Revisiting Decompression Sickness Risk and Mobility in the Context of the SmartSuit, a Hybrid Planetary Spacesuit

Gas pressurized spacesuits are cumbersome, cause injuries, and make completing tasks efficiently difficult. Decreasing the gas pressure of the spacesuit is an effective method of improving mobility, but reduction in the total spacesuit pressure also results in a higher risk for decompression sickness (DCS). The risk of DCS is currently mitigated by breathing pure oxygen before the Extravehicular Activity (EVA) for up to 4 hours to remove inert gases from body tissues, but this has a negative operational impact due to the time needed to perform the prebreathe. In this paper, we review and quantify these important trade-offs between spacesuit pressure, mobility, and prebreathe time (or risk of DCS) in the context of future planetary EVAs. These trade-offs are highly dependent on the atmospheric conditions used in the space habitat or space station, and therefore, these conditions are also important considerations for future planetary exploration activities. In our analysis, we include three habitat scenarios (International Space Station: 14.7 psia, 21% O2, Adjusted Space Shuttle: 10.2 psia, 26.5% O2, and Exploration: 8.2 psia, 34% O2) to further quantify these differences. In addition, we explore these trade-offs in the context of the SmartSuit spacesuit architecture, a hybrid spacesuit with a soft robotic layer that, not only increases mobility with assistive actuators in the lower body, but it also applies 1 psia of mechanical counterpressure (MCP). The additional MCP in hybrid spacesuits can be used to supplement the gas pressure (i.e., increasing the total spacesuit pressure), therefore reducing the risk of DCS (or reduce prebreathe time). Alternatively, the MCP can be used to reduce the gas pressure (i.e., maintaining the same total spacesuit pressure), therefore increasing mobility. Finally, we propose a variable pressure concept of operations for the SmartSuit spacesuit architecture, where these two MCP applications are effectively combined during the same EVA to maximize the benefits of both configurations. Our framework quantifies critical spacesuit and habitat trade-offs for future planetary exploration, and contributes to the assessment of human health and performance during future planetary EVAs.