Where will spacecraft of the future get energy from? Power supply system of the onboard complex of spacecraft (160.00 rubles) Design of the power supply system of the spacecraft

Copyright OJSC “Central Design Bureau “BIBCOM” & LLC “Agency Book-Service” Koroleva ”M.A. Petrovichev, A. S. Gurtov System of energy supply of the on-board complex of spacecraft was approved by the editorial and publishing council of the University as a training manual of Samara Publishing House SGAU 2007 Copyright OJSC BIBCOM“ BIBCOM ”ODC 629.78 .05 BBK 39.62 P306 C IONAL P R AT T E N A O R Y OJECTS Innovative educational program "Development of the center of competence and training of world-class specialists in the field of aerospace and geoinformation technologies" PR I Reviewers: Doctor of Technical Sciences A. N. Kopt ev, Deputy Head of the Department of the GNP RCC "TsSKB - Progress" S.I. Minenko P306 Petrovichev M.A. Power supply system of the onboard complex of spacecraft: textbook / M.A. Petrovichev, A.S. Gurtov - Samara : Publishing House of Samara State Aerospace University, 2007. – 88 pp.: illustration ISBN 978-5-7883-0608-7 The role and importance of the power supply system for spacecraft, the constituent elements of this system, special attention is paid to the consideration of the principles of operation and design of power sources, the features of their use for space technology. The manual provides a fairly extensive reference material that can be used in course and diploma design by students of non-electrical specialties. The textbook is intended for students of specialty 160802 "Spacecraft and Upper Stages". It can also be useful for young specialists in the rocket and space industry. Prepared at the Department of Aircraft. UDC 629.78.05 BBC 39.62 ISBN 978-5-7883-0608-7 2 Petrovichev M. A., Gurtov AS, 2007 Samara State Aerospace University, 2007 Copyright JSC Central Design Bureau BIBCOM & LLC Agency Book-Service Power supply system onboard complex of space vehicles Of all types of energy, electrical is the most versatile. Compared with other types of energy, it has a number of advantages: electrical energy is easily converted into other types of energy, the efficiency of electrical installations is much higher than the efficiency of installations operating on other types of energy, electrical energy is easy to transfer by wire to the consumer, electrical energy is easily distributed between consumers. Automation of flight control processes of any spacecraft (SC) is unthinkable without electrical energy. Electrical energy is used to drive all elements of spacecraft devices and equipment (propulsion group, controls, communication systems, instrument complex , heating, etc.). The power supply system (PSS) of the spacecraft is one of the most important systems that ensure the operability of the spacecraft. The main requirements for SES: the necessary energy reserve for the entire flight, reliable operation in zero gravity, the necessary reliability provided by the redundancy (in terms of power) of the main source and buffer, the absence of emissions and consumption of gases, the ability to operate in any position in space, minimum mass, minimum cost. All electric power necessary to carry out the flight program (for the normal mode, as well as for some abnormal ones) must be on board the spacecraft, since its replenishment is possible only for manned stations. Reliability of solar power plants is largely determined by redundancy of all types of sources, converters, switching equipment and networks. Weightlessness has a significant effect on liquids and gases, forcing the use of sources that do not contain liquids in a free state. This also ensures the operability of the equipment when the position in space changes. Given the small internal volume of the spacecraft, even a small amount of gas entering it significantly changes the composition of the atmosphere. Gases emitted from sources carry with them vapors of alkalis or acids, which lead to corrosion and failures, first of all, on-board computers and radio equipment. The use of such sources on board the spacecraft is undesirable. 1. Structure of the spacecraft power supply system The main power supply system of the spacecraft is the direct current system. This is determined by the fact that most of the sources that can be used on board are direct current sources. The AC network is auxiliary, used to power a limited number of consumers, for example, a traffic control system. The primary source (Fig. 1.1) converts any energy (chemical, light, nuclear) into electrical energy and must ensure the operation of consumers during the entire flight. Electricity consumption during flight is uneven: there are load peaks (usually during payload operation, deorbiting, etc.) and moments when the load is low. A buffer source is used to parry load peaks. For the first time, a bufferless power supply system was used on the reusable spacecraft "Shuttle". This is due to the fact that the aircraft uses three primary sources based on fuel cells, which allows varying the power generated by them. 4 Copyright OJSC "TsKB "BIBCOM" & LLC "Agency Kniga-Service" Distribution system Converter Converter Network Consumer Primary source Buffer source Fig.1.1. The structure of the space power supply system apparatus The buffer source is characterized by the fact that the total energy produced by it is equal to zero. It charges during low load on the network and gives energy during peaks. Usually, batteries are used as a buffer. Converters are used to match the characteristics of the battery with the primary source and the network (Fig. 1.1.). In the first case, this Charger, in the second - a voltage regulator that ensures the stability of the voltage in the network. The generated electricity must be delivered to the consumer in the right amount , at a given time, with the required quality. These tasks are handled by the distribution system and the electrical network. The distribution system connects the consumer to the appropriate source, provides redundancy (if necessary) and turns it off if the consumer is faulty. The technical implementation of these processes is carried out with the help of switching and protective equipment. Electricity is delivered to the consumer by the electricity network. It should be minimal in weight, but at the same time have low power losses and provide a reliable connection between the consumer and the source. 2. Classification of primary sources Chemical Solar battery elemme Electric machine generator Fuel magnetohydrodynamic accumulator to and thermoelectric Electrical energy mechanical thermal nuclear light Fig.2.1. Methods of generating electrical energy on board a spacecraft Only three types of energy can be used as primary energy on board a spacecraft: chemical, nuclear and solar. Moreover, chemical and nuclear are taken from the Earth, and solar comes directly during the flight. There are three ways of converting chemical energy directly into electrical energy, the so-called direct conversion method. In this case, we obtain sources with a sufficiently high efficiency (about 70%): galvanic cells, batteries and fuel cells (Fig. 2.1). 