ICES-2020-236

The Water Management on the Russian Segment of the International Space Station and Prospective Space Stations

Petr Andreychuk,1Sergey Romanov2 and Alexander Zeleznyakov,3 RSC Energia, Russia, Korolev.

Leonid Bobe,4Alexey Kochetkov,5 AlexanderTsygankov6 and Dmitry Arakcheev,7 NIICHIMMASH, Russia, Moscow.

Yury Sinyak8 IMBP RAN, Russia, Moscow

The paper summarizes the experience gained with the Russian Segment of the International Space Station (RS ISS) water management system during the missions ISS-1 (since November 2, 2000) through ISS-60. The performance data of the system for water recovery from humidity condensate (SRV-K) and urine feed and pretreatment (SPK-U) systems in the Russian orbital segment are presented. The key role of water recovery onboard the ISS and the need to supplement the RS water supply hardware with a system for water reclamation from urine SRV-U is shown. The prospects of regenerative water supply system development are considered.

Nomenclature “Electron-V” = oxygen generation system” CDRA = CO2 removal system CDCS = CO2 concentration system CDRS = CO2 reduction system HW = hygiene water ISS = International Space Station RS ISS = Russian segment of the ISS USOS = US orbital segment of the ISS LSS = life support systems MFR = membrane filter-separator PDV-U = urine distillation (water recovery) subsystem RMVD = rotary multistage vacuum distiller SOV = water purification facilities SPK-U = urine feed, separation and pretreatment system SRV = water regeneration system SRV-HG = hygiene water processing system SRV-K = the system for water recovery from humidity condensate SRV-U = urine reclamation system SRV-U-RS = updated urine reclamation system for RS ISS SVO = water management (water supply) system SVO-ZV = water supplies (stocks) system THP = thermoelectric heat pump WPCS = waste purification and collection system

1 Head of sector, LSS department, Russia,.141670 Korolev, Lenin street, 4a. 2 Deputy of chief designer, Russia,.141670 Korolev, Lenin street, 4a. 3 Head of science center, Russia,.141670 Korolev, Lenin street, 4a. 4 Head of laboratory SRV, Russia, 127015 Moscow, B.Novodmitrovskaya, 14. 5 Head designer, Russia, 127015 Moscow, B.Novodmitrovskaya, 14. 6 Head director, Russia, 127015 Moscow, B.Novodmitrovskaya, 14. 7 Senior research fellow, Russia, 127015 Moscow, B.Novodmitrovskaya, 14. 8 Head of department, Russia, 123007 Moscow, Khoroshevskaya street, 76a. Copyright © 2020 RSC-Energia, NIICHIMMASH, IMBP RAN I. Introduction. mplementation of promising orbital and interplanetary missions is associated with improvements in crew life I support systems (LSS). One of the LSS key components are water supply systems. The systems should provide maximum recovery of water from water-containing products of life and from bioengineering systems meeting the needs of minimum water consumption the crew. Experiences in the design and operation of “Salut”, “Mir” and the International Space Station (ISS) water supply systems as well as the use of supplies delivered made it possible to obtain the data on human water balance on the space station and the operation parameters of the recovery systems.1,2,3 In the near future, due to the energy, volume and mass restrictions, the water recovery systems will be based on physical/chemical processes. The processes selected depend on the trace contaminant content in the feed liquid and the requirements for the water recovered: a sorption/catalytic and an ion-exchange processes for humidity condensate from the cabin and greenhouse atmosphere, distillate from urine processor and water from carbon dioxide reduction; membrane filtration (ultra-filtration and reverse osmosis) with an ion-exchange post-treatment of hygiene water; the distillation method accompanied by distillate sorption/catalytic purification.4,5 The RS ISS uses water recovered from humidity condensate (SRV-K2), the system of reception and preservation of urine SPK-U, the system of water-supplies (SVO-ZV), and the water regeneration system from urine (SRV-U-RS) that is tested on RS ISS now. The paper summarizes the experience gained with the RS ISS water management system during missions ISS-1 (since November 2, 2000) through ISS-60. The performance data SRV-K and SPK-U are presented. The key role of water recovery onboard the ISS and the need to supplement the RS water supply hardware with a system for water reclamation from urine SRV-U is shown. The prospects of regenerative water supply system development are considered.

