EMU Elbow Torque Data as Measured by a Robotic Arm (RAESTAC) - an Update

For the past 60 years Extravehicular Activity (EVA) spacesuits have been designed to protect astronauts from the extreme environment of space outside of the spacecraft. However, these suits must also provide the mobility required to support EVA operations. Operations in Low Earth Orbit (LEO) have primarily required mobility at the elbow. Future exploration to the Moon in the Artemis Program will require mobility like that required for Apollo: mobility at the neck, waist, elbow, knee, and ankle. Mobility and energy expenditure are directly related to the torque required to deform the joint. In the past, torque has been measured by three methods, including robotic systems inside the suit, mechanical systems outside of the suit, and astronauts within the suit. At the 2023 IEEE Aerospace Conference, we presented the design of a new robotic arm to measure the elbow torque of a pressurized EVA EMU sleeve - The Robotic Arm for Evaluating Spacesuit Torque and Contact (RAESTAC). This paper presents the results of data generated by RAESTAC. RAESTAC was developed to measure joint torque at the elbow joint of a replica Size 4 EMU pressure garment to validate a Finite Element Analysis (FEA) model of an inflated garment that was created at the Aerospace Human Systems Laboratory (AHSL). RAESTAC incorporates a 3D printed arm generated from a 3dMD digital scan which is inserted into an inflated lower arm pressure garment assembly (pressure bladder and restraint). Driven by steel wire cables attached to a servo motor, a gear train assembly, and two S-type load cells, the RAESTAC system rotates the 3D printed arm at the elbow through a 120-degree arc at pressure garment pressures of 0-4.3 psid. Torque and pressure data are captured by means of a custom Python software program and the system is controlled through a Graphical User Interface (GUI). The RAESTAC elbow torque results are presented in the range of 1 psid to 4.3 psid through a 120 degree arc and demonstrate reasonable agreement with similar published torque ranges, although future design refinements are planned. In addition, the empirical data also demonstrates the hysteresis often observed between flexion and extension. Next steps include the addition of contact measurements between the arm and the sleeve. Additionally, experiments will be conducted to measure torque as a function of the number of flat pattern gores, the difference between the circumference of the arm and the sleeve, and the position of the elbow relative the sleeve.