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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.

Prototypes of electrically-heated gloves have been designed, constructed, and tested along side other glove designs to evaluate various approaches to glove features. Two glove designs and two heater-controller designs, developed in-house, plus two commercial glove systems and an experimental glove system developed by the Army were tested. Testing consisted of employing the gloves while performing tasks in cold chambers. The results sought and obtained are subjective. Testing indicated that the in-house-designed glove system provided sufficient warmth under the test conditions specified by NASA scientists who are experienced working in Antarctica. The insulating ability of the commercial gloves and the dexterity of the Army-designed gloves were found preferable to those of the NASA prototypes. Additionally, testing showed that a single feedback temperature sensor per glove is adequate, as compared with individual temperature zones for each finger and thumb.

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.

The microgravity and hypobaric environments encountered in space flight will alter the convective and evaporative heat and mass transfer coefficients that influence thermal comfort. In this paper, models of heat and mass transfer between the human body and the environment are presented. Three mode of convection are identified: (1) free convection governed by the temperature gradient between the skin and the environment and by the acceleration of gravity, (2) forced convection governed by the ambient gas movements, and (3) mixed convection combining the previous two modes. Mixed convection is shown to prevail in most situations on Earth. In microgravity the contribution of free convection to the convective heat exchange is negligible and only forced convection must be considered. The ‘classic’ Lewis analogy between the convective heat and mass transfer is commonly used on Earth to calculate the mass transfer coefficient from the convection coefficient.

A NASA Learjet was used to produce a low-gravity environment for two series of nucleate pool boiling experiments. Surface-temperature and heat-flux measurements and high-speed microphotography of bubble phenomena were made on 18 prepared boiling surfaces. The surfaces were polished copper disks, 25.4 mm and 19.1 mm in diameter, with variable artificial nucleation site densities from 0.2 to 32 sites/cm2. Both 1-g and low-g data were obtained for comparison. In every case, the boiling heat-transfer coefficient increased significantly to a new steady value for the duration of the low-gravity period. Rapid movement of the surfaces of the large vapor masses that were observed is indicative of considerable turbulent liquid motion, apparently induced by the bubble growth and coalescence. In no case was a decreased heat-transfer coefficient observed, which would be indicative of film boiling.

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.

A unique exercise facility has been developed and used to simulate orbital extravehicular activity (EVA). The device incorporates an arm ergometer into a mechanism which places the subject in the zero-g neutral body posture. The intent of this configuration is to elicit muscular, cardiovascular, respiratory, and thermoregulatory responses similar to those observed during orbital EVA. Experiments done with this facility will help characterize the astronaut's dynamic heat balance during EVA and will eventually lead to the development of an automated thermal control system which would more effectively maintain thermal comfort.

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.

Automatic control of the liquid cooling garment (LCG) worn by astronauts during extravehicular activity (EVA) would more efficiently regulate astronaut thermal comfort and improve astronaut productivity. An experiment was conducted in which subjects performed exercise profiles on a unique, supine upper body ergometer to elicit physiological and thermal responses similar to those achieved during zero-g EVAs. Results were analyzed to quantify metabolic rate, various body temperatures, and other heat balance parameters. Such data may lead to development of a microprocessor-based system to automatically maintain astronaut heat balance during extended EVAs.

The Space Station mission requirements for initial frequent use of EVA require the modification of the existing Shuttle suit and the Shuttle Extravehicular Mobility Unit (EMU). Options for a Space Station EVA space suit are described and evaluated in light of the Space Station mission human and environmental requirements. The evaluation is made to select the most cost-effective and technologically feasible alternative that meets the requirements. Requirements considered include; (1) the heavy, almost industrial use, of the suit, (2) long operational life, (3) on-orbit maintenance and fit check, (4) high mobility, (5) rapid don/doff, 6) high pressure for zero pre-breath, (7) radiation protection, (8) micrometeoroid/space debris protection, (9) thermal insulation, (10) contamination/ decontamination factors, (11) automatic checkout, and (12) low development and recurring costs.