high temperature real gas model and perfect gas model are solved for hypersonic entry process. Good agreement is achieved between numerical results, reference values and flight data of Viking, which validates physical-chemical models and numerical methods. Aerodynamic prediction of Mars Pathfinder proves that results of real gas model are close to LAURA. Perfect gas model with effective specific heat ratio is capable of computing lift and drag coefficients. At 2° angle of attack, MPF exhibits static instability along trajectory, which perfect gas model failed to catch on. It is considered that main reasons of static instability are sonic line shifting around shoulder in windward, subsonic area varying and subsonic bubble occurring in leeward. They result in different pressure change in shock layer and in transportation process from expansion zone to upstream.