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The temperature and humidity of the air within the habitable areas of the International Space Station are controlled by a set of hardware and software collectively referred to as the Temperature and Humidity Control (THC) subassembly. This subassembly 1) controls the temperature of the cabin air based on a crew selected temperature, 2) maintains humidity within defined limits, and 3) generates a ventilation air flow which circulates through the cabin. This paper provides descriptions of the components of the THC subassembly, their performance ranges, and the control approach of the hardware. In addition, the solutions of the design challenges of maintaining a maximum case radiated noise level of NC 45, controlling the cabin air temperature to within ±2°F of a setpoint temperature, and providing a means of controlling microbial growth on the heat exchanger surfaces are described.

The Environmental Control and Life Support System (ECLSS) on the International Space Station (ISS) utilizes the Major Constituent Analyzer (MCA) for monitoring major atmospheric constituents from sampling locations within the station. This paper describes the results of the protoflight testing of the first MCA unit. The MCA monitors six major constituents: oxygen, nitrogen, carbon dioxide, hydrogen, water vapor, and methane. In order to monitor these gases the MCA uses a permanent-magnet, single focusing mass spectrometer. This configuration was originally developed for the Skylab metabolic analyzer and most recently was used for the Spacelab's Gas Analyzer Mass Spectrometer, (GAMS). For the MCA application, the mass spectrometer and its support electronics were repackaged to meet the space station requirements.