49th International Conference on Environmental Systems ICES-2019-152 7-11 July 2019, Boston, Massachusetts
Water Supply of Long-term Space Flights on the Basis of Physical-Chemical Processes for Water Regeneration
Petr Andreychuk,1 Sergey Romanov 2 and Alexander Zeleznyakov, 3 RSC Energia, Russia, Korolev.
Leonid Bobe,4 Alexey Kochetkov,5 Alexander Tsygankov 6 and Dmitry Arakcheev,7 NIICHIMMASH, Russia, Moscow .
Yury Sinyak 8 IMBP RAN, Russia, Moscow
Realization of perspective orbital and interplanetary missions is associated with improvements in crew life support systems (LSS). One of the LSS key components is water supply systems. Due to energy, space and mass limitations physical/chemical processes would be used in water recovery systems of space stations in the near future. Bioengineering processes and food production are future problems that would be accomplished on planetary bases. The paper reviews some problems of water recovery management, systems and processes of water recovery for long-term space flights.
Nomenclature ISS = International Space Station; RS ISS = Russian segment of the ISS; USOS = US orbital segment of the ISS; LSS = life support systems; SVO = water management (water supply) system; SVO-ZV = water supplies (stocks) system; SRV = water regeneration system; SRV-K = the system for water recovery from humidity condensate; SRV-HG = hygiene water processing system; SPK-U = urine feed, separation and pretreatment system; SRV-U = urine reclamation system; SRV-U-RS = updated urine reclamation system for RS ISS; SOV = water purification facilities; WPCS = waste purification and collection system; “Electron-V” = oxygen generation system”; CDRA = CO 2 removal system; CDCS = CO 2 concentration system; CDRS = CO 2 reduction system; HW = hygiene water; PDV-U = urine distillation (water recovery) subsystem; RMVD = rotary multistage vacuum distiller; MFR = membrane filter-separator; THP = thermoelectric heat pump.
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 © 2019 RSC-Energia, NIICHIMMASH, IMBP RAN I. Introduction. hysical-chemical processes of water and atmosphere recovery will be used on the orbital space station in the P near future due to the energy, volume and mass restrictions. Biological processes are supposed to be used on planetary stations for a water and atmosphere recovery and food production also. At the present the structure of physical-chemical regenerative complex has been formed for the space station crew life-support. The regeneration systems need to provide the maximum recovery of water and oxygen from liquid wastes with minimal use of reserves for serving of the crew needs. The following main methods of water regeneration were formed based on the research and development works: - sorption-catalytic method for humidity condensate from living quarters and greenhouse, for distillate from urine processor, for water from the Sabatier reactor and for the condensate of the vapors formed during the waste drying; - distillation method for water reclamation from urine; - reverse osmosis with pre filtration and subsequent sorption and the bacterial purification for the regenerated hygienic water. Small-sized equipment working in space flight conditions is developed to implement these methods. Self-sufficiency of the life-support complex is determined by the coefficient of water recovery in the case where the oxygen is produced from reclaimed water and food is supplied from stocks. The recovery rate achieved on the space stations were: “Salyut” - 38%; “Mir” - 72%; Russian segment of ISS (in present) – 38%; Russian segment of ISS (in the future) – 88%; space station with a full range of regenerative life support systems – more than 94%. The minimization of mass of the LSS complex is provided with its maximum self-sufficiency and maximum efficiency of the systems. The report is based on the "Mir" and ISS operation data of water balance for a different variants of LSS complex design and technology, energy-and-mass characteristics of modern and perspective water regeneration systems and includes recommendations for LSS regenerative complex of future space stations.
II. The structure of the physic-chemical regenerative LSS complex for a space station crew. Structure chart of space station regenerative life support system complex (LSS) is presented in Figure I (systems with water are marked in blue). The LSS structure follows out of the chart. The LSS complex includes the systems of water recovery and atmosphere revitalization and the supplies of water, atmosphere and food [1,2,3,4,5 ].
