Supernumerary Robotic Limbs to Support Post-Fall Recoveries for Astronauts

This paper proposes the utilization of Supernumer- ary Robotic Limbs (SuperLimbs) for augmenting astronauts during an Extra-Vehicular Activity (EVA) in a partial-gravity environment. We investigate the effectiveness of SuperLimbs in assisting astronauts to their feet following a fall. Based on pre- liminary observations from a pilot human study, we categorized post-fall recoveries into a sequence of statically stable poses called “waypoints”. The paths between the waypoints can be modeled with a simplified kinetic motion applied about a specific point on the body. Following the characterization of post-fall recoveries, we designed a task-space impedance control with high damping and low stiffness, where the SuperLimbs provide an astronaut with assistance in post-fall recovery while keeping the human- in-the-loop scheme. In order to validate this control scheme, a full-scale wearable analog space suit was constructed and tested with a SuperLimbs prototype. Results from the experimentation found that without assistance, astronauts would impulsively exert themselves to perform a post-fall recovery, which resulted in high energy consumption and instabilities maintaining an upright posture, concurring with prior NASA studies. When the Super- Limbs provided assistance, the astronaut’s energy consumption and deviation in their tracking as they performed a post-fall recovery was reduced considerably.