Experimental Dynamic Stability Investigation on Orion Entry Capsule in Supersonic Flow

Re-entry capsules' success depends significantly on dynamic and static stability, particularly before deploying the main parachute. Determining the range of dynamic instability and investigating the underlying causes is crucial for designing the entry capsule's control system. Dynamic stability is analyzed in this study based on pitch moment coefficients obtained from forced oscillation experiments conducted in the trisonic wind tunnel for the Orion entry capsule. The results reveal that pressure fluctuations at the aftbody of this model begin at Mach 2. The findings and other research results emphasize the significant role of the aftbody geometry in generating dynamic instability at low supersonic speeds due to its interaction with vortex flow. The results also demonstrate that increasing the Mach number to 2.2 would result in a near zero-pressure coefficient on the capsule's aftbody, which implies that there is no acting force on the aftbody. The results show that as the freestream Mach number increases from M∞ = 1.8 to M∞ = 2.2, the pressure on the aftbody remains unchanged during the pitching motion due to approaching the shear layer towards the body and consequent shrinking of the aftbody vortex. Furthermore, the sensitivity of dynamic stability to the mean angle of attack was investigated. It is shown that a slight increase of approximately 5 degrees in the mean angle of attack can considerably enhance the re-entry capsule's dynamic stability.