Calorically perfect gas calculations of re-entry vehicles

Question

We know that pressure is least sensitive to high temperature gas effects. Thus, how much of calorically perfect gas calculations (for pressure alone) are used in space vehicle design? Historically, have we relied completely on calorically perfect gas calculations for space vehicle design? If so, what made us move to equilibrium calculations?

Answer 1

Real-gas effects weren't considered enough in preflight calculations and wind tunnel testing of Space Shuttle entry aerodynamics; this led to some mis-predictions of control surface positions on the first flight (see Is there such thing as plasma (from reentry) creating lift? for details of the mis-predictions.)

In those early days of pre-CFD,

NASA researchers developed an experimental technique to simulate this experience using a special test gas that mimicked the behavior of high-temperature air at the lower temperatures achieved during wind tunnel testing.

Later in the program CFD was used extensively

The use of computational fluid dynamics was eventually developed as a complementary means of obtaining aeroscience information. Engineers used computers to calculate flow-field properties around the shuttle vehicle for a given flight condition. This included pressure, shear stress, or heating on the vehicle surface, as well as density, velocity, temperature,and pressure of the air away from the vehicle. This was accomplished by numerically solving a complex set of nonlinear partial differential equations that described the motion of the fluid and satisfied a fundamental requirement for conservation of mass, momentum, and energy everywhere in the flow field.

Given its relative lack of sophistication and maturity, coupled with the modest computational power afforded by computers in the 1970s, computational fluid dynamics played almost no role in the development of the Space Shuttle aerodynamic database. In the following decades, bolstered by exponential increases in computer capabilities and continuing research, computational fluid dynamics took on a more prominent role.

Source: Wings in Orbit