Human Thermal Assessment of Traverse and Geology Task Iterations During Simulated Lunar Extravehicular Activity

Spacewalks or extravehicular activities (EVA) in microgravity are mentally and
physically demanding. Current microgravity EVAs are predominantly focused on upper body
tasks on engineered surfaces; however, the introduction of gravity means that crew members
during future lunar EVAs will be required to perform tasks that generate full body workloads
such as navigating natural lunar terrain while conducting geological sampling. To date, only 12
people have walked on the surface of the Moon resulting in limited knowledge of suited thermal
regulation under lunar-relevant physical workloads. To address this gap, a study is underway to
focus on spacesuit operations with simulated lunar EVA workloads. This study presents
methodology for collecting standard thermal measures during suit testing.

In this pilot study, two suited subjects underwent simulated lunar EVAs using the NASA
Active Response Gravity Offload System (ARGOS) to simulate the effects of partial gravity.
Each lunar EVA, lasting three to five hours, included various metabolically demanding EVA
tasks. Subjects donned the NASA Mark III (MK III) space suit and were offloaded to 1/6th G
(lunar gravity). A subset task circuit from one of these simulations replicated an EVA traverse to
a lunar crater, taking a geological sample, and returning to base. The suited subject walked one
1500 m (0% grade) and three 500 m traverses at three different grades (10, 20, 30%). Between
each traverse, subjects performed geology sampling tasks (0 and 10% grade). Thermal measurements included core and skin temperature, liquid cooling garment (LCG) inlet and outlet
temperature, and spacesuit gas inlet and outlet temperature and humidity.

Compared to baseline core temperature (S1 = 37.07±0.32 °C, S2 = 37.27±0.01 °C) and
mean skin temperature (S1 = 32.38±0.34 °C, S2 = 33.62±0.03 °C), after a 1500 m traverse, each
suited subject showed an increased core temperature (S1 = 37.23±0.12 °C, S2 = 37.41±0.11°C)
and decreased mean skin temperature (S1 = 32.16±0.17 °C, S2 = 31.53±1.15 °C) at a delta LCG
temperature (S1 = 1.86±0.24 °C, S2 = 2.20±0.76 °C) and delta suit humidity (S1 = 9.66±1.49 %,
S2 = 11.50±1.58 %). Core temperature continued to increase from compounding traverse and
geology tasks (S1 = 38.04±0.03 °C, S2 = 38.1±0.02 °C) accompanied by an increase in delta
LCG temperature (S1 = 2.24±0.13 °C, S2 = 2.67±0.12 °C) and delta suit humidity (S1 = 28±2.42
%, S2 = 31±2.13 %). Conversely, as the circuit progressed, mean skin temperature continued to
decrease due to sustained LCG heat rejection (S1 = 30.08±0.15 °C, S2 = 30.28±0.07 °C). During
the simulated EVA circuit core temperature increased to elevated values and remained elevated
as heat was retained while mean skin temperature decreased due to peripheral heat offloaded to
the LCG. The thermal measures collected during this study provided critical heat loading
dynamics during lunar EVA tasks. Including core and skin temperatures along with suited
thermal measures provides a standard data collection scheme for human thermal metrics during
EVA task management. Data collected in this configuration can be used to build future lunar
EVA task circuits and human thermal predictions.