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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.

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.

The existing Shuttle Extravehicular Mobility Unit (EMU) has served NASA well for sometime, however, it uses a large amount of consumables including water, O2 and lithium hydroxide. In order for extended missions to the Moon and Mars to be successful, two new portable life support systems (PLSS) designs have been proposed that will minimize the amount of consumables used and will be more reliable due to simplified designs. This paper considers one such PLSS, currently designated the Cryogenic-PLSS (CPLSS). The reason for this designation is because it uses liquid O2 to provide the breathing gas for the astronaut and to provide backup cooling for the astronaut. In order to understand how the system will function in space and to evaluate final design parameters, a transient thermal model has been developed using the software package MATLAB/Simulink.

A transient model of the Minimum Consumables Portable Life Support System (MPLSS) Advanced Space Suit design has been developed and implemented using MAT-LAB/Simulink. The purpose of the model is to help with sizing and evaluation of the MPLSS design and aid development of an automatic thermal comfort control strategy. The MPLSS model is described, a basic thermal comfort control strategy implemented, and the thermal characteristics of the MPLSS Advanced Space Suit are investigated.

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.

The NASA JSC Shuttle EMU computer model (SINDA EMU) is presently used to analyze the thermal behavior of the Space Shuttle EMU. This paper uses the SINDA EMU model along with EMU experimental and flight data to investigate and define several performance characteristics of the Space Shuttle EMU related to thermal comfort control.

This paper discusses the development of an exercise chamber as one of the requirements for a planned generalized EVA Simulation Test Bed. The design of the outer chamber and associated environmental control equipment is discussed, followed by a sensitivity analysis of the parameters of a human thermal model leading to a design for the inner chamber.

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 discusses several issues related to the PLSS thermal model requirements for a planned generalized EVA Simulation Test Bed. The existing models of the extravehicular mobility unit (EMU) are briefly discussed and then the paper focuses specifically on the NASA JSC Shuttle EMU model (referred to as SINDA EMU). After the SINDA EMU model review, the PLSS thermal model requirements for the EVA Simulation Test Bed are discussed in detail.

NASA is funding a research project at the University of Missouri - Columbia as part of a more general effort to learn about the human physiological response to the types of exercise that astronauts perform on EVA missions. The authors created a dynamic state-space mathematical model representing the thermal behavior of the NASA environmental chamber located at the Ames Research Center. This model predicts chamber performance from which the authors identify modifications to the system which will improve its accuracy and usefulness. Simulation results closely match expected values for chamber performance. Recommendations are presented to improve chamber performance and instrumentation measurement accuracy.

A detailed comparison has begun of the structure and function of two human thermal models, the 41-Node Man model and the Wissler model, being considered for use in a proposed simulation test bed to model the fully transient extravehicular activity (EVA) automatic thermal control problem. The evaluation is directed toward demonstrating the current state of the art in human thermal modeling methodology and performance. Internal formulative differences between the models is the primary focus.

Current NASA space suits use porous metal plate sublimators to reject the metabolic heat generated by the astronaut into space vacuum during EVA. Relying on tubular membranes instead of the flat plate of the sublimator, a proposed alternate unit has the potential to be smaller and lighter. This work outlines the operation of the proposed tubular membrane evaporator and the evaluation of possible membrane materials for the unit.

A transient thermal model of the portable life support system (PLSS) is being developed for use in thermal control studies. The transient thermal PLSS (TTPLSS) model has been developed and implemented using SIMULINK in conjunction with MATLAB. The TTPLSS has been developed with modularity and flexibility in mind so that alternative PLSS designs and configurations can easily be implemented and evaluated. The basic structure and functionality of the TTPLSS SIMULINK model is described and demonstrated. The various thermal dynamics issues associated with the PLSS such as time delays and the dynamics of individual components are discussed and considered.

Modeling the sweat regulation mechanism is important for reliable simulation of the human thermoregulatory processes. The complexity of the mechanism makes it very difficult to model using traditional techniques. An engineering or systems overview of the human thermoregulatory system is reported. An extensive review of previous attempts to model the human sweat rate forms an important part of this paper. In addition, this study investigates the applicability of neural networks to the problem of modeling the complex nonlinearities of the sweat regulatory mechanism. It is believed that neural networks provide better generalization capabilities for all the cited dependencies resulting in better sweat prediction models. The network is thus in a position to generalize based on the different operating conditions and provide more reliable outputs over an entire range of environments and metabolic profiles.

Long-duration, frequent extravehicular activity (EVA) will require automatic thermal control and improved thermo-mechanical design of portable life support system (PLSS) packs and suits. This paper addresses the control problem in EVA, previous attempts to develop automatic control, and relevant issues in human thermoregulation and is directed toward the development of a generalized computer simulation test bed for the investigation of alternative PLSS control strategies and designs.

As extended extravehicular activity (EVA), having duration on the order of 8 hours, becomes more common, it will be necessary to improve regulation of the thermal comfort of astronauts in order to increase their productivity and endurance. To facilitate the development of an advanced liquid-cooling and ventilation garment (LCVG) automatic controller, an accurate human biothermal model is required for simulation studies of new controller strategies and suit hardware. A critical comparative evaluation of several existing models is undertaken as a preliminary step in that direction.

The capability of Continuously Variable Transmissions (CVTs) to provide a continuous speed ratio change and smooth power flow has been widely recognized. These unique characteristics of CVTs make them especially suited for a variety of power transmission needs. Several studies have been accomplished in the past, to understand the power transmission characteristics of individual CVT concepts. However, few general analytical models and comparisons of different CVT concepts have been reported in the literature. In this work, different CVT concepts have been compared on an equitable basis in a selected operating envelope. Mathematical models of different CVT concepts have been developed from the published literature by normalizing the available information to allow comparison of different CVT concepts on an equitable basis. The models have been used next, to compute the efficiencies of individual CVTs at selected points covering the entire operating envelope.