Characterization of a lower-body exoskeleton for simulation of space-suited locomotion

In a previous analysis of suited and unsuited locomotion energetics, we found evidence that space suits act as springs during running. Video images from the lunar surface suggest that knee torques create, in large part, this spring effect. We hypothesized that a lower-body exoskeleton, properly constructed, could be used to simulate the knee torques of a range of space suits. Here we report characterization of a lower-body exoskeleton. Equivalent spring stiffness of each exoskeleton leg varies as a function of exoskeleton knee angle and load, and the exoskeleton joint-torque relationship closely matches the current NASA space suit, or Extravehicular Mobility Unit, knee torques in form and magnitude. We have built an exoskeleton with two physical non-linear springs, which achieve space-suit like joint-torques. Therefore space-suit legs act as springs, with this effect most pronounced when locomotion requires large changes in knee flexion such as during running.