Optimal space suit mass for Mars extravehicular activity

Enabling efficient extravehicular activity (EVA) is a key requirement for future human planetary exploration. Relative to unsuited human movement, space suits can impose substantial bioenergetic costs through their direct impact on load carried, as well as joint torques and inertial effects. This work focuses on the former, as represented by the weight of the space suit, taken to include suit, life support system, and other gear carried, which must be borne by astronauts during EVA. Gas pressure space suit legs can be treated as human-stabilized columns supported by air pressure, constraining the available forces for suit self-support. Here I model how suit pressure, gravitational acceleration, and gait characteristics interact to determine whether pressure suits are self-supporting or whether part of their weight must be carried by a suited astronaut. For the purposes of this model, optimal suit mass is defined as the maximum allowable mass at which the space suit is self-supporting across the range of human gait. The model suggests that complete suit self-support was achieved during Apollo lunar surface exploration despite 81 kg to 96 kg EVA system mass. However, on Mars, such a suit would not achieve self-support. Achieving Moon-like levels of self-support is estimated to require a 45 kg Mars suit. NASA EVA prototype suits for planetary exploration significantly exceed this mass but can compensate by operating at higher suit pressures. However, if low pressure (3.8 to 4.3 psi) operation is required to enable astronaut mobility, significant suit mass reductions will be required for astronaut explorers of Mars to avoid direct load carrying bioenergetics penalties and their associated impact on portable life support system sizing or performance margins.