O2 and N 2 DELIVERED SUPPLIES SUPPLIES Water Water WATER SUPPLIES Water SVO-ZV FOOD SUPPLIES Food N2 O2 Hardware HYGIENE WATER Hygiene water TRACE CONTAMINANT RECOVERY SYSTEM CONTROL SYSTEM Air (SRV-HG) «BMP» Purified air CREW PRESSURIZED Purified water CO 2 Gas MODULE Water contaminants Air Potable water CO2 CO 2 REMOVAL HUMIDITY CONDENSATE ASSEMBLY RECOVERY SYSTEM CONCENTRATION Air Condensate SYSTEM (CDCS) «VOZDUKH» Urine (SRV-K) URINE COLLECTION CO 2 AND PRETREATMENT Water Water SYSTEM Water CO 2 OXYGEN GENERATION Solid waste (SPK-U) REDUCTION O2 URINE REGENERATION Condensate SYSTEM SYSTEM Water Urine SYSTEM (CDRS) «ELECTRON-V» (SRV-U) Gas WASTE PROCESSING AND COLLECTION H2 WATER (WPCS) PURIFICATION CH 4 Brine FACILITIES Water (SOV) GREEN HOUSE
Water Water
Figure 1. Structure chart of space station regenerative life support physic-chemical system complex
2 International Conference on Environmental Systems The sources of water aboard the space station are human products of life: sweat and breath moisture are collected in an air-conditioning system i.e. humidity condensate; urine; carbon dioxide; plant evaporated moisture; hygiene water and as well as water produced by engineering systems, for example, by fuel sells of an electrochemical generator. The vapor released by the crew and condensed in the air conditioning system is purified to drinking conditions in the water regeneration system from the humidity condensate SRV-K. In the same system it is supposed to purify the condensate of water vapor (transpiration moisture) released by plants in the vitamin greenhouse. The urine emitted by a cosmonauts enters into the system of reception and preservation of urine SPK-U where it is separated from the air transporting it. Urine is preserved by a liquid acid pretreatment that prevents its chemical and bacteriological decomposition. Mixture of pretreated urine and water for flushing enters into the system of regeneration of water from urine SRV-U. Up to 90% of water is extracted from urine in the SRV-U system based on the distillation method. The remaining salt concentrate (brine) is stored or further dried to extract another 5% of water. Brine, feces, inedible green mass of plants, dirty wipes, towels and other water-containing waste can be dried in the waste collection system WPCS. Water extracted from urine can be used for oxygen production by electrolysis. Excess on balance water enters the system SRV-K, refined and saturated with food salts, microelements and ionic silver to the condition of drinking water. Water from the carbon dioxide reduction system and water from supplies can also be used for electrolysis and consumption via SRV-K system. All the water for electrolysis passes through an additional treatment of salts in the water purification facilities. Sanitary and hygienic water is formed during washing, hand washing, body washing (in the sauna and special shower), and other sanitary procedures. Closed circuit cleaning sanitary and hygienic water is organized in the regeneration system of sanitary-hygienic water SRV-HG. The water supply system of the space station also includes the system of water reserves SVO-ZV, replenished with water supplies from the Earth. The system stores specially purified Moscow tap water, preserved with ionic silver. The shelf life of water is several years. The following principle follows from the structure of the complex of life support systems LSS: if oxygen is obtained by electrolysis of water, the degree of closure of the LSS complex (coefficient of return of water and oxygen for consumption) is determined by the water balance [1,2,4]. This principle is used in further analysis.
