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The International Space Station (ISS) Temperature and Humidity Control/Intermodule Ventilation (THC/IMV) system for the U.S. Lab provides required cooling air for the U.S. Lab and also provides “parasitic” cooling air for Node 1 and its attached elements. This scheme provides cooled air from the Lab THC directly to Node 1 and also to elements attached to Node 1, at different stages of Space Station assembly. This paper reports on the results of Open Hatch ECLSS/ TCS Tests for International Space Station’s Lab Module. The hardware tested is referred to as proto-flight hardware. Upon satisfactorily passing these Open Hatch and later Closed Hatch, imposed ground based, proto-flight tests, the proto-flight hardware will become flight hardware. The Lab Module is scheduled for launch during late 1999. The particular ECLSS/TCS equipment discussed here are the Temperature Humidity and Control (THC) equipment and Intermodule Ventilation (IMV) equipment.

This paper updates the analytical rationale and the computed results from those presented in the initial paper delivered on this subject (see the first reference listed below). The operational scheme is the same in this paper as in the earlier paper. The ACS Ventilation and Relief Valve (VRV) in the depressurizing Lab Module is wide open due to the need to suppress a large fire in the Lab or to remove the contaminated Lab atmosphere. All crew-men have evacuated the Lab Module and all previously open hatches in the Lab Module have been closed.

A considerable amount of integrated Environmental Control and Life Support System (ECLSS) analysis has been performed and documented for the proposed habitable Space Station. Earlier analytic activities have resulted in highly refined models simulating Temperature and Humidity Control (THC) and Atmosphere Revitalization (AR) hardware. As the mechanisms by which these items affect the Space Station environment have become better understood (along with the effects due to operation of various Man Systems utilities), the next stage of the integrated analysis task has been accomplished; i.e., the simulation of the Atmosphere Control and Supply (ACS) subsystem. The focus of the present paper is upon the ACS function in the overall life support system. Modeling of the ACS is unique among the life support disciplines in that it requires accurate representation of all other ECLSS subsystems that interact with the cabin atmosphere (which has now been achieved) in order to be realistic.

This paper describes an analytical model of the Four-Bed Molecular Sieve (4BMS) proposed for the Space Station Freedom. The model was developed using modified components of the G189A Computer Program. Requirements and inlet conditions are specified for normal (four-man) and emergency (eight-man) operation. The G189A Generalized ECLSS Simulation routines for adsorption/desorption in a molecular sieve bed and for a vacuum pump have been modified to add new capabilities. The mass transfer and thermal differential equations, which are solved through numerical difference equations for the nodal networks for mass and thermal transfer within the beds, are presented. The bed adsorption/desorption routine has been modified to allow coadsorption of oxygen, nitrogen, carbon dioxide and water using ideal solution theory to adjust the pure constituent isotherms to account for coadsorption.

An advanced ECLSS Model has been developed using the G189A Environmental/Thermal Control and Life Support Systems Computer Program (1)* for simulating the atmospheric conditions on board Space Station Freedom. The model is similar in intent to that presented at the 1989 ICES Conference (SAE 891499) (2). However, significant changes have been applied to the previous model which allow for refined atmospheric simulation, while retaining the overall objective of avoiding rigorous models of individual components. The highlights of the advanced atmospheric model center around the inter-module linkage and ventilation, and the Atmosphere Revitalization System (ARS).

This paper contains a review of the requirements and design of the Environmental Control and Life Support System (ECLSS) for Space Station Freedom; a review of an ECLSS computer program model developed at Boeing for the complete configuration of pressurized elements or volumes; and some significant computed results from this model showing transient performance for subsystems responsible for Temperature and Humidity Control, Atmosphere Control and Supply, Air Revitalization, and Water Recovery and Management. The model referred to is a comprehensive ECLSS Model which has been developed using the G189A Environmental Control System simulation tool.(1)*. The development and potential application of the Model was presented at the 1989 ICES Conference (2). The Model has since been slightly revised and extensively operated, to obtain information regarding nominal and off-nominal ECLSS conditions onboard Space Station Freedom.

An analytical investigation of the design and transient performance of a representative space vehicle thermal control system is used to transfer waste heat from the vehicle's environmental control/life support system to a space radiator. The system was designed by suboptimizing system components on the basis of weight and power at various flow rates, and subsequently finding the minimum total system penalty and corresponding system flow rate. With Freon 21 as the heat transport fluid, the transient analyses indicated that heat loads as low as 20% of the design heat load were permissible without causing incipient freezing of the Freon in the radiator tubes.