Survey of Blunt Body Dynamic Stability in Supersonic Flow <s> D. Specific Heat Ratio <s> An experimental program has been conducted in ballistics ranges to investigate the aerodynamic characteristics of three candidate NASA configurations for a Mars probe/lander: a blunted 60° half-angle cone, a spherical segment, and a blunted tension shell. The drag, staticand dynamic-stability coefficients were determined in air for Mach numbers from 0.6 to 13. At supersonic and hypersonic Mach numbers, the drag coefficients corrected to zero angle of attack were slightly higher for the spherical-segment configuration than for the other two shapes. All three configurations were statically stable. The dynamic-stability coefficients for the 60° half-angle cone and spherical-segment configurations were stabilizing in the supersonic and hypersonic region. Destabilizing dynamic-stability coefficients were measured for all three configurations in the transonic region. <s> BIB001 </s> Survey of Blunt Body Dynamic Stability in Supersonic Flow <s> D. Specific Heat Ratio <s> Free-oscillation tests of three Viking-type blunt conical configurations were conducted in a wind tunnel to determine the important variables influencing their dynamic stability characteristics at Mach 1.76. The effects of sting geometry are shown to be significant at low angles of attack, while the effects of cross plane motions and tunnel vibration characteristics appear to be negligible. Variation of the reduced-frequency parameter and model base geometry caused significant effects in the data. An approximate technique was developed for converting effective data from either forced-oscillation or free-oscillation tests to values based on the instantaneous angle of attack. <s> BIB002 </s> Survey of Blunt Body Dynamic Stability in Supersonic Flow <s> D. Specific Heat Ratio <s> Interest in planetary probes has increased significantly in the last few years. Many of the proposed missions will use aeroassist for the capture and descent phases of the missions. This use of aeroassist will put a greater demand on having accurate aerodynamics for these vehicles. Reviews are presented of some of the aerodynamic requirements with particular emphasis on dynamic stability as well as the aerodynamic testing requirements and with particular attention on the use of the ballistic range. <s> BIB003
For missions with destinations to bodies with atmospheres unlike our own -Mars, Venus, Titan, etc. -it is often challenging for dynamic test facilities to match the test gas with one that is representative. Chapman and Yates BIB003 note that although the issues associated with chemically reacting flow are typically no longer of concern in the supersonic regime where dynamic stabilities are most prevalent, the effect of the specific heat ratio of the medium on the resulting dynamic behavior can still be important. It has been observed that surface pressure distributions and shockwave geometry are dependent on the specific heat ratio BIB001 ,  ,  . Given that the unsteady interactions of Figure 28 . Effect of reduced frequency parameter on damping of BLDT vehicle BIB002 pressure fields and shockwaves could possibly excite dynamic instabilities, there exists a clear means through which the specific heat ratio could modify dynamic stability. Krumins BIB001 quantified this effect by comparing the damping measured in air ( = 1.4) and Tetrafluoromethane (CF 4 , = 1.12) for bodies with sphere cone, spherical section, and tension shell forebodies. Shadowgraph images of the tension shell in Fig. 29 exhibit drastically modified shock structure with the change in test gas. For the sphere cone, tests in air revealed a stabilizing damping coefficient while tests in CF  found the same configuration to be dynamically unstable. This points to the composition of the medium as a possible reason for the higher than predicted oscillation growth that has been observed on missions such as Mars Pathfinder  . Given the exploration interest in bodies such as Mars and the potential implications of under predicting damping by testing in ground facilities utilizing air, further understanding of this phenomena and development of facilities with variable test gas capabilities may benefit the community greatly.