III. Water balance Technical water balance for one cosmonaut per day for the life support systems complexes (LSS) currently being implemented or under development is shown in Table 1 based on the analysis of water consumption at the Mir and ISS space stations [4, 5]. The table takes into account the coefficients of water recovery and loss of water in the regeneration systems. The balance depends on the composition of the LSS complex and water recovery factors in the regeneration systems. The right side of the table shows the sources of water regeneration, including the system of carbon dioxide reduction and waste drying. The values of the water obtained reflect the water recovery factors in the regeneration systems. The water return ratio is defined as the ratio of regenerated water to total consumption. It should be emphasized that the balance is made for the case of receipt of 0.5 l/person/day of water with food. The balance currently being realized in the Russian segment of the ISS is given in column 1 of Table 1 on water intake with the water return coefficient of 38%, where there is only a water regeneration system from humidity condensate. The water return coefficient will be 72% and the mass of water consumed from the reserves will decrease by more than 3 times with the introduction in the LSS complex a system of water regeneration from urine (column 2). Such a complex of regeneration systems was implemented at the Mir station and is expected to be implemented at the Russian segment of the ISS. The coefficient of the return water increases to 83% with the introduction in the LSS complex a carbon dioxide reduction system used of the Sabatier method (column 3). In the case of extraction of water from salt concentrate (brine) in the SRV-U system and drying of feces (column 4) the water balance practically converges. However it should be emphasized that 0.5 l / person a day of water comes from food, so the real water return rate is only 88%. A further increase in the water return coefficient can be achieved by a more complete conversion of carbon dioxide, for example by the Bosch method.
3 International Conference on Environmental Systems Table 1. The technical water balance per one cosmonaut per day Water consumption, liter/man-day Water providing, liter/man-day 1 2 3 4 Drinking and food 2.2 Humidity condensate preparation 1.5+0.2×0.5* 1.6 1.6 1.6 1.6 Water in food ration 0.5 Water in food ration 0.5 0.5 0.5 0.5 Personal hygiene 0.2 Water from urine Water for toilet flushing 0.3 (1.3+0.3)×0.9** 1.44 1.44 Water for electrolysis (1.3+0.3)×0.95** 1.52 production of oxygen 1.0 Water from CO 2 reduction system via Sabatier 0.45 0.45 method Water from feces 0.13 0.15×0.9**=0.13 Delivered water (water of 2.1 0.66 0.21 0.0 supplies) Total 4.2 4.2 4.2 4.2 4.2 Water return rate (recovery coefficient), % 38 72 83 88 * taking into account evaporation of 50% personal hygiene water; ** water recovery coefficient.
The circuit for cleaning of contaminated sanitary and hygienic and household water shown in Figure 1 is organized in more complete life-support system complex containing of means for face and body wash and laundry. The return of water with the introduction of sanitary equipment depends on the water loss and the recovery coefficient of water regeneration in the SRV-HG system. With the introduction of a vitamin greenhouse (acreage of 0.1m2 for one crewmember) the comfort of LSS increases dramatically but the water consumption and imbalance increase also. As you can see, the water return coefficient is larger the amount of regenerated water and the greater the water recovery coefficient in the regeneration systems. For example, in the system of water regeneration from the urine on Mir station the coefficient of water extraction from urine was 0.8, respectively, the coefficient of water return was 68.5% instead of 72% with the coefficient of water extraction 0.9 . If the processing of carbon dioxide is carried out to a greater depth and if extracted water from feces and drying of various water containing waste is provided, it is possible to further reduce the consumption of water from the reserves while reducing the water shortage to a minimum. It should be noted that the considered balance does not take into account water losses and water consumption for external activities. Let us further trace the reliability of the technical water balance given in Table 1 based on the results of the operation of Mir and ISS orbital space stations. Until November 2008, the regeneration water and the collection and preservation of urine on the ISS were carried out by the system of the SRV-K2M and SPK-UM on Service module of the ISS Russian segment. Receipt and water consumption on ISS per one crewmember is given in Table 2 from the beginning of manned flight 11/02/00 to 10/22/08. It should be noted here that the water consumption for electrolysis production of oxygen (0.65 l/person per day instead of 1 l/person per day) is lower than the normative one due to the delivery of oxygen with the atmosphere of space vehicles docking to the station. Less than the estimated amount of atmospheric moisture condensate was observed due to the lack of means for drying of wipes and towels. The average daily urine producing for this period was 1.33 l/person/day. From the materials of Table 2 it follows that the technical water balance for one crewmember per day, given in Table 1, is confirmed by the ISS flight data and can be used in the calculation of prospective water supply systems.
