Understanding Astronaut Shoulder Injury
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Human-Spacesuit Interaction: Understanding Astronaut Shoulder Injury by ALEXANDRA MARIE HILBERT B.S. Mechanical Engineering Cornell University, 2013 Submitted to the Department of Aeronautics and Astronautics in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN AERONAUTICS AND ASTRONAUTICS at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2015 © 2015 Massachusetts Institute of Technology. All rights reserved. Signature of Author Department of Aeronautics and Astronautics May 21, 2015 Certified by Dava J. Newman, Ph.D. Apollo Professor of Astronautics and Engineering Systems Director of Technology and Policy Program Thesis Supervisor Accepted by Paulo C. Lozano, Ph.D. Associate Professor of Aeronautics and Astronautics Chair, Graduate Program Committee 1 2 Human-Spacesuit Interaction: Understanding Astronaut Shoulder Injury by ALEXANDRA MARIE HILBERT Submitted to the Department of Aeronautics and Astronautics on May 21, 2015 in Partial Fulfillment of the Requirements for the Degree of Master of Science in Aeronautics and Astronautics ABSTRACT Extravehicular activities (EVA), or space walks, are a critical and complex aspect of human spaceflight missions. To prepare for safe and successful execution of the required tasks, astronauts undergo extensive training in the Neutral Buoyancy Lab (NBL), which involves many hours of performing repetitive motions at various orientations, all while wearing a pressurized spacesuit. The current U.S. spacesuit—the Extravehicular Mobility Unit (EMU)—is pressurized to 29.6 kPa (4.3 psi) and requires astronauts to exert a substantial amount of energy in order to move the suit into a desired position. The pressurization of the suit therefore limits human mobility, causes discomfort, and leads to a variety of contact and strain injuries. Shoulder injuries are one of the most severe injuries that astronauts contend with, and are mainly attributed to the EMU’s hard upper torso (HUT). While suit-related injuries have been observed for many years and some basic countermeasures have been implemented, there is still a lack of understanding of how humans move inside the spacesuit. The objective of this research is therefore to gain a greater understanding of this human-spacesuit interaction and potential for shoulder injury through two approaches: quantifying and analyzing the suit-induced pressures that arise in the shoulder region, and comparing the shoulder muscle forces that arise in the unsuited and suited conditions by modeling human-spacesuit interaction. The first approach provides an “inside look” of the pressure distributions and pressure profiles that arise at the interface between the human shoulder and the torso of the spacesuit, thereby suggesting which areas of the shoulder might be prone to contact injury. A commercially produced pressure sensing system is used to collect shoulder pressure data during a human subject experiment that involves three experienced subjects performing a series of upper body motions in both unsuited and suited conditions. Pressure distributions reveal that: 1) the least experienced subject generates the highest pressures, 2) for the majority of movements for all subjects, pressure is concentrated just above the clavicle over the soft musculature at the top of the shoulder, 3) the top of the shoulder is one of the regions in which maximum pressure is located most frequently, and 4) the shoulder blade is a secondary region of concern with regards to frequency of experiencing maximum pressure. Pressure profile analysis reveals that 1) for most subjects, general profile trends vary in shape across movement groups, 2) repetitions within each 3 movement group are consistent in shape, and for most subjects also in magnitude, 3) the highest pressures are typically found near the top of the shoulder, and 4) the shoulder blade area is of concern for at least one subject. As these results are primarily observational in nature, a statistical analysis is performed to assess the effects of motion type and anthropometric region on peak pressure magnitudes. This analysis shows that results cannot be generalized across subjects as they are likely affected by individual anthropometry, suit fit, and the biomechanics of how each subject performs the motion. However, a number of interesting trends regarding which motions or regions yield higher pressures are found for each of the individual subjects. The results are specific to the subjects, suit sizes, and experimental conditions used in this particular experiment; however, the application of these quantitative and repeatable techniques during future experiments, suit fit sessions, or NBL runs would lead to a more complete understanding of human-spacesuit interaction at the shoulder interface. The second approach analyzes the effects of spacesuits on muscle forces in the shoulder region. Data regarding spacesuit joint torques and the joint angles of a suited subject are integrated into an upper-extremity musculoskeletal model in