Underwater space suit performance assessments part 2: Reach envelopes as a comparative performance metric

Abstract

This study assessed the reach envelopes as a quantitative metric to compare the mobility of different spacesuit types, namely the existing extravehicular mobility unit (EMU) and the newly developed prototype Z2. With Z2, two different configurations were considered: 1) Z2 paired with the EMU lower torso assembly (Z2-ELTA) and 2) Z2 with the mobile lower torso assembly (Z2-ZLTA). Five subjects performed reach motions in the underwater microgravity analog, including isolated hand and arm reaches (IHAR: arm sweeps at the shoulder) and whole-body reaches (WBR: reaches at extreme whole-body stretching/bending poses). The analysis showed the IHAR envelopes were generally similar in shape between the Z2 and EMU, but Z2 exhibited improved reach characteristics, specifically in the coverage area, volume and cross-reach capability. The reach envelopes stretched further backward by 17 cm on average compared to the EMU (p < 0.05). The intersection surface area between the left and right hand envelopes is 3.6 times larger with the Z2 (p < 0.05), which indicates a substantially enhanced cross reach capability. With WBR, the envelope volume is 25% (Z2-ZLTA) and 21% (Z2-ELTA) larger than the EMU (p < 0.05). Also, the intersections between the left and right hand envelopes are 3.4 times (Z2-ZLTA) and 2.0 times (Z2-ELTA) larger than the EMU (p < 0.05). Overall, the reach envelopes demonstrated unique geometric differences between the suit types, which characterize the increased reach volume and cross-reach capability in the Z2, suggesting the enhanced joint and softgood mobility of the upper and lower torso assembly. Relevance to industryKinematic mobility patterns quantified from different spacesuits can help to optimize the task and hardware design for extravehicular activity.