Study of Crew Seat Impact Attenuation System for Indian Manned Space Mission

The descent phase of Indian Manned Space Mission culminates with a crew module impacting at a predetermined site in Indian waters. During water impact, huge loads are experienced by astronauts. This demands an impact attenuation system which can attenuate the impact loads and reduce the acceleration experienced by astronauts to safe levels. Current state of the art impact attenuation systems uses honeycomb core, which is passive and can only be used once (at touchdown impact) during the entire mission. Active and reusable attenuation systems for crew modules are still an unexplored territory. Three configurations of impact attenuators are selected for this study for the crew module configuration, namely, hydraulic damper, hydro-pneumatic damper and airbag systems. All the subsystems are mathematically modelled, and initial sizes are estimated using Genetic Algorithm and SQP optimization techniques. Semi-active control for Hydraulic and Hydro-Pneumatic dampers are implemented and evaluated against its passive counterpart. An airbag impact attenuation system is studied and its performance in two configurations, stuck and unstuck are evaluated. Venting will not cease for the former configuration, whereas it is pressure controlled for the latter. For zero-degree impact load case, Brinkley DRI (Direct Response Index), a NASA HSIR index on the risk of likelihood of spinal damage, is reduced by 36% for hydraulic damper and 22% for Hydro-Pneumatic damper using semi-active control and 15% for Airbag system. Hydraulic dampers were proven to be superior to Airbag and Hydro-Pneumatic systems within the spatial constraints imposed by the present crew module configuration.