4 International Conference on Environmental Systems Table 2. Water inflow and consumption for one cosmonaut per day in the period from November 02, 2000 till October 22, 2008 (2913 days, 8028 man-days) Water consumption, liter/man-day Water providing, liter/man-day
Recovered in SRV-K2M from Drinking 2.15 humidity condensate 1.48 Personal hygiene and watering of 0.10 plants Water in food 0.50 Water in food 0.50
Water for toilet flushing 0.30 From supplies
- for drinking 0.67
- for personal hygiene and watering of 0.10 plants - water for toilet flushing 0.30
Water for electrolysis production of - for electrolysis production of 0.65 0.65 oxygen oxygen Total 3.70 Total 3.70
IV. Water recovery systems of orbital space stations “Mir” and ISS In the water supply system of the "Mir" orbital space station were used water recovery system from humidity condensate SRV-K, the system of reception and preservation of urine SPK-U, the system of water regeneration from urine SRV-U, the system of water reserves SVO-ZV and it was briefly tested the system of regeneration of sanitary hygienic water SRV-SG. In the Russian segment of the ISS are using the system for water recovery from humidity condensate SRV-K2M, the system of reception and preservation of urine SPK-UM, the system of water-supplies SVO-ZV and it is planned to introduce a water regeneration system from urine SRV-U-RS.
A. The system of water recovery from humidity condensate SRV-K (Fig. 2) 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) play a determining role. The task is a complete purification to distilled grade. Then salts, microelements and biocide are added for providing the potable water. This method is used in the systems SRV-K on orbital space stations “Salut”, ”Mir” and ISS (Figure 2) [8,9,10,11,12 ]. Used processes are as follows: filtration in a gas/liquid stream (position 1); heterogeneous catalytic oxidation of organic impurities in gas/liquid stream by oxygen of carrier air at temperatures and pressure on a station (position 2); a direct-flow separation of a liquid through capillary-porous walls of pipes (position 3) with suction by a membrane spring pump (position 5); pumping a liquid (position 6); catalytic, ion-exchange and sorption purification of a liquid in a semi-static mode (position 7); the monitoring of water quality (position 8); contact injection of food salts and ions of silver (position 10); storage of liquids in containers with variable volume (positions 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 container 5. Before fill up of the membrane container the system (except of the equipment for preheating and distribution of water to the crew) is in standby mode and consumes virtually no energy. After filling the membrane container 5, the liquid is pumped out by the pump 6 for 16-18 seconds, and 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, ie. a system work period for the receipt and purification of humidity condensate is less than 10 minutes a day. Therefore, the system type SRV-K has a unique low energy consumption for the reception and purification of condensate – no more than 2 Wh per 1 liter of water. The average daily power consumption of the system for a crew of 3 people is 30 W taking into account the energy costs for heating water for drinking and cooking.
5 International Conference on Environmental Systems Air 4 9
3 13
5 6 8 11 14 2 15 16 13 7 10 1 12 I II III
Ambient Hot 17 water water I. Filtration, preliminary purification and separation subsystem.
Air-condensate II. Purification and mineralizing subsystem. mixture III. Potable water storage, heating and dispensing subsystem. CWC Figure 2. The SRV-K2M system for water recovery from humidity condensate on ISS. 1. Gas/liquid mixture filter. 2. Filter/reactor. 3. Separator. 4. Separator life sensor. 5. Condensate receiver. 6. Condensate pump. 7. Multifiltration unit. 8. Water quality sensor. 9. Valve unit. 10. Mineralizing. 11. Service water tank. 12. Potable water tank. 13. Tank empty/full indicator. 14. Recovered water feed pump. 15. Heat exchanger. 16. Heater. 17. Condensate feed unit. CWC – tank for condensate collection from USOS. 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); 21100 L (ISS November 30, 2018).
The system consists of blocks that are replaced as the resource on the blocks of spare parts or 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. For all the time of operation the quality of regenerated water met the requirements. 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 by 10 times without increasing energy costs.
B. Urine feed and pre-treatment (SPK-U system, Fig. 3) In the system SPK-U (Figure 3) [2,8,9,10,11,12 ] 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, impurities being removed via sorption in the filter (13) and vented to the atmosphere. 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.
