Finite Element Analysis (FEA) Model of the Apollo A7LB Extravehicular Activity (EVA) Suit Sleeve

The development of EVA spacesuits is critical to human survivability in the hostile environment of space. Whether in Low Earth Orbit (LEO), on the surface of the Moon, or on Mars, astronauts will encounter extremely low atmospheric pressures (such as vacuum in LEO and on the surface of the Moon) and temperature extremes (e.g. -250F to +250F in LEO) that are lethal to humans. Although EVA spacesuits must protect humans against these conditions, maintaining an astronaut’s mobility is equally important in order to achieve mission objectives, such as a return to the Moon as defined by the Artemis architectures. Improved mobility which is designed into an EVA suit should reduce energy expenditures and therefore fatigue. Spacesuit mobility is largely driven by the design of joints, such as the knee, elbow, ankle, waist, and shoulder joints. Joint design has evolved considerably since the first pressure flight suits designed in the 1930’s. One of the earliest designs was the convolute joint that has been implemented in several spacesuits, from the Apollo A7LB to the finger joints of the current Extravehicular Mobility Unit (EMU) spacesuit glove. For the Apollo A7LB spacesuits, full circumferential rubber-dipped nylon convolutes were utilized in the elbow, shoulders, elbows, wrists, hips, knees, and ankles. The current Space Shuttle/International Space Station (ISS) EVA EMU incorporates a flat pattern half circumferential gore design at the elbow. An understanding of the mobility of A7LB style elbow joint design, in comparison to the flat pattern gore design, could provide new insights for the development of future spacesuits. Our Aerospace Human Systems Laboratory (AHSL) previously developed and published a preliminary Finite Element Analysis (FEA) model of the EMU sleeve in order to predict torque as a function of "fit", number of gores, and pressure. This ‘Virtual Twin’ research is part of an ongoing effort to model human performance based on individual anthropometrics and EVA suit design variables prior to manufacturing the EVA suit. In this paper, an ABAQUS/Explicit FEA model was developed to predict elbow joint torques during pressurized convolute sleeve bends using the Apollo A7LB pressure garment assembly (PGA) arm configuration. Design data was extracted from available literature and images. The model was scripted to allow for adjustment of the number of convolutes, convolute and restraint cable geometry, sleeve thickness, internal pressure, and elbow bend angle. The results from this torque/mobility comparison are reported as a function of the effects of the identified design variables. This research could provide insight into the relative impact of the various design variables including the operational pressure differential on joint torque and, therefore, expected mobility and energy expenditure.