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It was shown in a previously-published study, that for the light crewmember activity levels applicable to Space Station, ventilation velocities could be lower than 15 feet per minute, and still provide for crew comfort. However, the previous calculations to determine the effects of ventilation velocity upon heat flux were conducted only for nominal values of other environmental parameters. As described in this paper, the study has been expanded to establish envelopes of operation in terms of five main independent variables: crewmember activity levels (metabolic rates), cabin air temperatures, cabin air relative humidities, ventilation velocities, and levels of clothing. The results are presented in terms of data tables, such that the boundaries for achieving acceptable crew comfort can be determined for combinations of the five independent variables over realistic ranges.

The ventilation velocity requirements for crew comfort and heat transfer were assessed, as one of several initiatives to ensure that sufficient electric power will be available for Space Station Freedom during the early Man-Tended Capability (MTC) Phase of operations. A rigorous heat transfer analysis, to accommodate microgravity and reduced pressure conditions, was conducted to characterize cabin air effectiveness in transferring metabolic heat away from crewmembers. Maximum possible sweat evaporation rates were estimated based upon rigorous mass transfer correlations. In the range of low work rates applicable to MTC, no single mechanism dominated the heat transfer. Those mechanisms not dependent upon ventilation velocities, radiation and respiration, appeared to be as important, under the nominal conditions, as forced convection and sweat evaporation. It was shown that ventilation velocities could be lower than 15 feet per minute, and still provide sufficient heat flux.

As a result of a 1989 program rephasing, Space Station Freedom's system-level water balances have been materially shifted. The average and the most likely values of the water balance, and the components of variability, were evaluated in this study. The Assembly Complete configuration has a large excess of ECLSS potable water but a deficit of ECLSS hygiene water. In contrast, there is a small ECLSS potable water deficit but an excess of ECLSS hygiene water for the “Permanent Manned Capability” (PMC) configuration. Upon considering the Orbiter fuel cell water supply to the station and the combined demands for station water, the average and most likely values for the overall excess quantity are 6,800 and 9,000 pounds per year for the Assembly Complete configuration. Comparable values for the PMC configuration are 6,600 and 6,400 pounds per year.

The Baseline Space Station Freedom architecture calls for separate and independent water electrolysis subsystems in ECLSS and in Propulsion. A study to assess the potential benefits and impacts of electrolyzer commonality evaluated fifteen sets of ECLSS and Propulsion architectural options with graduated levels of commonality, first by quantifying the electrical power, weight, volume, and heat rejection requirements; and then qualitatively according to safety and redundancy, reliability and maintainability, integration and verification, and assembly. There were no compelling quantitative or qualitative advantages of the options incorporating commonality which would drive a decision to alter the Baseline. The options were also compared with respect to estimated program costs. The maximum projected savings were less than five per cent, likely within the uncertainty of the estimation process.