Determining Spacesuit Reach and Range of Motion (ROM) Using 3D Photogrammetric Motion Capture

Determining a crewmember“s range of motion (ROM) and reach are important for designing spacecraft and for determining the effects of pressure suit design on crew fit and mobility for extravehicular activity (EVA) and intravehicular activity (IVA). This paper reports on the results of utilizing the 3dMD photogrammetric full body motion capture scanning system for determining both measurements with more accuracy than current methods. such as infrared cameras (e.g., Vicon, and OptiTrack) which are used in combination with reflective markers placed on the subject to track human motion. Because IR systems track individual markers placed on the body in specific locations, they do not map the surface area of the subject and do not register the body image to the ROM data cloud. To overcome these limitations, our laboratory previously demonstrated a proof-of-concept for more precisely capturing ROM and reach data using the 3dMD motion capture system, a 3D photogrammetric scanning system capable of tracking complete surface data of a subject in motion over 20 seconds at 10 frames/second to within 1 mm accuracy. At that time, scans were made of a seated unsuited subject and of a subject in a loaned unpressurized SOKOL pressure suit. The 200 individual 3D mesh frames were analyzed using a proprietary software program, 3dMDvultus. Landmarks were manually/digitally placed at the end of the index finger on the scanned mesh for each frame. Accuracy was approximately ±0.01 mm. A custom MATLAB code, using Delaunay Triangulation, was used to create a 3D mesh reach envelope from the landmark coordinates which was then used to calculate the total volume. The ROM was registered to and superimposed over the subject image. The initial proof-of-concept was successful, but it was determined that the ROM envelope accuracy could be improved by implementing the following methodologies, which are presented in this paper: (1) the effect of operator skill and consistency for placing the landmarks was evaluated with the most consistent operator selected for final data processing, (2) the number of frames captured for each arm was increased from 200 to 800 (slower motion, therefore reducing transit distance between frames), and (3) the Abercromby arm motion strategy was used to provide consistency between subjects and the area covered. The operator with the least variance of ROM calculations performed landmarking analyses for a single unsuited and SOKOL suited-unpressurized subject. Additional anthropometric landmarks were also measured, including maximum anterior, superior, and lateral reach limits. Results show that utilizing the 3dMD system with this methodology results in highly accurate and repeatable measurements for calculating ROM and reach data and produces a geometric volume which can also be registered to the subject image. This allows better comparative analysis of ROM for crewmembers in unsuited, suited without pressure, and suited with pressure for both EVA and Launch and Entry Suits (LES). Future work includes the development of “automatic” landmark tracking software.