II. The System of Water Recovery from Humidity Condensate (SRV-K)

The method for the removal of dissolved impurities includes sorption/catalytic and ion-exchange processes, first in the gas-liquid and then in the liquid phase is used in this system. The processes of catalytic oxidation of hard-to- sorption low-molecular organic compounds (for instance alcohols and glycols) are the most difficult to implement. The task is a complete purification to distilled grade. Then salts, microelements and biocide are added to the potable water. This method is used in the systems SRV-K on orbital space stations “Salut”, ”Mir” and ISS (Figure 1).6,7,8,9 Figure 1 shows a diagram for SRV-K. Each process steps are described here: (#1)filtration in a gas/liquid stream; (#2) heterogeneous catalytic oxidation of organic impurities in gas/liquid stream by oxygen of carrier air at temperatures and pressure on a station; a direct-flow separation of a liquid through capillary-porous walls of pipes (#3) with suction by a membrane spring pump (#5); pumping a liquid (#6); catalytic, ion-exchange and sorption purification of a liquid in a semi-static mode (# 7); the monitoring of water quality (#8); contact injection of food salts and ions of silver (position 10); storage of liquids in containers with variable volume (# 11 and #12); recovered water heating and pasteurization in the subsystem III and supplying astronauts with hot and ambient potable water. The humidity condensate is transported from the air conditioning system to the SRV-K2M system by air flow. The liquid is purified and separated in the static separator into the membrane, #5, (Figure 1). Before filling up of the membrane (except of the equipment for preheating and distribution of water to the crew), the system is in standby mode and consumes virtually no energy. After filling the membrane (#5), the liquid is pumped out by the pump #6 for 16-18 seconds. Then, the system again switches to the standby mode. For a crew of 3 people (4.8 liters of condensate needs to be cleaned per day) such situation is repeated 27 times a day, i.e. a system work period for the receipt and purification of humidity condensate is less than 10 minutes a day. Therefore, SRV-K has a unique low energy consumption for the reception and purification of condensate – no more than 2 Wh per 1 liter of recovered water. The average daily power consumption of the system for a crew of 3 people is 30W taking into account the energy costs for heating water for drinking and cooking.

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Technical data for SRV-K type systems: Mass 140 kg (“Salut”); 104 kg (Mir); 115 kg (ISS). Specific mass consumptions, kg/L H2O: 0.12 (Mir);0.08 (ISS). Average daily energy consumptions for 1 crew member: 14 W-hour (Mir); 10 W-hour (ISS). Water recovered: 15500 L (Mir); 22265 L (ISS February 1, 2020) Figure 1. The SRV-K2M system for water recovery from humidity condensate on ISS.

The system consists of blocks that are replaced as spare parts are delivered from the ground. The specific weight (including the equipment to be replaced) for the production of 1 liter of water is 0.08 kg. The regenerated water met water quality requirements for the entire operation time. Power consumption and mass requirements of the water recovery system SRV-K (from November 2, 2000 until February 01, 2020) are presented in Table 1.

Table 1. The water recovery system SRV-K(from November 2, 2000 until February 01, 2020)

Mass of the initially installed system 115 kg Average daily power consumption for 3 person crew * for feed and recovery 0.4 W * for feed, recovery and heating 10 W/per 1 crew member

Specific energy for feed and recovery 2 W-hr/L H2O

The water recovery rate in SRV-K, % 100 Mass of the hardware replaced during the flight (ORU) * specific 0.08 kg/L H2O

3 International Conference on Environmental Systems Amount of water recovered from humidity condensate and 22265 L other water Amount of water consumed from SRV-K 34970 L

Savings in mass of water to be delivered in the absence of 26000 kg water recovering (including the mass of tanks 0.25kg/L minus mass of the replaced hardware delivery)

Thus, the process of sorption-catalytic purification of liquids such as humidity condensate is sufficiently effective and recommended for use in advanced water regeneration systems. The main objective of improving the system is to increase the resource and the corresponding reduction in the weight of the equipment. Such events are already taking place. For example, the introduction of a two-stage separation scheme using a membrane filter-separator allowed to increase the service life of the static separation unit of the system in 10 times without increasing energy costs.

