Date of Award

January 2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Space Studies

First Advisor

Pablo de Leόn

Abstract

Surface temperatures during extravehicular activity (EVA) in low Earth orbit range from -157°C to 121° C. Although spacesuits shield astronauts from such inhospitable extremes, metabolic heat production due to physical exertion is trapped within the garment, leading to increased internal temperature. Cooling garments are utilized to maintain human thermal equilibrium. NASA’s Liquid Cooling and Ventilation Garment (LCVG) has been in use for decades. Koscheyev, Leon, and colleagues developed a physiologically designed Shortened Liquid Cooling Warming Garment (SLCWG) at the University of Minnesota, focused on increasing the efficiency of the garment to support thermal balance. The current study assessed the thermoregulatory performance of the SLCWG within a pressurized spacesuit during a simulated microgravity EVA. Test subjects were suspended using the DL/H-1 spacesuit within a horizontal harness system while they performed a number of tasks eliciting a workload comparable to that of microgravity EVAs. Performance of the SLCWG was judged based on skin temperature measurements, spacesuit temperature and subjective thermal comfort ratings. A control phase was performed in which the water circulator supplying the SLCWG was switched off. It was found that the SLCWG used at a water inlet temperature of 20°C did not maintain thermal balance for all participants. Thermal comfort was maintained for 50% of participants during the test phase while none of the participants felt thermally comfortable at the end of the control phase. Average skin temperature during the test phase rose by 1.03°C, staying within the acceptance criterium of ±5% of the initial temperature measurement, as opposed to the control phase temperature rise. However, spacesuit temperature rise did not fall into the acceptance criterium at 2.9°C. This indicates significant heat was dissipated into the spacesuit, which was underlined by 50% of participants visibly sweating by the end of the test phase. Following a multivariate linear regression, a thermal development model for the DL/H-1 spacesuit was created which can be expanded upon via additional measures of latent heat dissipation and subject core temperature. Comparison between male and female subjects showed overall higher male skin temperatures, overall higher female skin temperatures, higher thermal discomfort scores in women and higher rises in skin and spacesuit temperature in women as compared to men. When subjects originating from hot and humid climates were compared to those originating from moderate climates they showed no visible signs of sweating, greater thermal comfort, lower skin temperatures and lower rates of sensible heat dissipation into the spacesuit.

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