NASA - National Aeronautics and Space Administration

The Crew Exploration Vehicle (CEV), named “Orion”, is America’s new spacecraft for human space exploration. It will be capable of ferrying crews and equipment to the International Space Station and to lunar orbit. The Orion module will descend to Earth with a parachute recovery system during the final phase of the module’s return to Earth or in the event of emergency escape during the launch phase of the mission. The module is being designed to be capable of a primary water landing as well as contingency land landings. Protection of the crew members during landing and recovery to both water or land presents a significant design challenge. However, with properly designed seats outfitted with side supports and restraints, even relatively high accelerations can be tolerated with no or minimal injury, especially for impacts with the astronauts lying on their backs.

One method being developed to assess potential crew injuries during Orion landings is to use a Finite Element (LS-DYNA) model of the Hybrid III dummy. Predicted crew member response is obtained by loading the dummy with landing load accelerations obtained from vehicle landing simulations. The landing load accelerations, combinations of vertical, horizontal, lateral and rotational accelerations, will be applied to numerical Hybrid III Finite Element numerical models properly positioned in models of the current Orion seat design. Injury criteria will be extracted from the simulations (e.g. neck forces, head accelerations, pelvic motion) and compared against the recommended injury criteria established in the Human Systems Integration Requirements (HSIR). While Orion landings generally produce primarily rear and spinal loads, there are potential landing scenarios, particularly when vehicle roll is prevalent, where lateral loads can occur. HSIR requirements also specify lateral direction- related criteria that must be satisfied by the Orion vehicle.

One issue being examined by NESC team members is that the Hybrid III manikin and models are normally not used, nor have been validated, for evaluating the effects of lateral impacts. The Hybrid III has been used extensively in the automotive industry to evaluate crash worthiness of automobiles, but has been used only limitedly for aerospace applications. Furthermore, the Hybrid III manikin is designed primarily to determine the effects of frontal- impacts, while Orion landings are primarily a combination of rear and spinal impact. To evaluate the Hybrid III numerical and physical models for application to Orion, impact sled tests were performed at the Air Force Research Laboratory at Wright- Patterson Air Force Base. The results of these tests were used to assess the behavior of the physical Hybrid III and to determine the accuracy of the numerical model of the Hybrid III for predicting the physical dummy response during loading conditions in the front, rear, spinal and lateral directions. Results from the Wright- Patterson tests are being used to quantify the accuracy of the numerical models and to determine their capabilities for predicting the injury criteria defined in the HSIR requirements.

Hybrid III seated for lateral sled testing	LS-Dyna numerical model of Hybrid III seated for lateral sled testing

The numerical Hybrid III model is being used to assess candidate Orion seat design’s ability to protect crew members during landings. Finite Element Models (FEMs) of the seats are created using Computer-Assisted Design (CAD) geometries provided by the seat design team, and material properties are incorporated into the model to replicate the protection offered by the seat padding. A harness is fitted to the Hybrid III and preloaded similarly to how an actual crew member would be secured in Orion seats. The transient dynamic structural analysis code, LS-Dyna is used, with Orion landing conditions as input, to predict the response of the Hybrid III, and injury criteria are extracted and compared to the injury criteria in the HSIR requirements. A comparison between various seat concepts and their ability to protect crew members during Orion landings is underway.

Numerical model of Hybrid III situated in Orion 606D seat concepts	Numerical models of Hybrid III situated in Orion Crew Module

Ultimately, it is desirable to incorporate the numerical models of the crew members directly into the numerical models of the Orion crew module. The benefit of an integrated model is that the dynamic interactions between the crew member and the crew module are included, whereas these interactions are not captured when the simulation of the crew module is decoupled from the simulation of the Hybrid III in the seat.