III. Urine Feed and Pre-treatment (SPK-U) System.

In the system SPK-U (Figure 2)2,6,7,10,11,12 urine from the crew is sucked in the urinal (1) with an air stream by the fan (12). Pretreatment chemicals (3) providing chemical and microbiological stability of urine in storage and subsequent processing and flush water (4) are metered out by the pump (2) in a gas-liquid flow. The urine is separated from the carrier air in the rotary separator (7). The carrier air passes through the backup static separator (9) filled with a water-retentive material and vented to the atmosphere. The impurities contained in the air are removed via sorption in the filter (13). The urine with pretreatment chemicals and flush water leaves the separator and is fed to the appropriate tanks for storage or for reclamation. The urine with pretreatment chemicals can be stored without chemical and bacterial decomposition more than one year.

Urine with Air to the air cabin 1. Urinal. 2. Pretreatment chemicals and flush water 13 12 metering device.

3. Pretreatment chemicals tank. 4. Flushing water tank. 11 5,6. Tank empty/full indicators. 7. Rotary separator. 8. Valve. Air from fecal 9. Urine feed tank (EDV). receiver 10. Back-up static separator. 11. Liquid droplet carryover sensor. 12. Fan. 13. Air filter.

4 9 10

Technical data for SPK-U system: Process: feed; centrifugal separation, chemical preservation; storage. Mass: 90 kg (Mir); 75 kg (ISS). Specific mass: 0.11 (Mir); 0.06 (ISS). Average daily energy consumption: 1.7 W/man-day. Urine processed: 11100 liters (Mir);31460 liters (ISS on February 01, 2020). Figure2. Urine feed and pre-treatment system SPK-U

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Table 2.SPK-U system operation on ISS SM from November 2, 2000 through February 01, 2020

Total amount of urine with flush water and pretreatment feed 31460 L Daily amount of urine feed 1.4 L/man.day Total amount of flush water 5860 L Power consumption for urine feed 120 W Average daily power consumption for 1-persson crew 1.67 W Specific energy consumption for 1 L of urine with flush water 24 W-hr/L of urine with flush water and pretreatment and pretreatment Initially installed mass 75 kg Specific mass of replaceable hardware for 1 L urine with flush 0.056 kg/L water and pretreatment

With a crew of 3 people, an average of 18 uses of the system for diuresis are performed, the total operating time in the reception mode is 1 hour/ day. Energy consumption for reception and preservation of 1 liter of urine is 20 Wh, the average daily power consumption of the system with the crew of 3 people is 5 W. The system consists of replacement units that are replaced at expiration of its service life with a pare parts or units delivered from the Ground. Specific weight (including replaced equipment) for the reception of 1 liter of urine is 0.07 kg; for the reception of 1 liter of urine with pretreatment and flushing water specific weight is 0,056 kg. It is also necessary to pay attention to additional weight needs when using of flushing water: 0.23 kg per 1 liter of urine in the absence of a water regeneration system from urine or 0.035 kg in the presence of a water regeneration system from urine. Thus, to reduce of mass consumption, it should work out a possibility of decrease in a consumption of flushing water. Thus, the process of preservation of urine acid pretreatment with centrifugal separation of urine from the transport air is quite effective and is recommended for use in advanced water regeneration systems. The main objective of improving the system is to increase the resource and the corresponding reduction in the weight of the equipment. Such events are already taking place.

IV. The System for Water Reclamation from Urine (SRV-U-RS) Multistage vacuum distillation in a rotary multistage distiller with an additional thermoelectric heat pump is employed on the Russian segment of ISS.2,3,4,5,11,12,13 The ISS distillation subsystem schematic is presented in Figure 3.

Figure 3. The updated and modernized SRV-U-RS system for water reclamation from urine on RS ISS 5 International Conference on Environmental Systems

