The International Space Station: Operating an Outpost in the New Frontier Page 341 (375 of 438)

341 SYSTEMS: ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEM—SUPPORTING THE HUMAN ELEMENT OF THE ISS CHAPTER 19 ARFTA – Advanced Recycle Filter Tank Assembly CCAAs – Common Cabin Air Assemblies CDRA – Carbon Dioxide Removal Assembly CWC – Contingency Water Container EDV - Russian Water Container EMU – EVA Mobility Unit OGA – Oxygen Generation Assembly Urine Plumbed to UPA Crew and Hygiene Condensate Sabatier Product Water Condensate from CHX Payload Condensate OGS Reject Water (iodinated) from N3 CDRA Flush EDV (22L) Waste and Hygiene Compartment PWD CWC (20L) PWR EMU CCAA CWC Payloads Waste Water Bus Potable Water Bus UPA ARFTA Urine Processing Assembly Water Delivery ORU Waste Water Processing Urine Processing SM EDV-U (22L) Archival Sample Waste Water Bus Water Processing Assembly WPA Water Storage Tank (56L) Condensate Tank (45L) WPA Waste Water Tank (45L) OGA Sabatier O2 CH4 H2 CO 2 Crew Consumption EMU Waste Water UPA WSTA (13L) ORU – Orbital Replacement Unit PWD – Potable Water Dispenser PWRs – Payload Water Reservoirs UPA – Urine Processor Assembly WHC – Waste and Hygiene Compartment WPA – Water Processor Assembly WSTA – Waste Storage Tank Assemble Figure 5. A schematic showing the overview of the water processing system. Wastewater from the Waste and Hygiene Compartment (WHC) is transferred to the Urine Processor Assembly and the WPA. From the WPA, clean water is placed on the potable bus where it can be transferred to the O 2 generator, the crew’s drinking station (Potable Water Dispenser), or the Sabatier, or used for EVA Mobility Units or for flush water in the WHC. is collected in the WPA wastewater tank. If the WPA wastewater tank is not available due to a failure, the crew can configure some jumpers and send the water to be stored in a condensate tank. If the tank gets too full, it is possible for the ETHOS flight controller to open a series of valves and vent some of the water overboard however, this is a last resort, as it results in loss of this precious liquid. The crew would offload the water into a Contingency Water Container (CWC) (Figure 6) prior to being full. The CWC is essentially a flexible bladder surrounded by fireproof fabric material that can hold about

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341 SYSTEMS: ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEM—SUPPORTING THE HUMAN ELEMENT OF THE ISS CHAPTER 19 ARFTA – Advanced Recycle Filter Tank Assembly CCAAs – Common Cabin Air Assemblies CDRA – Carbon Dioxide Removal Assembly CWC – Contingency Water Container EDV - Russian Water Container EMU – EVA Mobility Unit OGA – Oxygen Generation Assembly Urine Plumbed to UPA Crew and Hygiene Condensate Sabatier Product Water Condensate from CHX Payload Condensate OGS Reject Water (iodinated) from N3 CDRA Flush EDV (22L) Waste and Hygiene Compartment PWD CWC (20L) PWR EMU CCAA CWC Payloads Waste Water Bus Potable Water Bus UPA ARFTA Urine Processing Assembly Water Delivery ORU Waste Water Processing Urine Processing SM EDV-U (22L) Archival Sample Waste Water Bus Water Processing Assembly WPA Water Storage Tank (56L) Condensate Tank (45L) WPA Waste Water Tank (45L) OGA Sabatier O2 CH4 H2 CO 2 Crew Consumption EMU Waste Water UPA WSTA (13L) ORU – Orbital Replacement Unit PWD – Potable Water Dispenser PWRs – Payload Water Reservoirs UPA – Urine Processor Assembly WHC – Waste and Hygiene Compartment WPA – Water Processor Assembly WSTA – Waste Storage Tank Assemble Figure 5. A schematic showing the overview of the water processing system. Wastewater from the Waste and Hygiene Compartment (WHC) is transferred to the Urine Processor Assembly and the WPA. From the WPA, clean water is placed on the potable bus where it can be transferred to the O 2 generator, the crew’s drinking station (Potable Water Dispenser), or the Sabatier, or used for EVA Mobility Units or for flush water in the WHC. is collected in the WPA wastewater tank. If the WPA wastewater tank is not available due to a failure, the crew can configure some jumpers and send the water to be stored in a condensate tank. If the tank gets too full, it is possible for the ETHOS flight controller to open a series of valves and vent some of the water overboard however, this is a last resort, as it results in loss of this precious liquid. The crew would offload the water into a Contingency Water Container (CWC) (Figure 6) prior to being full. The CWC is essentially a flexible bladder surrounded by fireproof fabric material that can hold about

