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This paper gives an overview for a new human thermal model. A compromise between simplicity and accuracy when developing the new thermal model is determined. The human thermal model incorporates 2-dimensional (radial and angular) heat transfer along with arterial and venous countercurrent blood flow. In addition, this thermal model attempts to model the human digits in order to predict toe and fingertip temperatures that are of special interest in regards to possibility of controlling the thermal comfort of a subject.

Automatic thermal comfort control for the minimum consumables PLSS is undertaken using several control approaches. Accuracy and performance of the strategies using feedforward, feedback, and gain scheduling are evaluated through simulation, highlighting their advantages and limitations. Implementation issues, consumable usage, and the provision for the extension of these control strategies to the cryogenic PLSS are addressed.

This study investigates the complexities associated with quantifying human thermal comfort using indices. A detailed review of the literature is first performed. The uncertainties associated with comfort modeling are then highlighted. Possible indices are developed and evaluated using integrated human-suit-PLSS (Portable Life Support System) simulations developed at the University of Missouri. The study forms part of a larger project aimed at developing automatic thermal controllers for NASA space suits.

The prospect of using automatic control for astronaut thermal comfort regulation during extravehicular activity (EVA) requires an investigation of issues concerning the current state of the art of human thermal models. The analysis presented includes, but is not limited to, the discussion of assumptions and the accuracy, range and relative significance of parameters (e.g., thermal properties, physical dimensions, etc.) of transient human thermal models. The Wissler 1D model attracts primary consideration; however, there exists the appropriate inclusion of the 41-Node Man model for reflection and study.

This paper presents the quantified effects of uncertainties and errors relating to typical human thermoregulatory experiments involving liquid cooled garments in suit calorimeters. It reports on-going efforts to develop a state-of-the art facility to perform human thermal testing for space suit thermal comfort control. A systematic methodology using sensitivity derivatives combined with instrument uncertainties is applied to develop a bound of accuracy on measured experimental variables. As for unmeasured experimental variables, methods used to estimate and minimize these uncertainties are also included. During actual experimentation with human subjects, the variability in experiments associated with subjects is modeled; steps taken to minimize errors and ensure repeatability are also reported. Results from this analysis will suggest specific improvements to the experimental setup in the most effective manner from the experimental accuracy and cost standpoint.

Previous sweat modeling attempts have produced several models of the human sweat regulation mechanism. To effectively use the models for control purposes, the sensitivity of the models to their parameters must be quantified. The characteristics of several meaningful sweat models are discussed. The parameters of each model are ranked in order to identify which parameters are the most important to the models. An objective of the study is to quantify the uncertainties in such models, to the extent possible. The sensitivity needed to measure the evaporative heat loss is calculated for a subject in the calorimeter being developed at University of Missouri-Columbia. This study is part of a larger effort at the University to develop reliable human thermal models for space suit thermal modeling studies.

The duration and frequency of extravehicular activity (EVA) is expected to increase with the anticipation of challenging missions ahead. This necessitates the development of an automatic controller for astronaut thermal comfort regulation. A reliable human thermal model is essential in order to predict the thermal response of subjects under various conditions to aid in automatic controller development. This paper examines thermal response sensitivity to several parameters and input modifications using a popular human thermal model. These parameter and input variations are based either on values reported in the literature or realistic estimates.

This paper presents a definition of human thermal comfort that can be used for control purposes. A control strategy and architecture based on a Proportional Integral Derivative (PID) controller format is developed. Problems and limitations are discussed and the results from both simulations and experiments are used to demonstrate the practicality of the comfort definition.