The key unit of the subsystem is the rotary multistage vacuum distiller (RMVD). The distiller provides urine and condensate circulation as well as multistage vacuum distillation with heat of vapor condensation recovery for water evaporation from urine. The heat of vapor condensation generated in the 1st distiller stage is used for evaporation in the 2nd stage, vapor from 2nd stage – in the 3rd stage, etc. The temperature difference is ensured owing to the pressure reduction from stage to stage. In the first stage, evaporation is affected by the heat supplied by the circulating urine from the outside source – the thermoelectric heat pump (THP). The vacuum pump VP-1 performs the primary vacuuming of the distiller and receiver, the vacuum pump VP-2 vacuums the container housings, and the vacuum pump VP-3 vacuums the distiller during distillation cycle. The static separator captures the condensate of the escaping vapors. The system works cyclically in the following mode: the vacuuming; the distillation of urine from “EDV for Urine” up to filling the “Distillate Tank” with volume of 5.1 liters, washing the urine circulation loop from the tank “EDV for Urine” into brine tank “EDV for brine” by BP pump; the distillate pumping from “Distillate Tank” to “EDV for distillate”; turn off the system until the next operation cycle. Theoretically, the condensate capacity in the “n”-stage apparatus is “n” times more than in the single-stage one with the same power consumption (actually 25-30% less). In the thermoelectric heat pump (THP) installed in the urine and condensate circulation loops the heat of condensation for urine heating is additionally recovered with the heat coefficient [email protected] water capacity of the system will be 3 – 4 l/h. Estimated energy consumptions for SRV- U-RS system would be not more than 120 W-hr/kg.H2O (recovered water). Initial mass of the system is 130 kg, energy consumption in distillation mode is 370 W. Average daily energy consumption for the crew of 3 people is 25 W, mass consumption of the unit (excluding distillate purification) is 0.08 kg/kg of produced water. As it is evident the production rate of the new system 10 times as large and the power consumption 10 times less than of the system operated on Mir space station. At the first stage of the space experiment we obtained following results. 1. It was confirmed the efficiency of the process of water reclamation from urine by vacuum distillation with a 5- stage rotary distiller and a thermal thermoelectric heat pump in the system type SRV-U-RS. The parameters of the system operation in microgravity conditions on the ISS correspond to similar parameters when operating an analog of the system during long-term autonomous tests on Earth. 2. The separation efficiency in the distiller and the required quality of the distillate were confirmed. The distillate samples delivered to Earth meet the requirements and practically do not contain salts carried away with a drop liquid. The regenerated water can be used for flushing in the ACY-SPK-UM, for consumption after post-treatment in the SRV-K2M system, and for obtaining electrolysis oxygen after post-treatment in the water purification facilities. 3. The centrifugal 5-stage vacuum distiller steadily implements the processes of thin-film evaporation, condensation and separation of the liquid from the vapor-gas medium. The heat transfer and mass transfer coefficients correspond to the calculated ones and do not depend on gravity. Thermal energy recovery in the THP is implemented in accordance with the calculation. 4. The determination of the permissible coefficient of water extraction from urine during operation of the system on the space station has not been completed. Now the water recovery coefficient that has been realized in this system, is up to the range of0.82. The coefficient of water extraction from urine, achieved during long-term tests on Earth was 0.86.

Sorption-catalytic purification of condensate is provided in the SRV-K2M system. The tests confirmed the compliance of the regenerated water quality with the requirements of the electrolysis system and the standards for drinking water on the ISS. The system is currently being tested on the RS ISS. The recovery water is consumed by the crew. Thus, the process of water regeneration from urine by vacuum distillation in a rotary distiller with heat recovery is sufficiently effective and recommended for use in advanced water recovery systems. The main objective of improving the system is to increase the resource and the corresponding reduction in the weight of the equipment and increase the water recovery factor. Such events are already taking place.

6 International Conference on Environmental Systems V. The system of water-supplies (SVO-ZV). Water supply and consumption on ISS SM from November 2, 2000 through February 01, 2020 is presented in table 3. Table 3. Water supply and consumption on ISS SM from November 2, 2000 through February 01, 2020.

Water source and specified purpose Water feed / water Part of feed water, % consumption, liters

Water recovered from humidity condensate by 21165 37 SRV-K system for drinking and food preparation The consumption of water delivered to the station 36510 63

The consumption of recovered and delivered water 57675 100

As it seen the amount of water delivered to the RS ISS is 36270 liters. This water is delivered from Earth by “Progress” cargo vehicles in the “Rodnik” tanks and stored and distributed at the station using of the water-supplies SVO-ZV system.

КВ1, КВ2– manual valves of water line; КН1, КН2 – manual valves of air line; КД1, КД2 - manual drainage valves; В1, В2, Д1, Д2, Н1, Н2 – self- locked hydroconnectors; БВ-1, БВ-2 – water tanks of Service module Rodnik system.

Figure 4. The system of water-supplies (SVO-ZV).