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Figure 3. Urine feed and pre-treatment system SPK-U 1.Urinal. 2. Pretreatment chemicals and flush water metering device. 3. Pretreatment chemicals tank. 4. Flushing water tank. 5,6. Tank empty/full indicator. 7. Rotary separator. 8. Valve. 9. Urine feed tank (EDV). 10. Back-up static separator. 11. Liquid droplet carryover sensor. 12. Fan. 13. Air filter.
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); 0.08 (ISS). Average daily energy consumption: 2 W/man-day. Urine processed: 11100 liters (Mir); 23660 liters (ISS on 30 th November 2018).
With a crew of 3 people, an average of 18 approaches to the system are carried out, the total operating time in the reception mode is about 1 hour per 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 spare parts or units delivered from the Ground. Specific weight (including replaced equipment) for the reception 1 liter of urine is 0.07 kg; for the reception 1 liter of urine with pretreatment and flushing water specific weight is 0,057 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. It is necessary to work 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.
C. The system for water reclamation from urine on “Mir” space station (SRV-U system, Fig. 4) The method of water vapor extraction from the solution via distillation followed by sorption/catalytic purification of distillate was used in order to reclaim water from urine containing a considerable quantity of dissolved salts. The method of low-temperature membrane distillation was used on space station “Mir” as the most simple and reliable in microgravity [2,13,14,15,16 ]. This method offers the process temperature required (not higher than 45°C) as a result of liquid evaporation from the membrane surface into the vapor-gas medium. In the SRV-U system was used the process of water reclamation from urine via membrane distillation with a vapor/air cycle at atmospheric pressure and moderate temperature. A schematic diagram of the distillation subsystem is given in Figure 4. The subsystem incorporates liquid and air circulation loops. The centrifugal pump (1) circulates the urine through the heater (2) and the evaporator (3).
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Figure 4. System for water reclamation from urine SRV-U of “Mir” space station (PDV-U – urine distillation subsystem) 1 – pump; 2 – heater; 3 – evaporator; 4 – condenser; 5 – membrane tank; 6 – condensate pump 7 – separator; 8 – air filter; 9 – blower; 10 – solenoid valve; 11 - brine tank; 12 – pressure sensor.
Technical data for SRV-U system: Process: membrane distillation with vapor/air cycle and distillate’ sorption/catalytic purification. Mass: 70 kg (Mir). Specific mass: 0.23 kg/liter H 2O. Average daily energy consumption for the crew of 3 people: 266 W. Reclaimed water processed: 6000 liters.
The heater supplies the heat required for evaporation and the evaporator effects water evaporation from the membrane surface to the circulating air stream. The liquid temperature does not exceed 45°C. The liquid/ gas phases are separated by the use of a hydrophilic/ hydrophobic membrane. Concentrated brine is displaced to the tank (11) on final stage of distillation. Vapor from the circulating air is condensed in the condenser (4) followed by condensate separation in the separator with capillary/ porous elements (7). The condensate is drawn off by the springing membrane tank (5) and is pumped by pump (6) for additional purification. Condensate (distillate) quality is monitored by electric conductivity. Distillate is purified in the same way as in the system SRV-K by the sorption/ catalytic method. The salts are not added to recovered water as it is intended for oxygen generation by water electrolysis. The system is modularized with replacement units in case of life run-out or modernization. Basically the units are serviceable allowing for item replacement. The system is designed for automatic operation with a control panel providing necessary communication with the space station board. The SRV-U system was used on the space station start from module “Kvant-2” docking up to completing manned flight. The system performance data are given in Figure 4. More than 6000 liters of water for oxygen generation by electrolysis was produced on “Mir" space station. The system was operated in the distillation mode when the power supply was available. The subsystem for urine feed, separation and pretreatment was used for the whole period of module “Kvant-2” flight taking in about 11000 liters of urine. The advantages of the system are the operation at atmospheric pressure and gas/ liquid phase separation by the polymeric membrane. The disadvantages are relatively high power consumption and low output due to the use of a vapor/ air cycle.
