Soft Exoskeleton Knee Prototype for Advanced Space Suits and Planetary Exploration

Existing gas-pressurized space suit designs aim to provide astronauts with a wide range of joint motion while minimizing joint torque during extra-vehicular activity (EVA). However, current space suits have limited joint range and stiff knee and elbow joints, which impedes performance. Future designs should consider that some joint torque can be beneficial in storing elastic energy for locomotion in reduced gravity planetary EVAs. Though current gas-pressurized space suits restrict astronaut movement, they are capable of partially supporting their own mass and storing elastic energy in the lower body, allowing metabolic cost reduction during locomotion in reduced gravity, such as on Mars or the moon. The BioSuit™, developed by the Massachusetts Institute of Technology (MIT), is an advanced, skin-tight compression garment concept, which exerts mechanical counterpressure (MCP) directly on the astronaut's skin with the benefits of increasing range of motion and performance and reducing mass when compared to gas-pressurized space suits. We designed a BioSuit™ soft knee exoskeleton with tunable knee-joint stiffness to minimize metabolic expenditure during locomotion in partial gravity, maximize mobility, and enhance performance of astronauts. This paper summarizes the design and development of prototype actuation in a soft exoskeleton, in collaboration with the Dainese D-Air Lab (Vicenza, Italy), that can apply varying stiffness/torque to the knee while permitting full range of motion for flexion and extension. Additionally, a proof-of-concept sleeve was produced to investigate and demonstrate the capability of WholeGarment knitting to aid in producing sufficient mechanical counterpressure for safe use in space. Design criteria, fabrication techniques, and performance metrics are discussed. The soft knee exoskeleton was shown to exert stiffness parallel to the knee, analogous to stiffness exerted by a space suit. Range of motion of the knee and arm was larger for the MCP prototypes when compared to current space suits. These prototypes were developed to maximize locomotion in reduced gravity while minimizing metabolic cost associated with locomotion and space suit inflexibility. The results of this paper demonstrate the ability to integrate a soft knee exoskeleton into the BioSuit™ to improve space suit design to enable longer, safer, and more complex EVAs in partial gravity.