Two different types of tanks are used for water delivery and temporary storage: (1) the stationary irreplaceable tanks of “Rodnik” system (two tanks for one system) with a volume of 210 l each; (2) portable water tank EDV with a volume of 22 l. The design of water tanks of both types developed for microgravity conditions does not differ. Internal soft fluoroplastic bag inside the metal case is intended for water storage. Water transfer can be made by means of the water pump (transfer pump unit), or by displacement method by the excess pressure created in a cavity between a soft cover and the rigid case by the air pump (the electromechanical compressor or the manual pump). The irreplaceable spherical tank of “Rodnik” system settles down outside of tight compartments of the "Progress" vehicle or ISS Service module (2 tanks with volume of 210 l each on each “Progress” and on the Service module). One "Progress" vehicle provided delivery of 420 l of potable water in 2 tanks. EDV has a folding design for compact transportation of several tanks in cargo module of "Progress" or for storage in ISS. The EDV case has the form of the truncated cone, and soft fluoroplastic bag fastens to a metal cover and in the disassembled condition is closed by a protective casing that allows to stack empty EDVs in compact piles of covers and cases. Assembled EDV can be filled from 0 to 22 l of water at use as service tank in ISS, or for delivery of 22l of water with placing EDV in the cargo compartment of the "Progress" vehicle. The material of the soft bag (fluoroplastic film) is as much as possible inert for ionic preservatives of water 7 International Conference on Environmental Systems providing possibility of long storage of water. The guaranty period of storage of the potable water initially preserved by 0.5 mg/l of ionic silver makes not less than 1 year in EDV and not less than 3.5 years in the “Rodnik" tank. This period of water storage was determined by long-term ground tests and confirmed by analyses of water samples returned from space station.

VI. The Prospects of Regenerative Water Management Systems Development Main goals of regenerative water management systems upgrade for RS of ISS and perspective stations are: • Increase of degree of closure of the life-support regenerative complex • Increase systems and units reliability • Reduction of spare delivery cost Specifics plans of modernization for various systems are listed in Table 4. Table 4 also includes both current and planned future works.

Table 4. Regenerative water management systems modernization plans System/unit Actions Water recovery from humidity condensate system (SRV-K) Filter/reactor and multifiltration unit Upgrade of units with resource increase in 2 times. Urine feed and pre-treatment system (SPK-U) Dose pump for pretreatment The new dose pump without of flush water is being developed Rotary separator The new rotary separator with 1.5 less mass and 2 times longer service life is being developed Pretreatment tank The new pretreatment tank with two protection barriers are being developed Pretreatment quality sensor The new pretreatment quality sensor with the possibility of adjustments is being developed Pretreat tank emptying sensor The new pretreat tank emptying sensor is being developed that will allow to reduce a residual of pretreatment in the tank and its delivery needs Control panel The new control panel for updated system.is being developed Water reclamation from urine (SRV-U-RS) SRV-U-RS The using of the system into permanent operation

The total effect of the SRV-K upgrade will reduce the specific mass of the delivered spares from 0.08 to 0.05 kg/l of regenerated water. Modernization of the SPK-U will provide a saving of the mass of the delivered equipment. There will also be a reduction in crew labor costs due to the planned increase in system reliability. The design of upgraded SPK-U units (centrifugal separator and dose pump) can provide their autonomous operation, which will allow to use of the updated toilet replacement units in any place of the station where power is available in case of main toilet failure. This will significantly increase of the crew safety.

VII. Summary 1. From November 2, 2000 until February 1, 2020 the SRV-K system provided 16155 liters of water recovered from humidity condensate. It amounts to 63% of crew needs for potable water and 37% of the total demand for water onboard the station. The quality of recovered water fully complies with the specifications made for ISS SM. 2. Specific mass expendables for water recovery from humidity condensate were 0.08 kg per liter of recovered water. Savings in water mass delivery was 26000 kg.

3. From November 2, 2000 until February 1, 2020 the SPK-U system collected 31460 liters of crew urine, with its pretreatment and storage. Average daily amount of urine feed is 1.4 L/man-day. Specific mass expendables for urine feed and pretreatment were 0.056 kg per liter of urine with pretreatment and flush water.

4. Current plans of RS regenerative water management systems modernization should result in increase of closure degree of the life-support regenerative complex, increase of systems reliability and reduction of spare delivery cost.

5. The SRV-U-RS system is incorporated and tested on the RS ISS. Introduction of this system into regular operation will reduce the water delivery needs in five times.

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