Design of supernumerary robotic limbs for the augmentation of astronauts performing partial-gravity extra-vehicular activities (EVAs)

This article presents a methodology for the design of a pair of wearable robotic appendages, known as Supernumerary Robotic Limbs, or SuperLimbs for short. Specifically, we aim to design SuperLimbs for assisting astronauts while they perform partial-gravity Extra-Vehicular Activities (EVAs) on the Moon. NASA has identified recovering from a fall as a high-risk process needing an effective countermeasure. Preliminary human study data discovered uniform behavior in astronaut’s poses as they performed a post-fall recovery wearing a space suit assembly. Based on this observation, this paper presents a complementary biomechanical model which estimates the torques required by an astronaut to navigate their body through a post-fall recovery. By comparing maximum allowable joint torques of the astronaut with the required joint torques, we identify the gap that SuperLimbs must fill by exerting necessary forces along a desired trajectory. A parametric optimization problem is formulated for designing SuperLimbs that meet these requirements with least energy consumption. A two-phase design optimization method is developed. Phase 1 consists of utilizing a coarse-grid AI searcher that rules out invalid designs that do not meet basic functional requirements. Phase 2 uses the optimal permutation from Phase 1 as an initial estimate for a fine-grid parameter-sweep optimization where energy dissipation across the actuators and task-space tracking accuracy are used as performance metrics. Based on the optimal design, an Earth-based prototype is built in-house at the NASA Jet Propulsion Laboratory, and its feasibility for astronaut’s fall recovery assistance is evaluated.