BLUNT BODY DYNAMIC STABILITY DURING PARACHUTE REEFING STAGES

Dynamic stability of blunt entry bodies is an area of ongoing research. Predictive knowledge of dynamic stability is critical to entry, descent and landing system design in that it allows the engineer to balance risk and performance in designing final staging events, primarily parachute deployments. The parachutes themselves, change the dynamics of the vehicle and thus dynamic stability. There may be several reefed stages, as in Apollo and Orion MPCV, that change the dynamics in a time varying way. In this paper, we present a closed form method to calculate the damping ratio and natural frequency for a system with multiple reefed stages, a way to bound the pitch motion evolution for this system, and provide insight into the design and environmental parameters that drive stability. Examples from Apollo parachute drop tests are included to anchor the analysis.