Crew Population Characteristics: Perspectives for Spacesuit Fit

Constructing an Extravehicular Activity (EVA) suit that properly fits the full crew population is both uniquely challenging and critical to EVA operations. NASA’s current generation suit, the Extravehicular Mobility Unit (EMU), uses a discrete sizing scheme for the Hard Upper Torso (HUT). Five HUT sizes were designed to accommodate from 5th percentile female to 95th percentile male for critical anthropometric dimensions; however, only three of the planned HUT sizes were developed, so the actual accommodated range is 40th percentile female to 95th percentile male. Inadequate HUT fit can lead to fatigue, injury, reduced suited functional strength and mobility, and an inability to complete EVA tasks.

There is a demonstrated need for a more robust HUT sizing schema. While a discrete sizing scheme with a fixed number of unique suit sizes can facilitate logistics and reduce cost, accommodating the large variations in crew anthropometry and complexity in EVA tasks requires building a spacesuit that more precisely matches the body shape and biomechanical characteristics of individual crewmembers. Technical developments in additive manufacturing and 3D body imaging have facilitated the feasibility of custom suits. Fully individualized HUTs can reduce risks associated with poor fit and increase the accommodated anthropometric range to fit the entire crew population, including current crew who are not accommodated by the existing hardware design schema. This may also enable a flexible method to construct HUTs for a person based on their anthropometry while accounting for body shape changes resulting from entering a new gravitational environment.

The goal of this project is to leverage statistical 3D body shape models and historical spacesuit fit data to develop a technical framework for custom sized HUT design. This work is based on the premise that body scan geometry can provide essential data to accurately predict the HUT geometry that maximizes the likelihood of achieving an optimal fit. A statistical model was trained to estimate the suit-to-body contact patterns when a person wears an “optimal-sized” HUT. This model was then transformed to generate the HUT internal surface geometries expected to produce the targeted suit-to-body contact pattern for any given person.

Human subject testing is conducted to build sample case studies and validate the model. Subjects are scanned using a 3D whole-body scanner, and their body scans are used to predict their ideal HUT geometry based on the historical fit data collected through Shuttle EMU fit check, training, and flight data. For each subject, the model generates three HUT sizes: an “optimal” HUT, a one size larger than optimal HUT (“optimal + 1”), and a one size smaller than optimal HUT (“optimal - 1”). Every HUT configuration is fabricated using 3D printed components and Commercial Off-the-Shelf (COTS) hardware. Each subject wears each of their three individualized HUT configurations and completes a series of activities, including subjective evaluations, reach envelopes, body scans, and functional mobility tasks. This allows the evaluation of each HUT geometry’s impact on fit, indexing, and functional ability.

Once validated, the models are packaged into a suit design assistance tool. Users can upload a subject’s body scan data or generate data for an arbitrary person with given dimensions. Additionally, they can upload a HUT geometry or select one from a pre-loaded architecture. Using the model package, users can predict the fit and indexing of the selected HUT-human combination, visualize the contact pattern between the body and the suit, and generate the optimal HUT geometry for a person based on body geometry data. This project serves as a proof of concept for statistically generated individualized HUTs as well as a stepping stone to move forward into a new era of suit design for the human.

ACKNOWLEDGEMENT: This study is funded by NASA HRP Human Factors and Behavioral Performance Element Directed Study.