## 1 Introduction  
Critical to the longer-term Mars and future lunar missions is the capacity for astronauts to mobilize (i.e., stand, walk, and perform functional tasks) while donning a cumbersome Extravehicular Activity (EVA) spacesuit [1]. The newest EVA spacesuit design is the Exploration Extravehicular Mobility Unit (xEMU) spacesuit. Overall, balance-related studies involving the new xEMU spacesuits and prior EVA spacesuits are few, if any. Thus, technological and knowledge gaps exist tied to crewmembers' mobility, function, performance, injury-risk mitigation, and overall safety [2]. Donning the xEMU spacesuit affects their center of gravity (CoG) location. The CoG is the hypothetical point location at which the total weight of the body is concentrated. The ability of an object (or person) to balance is related to the position of the CoG [3]. While donning the xEMU spacesuit, one's CoG is shifted superiorly on the torso and away from the body. This shift could potentially affect the ability of the suited crewmember to perform mission tasks [1]. However, balance and posture studies in the xEMU spacesuits have been nascent, and the shift in CoG effects on balance is left uncharacterized. In one recent study [4], NASA researchers developed a computer-based model that estimated the true CoG location in a microgravity environment of a participant donning the xEMU spacesuit and allowed for predictions of CoP area shifts tied to balance. The CoP is the point location of the vertical ground reaction force vector, and it represents the weighted average of all pressures of the surface area in contact with the support surface (ground). Measurements were taken while the participants were in the Neutral Buoyancy Laboratory (NBL), which simulated planetary EVAs. Three \"weighouts\" (i.e., how the weight of the spacesuit and attached components are distributed) were investigated: a baseline weight (derived from data collected from past microgravity runs at the NBL), an exaggerated weightout (a large amount of weight from the portable life support system (PLSS) moved to the waist belt), and a weightout that was derived from the computer-based model that altered the individuals' CoG location [4]. Researchers tested the stability and reachability of the subject donning the spacesuit for each weightout while in the NBL [4]. Results were limited to an overlay comparison of CoP excursion areas for eyes-open and eyes-closed. The CoP displacement time series and parameters extracted from it, such as root-mean-square displacement, velocity, and frequency measures [5], can be used to interpret how a person balances. However, in this paper, these measures were not shown nor compared, and further, tests for the statistical significance of the changes in the CoP excursion area were not determined. Previous studies did not investigate balance nor postural control while the individual was suited. However, there are several studies of spacesuit components performance, spacesuit ergonomics, and/or if the participants (astronauts) could complete certain tasks while donning the spacesuit. A previous study investigated the mobility of a suited subject versus an unsuited subject [6]. Agility during locomotion and functionality of the hip brief assembly were examined for the Mark III spacesuit architecture. It was determined that degrees of freedom were limited, the operator's mobility and agility were restricted, and thus, increased hip joint torques were required [6]. Several studies investigated measurements in-suit and suit fit. There are multiple studies examining suit counter pressure for specific joints, such as the shoulder [7], the elbow [8], and the hands/gloves [9], with many more not listed here. Studies for injury mitigation in gloves [10] and suit padding [11] have been conducted. There was a study investigating energy expended and recovered during walking vs. skipping vs. running as the choice of locomotion on Earth and simulated lunar and Martian gravity [12].