6 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service Galvanic cells store chemical energy directly in the body, and as it is consumed, the cycle of work ends. In batteries, double conversion is possible: when charging, chemical energy is accumulated, when discharging, chemical energy is converted into electrical energy (the arrows in Fig. 2.1 show the direction of energy conversion). For the first time, a silver-zinc alkaline battery (SCA) was used on board due to the fact that it is the lightest, can work in any position and does not emit or consume gases. SCA gave impetus to the development of a number of batteries. Currently, batteries are most widely used as main and buffer sources. In fuel cells, chemical energy is continuously replenished from outside. The most developed are fuel cells, which use H2 and O2 as "fuel". The chemical reaction of hydrogen oxidation is separated into two electrodes. As a result, we get electricity, heat and water. This source is quite difficult to operate, but has a small mass, a fairly long service life (up to 5000 hours) and good efficiency. In combination with a device that decomposes water into H2 and O2, it can provide a full cycle of a buffer source with a long service life, lighter than the best battery and has a fairly high efficiency. All primary energy sources (chemical, nuclear and light) can be used to generate heat. The conversion of thermal energy into electrical energy is possible in three ways: a thermoelectric generator, a thermionic (thermoionic) generator, and a magnetohydrodynamic generator (MHD). Thermoelectric generators originally had an efficiency of 0.7% and were used as temperature meters under the name "thermocouple". The use of semiconductors made it possible to increase the efficiency up to 7-10%. Thermoelectric generators in combination with isotope heat sources form extremely reliable and long-lasting sources of electrical energy of low power. They are used on board as super-emergency sources. Thermionic generator is based on the principle of an electron tube. It has a slightly higher efficiency, but the presence of high temperature makes its use on board irrational. In the 80s of the last century, designers of space technology turned their attention to machine generators, which are widely used in terrestrial conditions, despite the triple energy conversion, the presence of vibrations, the complexity of work under vacuum conditions. These generators turned out to be the cheapest, studied in detail, having good characteristics and an efficiency slightly below 40% and giving a lot of power in a small volume ("Shuttle"). When using electric machine generators, it is necessary to solve the problems of their operation in a vacuum, drive, and ensuring frequency stability. Solar batteries (SB) use direct conversion of solar energy using semiconductor converters into electrical energy. SBs have an efficiency of up to 30%, but worsen the spacecraft's maneuverability, have a short service life, and do not operate in the shadow segment of the orbit. In recent years, SBs have attracted the close attention of scientists around the world, since it was possible to obtain an efficiency of more than 40%. The use of gallium arsenide makes it possible to obtain ultra-thin SBs, of low mass, with a long service life. It is rational to use it in near-Earth orbits to supply manned space stations with electricity. All the sources of electrical energy listed above are extremely expensive, so the cost of 1 kWh obtained from solar panels reaches $40. 3. CHEMICAL SOURCES OF CURRENT (CHS) 3.1. General information about chemical current sources (CHS) A chemical current source (CHS) is a device in which the energy of a chemical reaction is directly converted into electrical energy and vice versa. A wide variety of CPS, differing in size, design features and the nature of the current-generating reaction occurring in them, is due to their wide use in various conditions and branches of technology. According to the principle of operation, HIT are divided into the following groups: galvanic cells (one-time elements), these cells contain a certain supply of reagents, after which they are used up, they lose their efficiency; accumulators (elements of reusable action, recharged or reversible). Batteries after discharge allow recharging by passing current from the external circuit in the reverse direction, while the initial substances are restored from the reaction products. Most batteries allow for a large number of charge-discharge cycles; fuel elements. During operation, new portions of reagents are continuously supplied to fuel cells and reaction products are simultaneously removed, so they can operate continuously for a long time. Since the most widely used batteries, the present work aims to familiarize with their most common types. 3.2 Silver-zinc batteries Silver-zinc (ZZ) batteries are a variant of the alkaline battery with a zinc negative electrode and a silver positive electrode. The electrolyte is a solution of chemically pure caustic potash with a concentration of about 560 g/l (electrolyte density is about 1.4). The current-generating reaction can be represented by the following equations: 2Ag + Zn О charge discharge Ag2 O + Zn Ag 2O + Zn charge discharge Ag + Zn О. Ag0, on the negative reduction of zinc oxide (Zn0) to metallic zinc (Zn). The presence of two stages of a chemical reaction causes two stages of charging and discharging SC batteries (see Fig. 3.3-3.4). In addition to the main reactions during operation and storage of SC batteries, a number of side reactions may occur. One of the side reactions is the self-dissolution of metallic zinc (corrosion), accompanied by the release of hydrogen gas. At a temperature of 20°C, 0.3-0.4 ml of hydrogen is released per day from one ampere-hour of battery capacity, at a temperature of 0°C - 0.13 ml, at a temperature of 40°C - 2 ml. The reference designation of silver-zinc batteries consists of the letters SC, which determine their affiliation, the letter characterizing the design variety and discharge time: 9 - hourly); C - medium (from 1 hour to 10 hours); D - long (from 10 hours or more); K - medium, multi-cycle; B - buffer, multi-cycle, and a number that conditionally shows the capacity of the battery. Through the fractional line to symbol battery, a four-digit or five-digit number of the technological version is indicated. Batteries connected in series form batteries and form a power supply. 