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The International Space Station Alpha (ISSA) conceptual design has several notable differences from previous Space Station design efforts. One key difference centers around the Intermodule Ventilation (IMV). While previous IMV designs incorporated standalone ducts at each element-to-element interface, the present approach includes several IMV ducts which are configured into the central Temperature and Humidity Control (THC) ducting networks. A simplified analytic technique is presented, which assesses compliance of the overall IMV approach to the established requirement which limits IMV short circuiting to a maximum of 40% at a fan flow rate of 140 cfm. Test results (from the Space Station Freedom IMV Test) and theoretical performance results are input to the analytic technique.

The International Space Station Alpha (ISSA) Temperature and Humidity Control (THC) subsystem has been reconfigured and tested for both Node 1 and US Laboratory modules. Each element shares conditioned air that originates in the Lab module and is distributed into either the Lab, Node 1, Mini-Pressurized Logistics Module (MPLM), or the Cupola. This “parasitic” cooling scheme was tested at the McDonnell Douglas Space System Laboratory in Huntington Beach, California, during the summer of 1995. This test involved the use of standard and nonstandard techniques of measuring air flow through a complex system of ducting. Flow balancing was achieved through a series of additional dampers and orifices throughout the system. The purpose of this paper is to review some of the air flow measurement techniques and compare some of the test results with traditional theory. Techniques used for flow balancing, and test conclusions and recommendations, are also included.

Space Station Freedom (SSF) has an extended mission duration of 30 years. Trade studies for extended missions of manned spacecraft almost invariably show that large resupply weight and consequent cost savings can be achieved by recovering potable water from wastewater sources. This rationale has led to the present baseline Water Recovery and Management (WRM) system for the Permanently Manned Capability (PMC) phase of SSF. The baseline WRM includes the Vapor Compression Distillation (VCD) subsystem for recovering water from urine. This process serves as a preliminary processing step in achieving potable water from wastewater sources. The basic principle of the VCD is that water is evaporated from urine and then condensed in a zero-gravity device containing an evaporator and a condenser in a rotating drum. The VCD was selected for the baseline WRM following the assessment of test results from competitive urine processing subsystems obtained from the Comparative Test (CT) program.

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.

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.

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.

The International Space Station (ISS) Temperature and Humidity Control (THC) system has been reconfigured from the Space Station Freedom (SSF) configuration to meet new interface requirements and to implement a new “parasitic” air cooling scheme. This scheme provides Lab THC cooled air to Node 1, and more critically integrates Node 1 ports at different stages of space station assembly. A joint development test of the complex U.S. Lab and Node 1 integrated THC/IMV ducting system was conducted in the summer of 1995 at the McDonnell Douglas test facility in Huntington Beach, California. The purpose of the test was to show overall capability of the ducting system to meet basic requirements, and to provide detailed flow and pressure drop performance data for individual duct segments. This paper provides correlations of the test data with analytical data obtained from a computerized model of the THC/IMV ducting system.

This paper presents the basic test data obtained from tests of a cabin air distribution system in a simulated Space Station Man-Tended Capability (MTC) configuration and correlations of some of this data with the results from analytical modeling of the test setup flow conditions. The MTC configuration simulated in the test setup includes: Lab-A, the Node, the Cupola, and the Pressurized Module Adaptor (PMA). The test data and analytical data presented are confined to those for the Lab module. The cabin air distribution system controls the flow of air in the open space of a Space Station module. In order to meet crew comfort criteria the local velocities for this cabin air are required to be distributed within a specified range with upper and lower limits.

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.

In performing this analysis the G189A analytical tool was used to model the wide open ACS Ventilation and Relief Valve (VRV) in the depressurizing Lab Module. Hardware items relevant to each analytical case, in addition to the VRV were modeled in the G189A analytical tool. The objective of the analysis was to determine time/pressure profiles for venting of USOS modules to space via the VRV. When it became apparent that the ice accumulation in the Lab Module presented a potential problem to the VRV valve screen, and other parts of the VRV assembly, further analytical efforts were made to understand the problem. Additional analytical efforts were also made to solve the problem: allow for partial blockage of the VRV screen due to ice accumulation and still meet depress time limits, installation of a heater element to the screen to melt ice and allow the Temperature and Humidity Control system fan to run during depressurization events.

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. A development test of the U.S. Lab and Node 1/attached elements' integrated THC/IMV ducting system was performed in the summer of 1995. This test included the U.S. Lab's development level Common Cabin Air Assembly (CCAA), which removes sensible and latent heat from the circulated and ducted cabin air. A referenced 1996 ICES Paper contains the initial correlation results. An analytical model has been developed, which has been used to predict flow and pressure drop performance of the system for several potential and actual changes from the Development Test configuration.

The International Space Station (ISS) Temperature and Humidity Control (THC) system has been designed with the intent of supplying the air cooling needs of various elements from the U.S. Lab heat exchanger assembly. Elements without independent air cooling capability are known as “parasitic” elements; these are Node 1, the Cupola, and the Mini Pressurized Logistics Module (MPLM). Analysis results are presented which show expected temperatures in the MPLM, and Node 1, as various heat loads are present in the respective elements. Analyses within this paper are coordinated with the results obtained from the Development Test of the complex USL/Node 1 integrated ducting system. This test was conducted in the summer of 1995, at the McDonnell Douglas test facility in Huntington Beach, California.

This paper presents the basic test data obtained from tests of a cabin air distribution system in a simulated Space Station U.S. Lab-A module. The cabin air distribution system controls the flow of air in the open space of a Space Station module. In order to meet crew comfort criteria the local velocities for this cabin air are required to be distributed within a specified range with upper and lower limits. Achieving this desired velocity distribution is dependent upon the: (1.) design of the cabin air supply equipment and cabin air return equipment, (2.) total flowrate of air supplied to and subsequently returned from the cabin, and (3.) interactive effects of any other additional air flow streams which enter and exit the cabin. The basic Space Station design for the cabin air supply and air return equipment was used in this test program. Only directional adjustments to vanes in supply air diffusers were made during the test.

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.