Sudhakar Rajulu, Phd NASA Johnson Space Center EXPLORATION CAMPAIGN
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Ergonomic Assessment of a Space Suit: From the Perspective of Population Analysis, Fit, Accommodation, Comfort, and Performance Sudhakar Rajulu, PhD NASA Johnson Space Center EXPLORATION CAMPAIGN 2 Space Suits and Exoskeletons • Protection • Safety • Population variation Fit, Mobility, Reach, Exertion Performance • Potential Injury and Discomfort Restrictions Movement Excursion Incompatibility Compensatory adjustment issues Safe Limits Population based Assessment is Critical History of NASA Space Suits Apollo A7LB, Shuttle EMU, MK III Space Suit Design for Diverse Body Sizes • Body sizes used be “homogeneous” in early space program • Today, crews are in a wide variety of body size, shape, and physical skill • Smaller population needs to be included from early design stage Crewmembers in 1960’s Crewmembers in 2000’s Smaller Population Accommodation Apollo Sizing EV TLSA (Torso Limb Suit Assembly): The torso portion of the TLSA is custom sized and the limb portions are graduated in size and adjustable to accommodate individual crewman limb lengths Shuttle EMU (Extravehicular Mobility Unit) MK III Sizing Kosmo et al., 1988. Development of the NASA ZPS Mark III 57.2-kN/m2 (8.3 psi) Space Suit Anthropometric Measurements for Suit Design Early Technique based on Linear Measurements: • Take critical body measurements (stature, shoulder breadth, etc.) • Compare linear dimensions between suit and crewmembers • However, linear measurements do not represent 3-D body and suit geometry Special Consideration for Suit Fit and Accommodation Shoulder-to-Suit Clearance and Interactions: • Space suits have a very restrictive space and if not properly sized can result in discomfort, pain or injury • Suboptimal suit fit, in particular at the shoulders, has been identified as one of the predominant risk factors for shoulder injury while wearing a space suit. Shoulder clearance in the suit Restricted shoulder motion by Shoulder irritation immediately after hard upper torso (HUT) assembly extravehicular activity training 3-D Body Scan Technique Vitus 3-D Laser Scanner “Average” 3-D Body Shapes 3-D Virtual Suit Fit Assessment • Overlay 3-D body scans with suit CAD drawing to assess overlap and clearance • Greatly improved design process for suit fit and mobility • However, scans do not represent the entire ranges of crewmember body shapes • Scans are essentially static: Diverse poses are necessary to fully assess suit-to-body interactions Medium Size Suit Large Size Suit X-Large Size Suit 3-D Body Scan Overlaid with Hard Upper Torso Geometry Shoulder Shape Variations from Different Poses • Elevation of the acromioclavicular joint occurs after 90 degrees of abduction • Resultant variations in shoulder geometry induces tissue compression at scye openings Parametric Reposable Model for Suit-to-Body Interaction Assessment Body Shape = f (anthropometry, posture) • Subjects were scanned in multiple different poses • Developed a resizable and reposable model Expansion Into Current and Future Crew Population • A statistical model developed using the US Army data • Model can predict body shape as a function of any anthropometry dimensions body shape = 0 + 1 stature + 2 body weight + … + error determine 훽0 , 훽1 , … , 훽푛 , which minimize error Suit-to-Body Interaction Assessment (Cont’d) • Model-estimated body shapes were incorporated with the CAD drawings of a medium-size Extravehicular Mobility Unit (EMU). • CAD incorporation enables the quantification of the contact volume and clearance between the suit and body surfaces. Expansion Into Current and Future Crew Population Virtual suit fit test for all permutations of suit size and body shapes Suit Type A Unlikely to fit Suit Type B Likely to fit Body Dimension A Dimension Body Body Dimension B Monte-Carlo Suit Fit Analysis: Automatic Body Positioning & Quantifiable Suit Fit Metrics • Develop quantifiable suit fit metrics using suit-to-body clearance and overlap measurements • Automatically calculate the suit-to-body overlap area, volume and penetration depth Suit-to-Body Overlap Area and Volume Assessment Penetration Depth Calculation Penetration Depth (mm) Penetration Preliminary Results: Overlap Volume Estimation • Suit-to-body overlap volumes were estimated from a large number of samples • Preliminary analysis revealed the trend of overlap volume covarying with anthropometry Male (n=1,743) Female (n=628) Virtual Population Fit Analysis Small-Size HUT (Hard Upper Torso) Assembly Fit Assessment Outcome Unfit Unfit Fit Fit Constrained Mobility of Space Suit Motion in the suit can be substantially different from “natural” unsuited motions due to: - Suit weight (200 lbs) - Pressurization - Mechanical limitations - Sub-optimal size matching Suited Posture and Mobility Capacity (MK III) Mobility Assessment and Modeling Conclusion Exoskeletons and Space suits share the common needs Accommodate a major portion of the eligible population Comfortable to wear and perform functional tasks Adjustability features do not expose the user to unsafe conditions As such, Virtual evaluation of the entire population is a must Insufficient to test a small sample of users who may or may not represent the entire range of the user population Contact Information Sudhakar Rajulu, PhD. Anthropometry and Biomechanics Facility NASA Johnson Space Center Office: 281.483.3725 Email: [email protected].