Gail P. Perusek

Exercise Countermeasures and a New Ground-Based Partial-g Analog for Exploration

The enhanced Zero-gravity Locomotion Simulator (eZLS) at NASA Glenn Research Center is described and summary data from a pilot research study comparing comfort and pressure data from two different International Space Station crew exercise harness designs are presented. This new ground-based simulation capability was developed to help address the detrimental physiological effects of spaceflight on the musculoskeletal system through improved exercise countermeasures systems, and to evaluate exercise countermeasures devices and prescriptions for space exploration. Aside from space applications, experiments conducted using the eZLS may help medical researchers develop insights into the role of exercise in the prevention of osteoporosis in the terrestrial population since the mechanism of bone and muscle loss is very similar, though greatly accelerated during space travel. The eZLS will be used as a ground-based testbed to support future missions for Space Exploration, and will eventually be used to simulate planetary locomotion in partial gravity environments including the Moon and Mars.

The use of artificial muscles in space suit simulation for partial gravity experimentation and training

The Aurora/MIT project team has developed a knee joint prototype for a space suit simulator that is designed to be lower weight and form-factor than previous simulators, while mimicking the resistive properties to human motion that pressurized space suits necessarily impose. Specifically, we employed “artificial muscle” pneumatic actuators to actively control the joint torques for any given limb angle, in order to closely reproduce the nonlinear hysteretic relationship and also allow for tuning of the joint to mimic any space suit design. For this initial feasibility study, we tested the prototype on MITs Robotic Space Suit Tester (RSST) with an example control scheme, intended to emulate NASAs Extravehicular Mobility Unit (EMU) space suit. Testing indicated that the torque-vs.-angle relationship of the prototype knee mimics that of the EMU knee with 15%, ranging from −12 to 25 Nm (the EMU torque range is −8 to 29 Nm). Results from this preliminary design and the associated testing suggest that a full-body actively-controlled space suit simulator may accurately emulate the properties of multiple space suits.1,2

Ground-Based Simulations of ISS Exercise Countermeasures at NASA Glenn Research Center's Exercise Countermeasures Laboratory: Compliant Interface Dynamics Using a Floating Treadmill

The enhanced Zero-gravity Locomotion Simulator (eZLS) at NASA Glenn Research Center is currently being utilized to investigate the dynamics of walking and running on a compliant treadmill surface to study the effects on musculoskeletal health as well as verify the performance of the vibration isolation system being developed for the second treadmill (T2) to be used on the International Space Station (ISS). This is particularly important to Astronaut exercise prescriptions for bone health since the exercise equipment on the International Space Station is required to provide isolation to minimize the loads transmitted to the ISS structure. The consequence of locomotion on a compliant interface is that the peak ground reaction forces important to bone density maintenance are significantly reduced. To counteract these detrimental effects, adjustments to exercise prescriptions must be made to provide and adequate level of Daily Load Stimulus (DLS) to the body. To facilitate this work, the eZLS is capable of providing from 1 to 3 degrees of freedom (DOF) and variable compliance and mass to simulate the walking and running conditions on a vibration isolated treadmill aboard the ISS.

Kinematics Analysis and Joint Hysteresis Modeling and Control for a Space Suit Simulator

NASA is supporting the development of a Space Suit Simulator (S3) for ground-based training and research. Pressurized flight-like spacesuits are complex, expensive to operate, and have very limited availability. The S3 substitutes for a flight-like space suit by replicating the mechanical influence of the space suit on the wearer in terms of resistance to motion. The S3 is envisioned as an open exoskeleton with articulated joints. Actuators spanning the joints provide motion resistance that mimics that experienced when moving within a pressurized space suit. To this point, two prototypes have been developed for a single degree-of-freedom knee joint. The challenge moving forward is to develop a lower limb (ankle, knee, hip) exoskeleton and then a whole-body exoskeleton that includes multiple interconnected joints with some joints having multiple degree-of-freedom, such as the hip and shoulder. In this phase of the development, we used the Denavit-Hartenberg notation to derive the Jacobian matrix describing the kinematic structure of the exoskeleton leg. The Jacobian matrix was explored for singularities to ensure that the exoskeleton leg does not lock up while the human wearer is attempting to move within physiological ranges of motion. The identification of singularities prompted a modified design that eliminates these conditions. Using a modified Preisach model, we have developed control algorithms that will allow linear tensile joint actuators to produce joint resistance torques that will mimic the hysteresis behavior typically seen in fabric space suit joint torque profiles.