CHAPTER 19 SYSTEMS: ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEM—SUPPORTING THE HUMAN ELEMENT OF THE ISS 344 passes through a particulate filter, followed by the Multi-Filtration Beds, which removes nonvolatile organics and inorganics such as soaps and salts. The water then is purified more in a catalytic reactor, which oxidizes low-molecular- weight volatile organics (this process uses small amounts of the O2 that is stored in the tanks on the airlock). Next comes the gas separator, which removes gasses created during the oxidation process. This gas needs to be removed to avoid clogging the fine filters downstream that are used throughout the potable bus systems. This gas is returned to the cabin to be breathed by crew, thus preventing the waste of any O2. Small amounts of iodine are added to the water to prevent microbial growth from occurring. This clean water is then output to the Product Water Tank where it can be fed to the potable water plumbing. Crews can extract water for drinking or rehydrating food via the Potable Water Dispenser (PWD) attached to this line. Wastewater from the UPA is also processed. People are often surprised that astronauts drink recycled urine. However, the processing is so good that what is left is virtually pure water. In fact, crew members have commented that the water tastes funny, which is actually a result of it being more pure than the water that is consumed on Earth. The OGA also uses the water from the potable water lines. The WPA can process 13 L (29 lbs) per hour. Oxygen Generation Assembly Water Recovery System Rack 1 Rack 2 Power Supply Module N2 Purge ORU Deionizer Bed Sabatier Reactor Health Sensor ORU Particulate Filter Urine Processor Pumps Gas Separator Catalytic Reactor Water Processor Pump and Separator Water Processor Waste Water Tank Multi- Filtration Beds Advanced Recycle Filter Tank Assembly Distillation Assembly Waste Storage Tank Assembly Product Water Tank Pumps, Valves Firmware Controllers Electrolysis Cell Stack Water Processor Delivery Pump Figure 9. Images showing OGA and the Water Recovery System racks. As discussed above, the OGA takes water and produces H2 and O2. Prior to the arrival of the Sabatier system, the H2 was vented overboard. With the arrival of the Sabatier rack in October 2010, the H2 would no longer be wasted. The rack takes H 2 and CO 2 and uses a catalyst at high temperature and pressure to produce water and methane via a chemical reaction first discovered by chemist Paul Sabatier. No further processing of the methane is possible on the ISS, thus it is vented overboard. Although water is processed in a nearly closed-loop fashion (i.e., little water is lost to the system), management of this process requires a lot of diligence by the ETHOS team. Various factors are always affecting the balance in the system. For example, some crews drink more water than others individuals also perspire and urinate at different rates. If any of the systems experiences a malfunction, part of the processing loop stops and input backs up. ETHOS can also tune the system to adjust water balance. For example, the temperature for the Low Temperature Loop system can be