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The Internal Thermal Control System (ITCS) has been developed jointly by Boeing Corporation, Huntsville, Alabama and Honeywell Engines & Systems, Torrance, California to meet the internal thermal control needs for the International Space Station (ISS). The ITCS provides heat removal for the critical life support systems and thermal conditioning for numerous experiment racks. The ITCS will be fitted on a number of modules on the ISS. The first US Element containing the ITCS, Node 1, was launched in December 1998. Since Node 1 does not contain a pump to circulate the fluid it was not filled with ITCS fluid until after the US Laboratory Module was installed. The second US Element module, US Laboratory Module, which contains the pumps and all the major ITCS control hardware, was launched in February 2001. The third US Element containing the ITCS, the US Airlock, was launched in July 2001.

This paper presents the development of a Thermal Math Model (TMM) of the space station U.S. Laboratory-A module. The TMM is used to predict operating thermal environments for all interior and exterior areas of the laboratory module. The model was constructed as a tool for performing developmental design analyses providing payload designers and analyzers a means for accurately predicting payload environments. The TMM determines the overall effect of a payload rack on neighboring subsystem and payload racks, standoffs, endcone regions, and the module cabin. The TMM has also been used to assess the percentage of Internal Thermal Control System (ITCS) cooled electronic equipment input power that dissipates to the module cabin air system. Active and passive thermal systems of the laboratory module are integrated in the TMM, providing the capability of predicting the interaction of the two thermal systems.

A U.S. Laboratory-A (U.S. Lab-A) payload rack has two primary thermal control systems designed for cooling payloads: a water cooling system and a distributed avionics air cooling system. This paper gives an overview of the rack-level thermal control systems available in a U.S.Lab-Arack. This paper also presents an analysis of the existing sensible payload heat removal capability of the laboratory module cooling system. In the U.S. Lab-A, all payload rack locations are configured as per the international Standard Payload Rack (ISPR) configuration. This paper begins with an overview of the ISPR with emphasis on the liquid and air cooling interfaces. An overview of both the liquid and air cooling systems is presented, showing general capability and limitations, payload rack flow control modes and optional payload rack thermal configurations. Performance data showing a sample overall system-level thermal energy balance is presented.