by Prof. Leonid BOBE, Dr. Sc. (Tech.), head of the Water Recovery Space Systems Laboratory of the Research and Design Institute of Chemical Engineering (NIICHIMMASH); Lev GAVRILOV, Cand. Sc. (Tech.), Deputy Chief Designer of air regeneration space systems at the same institute; Alexei KOCHETKOV, Chief Designer of life support systems at the same institute; Alexander ZHELEZNYAKOV, head of the space life support division of the Korolev RSC "Energia"

Longtime orbital and, in prospect, interplanetary space missions largely depend on upgraded life support systems designed to cater to the needs of crews in water and oxygen at minimum resupply. Achieving a maximum level of air and water recovery within an orbiter's limited space posed hard science and engineering problems. Our scientists, engineers and designers have coped with their job by building the life support systems (LSS) for the Salyut-4, -6, -7 and the "MIR" orbital space stations and the International Space Station (ISS) now in orbit.

An astronaut's water and oxygen balance.

The orbiting of the world's first artificial satellite of the earth (SPUTNIK) in USSR (Russia) on October 4, 1957, and Yuri Gagarin's pioneering flight on April 12, 1961, ushered in a space exploration era. Great headway has been made since then in space engineering, flight duration and in the makeup of crews. There are higher demands on life support systems as well. An astronaut consumes as much as 4 to 12 tons of water, oxygen and food a year. Putting this amount of supplies into orbit is costly (about 22,000 US dollars per kg). Hence there should be an ecological cycle of water and oxygen turnover, and air regeneration systems on board. Under natural conditions these processes occur but slowly and are not limited all to much in volume. The situation is quite different in space conditions. High-intensity, low-energy consumption as well as waste-free processes controlled, both physically and chemically in microgravity conditions, are needed within the narrow confines of a "space home".

In 1962 and 1963 this job was entrusted to such bodies as the Special Design Office-1 (RSC "Energia" today), the Institute of Space Biology and Medicine (RAS Institute of Medical and Biological Problems, IMBP today) and the Ail-Union Research and Design Institute of Chemical Engineering (NIICHIM-MASH JSC today). Taking part were leading research bodies, R&D companies as well as colleges and universities.

In 1967 and 1968 IMBP tested a unique complex of physicochemical recovery systems fitted with equipment designed and made at NIICHIMMASH). Nikolai Samsonov, Chief Designer of life-support regeneration systems (in 1965 to 2007), was in charge of this work. Three testers (Andrei Bozhko, Hermann Manovtsev and Boris Ulybishev---Tr.) were cooped for a year, from November 1967 to November 1968, within a hermetic spaceship imitation module equipped with an air regeneration system; they ingested water and oxygen reclaimed from their waste products.

In such systems water and oxygen are recovered from the water vapor and carbon dioxide exhaled by crew members, from their body and lungs perspiration, urine and from their solid wastes. This is done by cleaning the humidity condensate, by distilling the water from urine and drying up the solid excreta. Oxygen is obtained through regenerated water electroly-

sis. The carbon dioxide (CO₂) exhaled by crew members is fed into the air regeneration system; it is catalytically decomposed into methane and water (by the Sabatier method*) or into water and oxygen (by the Bosch method**) by reacting with hydrogen formed through electrolyzing generation of oxygen. An extra amount of water obtained in the process is used for electrolyzing generation of oxygen. The regeneration system purified the air from carbon dioxide and impurities coming from man, furnishings and technical equipment. The dirty water drained after showers and laundry washing is cleansed, and then it is fed into a closed system for reuse. The greenhouse water vapor is condensed, purified and used for watering of plants. The recovered water should be safe to man (the medicobiological aspects of water regeneration were the responsibility of Dr. Yuri Sinyak of IMBP).

* Named so after the French chemist Paul Sabatier, it is a hydrogen/ carbon dioxide reaction proceeding at high temperature and pressure in the presence of a catalyst and producing methane and water.---Ed.

** Named so after Karl Bosch (a German chemist, Nobel Prize in chemistry, 1931), it is a chemical process whereby carbon dioxide, reacting with molecular hydrogen in the presence of a catalyst, produces water and carbon.---Ed.

The more effective onboard regeneration processes, the less need for cargoes brought in. In theory the closed cycle efficiency can be brought up to 95 percent and even close to 100 percent. In practice this factor depends on the effectiveness of life support systems, the degree of recovery of end products, and on air and water losses on board.

Appropriate onboard equipment was designed after thorough research and ground tests. At first this outfit included systems of water regeneration from humidity condensate (SWR-C) at Salyut orbital stations. In January of 1975 the crew of Salyut-4 (1974-1977), Alexei Gubarev and Georgi Grechko, consumed the potable water recovered from the condensate. It was the world's first experiment of this kind. Similar units were aboard Salyut-6 (1977-1981) for 570 days, and at Salyut-7 (1982-1986), foras long as 743 days. The SRV-K unit was supplying the crews with water--hot water, too--for consumption and sanitation and hygiene needs.

Yet another "first": the orbital station Mir (1986-2000) was equipped with a setup of physical and chemical systems of air and water regeneration that contin-

ued in operation at the station for a long time (this complex, however, did not provide for CO₂ concentration and utilization). H₂O recovery from air humidity condensate, urine and hygiene water was realized by SRV-K, SRV-U and SRV-HW setups respectively; Electron-V made use of the electrolysis method to obtain oxygen from urine-regenerated water. Another two systems revitalized the air by cleaning it of micro-impurities and of surplus carbon dioxide. Those were high-performance setups: in the 13.5 years that Mir had been in orbit as much as 15,500 liters of water was recovered from air condensate and 6,000 liters from urine; 5,250 kg of oxygen was obtained by electrolysis. As to water supplies, they were brought in by Progress cargo ships (for greater detail, see articles of N. Samsonov, L. Bobe, Yu. Sinyak, S. Romanov and other authors published in the Proceedings of RAS, Energy, No. 1, 2009 (Russian version, Izvestia RAN. Energetika).

