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The International Space Station (ISS) requires stores of Oxygen (O2) and Nitrogen (N2) to provide for atmosphere replenishment, direct crew member usage, and payload operations. Currently, supplies of N2/O2 are maintained by transfer from the Space Shuttle. Following Space Shuttle retirement in 2010, an alternate means of resupplying N2/O2 to the ISS is needed. The National Aeronautics and Space Administration (NASA) has determined that the optimal method of supplying the ISS with O2/N2 is using tanks of high pressure N2/O2 carried to the station by a cargo vehicle capable of docking with the ISS. This paper will outline the architecture of the system selected by NASA and will discuss some of the design challenges associated with this use of high pressure oxygen and nitrogen storage in the human spaceflight environment.

High pressure oxygen onboard the ISS provides support for Extra Vehicular Activities (EVA) and contingency metabolic support for the crew. This high pressure O2 is brought to the ISS by the Space Shuttle and is transferred using the Oxygen Recharge Compressor Assembly (ORCA). There are several drivers that must be considered in managing the available high pressure O2 on the ISS. The amount of O2 the Shuttle can fly up is driven by manifest mass limitations, launch slips, and on orbit Shuttle power requirements. The amount of O2 that is used from the ISS high pressure gas tanks (HPGT) is driven by the number of Shuttle docked and undocked EVAs, the type of EVA prebreath protocol that is used and contingency use of O2 for metabolic support. Also, the use of the ORCA must be managed to optimize its life on orbit and assure that it will be available to transfer the planned amount of O2 from the Shuttle.