8 International Conference on Environmental Systems D. The modernized system for water reclamation from urine for ISS (SRV-U-RS system, Fig. 5) The more advanced and less power-intensive method of multistage vacuum distillation in a rotary multistage distiller with an additional thermoelectric heat pump will be employed on the Russian segment of International Space Station. The distillation subsystem schematic is presented in Figure 5 [2,8,9,10,11,12]. 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 effected by the heat supplied by the circulating urine from the outside source – the thermoelectric heat pump (THP) or vapor compressor. Theoretically, the quantity of the condensate produced in the “n”-stage apparatus is “n” times more that of 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 loop the heat of condensation for urine heating is additionally recovered with the heat coefficient k ≅2.5. The 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 H 2O.
Figure 5. The updated and modernized SRV-U-RS system for water reclamation from urine on RS ISS 1. Rotary multistage vacuum distiller. 2. Thermoelectric heat pump THP. 3. Cool exchanger. 4. Control unit. 5. Solenoid valve. 6. Hydrovalve HV. 7. Pump. 8, 9. Distillate tanks. 10. Urine tank. 11. Brine tank.12. Coolant from termal control system. 13. Vacuum line. 14. Vacuum unit. 15. Vacuum pump. 16. To cabin.
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 that of the system operated on Mir space station. 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. 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.
9 International Conference on Environmental Systems V. Results of operation of water regeneration systems at space stations Mir and ISS The results of operation of the systems for water recovery from humidity condensate and from urine and system of the reception and preservation of urine on orbital space stations "Mir" and ISS (in 18 years of flight) are shown in Table 3. The table shows the decisive contribution of water regeneration systems to the water supply of the space station crew and the reduction in the mass of deliveries. In total, 37050 liters of drinking water were consumed in the Russian segment of the ISS, i.e. 57% of the water needs for drinking and cooking were provided by the regeneration of water from the condensate of atmospheric moisture. On November 30, 2018 the total water consumption in the RS ISS was 54744 liters of water. Regeneration of water from the humidity condensate provided a return to the cycle of consumption of 38.5% of water.
Table 3. Results of operation of water regeneration systems at MIR and ISS. System RS ISS Space station “Mir” 11/02/2000 – 11/30/2018 Results of operation SRV-K SPK-U SRV-U SRVK-2M SPK-UM Initially installed mass, kg 104 80 70 115 75 Specific mass (including replacement 0.14 0.11 0.23 0.08 0.07 equipment) for production of 1 kg of water- kg / kg of water and 1 kg of urine-kg / kg of urine The recovery rate of water in SRV-K and in 100 100 80 100 100 SRV-U and separation in the SPK-U, % Average power consumption at the crew of 3 40 5 266 30 5 people, W (including water heating for drinking and cooking in the SRV-K system)
Specific energy consumption for production 2 30 1200 2 20 of 1 kg of water in SRV-K and SRV-U and 1 kg of urine in SPK-U, Wh/kg The total sum of the regenerated water (urine 15500 11100 6000 21100 23660 in the SPK-U), l Saving the mass of water deliveries, taking 16500 --- 6150 24700 into account the weight of containers (1.25 kg / l. water), kg
VI. Evaluation of the effectiveness of operation of systems, water reclamation, and SVO complex. The equivalent mass (taking into account energy costs) of the SVO complex ( Mequ in kg) is calculated according to the following relations [7]: Mequ=M 1+M 2+M 3 +M 4 +M 5 (1). Here: M1- initially installed system mass in kg; M2 - mass of spare parts in kg: M2=0.1M1 ×τ (2), where τ is the operating time in years; M3- equivalent weight of power supply and thermal control systems in kg: M3=Naverage daily×K3 (3), where N is the power consumption, W, K3 is the mass coefficient for power supply and thermal control systems, K3 = 1 kg / W; M4-variable weight in kg, reflecting the cost of mass elements of the system in the operating time of the target product: M4=V Н2О×K 4 (4), where VН2О is the total mass of the target product during operation, kg(l),
