Validation of a Human Thermal Model for Assessing Crew-Induced Loads in Spacecraft

Human space exploration missions that require exercise prescriptions at high metabolic rates for the crew can make sizing the Environmental Control and Life Support System (ECLSS) challenging. An accurate human model is needed to calculate O2 consumption and the production of CO2, water, and metabolic heat of astronauts during exercise. In typical human thermal models, clothing is often not rigorously considered, but treated simply as a boundary condition at the skin described by its thermal and evaporative resistances. While this approach may be sufficient for modeling humans operating at relatively low metabolic rates, a clothing thermal model that does not explicitly consider the transport of moisture and heat through individual clothing layers can yield incorrect results in scenarios involving high activity levels. Additionally, many human models do not track the amount of sweat that accumulates on the skin or within the clothing during exercise; this sweat may only evaporate after the exercise routine is finished. Tracking all moisture sources is essential for the calculation of crew-induced loads. To address these limitations, in previous work, we developed and validated a clothing model that considers heat and moisture transport within the fabric layers. The clothing model was integrated within the TAITherm Human Thermal Model (HTM), which uses an explicit geometric representation of the human body to predict thermo-physiological state by resolving the body in terms of its individual tissue thermal properties and simulating its thermoregulation mechanisms. In this paper, we describe validation of the model for simulating crew-induced loads during periods of vigorous exercise. The HTM�s predicted total moisture output is within 23g of a linear fit through measured values from human subject tests performed at NASA. This study lays the groundwork for conjugate assessments between crew and spacecraft for evaluating an exploration vehicle�s thermal control, environmental control, and life support systems.