OpenSim to evaluate which muscles are most affected by the spacesuit. Looking specifically at a shoulder abduction/adduction motion, shoulder abductors, adductors, and stabilizer muscle groups are evaluated for significant changes in force from the unsuited to suited condition, and individual muscles within the shoulder region are also evaluated for significant changes from the unsuited to suited conditions. From a statistical analysis of the musculoskeletal simulation results, it is found that of the three investigated muscle groups—shoulder abductors, adductors, and stabilizers—only the abductors experience a statistically significant change in total muscle force between the unsuited and suited conditions. Looking specifically at the individual muscles that constitute the abductors and stabilizers, we find that only the middle deltoid experienced a statistically significant change in force from the unsuited to suited condition. A number of explanations are provided for the observed force profiles and the statistical results. The presented results are specific to the subject’s motion data, suit torque data, and the musculoskeletal model that are used; however expanding this analysis to more subjects, other body joints, and a more complex musculoskeletal model would provide useful results for industry experts. Valuable information could be provided to EVA operations teams, flight doctors, and spacesuit designers regarding which movements or tasks should be avoided or performed minimally to prevent injury. The resulting muscle forces could also be used to set limits on the joint torques that are engineered in future spacesuits. Each of the approaches implemented in this thesis provides a different avenue for addressing the issue of shoulder injury in the spacesuit. While the pressure analysis contributes to the understanding of human-spacesuit interaction by informing on the anthropometric regions that might be most susceptible to contact injury, the musculoskeletal analysis provides insight as to which individual muscles are most susceptible to strain injury. Both of these quantitative, evidence-based approaches contribute to an increased understanding of the potential for shoulder injury in the spacesuit. Thesis Supervisor: Dava J. Newman, Ph.D. Title: Apollo Professor of Astronautics and Engineering Systems Director of Technology and Policy Program Massachusetts Institute of Technology 4 ACKNOWLEDGEMENTS First and foremost, I would like to thank my wonderful advisor, Professor Dava Newman, for providing me with numerous once-in-a-lifetime opportunities during my short grad school experience. I feel extremely fortunate to have had you as an advisor as your energy and passion for space exploration are truly inspiring. My experience at MIT would not have been the same without your support, guidance, and encouragement. I wish you the best in your own new adventure over the next few years! To Professor Leia Stirling and Dr. Aleksandra Stankovic, thank you for helping me with the design of my statistical analyses. To Gaurav, Alex, Ana, and Dustin, thank you for taking the time to help me with all of the intricacies of OpenSim. To all of our collaborators at David Clark and NASA—particularly Shane Jacobs, Shane McFarland, Lindsay Aitchison, and Amy Ross—thank you for allowing us to perform our experiments in your facilities and for taking the time to give us invaluable feedback on our research. To Allie and Ana, thanks for leaving me some work to do! But really, thank you for paving the way for me and getting me up to speed on the whole astronaut injury project. I really appreciate that both of you were always taking the time to explain things to me and help me come up with good ideas for my Master’s thesis. Your previous work made my life a lot easier! To Ana and Raquel…I know it sounds super cliché, but you guys know it’s true…thank you for being the best officemates ever! You were both so welcoming from my very first day at MIT, and I could not imagine lovelier ladies to share an office with. Thanks to both of you for never being “too cool” to hang out with the new students. Ana - from our coffee outings when we were first getting to know each other to our seven hour road trips to upstate New York (and the romantic McDonald’s dinners at Lee along the way), it has really been a fun two years. I’m so excited for you to graduate and to see all of the amazing things that you do in the future. Raquel – we took a little bit longer to get to know each other well, but before long I really felt like you were a sister to me. Thank you for always being there to listen to me (whether I was having a hard time or just chatting away to avoid doing work), and for bringing a little piece of Texas to my life in Boston. Also, don’t forget to look for jobs in Colorado! I know I will see both of you before too long, whether it’s in Colorado, Texas, or Ithaca, but the three of us should plan an exotic reunion trip sometime within the next couple of years! To Pierre….where to begin?! Thank you for being my partner in crime over the past two years.