3.2.1 Main technical and operational characteristics: Specific energy -<=130 Вт-ч/кг. Ресурс - до 100 зарядно-разрядных циклов. Срок службы - до 0.5 – 1 год. Диапазон рабочих температур - от 0 до 40 С. В чем причина установки серебряно-цинковых аккумуляторов на борт космических аппаратов? 1. Аккумулятор самый легкий из всех существующих. Удельная энергия СЦ до 130 Вт-ч/кг, а у свинцового всего - 22. Это объясняется тем, что у СЦ аккумуляторов используются пористые электроды, в которых работает вся масса электрода, а в свинцовых – сплошные, и реакция в них происходит только в поверхностном слое. 2. 3. 10 Как видно из уравнения химической реакции в СЦ аккумуляторе реакция происходит без выделения и поглощения газов, что позволяет делать аккумуляторы герметизированными. Это особенно важно для космических аппаратов с их малым свободным объемом. Если бы происходило выделение или поглащение газов, то атмосфера КА наполнялась парами щелочи, что отрицательно сказалось на работе электронной аппаратуры, особенно БЦВМ. В процессе работы аккумулятора не расходуется электролит, что позволяет использовать небольшие количества электролита, который находится в пластинах электродов и сепараторе. Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» 1. 2. 3. Отсутствие «свободного» электролита позволяет использовать аккумулятор в любом пространственном положении. К недостаткам аккумулятора можно отнести: Малый срок службы. Двухступенчатость зарядно-разрядных характеристик, что усложняет и удорожает зарядное устройство, и неудобно для потребителей электроэнергии. Высокая стоимость аккумулятора (серебро). 3.2.2. Устройство серебряно-цинковых аккумуляторов Положительный электрод серебряно-цинкового аккумулятора изготавливается из серебра. Характерной особенностью серебра является легкость его восстановления до металла из соединений. Благодаря этому и хорошей электропроводности на основе его соединений можно конструировать разные химические источники тока. Положительные электроды аккумуляторов изготавливаются из порошка серебра, который прессуется на каркас из серебряной проволоки, отрицательный электрод изготавливается из цинка. В серебряно-цинковых аккумуляторах используется нерастворимый отрицательный электрод. В этом электроде, благодаря применению высокопористого цинкового электрода и малого количества электролита, который в основном находится в порах электрода и сепараторного материала, обеспечиваются значительно лучшие условия для работы цинкового электрода. В отечественных аккумуляторах отрицательные электроды изготавливаются так называемым намазным способом - паста из порошка цинка намазывается на каркас из освинцованной медной проволоки, затем осуществляется подпрессовка и прокалка. Использование пористых электродов позволяет значительно снизить массу аккумулятора (увеличить удельную энергию), поскольку в процессе образования тока участвует весь объем электродов. Для того, чтобы ионы успевали проникать внутрь электродов, их приходится делать тонкими, поэтому в одном корпусе (банке) располагается большое количество положительных Ag и отрицательных Zn электродов, разделенных изолирующим материалом - сепаратором. В ходе разработки серебряно-цинковых аккумуляторов одной из основных проблем явилась проблема сепарации, при малом электрическом сопротивлении и хорошей химической стойкости в щелочи, сепарация 11 Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» должна препятствовать продвижению через нее частиц серебра и дендритов цинка. В настоящее время в серебряно-цинковых аккумуляторах получила применение сепарация из целлюлозы, в которую «одевается» отрицательный электрод (рис. 3.2). Эта сепарация не имеет сквозных пор, через которые электролит мог бы свободно диффундировать от одного электрода к другому. Целлофановая сепарация после помещения ее в раствор щелочи впитывает в себя электролит, набухает и увеличивает свою толщину в 2-5 раза. Перенос ионов через такую сепарацию происходит принудительно (под влиянием электрического поля, возникающего в работающем аккумуляторе). Целлофановая пленка довольно легко подвергается окислению окислами серебра и кислородом, выделяющимся на серебряном электроде при перезаряде (заряд свыше номинальной емкости) аккумулятора. Для уменьшения окисления сепаратора на положительный электрод одевается дополнительная сепарация из капроновой ткани – «капроновый чулок». Сборка аккумуляторных блоков в сосуде производится с таким расчетом, что набухающая сепарация создает достаточное давление, препятствующее сползанию активной массы отрицательного электрода и уменьшению роста дендритов цинка. Следует отметить, что целлофановая пленка не отвечает в полной мере требованиям, предъявляемым к сепарации серебряно-цинковых аккумуляторов. При определенных условиях дендриты цинка могут прорастать через целлофан за счет восстановления цинка в толще сепарации, замыкая пластины аккумулятора - основная причина малого срока аккумулятора. Постепенное химическое разрушение сепаратной пленки за счет окисления является другой причиной, ограничивающей в настоящее время срок службы серебряно-цинковых аккумуляторов. Практически электролит в аккумуляторе не расходуется, поэтому oбщее количество его обычно невелико - в порах активных масс и сепарации. При неплотно закрытых пробках он начинает поглощать углекислый газ из воздуха, что ведет к увеличению внутреннего сопротивления аккумулятора. С ростом числа разрядно-зарядных циклов уровень электролита начинает понижаться за счет разложения воды в конце заряда. 12 Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» Сосуды для аккумуляторов (банки) (рис.3.1,поз.1), в которых размещаются пакеты электродов, и крышки (рис.3.1,поз.2) изготавливаются из полистирола или полиамида методом штамповки или литья под давлением. В крышке аккумулятора имеется отверстие для заливки электролита и вентиляции. Заливочное отверстие закрывается газоотводной пробкой Рис.3.1. Внешний вид аккумулятора (см. рис.3.1 поз. 4). В пробке предусматривается отверстие с клапаном для выпуска скопившихся газов. Пробки водонепроницаемы и открываются только при опреде-ленном избыточном давлении внутри аккумуляторного суда. Сборка аккумуляторного блока (рис.3.2) производится следующим образом: две отрицательные пластины 1 заворачиваются в целлофановую пленку 2, а затем сгибаются по линии 3. 13 Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» 1 2 3 4 Рис.3.2. Сборка электродов в аккумуляторный блок: 1-отрицательный электроды, 2-целофан, 3- линия сгиба, 4- выводы отрицательных электродов. Между ними помещается положительный электрод, на который надет капроновый мешок. 