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One of the main functions of the Environmental Control and Life Support System (ECLSS) for Space Station Freedom (SSF) is the provision of Temperature and Humidity Control (THC) for the atmosphere in the interior of the SSF pressurized elements. This function will be provided for the early man-tended capability (MTC) and later for the permanently manned capability (PMC) which are described later in this paper. This paper presents results from application of the computer programmed software which is being used in the design and development of the THC subsystem components and the computer control algorithms. The software consists, in part, in (1) the control logic which runs in real time and will be used to control the actual THC subsystem hardware, and (2) a “plant” model which simulates, in real time, the actual THC subsystem hardware and the pressurized element or cabin in which a THC subsystem is located.

This paper contains a partial review of the requirements and design of the Environmental Control and Life Support System (ECLSS) for Space Station Freedom (SSF); a review of G189A ECLSS computer models developed for different SSF configurations; and some significant computed results from these models showing transient dew point responses during maximum and minimum dew point conditions on board SSF. SSF operational requirements which pertain to dew point have two major thrusts: 1) Quantification of high and low moisture contents allowable in the atmosphere; i.e., dew point within the range of 40°F to 60°F, and relative humidity within the range of 25% to 70%. 2) Prohibition of condensation on any interior surfaces (such as the interior pressure shell wall, or cool air/water lines) (1).* Detailed computational results presented in the paper pertain primarily to the verification of compliance with the first of the two items mentioned above.

This paper presents an assessment of test data for the Sabatier CO2 Reduction Subsystem which has been selected for the Environmental Control and Life Support System (ECLSS) for Space Station Freedom (SSF). The assessment is facilitated through the application of a developed mathematical model for the subsystem. The Sabatier CO2 Reduction Subsystem is one of several subsystems included in the regenerative portion of the overall ECLSS for SSF. It provides the important function of reducing collected metabolic CO2 from the crew with H2 generated by the water electrolysis unit. (Water electrolysis primarily generates makeup O2 for the crew and for space cabin leakage.) The product water resulting from the CO2 reduction is supplied to a water recovery subsystem for further processing. The test data for the Sabatier subsystem were obtained from the comparative test (CT) program performed by the Boeing Missiles & Space Division at Huntsville, Alabama.

This paper reviews the recent G189A computer program developments in the area of humidity control for the U.S. Lab Module in the Space Station. The humidity control function is provided as an indirect or passive function by the Common Cabin Air Assemblies (CCAA) in pressurized elements or modules in the Space Station. The CCAAs provide active cabin temperature control through implementation of a digital/electromechanical control system (i.e., a proportional/integral (PI) control system). A selected cabin temperature can be achieved by this control system as long as the sensible and latent heat loads are within specified limits. In this paper three pertinent analytical cases directed to determining minimum or maximum dew point temperatures are discussed. In these cases the basic sensible heat loads are set at constant values.

A parametric analysis of the life support systems was completed, from which scaling laws were developed and adapted to computer solutions. This new tool permits the evaluation of a great variety of life support system types and combinations. The interdependencies and interrelations within the life support system itself can be evaluated, as well as the interactions between the life support system, spacecraft, and other systems. Representative data are presented for several partially closed life support system configurations usable for manned Earth orbital missions. The life support systems are principally affected by alternative degree of closure, the functional methods selected for the various subsystems, and mission requirements.

The G198A generalized environmental control and life support system (ECLSS) simulation computer program has a library of ECLSS component and subsystem subroutines that can be used to model the complexity of planned ECLSS's for advanced manned spacecraft. The G189A program has successfully provided the necessary mathematical modeling functions for the Skylab and the Space Shuttle orbiter. This paper presents developments at Rockwell International concerning the preparation of the user-friendly computer program (PrepG189) for facilitating G189A program schematics and input data preparation. The two major subprograms in PrepG189 are the schematic processor and the panel processor. The program is operated on a VAX computer terminal. A high level of maneuverability has been achieved in moving between the subordinate portions of the program that participate in numerical data and schematic preparation.

The initial development and subsequent evolution of the Environmental Control and Life Support System (ECLSS) for the manned Space Station requires a numerical modeling computer program that can accurately simulate the ECLSS. The G189 program has successfully provided this modeling function for the Skylab refrigeration system and for the Environmental Control System (ECS) in the Space Shuttle Orbiter. Presently being developed at Boeing Aerospace is an overall Space Station ECLSS model, which is being constructed and operated at increasing levels of complexity. This paper presents and discusses the Boeing G189A model of the baseline Space Station ECLSS. The model is in an early stage of refinement and includes all ECLSS functional operations except Fire Detection and Suppression (FDS) (which is in the detection mode only during normal Station operation) and the Avionics Air Cooling/Heating portion of the Temperature and Humidity Control (THC) Subsystem.

The initial development and subsequent evolution of the environmental control and life support system (ECLSS) for the manned Space Station requires a numerical modeling computer program that can accurately simulate the The G189 program has successfully provided this modeling function for the Skylab refrigeration system and for the environmental control system (ECS) in the Space Shuttle orbiter. Recent developments at Rockwell International are presented here for a user friendly computer program for facilitating G1S9 program input data preparation, and a Space Station ECLSS model simulation. For this paper, a candidate Space Station ECLSS configuration was modeled. Functions modeled included O2 generation, CO2 removal, CO2 reduction, water recovery, cabin atmosphere composition and pressure control, cabin temperature and humidity control, and trace contaminant control.