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CHAPTER 19 SYSTEMS: ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEM—SUPPORTING THE HUMAN ELEMENT OF THE ISS 340 Temperature and Humidity Control Not only does the crew need to be comfortable, some equipment requires the air in the ISS to remove excess heat (i.e., air cooled). CCAAs in the Laboratory, Node 2, Node 3, and airlock, and similar air conditioners in the International Partner modules, circulate, cool, and dehumidify the air. The CCAAs are connected directly to the IMV ducting (Figure 4). The ducting passes air between all the modules to ensure uniform mixing. Air is pulled into ducts that feed the CCAAs and passes through High Efficiency Particulate Air (HEPA) filters, in the same way as household systems do on Earth. Although the crew and spacecraft are kept as clean as possible on the ground, a fair amount of particulates are present on the ISS. These filters have to be vacuumed fairly regularly since, in microgravity, objects collect on the inlet of vents and not on the floor. This process also acts as a handy way to find missing items—e.g., lost screws, misplaced washers, small tools, or even a pack of gum or a fork. A fan pulls the air in through the HEPA filter and past the Condensing Heat Exchanger (HX). The air passes over metal layers that are cooled by water from the Low Temperature Loop (see Chapter 11). When air hits the cool plates, the water condenses on a plate where it is drawn into small holes and separated from the air. The cooler and dehumidified air is then vented directly into the cabin. If the crew members want the air temperature to be warmer, they (or the ETHOS flight controllers) can command the system to slightly close doors within the ducting of the fan, which reduces the amount of air passing over the cooler plates. For a cooler cabin, the doors are opened more fully, thus more air is passed over the plates. Since air is used to push the water into the collection holes, a mixture of water (~90%) and air (~10%) comes out the other side. The water enters a small centrifuge. As the centrifuge spins, the heavier water is pulled out from the air. The water is then routed to the condensate tubing where it can go either to a big condensate tank for storage or into the Water Processor Assembly (WPA). Why do we process the urine on the ISS instead of taking up fresh water? The basic answer is cost. Six crew members produce about 9 kg (~20 lbs) of urine a day. About 70% of that, or 7.7 kg (17 lbs), is processed into water. In 2015, it cost about $25,000 to launch 0.5 kg (1 lb) of water to the ISS. This translates into approximately $425,000 of cost savings per day, or more than $155,125,000 a year in water that doesn’t have to be launched. Table 1. Types of Water in use on the ISS Type Use Potable Water Drinking water via the Russian systems for the crew containing a silver-biocide to retard microbial growth and minerals for taste. Technical Water Contains silver-biocide to retard microbial growth and is used for crew hygiene, Russian toilet flush water, and in the Russian O2 generator to produce O2. Condensate Water recovered from the atmosphere, which is processed back into potable water. Waste Urine or water that was used in the EMU (see Chapter 17). Special Fluid Water used for the internal cooling system or other uses, and which may contain chemicals to retard biological growth or chemical reactions and cannot be used for drinking. Iodinated Similar to technical water but with iodine biocide this type of water is used in the USOS water systems for toilet flush, the OGA, and, when stripped of iodine, the crew drinks it. Water Recovery and Management As on Earth, water is a precious commodity in space and, therefore, is managed carefully by the flight control team. Water is transported to the ISS by one of the various cargo vehicles. The six types of water on the ISS are listed in Table 1. One of the key functions of ETHOS is to track the various quantities of water to ensure an adequate amount of each type. This section will discuss the life cycle of water on the ISS, which is depicted in Figure 5. As mentioned in the previous section, condensate water from the USOS

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CHAPTER 19 SYSTEMS: ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEM—SUPPORTING THE HUMAN ELEMENT OF THE ISS 342 Figure 6. A full CWC (left) and the “water wall” in Node 1 (right). Note that a CWC is about 61 cm (24 in.) long with a diameter of 24 cm (18 in.) and can hold about 43 liters (12 gal) of water. Wastewater Tank Fluids Pump 2 3 4 1 5 Urine from Waste and Hygiene Compartment or Russian Water Container Recycle Filter Tank Assembly (Accumulates and stores brine for disposal) Purge Pump (Removes gases from Distillation Assembly) Coolant (Promotes condensation within Purge Pump) Purge Gas to Cabin Separator (Separates water from Purge Gases) Product water to Water Processor Assembly Distillation Assembly (Distills wastewater) Figure 7. The Urine Processor Assembly schematic. Water comes from the waste storage tank to the Advanced Recycle Filter Tank Assembly and through a distillation process before gases are removed in the purge pump.

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