3.2.3. Основные рабочие характеристики серебряно-цинкового аккумулятора: а) Приведение в действие. Для этого необходимо выполнить три операции: заливку и пропитку его электролитом, формирование электродов, рабочий заряд. Процесс формирования электродов серебряноцинковых аккумуляторов сложен и занимает длительное время ~ от 70 до 100 часов, поэтому в последние годы разработаны и выпускаются сухозаряженные аккумуляторы, способные работать непосредственно после заливки электролитом и пропитки им сепарации и электродов; Заряжаются обычно аккумуляторы номинальным током. Для большинства серебряно-цинковых аккумуляторов им является ток 10-20 часового заряда. б) Зарядно-разрядные характеристики. На рис. 3.3. представлены зарядные характеристика аккумулятора. Первая ступень (напряжение 1,62-1,65В) соответствует образованию полуокиси серебра и составляет около 25-50% от общей длительности заряда. Вторая ступень (напряжение 1,92-1,95В) соответствует образованию окиси серебра, и заряд на этой ступени занимает около 70% времени. 14 Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» Когда зарядное напряжение достигает 2В, начинается разложение воды и выделение кислорода на положительном электроде. Продолжение заряда аккумулятора не только бесполезно, но и вредно, поскольку при этом происходит только разложение воды, выделяющийся на серебряных электродах кислород окисляет целлофан, уменьшая его механическую прочность. Пологие участки зарядной характеристики имеют очень малый наклон. Это объясняется тем, что потери в СЦ аккумуляторе малы. Зарядная характеристика СЦ аккумулятора чрезвычайно неудобна в работе: а) зарядное устройство должно обеспечивать скачок напряжения. Это должен быть источник тока (внутреннее сопротивление источника должно быть большим, чтобы ток не зависел от сопротивления нагрузки); U, B 2Iн 2.0 Iз=Iн 10Iн 1.8 1.6 1.4 0.25 0.5 0.75 1.0 Qз/Qн Рис.3.3. Зарядные характеристики при различных токах заряда б) в силу пологости характеристик нельзя определить заряжен аккумулятор или нет; в) категорически запрещено включать на зарядку акку-муляторы параллельно, поскольку у одного аккумулятора можно «высушить» электролит, разлагая воду. Заряд аккумулятора токами больше чем номинальный приводит к тому, что он принимает меньший заряд (рис. 3.3), поскольку при 15 Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» увеличении тока заряда химические процессы происходят только на поверхности электродов, что приводит к уменьшению емкости аккумулятора. в) Разряд аккумулятора. (разрядные кривые представлены на рис. 3.4.) По оси аргументов использована относительная координата: отношение отдаваемой емкости Qр (а-час) к емкости разряда при номинальном разрядном токе Qн. С ростом разрядного тока величина напряжения на клеммах аккумулятора падает, уменьшается также отдаваемая емкость (рис.3.4). При разряде аккумулятора небольшими токами (Iраз= 200ºС – nickel Ni. To ensure the normal operation of fuel cells, special electrodes are required (Fig. 3.20). This plate thickness is enough to provide a pressure difference between liquid and gas of ±0.5 atm. The electrode must be two-layer. The first thin layer with small holes is coated with a wetting agent, which creates a capillary force that pushes the liquid towards the gas. The second, thicker part of the electrode has holes of 30-50 microns, which are covered with a non-wetting substance, which tends to push the liquid towards the electrolyte. For example, the pressure in the liquid has increased. Due to this, the liquid moves towards the gas, the non-wetting force increases, compensating for the excess pressure. Currently, electrodes are made of wire using the metal-rubber technology. Theoretically, the dimensions of the fuel cell can be arbitrarily large. However, in practice, several cells are combined into small modules or batteries, which are connected either in series or in parallel. 3.5.2. Classification of fuel cells There are different types of fuel cells. They can be classified, for example, according to the fuel used, the operating pressure and temperature, and the way the water is removed. a) by type of fuel: based on H2 and O2. The product of the reaction is heat, electricity and water. For spacecraft, this is the most convenient type of fuel, since water and oxygen can be used in the life support system (LCS). in principle, fuel cells can operate on any fuel. b) by operating temperature: low-temperature - up to 100ºС ("Shuttle", "Gemini"). The allocation of the low-temperature group of fuel cells is explained by the methods of collecting water, since for these fuel cells it is in a liquid state; medium temperature - up to 260º–300ºС ("Apollo"). These fuel cells are characterized by the maximum reaction rate. high-temperature - 1000ºС. The use of such fuel cells on spacecraft is problematic due to the high temperature and the complexity of heat removal. Intensive work is underway to create fuel cells for earthly needs, operating on natural gas and atmospheric oxygen at a temperature of 500-7000C with an efficiency of about 70%. c) according to the method of collecting water: wick (as in a kerosene lamp). Used on Gemeni, very slow adjustability; 32 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service evaporative, typical for medium-temperature fuel cells, where water is in a gaseous state; dynamic: a chamber with a low partial pressure of water is used, connected to the hydrogen gas chamber by a membrane with one-sided water conductivity. d) by type of electrolyte: liquid, KOH melt is used at a temperature of about 2500 C; solid (ion-exchange membrane), charge carrier - hydrogen ion; matrix, a material with micropores is used - asbestos, into which a liquid electrolyte is poured. 3.5.3. CVC of the fuel cell B 1.23 1 2 3 J A/cm2 0 50 100 150 200 250 Fig.3.21. Current-voltage characteristic of FC The volt-ampere characteristic of fuel cells on oxygen - hydrogen (Fig. 3.21.) can be divided into three sections depending on the process that determines the voltage drop. The EMF of such a fuel cell is 1.23 V. 1st section: characterized by energy consumption for organizing a chemical process (chemical polarization) (Fig. 3.21, section 1); 33 Copyright JSC "Central Design Bureau" BIBCOM " & LLC "Agency Kniga-Service" 2nd section is characterized by a predominant voltage drop on the "ohmic" elements - on the electrodes and electrolyte; 3rd section - ions do not have time to enter the electrodes, lack of ion concentration (concentration polarization). An increase in the electrolyte temperature leads to a decrease in energy costs for the organization of the chemical process, and at a temperature of about 20,000 C, the process proceeds independently. A change in temperature has little effect on the magnitude of the voltage drop in section 2. In section 3, the initial increase in temperature leads to an increase in the ion energy - the slope decreases. An increase in temperature causes an increase in the vibrations of the electrolyte molecules, which makes it difficult for the movement of ions, the speed of movement of the ions decreases. Thus, there is an optimal electrolyte temperature at which the voltage drop in section 3 will be minimal. For electrolyte KOH with