Now about water regeneration methods in orbital flights. There are several, and it depends on the concentration of impurities in the source liquid and on recovered water standards which method in particular should be chosen. For lowly contaminated liquids (e.g., air humidity condensate containing up to 1 g/l of dissolved admixtures and with possible presence of as many as 350 organic and inorganic impurities), all-out purification is effected, with the use of sorption-catalytic and ion exchange processes first in the liquid gaseous and then in the liquid phase. Salts and microelements are added to the recovered potable water; it is disinfected with ion silver and pasteurized. For mid-level contaminated liquids, e.g., hygiene water containing organic and inorganic impurities and detergent (at a concentration of 2 to 3 g/1), filtration and membrane processes are best. And last, for much contaminated liquids like urine (having as much as 5 percent of dissolved salts, NaCl and urea, and more than 120 dissolved organic and inorganic admixtures) yet another reclamation method is used, and this is distillation of recovered water followed by sorption-catalytic purification of the distillate.

Oxygen for onboard air regeneration is reclaimed via electrolysis of an alkaline water solution with the use of urine-recovered water. The air is cleared through the sorption-catalytic method on sorbents.

The above techniques are quite productive, energy-saving, ecofriendly and reliable. Under zero gravity conditions special devices should be used, in which gravitational forces are changed to those of dynamic inertia and intermolecular surface tension. This is necessary to keep liquid gas setups working and to sustain the processes of gas media separation, condensation, evaporation, boiling, and so on. The onboard facilities capable of withstanding impact and vibratory overloads are padded with special synthesized vibration-strength ion-exchange resins, carbon sorbents and catalysts.

These technologies apply to water and oxygen regeneration only. As to victuals, the crews get them from storage supplies. Well, is it possible to reproduce food in sufficient amounts in flight? Hardly. As much as 30 m² of cultivated area, 300 liters of water and 30 kW power capacity will be needed for one crew member alone. So a very large generator will have to be built. Thus at this stage the above proposition is too far off. That is why due to mass, power and space constraints life support provision will have to be based on low-energy, waste-free physicochemical methods of water, oxygen and air recovery, all that predicated on chemical technologies. Biological methods of food recovery will become possible only in the future, most likely they will be realized on interplanetary bases.

Now concerning the life support complex of the Russian section of the International Space Station (ISS). By and large, it is similar to one that was in operation aboard Mir. Upgraded systems of water regeneration from air humidity are operating in the service module there, and so is urine feed and pretreatment unit (at work in the American segment of the station, too), along with the electrolysis setups providing of oxygen, and those of microimpurities and carbon dioxide purification.

The water recovery index depends on the makeup of onboard life support systems and the regeneration performance of each system in particular. A water recovery maximum (72 percent) under in-flight conditions was attained at the Mir orbital station.

In the Russian segment of ISS, where water is reclaimed from air humidity condensate, the recovery index is equal to 38 percent. The water recovery index is to be upped to 72 percent and 83 percent with the commissioning of a new module equipped with a setup recovering water from urine (SRV-U) and that of carbon dioxide reduction system SPUG by the Sabatier method. The water recovery index will be up to 95-98 percent after a hygiene sewage regeneration unit and a greenhouse have become available (in the greenhouse the water evaporated by plants and by drying up solid wastes is to be reclaimed for irrigation).

It is a fact that the upgraded life support systems at ISS are much better than those at Mir--better in output and mass and power expenditure. For instance, the Electron-VM system (responsible for electrolyzing recovery of oxygen) has twice as much productivity as its former analog at Mir, and is producing as much as 160 norm liters of oxygen per hour (enough to supply a crew of six). The system responsible for cleansing the air from microimpurities is now fitted with a high-temperature catalytic filter that purifies the onboard atmosphere from methane. The SRV-K2M (recovering water from air humidity condensate) and Electron-VM systems had their energy expenses on end product output cut almost nearly by half. From November 2, 2000 (the beginning of the ISS flight in the piloted mode) to January 1, 2014, as much as 16, 100 liters of air humidity condensate had been brought to potable water by the SRV-K2M system; the Electron-VM system had gained 8,150 kg of oxygen by January 1, 2014; and the carbon dioxide elimination system Vozdukh ("Air") used for air revitalization had removed as much as 13,000 CO₂ by the same date. The table below sums up some of the major indices

Space station's physical-chemical life support complex.

Altogether the water, oxygen and air regeneration systems first at Mir and then at ISS recovered (by January 1, 2014) as much as 37.6 tons of water, 13.4 tons of oxygen; they eliminated 24.5 tons of carbon dioxide, and thus cut resupplies by 150 tons.

The systems of water, oxygen and air regeneration based on chemical technologies made for a longtime operation of the Salyut-4, Salyut-6 and Salyut-7 or- bital stations as well as Mir and ISS. Designed by native scientists, these systems ensured our country's priority in this field for more than 35 years. American systems began trial runs at ISS only in 2009.

The hands-on experience in creating air and water regeneration systems has given birth to a new trend, that of life support systems as part of the space science.

In 2012 the research collective headed by Dr. Nikolai Samsonov merited a government prize for their inventive work in creating air, oxygen and water regeneration, and life support systems for longtime space stations. Dr. Samsonov was LSS Chief Designer at NIICHIMMASH in 1965 to 2007.