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The International Space Station (ISS) Active Thermal Control System (ATCS) (Ref. 1,2) has changed over the past several years to address problems and to improve its assembly and operation on-orbit. This paper captures the ways in which the Internal (I) ATCS and External (E) ATCS have changed design characteristics and operations both for the system currently operating on-orbit and the new elements of the system that are about to be added and/or activated. The rationale for changes in ATCS design, assembly and operation will provide insights into the lessons learned during ATCS development. The state of the assembly of the integrated ATCS will be presented to provide a status of the build-up of the system. The capabilities of the on-orbit system will be presented with a summary of the elements of the ISS ATCS that are functional on-orbit plus the plans for launch of remaining parts of the integrated ISS ATCS.

The possibility of a leak in one of the International Space Station (ISS) External Active Thermal Control (EATC) loops is real and has been addressed in conceptual studies and in equipment preparation. Leak location and repair is essential to restore the functionality of the loop affected. However, it is a difficult task due to the large size of the ISS EATC loops and the harsh environment in which they operate. The rapid dispersion of leaking ammonia into the vacuum of space makes leak location particularly difficult. Repair must be performed via ExtraVehicular Activity (EVA) by doing what amounts to plumbing work on a high-pressure container in the thermal vacuum environment of space. This paper provides insights into the preparation NASA and Boeing have taken to address the leak contingency. The design capabilities that allow leak location and repair for some scenarios are presented.

The Test and Verification (T&V) approach for the thermal control systems of the ISS involves a combination of test, analysis and other approaches to confirm that the design meets ISS requirements. The maturity of the designs used in ISS varies from a design for Functional Cargo Block (FGB) that has been proven to be functional on the Mir space station to new design developments for heat pipe passive cooling networks and single phase ammonia systems for thermal conditioning of the USOS. The approach to thermal T&V considers the design maturity and the nature of the system under evaluation. The approach for each area of the ISS is described in this paper as is the status of the T&V activities. In addition to the approach taken in each area, an overview of the results obtained is provided.

Many changes have been approved for implementation into the International Space Station (ISS) design for Thermal Control (TC) since the System Design Review (SDR)conducted in March 1994. Some of the changes have resulted in changes in the basic content of the ISS TC Subsystem (TCS) while others have addressed more efficient ways of developing the system. The design changes were made to address several distinct facets of the program. Foremost was the intent to control costs of the ISS program. The intent to ensure that the ISS is not completely dependent on any one partner was a major reason for other changes. Refinement of the SDR design and identification and solution of problems with the SDR design resulted in other design changes. While the technology to be used for the ISS TC has remained the same during this period, significant changes have been made to the way the ISS thermal control technology is implemented.

In the Spring of 1993, the Clinton administration called for a scaled down space station as part of a reduction in the funding level available for NASA projects. To take advantage of the products of the SSF program in containing costs, NASA considered the use Space Station Freedom (SSF) components and concepts to develop a new design. The redesigned space station concept that was developed calls for a significantly different Thermal Control (TC) than was used in the SSF design. This paper provides an overview of the redesigned space station thermal control system. The top level design requirements are summarized as they relate to the functions the TC is to provide. The functional link of TC components and space station elements into the Internal Active TC (IATC), External Active TC (EATC), Photovoltaic Active TC (PVATC), Russian Segment TC (RSTC) and Passive TC (PTC) subsystems is discussed and presented in system schematics.

The Space Station Freedom (SSF) Thermal Control System (TCS) has evolved over a 12 year period in concert with a variety of configurations that have been proposed for SSF. The concepts for SSF have been influenced by the capabilities SSF will provide and by fiscal and schedule constraints. Changes in the capabilities the TCS must provide and the basic nature of the TCS design have been required to accommodate SSF needs and resources available. During 1991 the SSF configuration has reached a level of maturity and stability and details of the design are being worked. The design decisions that have lead to the present SSF and TCS design are described with the rationale that has contributed to the decisions. The TCS evolution through each of the design reviews (sometimes referred to as design “scrubs”) is presented to “capture” the major decision drivers that have contributed to the present TCS design.

A conceptual design for the interface of the Space Station Freedom (SSF) two-phase thermal bus with the heat rejecting radiator panels has been developed. The concept uses baseline technology for the radiator panels and the thermal bus condenser and replaces the current baseline interface hardware with a direct bus-to-radiator heat pipe integral connection. The concept integrates the radiator panel and condenser units into a single unit and is referred to as the “integral heat exchanger (IHX)” concept. It addresses the substantial weight and assembly complexities and inefficiency of the current contact heat exchanger mechanism. This paper presents a brief overview of the SSF testing that has led to development of the IHX concept, describes the concept and addresses the savings that could be achieved using the IHX concept to maximize radiator surface temperature and thereby heat rejection capability.