a concentration of 1.8, the optimum temperature is about 250o C. In order for the electrolyte to remain liquid, a pressure of about 4.5 atm is required. For fuel cells, there is no thermodynamic limitation on the energy utilization factor. In existing fuel cells, 60 to 70% of the fuel's energy is directly converted into electricity. Fuel cells may in the near future become a widely used source of energy in transport, industry and households. The high cost of fuel cells has limited their use in military and space applications. The intended uses of fuel cells include their use as portable power sources for military needs and compact alternative power sources for near-Earth satellites with solar panels when they pass through extended shadow sections of the orbit. The small size and mass of fuel cells made it possible to use them in manned flights to the Moon. Fuel cells aboard the three-seat Apollo spacecraft were used to power on-board computers and radio communication systems. Fuel cells can be used to power equipment in remote areas, for off-road vehicles, such as in construction. Combined with a DC electric motor, the fuel cell will be an efficient source of vehicle propulsion. 34 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service For the widespread use of fuel cells, significant technological progress is required, as well as a reduction in their cost and the possibility of efficient use of cheap fuel. When these conditions are met, fuel cells will make electrical and mechanical energy widely available throughout the world. 3.5.4. The device of the liquid fuel cell FC with liquid electrolyte was used during the flights to the Moon of the Apollo vehicles. A KOH melt with a concentration of 1.8 was used as the electrolyte. At temperatures below 200 degrees, this electrolyte does not conduct electricity, so for work it must be preheated using some kind of source. Nickel is used as the main structural material because it works well at elevated temperatures and is a catalyst. The service life of such a fuel cell is about 500 hours. Main advantages: the possibility of obtaining a high current density - up to 250 milliamps per square centimeter, the use of a cheap catalyst and construction material, since the electrolyte does not participate in the reaction, the fuel cell has a small amount of it, so the thickness of the fuel cell is several millimeters. 35 Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Book-Service" Pic. 3.22. Liquid fuel cell device 1 - flexible body made of Ni, 2 - gas-oxygen chamber made of Ni, 3 - oxygen electrode, Ni-wire, 4 - electrolyte, KOH melt, 5 - fluoroplastic separator, 6 - hydrogen gas chamber, 7 - negative electrode, 8 - an insulator. Disadvantages of fuel cells with liquid electrolyte: to start the operation of the fuel cell, it is necessary to heat it up to a temperature of 200-2500 C, to maintain the fuel cell in working condition, it is necessary to consume electric current, regardless of whether it is needed at this time or not, a short service life, a good cooling system is needed. Structurally, the fuel cells are made in the form of two halves of a nickel housing (Fig. 3.22, pos. 1), separated (electrically) by an insulator 8. The electrodes are two-layer, made of nickel wire. Gas chambers 2 and 6 are obtained by stamping from nickel and welded in several places to the electrodes. Between the electrodes, to prevent a short circuit, there is a fluoroplastic separator 5. To ensure pressure inside the fuel cell, its body 1 (Fig. 3.22) is made flexible. The required number of fuel cells (to obtain a voltage of 27V, the fuel cells are connected in series) is placed in the cylinder, where internal pressure is created. Since the body is not connected to the external environment, no air bubbles are formed inside it, thereby ensuring the reliability of the fuel cell. To remove heat and ensure the desired temperature of the electrolyte and H2 electrode, H2 is blown through the hydrogen gas chamber. Together with hydrogen, H2O vapors are carried out of the gas chamber, which are condensed by cooling. A distinctive feature of the fuel cell is that only H2 and O2 react. All impurities that are present in the gases accumulate in the gas chambers, reducing the contact area of ​​H2 and O2 with the electrolyte, and the current or voltage decreases. To prevent this, the gas chambers are periodically purged, throwing out their contents. Losses of H2 and O2 due to purge - 10-14%. 3.5.5. Fuel cell with ion-exchange membrane (IEM) The fuel cell based on IEM has been operated on the Shuttle small spacecraft for many years. These cells have a number of advantages compared to cells with liquid electrolyte: long service life (up to 5000 hours); constant readiness for work; in the absence of energy consumption, no fuel is consumed. IOMs use the lightest ion - H + (Fig. 3.23.). This allows you to spend a minimum of energy on its movement and obtain a high speed of ion movement. There are 2 types of IOM: 1. with a limiting temperature of 42ºС; 2. based on fluorine with a temperature limit of 82ºС. 37 Copyright JSC "Central Design Bureau "BIBCOM" & OOO "Agency Book-Service" Pic. 3.23. FC device with ion-exchange membrane 1 - gas-oxygen chamber, 2 - STR, 3 - H2O collection system, 4 - positive electrode, 5 - solid electrolyte - ion-exchange membrane, 6 - hydrogen electrode 7 - hydrogen gas chamber. IOM-based fuel cells are low-temperature. The maximum current density of the first PTO is 25-30 mA/cm2, the second PTO is up to 200 mA/cm2. In this fuel cell, H2O is formed at the oxygen electrode and heat is released. IOMs are critical to temperature and humidity. When drying, IOMs crack (with increasing temperature), reducing the output current. The gas chambers are made of titanium Ti, the electrodes are made of titanium wire coated in one or two molecular layers with platinum Pt. Water was collected on the first fuel cells with the help of wicks, on modern fuel cells - by using a chamber of low partial pressure of water and its dynamic suction. The service life of a modern fuel cell with IOM reaches 5000 hours. 