The International Space Station (ISS) currently provides potable water dispensing for rehydrating crewmember food and drinking packages. One system is located in the United States On-orbit Segment (USOS) and one system in the Russian Segment. Shuttle mission STS-126 delivered the USOS potable water dispenser (PWD) to ISS on ULF2 [utilization logistics flight 2]; subsequent activation occurred on November 2008. The PWD is capable of supporting an ISS crew of six, but nominally supplies only half this number. The design provides incremental quantities of hot and ambient-temperature potable water to U.S. food and beverage packages. PWD receives iodinated water from the U.S. Water Recovery System fuel cell water bus, which feeds from the water processing assembly. The PWD removes biocidal iodine to make the water potable prior to dispensing. A heater assembly contained within the unit supplies up to 2.0 L of hot water (65 to 93°C) every 30 min. During a single meal, this quantity of water supports three to four crewmembers' food rehydration and beverages. The unit design has a functional life expectancy of 10 years, with replacement of limited-life items, such as filters. To date, the PWD on-orbit performance is acceptable. Since activation of the PWD, several differences were noted between on-orbit functionality and expected performance of hardware design. The comparison of on-orbit functionality to performance of hardware design is discussed for the following key areas: 1) microbial contamination, 2) no-dispense and water leakage scenarios, and 3) under-dispense scenarios.
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