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The on-orbit oxygen and nitrogen supply for the United States On-Orbit Segment (USOS) of the International Space Station (ISS) is provided in tanks mounted on the outside of the Airlock module. Gasses are supplied, for distribution to users within the USOS, via pressure regulators in the Airlock. The on-orbit storage can be replenished with gas that is scavenged from the Space Shuttle, or by direct replacement of the tanks. The supply and distribution system are described in this paper. The users of the gasses are identified. The system architecture is presented. Operational considerations are discussed.

The Pressure Control Assembly (PCA) will provide cabin air pressure control functions for the United States elements of the International Space Station. A PCA will be located in each of the US Laboratory, Habitation, and Airlock modules of the International Space Station. The PCA will provide the capability to vent cabin atmosphere to space, inject nitrogen and oxygen into the cabin, and monitor the cabin air pressure. In this paper, the functionality, operation, design, physical characteristics, and expected performance of the on-orbit PCA are presented.

The on-orbit automation currently planned for the Environmental Control and Life Support System (ECLSS) and the Internal Thermal Control System (ITCS) of the United States on-Orbit Segment (USOS) habitable modules of the International Space Station (ISS) are examined. The discussion includes an overview of the ECLSS, ITCS, and Command and Data Handling (C&DH) system, and features the direct applicability of the planned real-time software control functions to the planned on-orbit ECLSS/ITCS functions.

A dynamic model of the cabin atmosphere onboard Space Station Freedom is presented. Hardware to regulate the pressure and temperature is modeled. Control laws that provide regulation of cabin pressure, Oxygen partial pressure, and temperature are presented. The performance of the proposed controller design concept is evaluated.