3.5.6. FC-based energy system As noted above, FC can operate only if supporting systems are available. The system of storage and supply of components (SHiP) of working fluids (Fig. 3.24.) provides storage of hydrogen and oxygen and their supply to the fuel cell at a given temperature and pressure. The system can be built on the basis of gas balloon and cryogenic storage of working fluids. One of the advantages of hydrogen-oxygen fuel is its high H2 O ECH storage and supply system Consumers STR Control system H Q Fig. 3.24. The structure of the power supply system based on fuel cells specific energy q=2540Wh per kilogram of mass. It can be seen from the table that for hydrogen-oxygen fuel cells, cryogenic storage of working bodies is most expedient. Table. Methods of storage and supply of hydrogen and oxygen No./No. Method of storage Specific energy, Wh/kg 1 without storage and supply systems 2540 cylinder storage system 130 2 metal cylinder storage system 260 3 composite 4 cryogenic storage system 1580 Gas cylinder system allows storing fuel reserves for quite a long time during long interruptions in work, provision and regulation of a given pressure of hydrogen and oxygen is carried out 39 Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" is simple, but the cylinders are heavy, which significantly reduces the specific energy of the solar cell. Cryogenic SHiP provides a high value of specific energy, but is very complex, expensive and allows you to fly no more than 2 weeks. The preservation of the components in the liquid state is carried out by "cooling down", i.e. evaporation of components. Therefore, if there is no consumption of components, their consumption continues, providing a liquid state due to the heat of evaporation. The cryogenic tank consists of two polished containers inserted one into the other, the space between them is evacuated. When operating a fuel cell, the required amount of oxygen and hydrogen depends on the electricity consumed. To obtain the required amount of gaseous hydrogen and oxygen, there is a heater inside the tank controlled by the pressure in the tank. The tank also has a fan that provides liquid mixing (which is especially important in zero gravity conditions). High pressure protection is provided by a drain valve. At the outlet of the cryogenic tank, there is a pump that provides the necessary gas pressure in the working chambers of the fuel cell. Considering the complexity of the cryogenic system and the special conditions of its operation, it is understandable why the first accident with the solar power plant occurred on Apollo 13, where an oxygen cryogenic tank exploded. An electrochemical generator (ECG) is a generator of electrical energy based on fuel cells combined into a battery. To obtain the required voltage, up to 30 fuel cells are connected in series, while the gas chambers of the fuel cell are energized relative to each other, therefore, pipelines made of insulating material must be used to supply hydrogen and oxygen to the fuel cell. Typically, the supply of working fluids and purge are provided through pipelines connected in parallel. The ECG also includes water and heat removal subsystems. The water collection subsystem can be static using wicks or creating a water vapor pressure gradient from the electrochemical reaction zone into the dehumidifying cavity or dynamic with hydrogen circulation through the drying chambers. Water is typically used in the life support system (LCS) of the crew. 40 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service The subsystem of heat removal from the fuel cell ensures the collection of heat and its transfer to the thermal control system (STR) of the spacecraft. The control system (CS) provides automatic control of all elements of the power system depending on the amount of electricity consumed. As an example, let's consider the main parameters of the power system of the reusable spacecraft "Shuttle" based on fuel cells. Power, kW: 4 minimum 14 maximum peak: 20 for 60 min. 24 for 2 min Type of current Direct DC voltage, V 27.5 – 32.5 Energy intensity, kWh: 1480 nominal 50 for payload 120 emergency Resource of one cycle, days 7 Number of cycles 100 Total resource, hour 5000 Life time, years 10 Duration of pre-launch preparation, 24 hours Duration of maintaining readiness for the 24th launch, hour 4. Thermoelectric generators The use of the principle of direct conversion of thermal energy into electrical energy 41 Copyright OJSC "Central Design Bureau" BIBCOM " & LLC "Agency Kniga-Service" allows you to solve the problem. Among the well-known systems using this principle (thermionic, thermoelectric converters and MHD generators), with electric power up to several kilowatts, long service life (more than ten years), high reliability, autonomy, only systems with thermoelectric converters currently have, which makes them most preferred for use as autonomous current sources. Operating principle. When one end of the conductor is heated, the carriers of electricity move from the heated end to the cold one, creating a potential difference (Fig. 4.1a). T1 T1 - - T1 EMF T2 T2 + heat a) b) Fig. 4.1. The principle of operation of a thermoelectric generator To remove the potential difference, a second conductor is required, one end of which will also heat up and a potential difference will be created in it (Fig. 4.1b). If we take conductors from the same material, then the total potential difference will always be zero. The conductors must be of different materials. The best pair of metal materials copper-constantan has an EMF of 46.3 millivolts at a temperature difference of 1000° and an efficiency of about 0.7%. The efficiency of a thermoelectric converter is determined by the thermal and conversion efficiency η = ηt *ηpr The thermal efficiency depends on the temperature difference between the hot Т2 and cold Т1 ends ηт = (Т2 - Т1)/ T2, and for a metal thermoelement the maximum will be about 80%. Therefore, the conversion efficiency does not exceed 10%. This is explained by the fact that in the metal the same carriers are electrons, and the potential differences obtained in each conductor are subtracted (Fig. 4.1b). A connection of conductors that is subjected to heating is called a “hot junction”, and an unheated connection is called a “cold junction”. Such a thermoelement is not used to generate electricity, but is used to measure temperature and is called a "thermocouple". To obtain electricity, it is necessary to increase the conversion efficiency, which can be done using semiconductors with different carriers - p and n. In this case, the conversion efficiency becomes much higher. However, for the most common silicon semiconductors, the limiting temperature is 1500 C and the overall efficiency does not exceed 7-10%. Semiconductor materials used in such generators should have the highest possible thermo-emf coefficient. , good electrical conductivity and low thermal conductivity. p Connection plates n p heat fig. 4.2. Semiconductor TEG device 43 Copyright OJSC "Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" The latter is necessary in order to obtain a significant temperature difference between the cold and hot junctions of the crystals. These requirements are best met by heavily doped semiconductor materials (semimetals). 