10 International Conference on Environmental Systems K4-variable mass coefficient, of the product (water), kg / kg(l), M5-weight of water reserves in kg including delivery tanks: M5=V 5×1.25 (5), where V5 is the total amount of unbalance of water during operation in liters (delivered water according to Table 1), 1.25 is the coefficient taking into account the mass of water delivery tanks. It is assumed that the amount of heat released is equivalent to the amount of electrical energy. According to the literature data, the equivalent weight of energy WEN is 0.4 kg/W; equivalent weight of termo- control system WTCS is 0.6 kg/W; total is 1.0 kg / W. As can be seen from further assessments the energy consumption of water regeneration systems is relatively small and does not pose a problem in the design. A distinctive feature of the proposed method of calculating the equivalent mass is the accounting for the mass of water reserves (or delivered water) M5 determined by the unbalance of the water for the considered version of the SVO complex. The variable mass coefficient K4 reflects the mass of the system components consumed, such as sorbents, and equipment with limited resources to be replaced during operation, and is an important characteristic of water recovery systems. K4 for a complex of water supply systems is determined by the values of K4 of individual systems and the additivity of the contribution of systems to the production of the target product – regenerated water. Below are the results of the calculated estimation of the equivalent mass of the water supply systems SVO complex of the Russian segment of the ISS for the following variants of the water supply: 1. The SRV-K2M +SPK-UM+SOV+SVO-ZV (col.1 Table 1). 2. SRV-К2М +SPK-UM+SRV-U-RS+SOV+SVO-ZV (col.2 Table 1). 3. SRV-К2М +SPK-UM+SRV-U-RS+SOV (CDRS)+SVO-ZV (col.3 Table 1). 4. SRV-К2М +SPK-UM+SRV-U-RS+SOV (CDRS)+WPCS+SVO-ZV (col.4 Table 1). The mass estimate of the ISS water supply system during the flight of 3 cosmonauts during the year is presented in Table 4.
Table 4. Mass estimate of the ISS water supply system during the flight of 3 cosmonauts during the year.
М*1,2 M3, kg M5**, K4 current, kg/l K4=0.02, kg/l kg (W) kg M4, kg Mequ , kg M4, kg Mequ , kg 1 300 35 2875 265 3475 70 3275
2 420 60 900 390 1770 100 1480
3 440 60 290 445 1300 125 980 +65***
4 460+ 100 0 465 1140 130 805 65***+ 50****
* hardware SVO included with a mass of 90 kg. ** normative water supply is not taken into account. *** mass of CDRS **** mass of WPCS The calculations are estimates but allow us to make the following observations: For low-energy water supply systems of the Russian segment of the ISS, the greatest impact on the mass reduction of the SVO complex is its degree of closure, determined by the composition of the complex systems and the water extraction coefficients of individual systems, and the resource characteristics of the systems that determine the variable mass coefficient K4.
VII. Summary 1. Due to the current and foreseeable future energy, volume and mass limitations space stations will use physical and chemical processes of water and atmosphere regeneration. 2. The most probable composition of the complex of regeneration life support systems and the resulting structure of the regeneration water supply of the space station are presented in Figure 1.
11 International Conference on Environmental Systems 3. From the structure of the complex of LSS follows the following principle: if oxygen is obtained by electrolysis of water, the degree of closure of the complex of life support systems LSS (coefficient of return of water and oxygen for consumption) is determined by the water balance. 4. Based on the analysis of water consumption at the Mir and ISS space stations the technical water balance per cosmonaut per day is calculated for the life support systems currently being implemented or under development (Table 1), taking into account the water recovery factors and water losses in the regeneration systems. The balance depends on the composition of the SVO systems complex and water recovery factors in the regeneration systems. 5. On the basis of the operation data of water supply systems of space stations "Mir" and the ISS a method for estimating the mass of the complex of regenerative water supply systems is proposed. A distinctive feature of the proposed method of calculating the equivalent mass is the accounting for the mass of water reserves (or delivered water) M 5, determined by the unbalance of the water for the considered version of the SVO systems complex. 6. Calculations have shown that for low-energy water supply systems of the Russian segment of the ISS, the greatest impact on the reduction in the mass of the SVO complex is its degree of closure determined by the composition of the systems complex and the water extraction coefficients of individual systems and the resource characteristics of the systems that determine the variable mass coefficient K4.
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