0.25 Voltage, V 0.2 0.15 0.1 0.05 0 0 2 4 6 8 10 12 14 Current, A 4.3. Volt-ampere characteristic of TEG The device of a semiconductor TEG is shown in fig. 4.2. The battery of thermoelements is assembled from p and n crystals placed between the heated and cooled surfaces (Fig. 4.2.). Semiconductor elements p and n are arranged alternately so that the emfs are summed (shown by arrows). Metal plates are used to connect semiconductor elements. Since a high purity of the materials used is not required for operation in a thermoelectric generator, the generators are relatively cheap and operate successfully under conditions of penetrating radiation. For heating, side heat can be used (sunlight, the wall of the installation warming up during operation) and heat from a special generator (radioisotope, nuclear reactor). Despite the low efficiency, not exceeding 10%, thermoelectric generators are widely used to power portable electronic devices. This is explained by ease of operation, high reliability, low cost. The external characteristic of one of the thermoelements (Fig. 4.3) falls rather steeply, therefore short circuits are not dangerous for such a generator, but TEG can be used because of this as individual sources. Rice. 4.4. External view of radial-ring design thermoelectric generators In domestic industrial and experimental thermoelectric generators (TEG) on natural gas, the maximum unit electric power does not exceed 150 W. The unit power of operating TEGs with atomic reactor heating reaches 5 kW. Isotopes are the most rational source of heat for spacecraft. This combination of a semiconductor TEG and an isotope makes it possible to create sources that operate reliably for many years. TEGs for space technology have a low power and are used as extra emergency sources for the purpose of turning on pyrotechnics. On inhabited satellites, such a source is too heavy due to radiation protection. Thermoelectric batteries (TEB) can be both flat and radial-annular. A common disadvantage of a flat geometry thermopile is a significant degradation of electrical power and system efficiency during multiple thermal cycling and due to an increase in internal electrical resistance. These shortcomings can be eliminated by using a thermopile of radial-annular geometry (Fig. 4.4.). It allows to significantly reduce heat losses through structural elements. Cylindrical elements with heat transfer along the radius structurally fit well with the most common tubular designs of heat exchangers both in nuclear power engineering and in heat engineering. This makes it possible to obtain higher specific energy characteristics in cylindrical structures by reducing the mass of structural elements. radial-ring design. Table. 4.1. Some thermoelectric generators manufactured in the USSR Thermal power of RHS, W KP Electric D, th % power of RTG, W Output electric Mass Starting RTG production Voltage a, kg RTG, V Ether- 720 MA 30 4.2 35 1250 1976 IED- 1 2200 80 3.6 24 2500 1976 Gong 315 18 5.7 14 600 1983 IEU1M 2200 120 (180) (3300) 5.4 5 28 2 (3) x 1990 1050 RTG is a radioisotope thermoelectric generator. Table 4.2. Thermoelectric generators used on US satellites Characteristics SNAP-9A SNAP-11 IMP COMSAT Space Transit – 4 Surveyor IMP COMSAT vehicle Fuel Pu238 Cm242 Pu238 Sr90 Maximum electric power 25 21-25 25 30, W Efficiency, % 4.8 – 5.2 Mass, kg. 12.3 13.6 9.6 11.4 1-3 Service life, months 6 2-6 5-10 years of the year 5. Solar panels 46 take that. Therefore, already in 1958, the USSR and the USA developed and put on board the first solar batteries. The solar battery is a combination of light-to-electricity converters (PVC) and structural elements - panels that provide mechanical strength, geometric invariability and fastening them to the spacecraft structure. In a short period of time, there was a rapid development of the theory of photoconverters (PVC), new design and technological solutions were developed. Thus, the efficiency of solar cells increased from 7% of the first solar cells to 42% in experimental installations. The size of solar cells has increased from 10*20 mm to 150*150 mm in modern batteries, which allows reducing the weight due to switching connections and reducing the area of ​​the battery. The service life is increased due to the use of a flexible FEP connection, which reduces mechanical stresses in the transducers during the transition from the illuminated side to the shade and back. The main advantages of solar batteries include: the primary energy for generating electricity is in space. Disadvantages: 1. short service life (together with sunlight, microparticles flying from the Sun get on the solar cell); 2. The maneuverability of the spacecraft significantly deteriorates not only due to a significant increase in the moment of inertia of the spacecraft, but also due to a decrease in the maximum angular velocities and accelerations determined by the strength of the solar panels; 3. the complexity of placing panels under the fairing; 4. high cost of electricity due to the use of a large mass of single-crystal silicon (the cost of 1 kWh of electricity reaches $ 40); 5. relatively low efficiency (about 15%); 6. It is rational to use them only in near-Earth orbits and for flights to Mars and Venus. 5.1. Photoelectric converters Solar radiation as a primary source of energy has a number of specific features that must be taken into account when determining rational ways and means of using this source. It is possible to single out several characteristics of the Sun as a source of energy in that place in space where the flight path of the spacecraft passes. Energy characteristics are the dependence of the solar radiation flux density on the wavelength and distance from the Sun to the surface perpendicular to the light flux. The sun has a continuous spectrum of radiation. The distribution of energy in the spectrum of the Sun is very uneven and the true spectral density curve has a rather complex form, however, the distribution of energy in the spectrum of the Sun is quite close to the spectrum of a black body at a temperature of 58000 K (Fig. 5.1.). The main part of the Sun's energy is in the short part of the spectrum - blue and ultraviolet. The long part of the spectrum, having low energy, is not capable of creating electricity, but leads to heating of solar panels, so they try to get rid of it. The first solar batteries used a blue protective coating (which does not transmit the red and infrared parts of the spectrum), at present photoconverters are made transparent for this part of the spectrum. 2500 Specific energy 2000 1500 1000 500 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Wavelength, µm 5.1 Spectral characteristic of solar radiation 48 Copyright JSC Central Design Bureau "BIBCOM" & OOO "Agency Kniga-Service" In view of the finite and rather large size of the Sun, the sun's rays are not parallel and have some angular parameter. This parameter is especially important when solar energy is concentrated. Table. Energy and geometric characteristics of solar radiation Parameter Mercury Energy Е, 9250 W/m2 Angle, ψ, 81 arcsec. Venus Earth Mars Jupiter Saturn 2730 1373 610 52 15.4 44 32 21 7 4 The table shows that it is rational to use solar radiation within Venus-Mars. The main useful types of energy used on board are electrical, mechanical, thermal and light. A variety of onboard equipment consumes mainly electrical energy. It should be noted that solar radiation is the only primary source whose energy can be directly converted into all useful forms of energy (Fig. 5.2). 49 Copyright OJSC "TsKB "BIBCOM" & LLC "Agency Kniga-Service" Sunlight Photoconverters Electricity Solar heat sources Solar sail Direct converters. heat Rice. 5.2. space Concentrators Light Mechanical energy. Scheme of the main ways of converting solar energy into electricity Converters based on pn-junction, made of silicon and, less often, gallium arsenide, are most widely used as a light-to-electricity converter. The photoelectric converter (PVC) is a flat plate, ranging in size from 20*10 mm to 180*180 mm. The FEC is based on the pn junction formed by the corresponding semiconductor wafers (Fig. 5.3, pos. 3 and 4). From above, the solar cell is closed with a protective coating 1. The protective coating performs several functions: a) protect the junction from the introduction of impurities into semiconductors (microparticles flow along with the flow of sunlight); b) the surface of the protective coating should have a low reflectivity so that the energy of the sun's rays is used as fully as possible; c) until recently, the protective coating was blue, to protect against the red part of the spectrum. Currently, the protective coating is transparent to the red part of the spectrum. The current collector 2 (Fig.5.3.) Should, on the one hand, be located over the entire surface to reduce the contact resistance. C 50 Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Book-Service" is different - its area should cover the semiconductor as little as possible. In practice, the current collector 2 is made in the form of metal strips, occupying about 11% of the solar cell area (11% of the solar cell is not illuminated by the Sun and does not generate electricity). The solar cell itself is most often made of two semiconductors of n and p - types, and the n semiconductor is made thin (Fig.5.3, pos.3) so that light passes through it without spending its energy, and in the second thick layer (Fig.30 , item 4) gave off energy, releasing the carrier. The thickness of the p-layer must be greater than the free path of a photon of light (about 0.5 mm.). At present, the lower current collector 5 is made mirror-like, and the thickness of the p-semiconductor is halved. The lower current collector 5 for solar batteries of low-flying satellites is made solid and mirrored on both sides. It turned out that the light and heat reflected from the earth's surface heat up the solar cell and reduce its energy by 20%. In the latest developments of the solar cell, three layers of semiconductors are used, the energy reflected from the Earth is used, the efficiency of the solar cell increases by 20%, respectively. The principle of operation of the solar cell is based on the fact that a photon of light, having passed through a thin n-semiconductor, gives up its energy in a thick p-layer, creating an electron-hole pair, which pass into the corresponding region. 51 Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Book-Service" 1 2 3 4 5 Pic. 5.3 Structure of photoelectric converter 1 - protective coating, 2 - current collector, 3 - n-semiconductor, 4 - p-semiconductor, 5 - current collector and metal mirror. The EMF of a silicon solar cell at the level of the Earth's orbit (the light flux is perpendicular to the solar cell plate) is about 0.6 V. The current-voltage characteristic of an ideal solar cell is a combination of characteristics of a voltage source (the voltage value does not depend on the load current) and a current source (the current value does not depend on the load resistance) (Fig. 5.4. curve 1). The voltage drop with increasing load current is due to the presence of resistances of the current collectors and the semiconductor itself. In the event of a short circuit of the cell, the current is limited, since its value is determined by the number of photons. On the one hand, such a characteristic of the solar cell is good, since it is impossible to disable it even with a short circuit. On the other hand, sometimes it is required to slightly increase the current, but the FEP cannot do this and produces zero voltage, that is, it disconnects the load. Photovoltaic modules with a protective coating of textured tempered glass based on single-crystal silicon photoelectric light conversion - 15-20%. Voltage, V elements have high efficiency 1 0.6 2 0.4 0.2 0 0 0.01 0.02 Current density 0.03 A/cm2 Fig.5.4. Volt-ampere characteristic of silicon solar cell 1 - ideal solar cell, 2 - real solar cell. The efficiency of solar panels has reached a record high of 42.8 percent. The previous record was 40.7 percent, but in an area where a 0.2 percent win is the norm and a 1 percent break is a very significant step. To achieve the result, the combined efforts of a number of laboratories, research centers and commercial enterprises were needed. The ultimate goal is to create a cheap portable solar battery. The scientists were tasked with bringing the efficiency up to 50 percent. Currently, the next stage of the project is being launched: the transition from laboratory research to the creation of a working prototype. This is expected to take three years and cost about one hundred million dollars. 53 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service The main energy losses in solar batteries are associated with the reflection of part of the solar radiation from the surface, the passage of part of the radiation through the converter without absorption, the internal resistance of the converter and other physical processes. In a silicon battery developed by the University of Delaware, to reduce losses, sunlight is split by a special optical system into three regions with different energy levels and sent to three cells of different sensitivity: high, medium and low. 5.2. Solar batteries Spacecraft solar batteries are complex electromechanical devices that provide electrical connection of solar cells, their placement on a single carrier base, strength and stability of the entire structure during vibration and maneuvers, placement under a fairing, the possibility of opening, mounting and orientation in space conditions. Solar panels (SB) are oriented and non-orientable. SB orientation can be carried out along one or two coordinates. Non-orientable SBs are rigidly attached to the spacecraft body or are an integral part of the spacecraft body. Depending on the mechanical characteristics of the bearing support, or substrate, SBs are divided into structures with rigid, semi-rigid and flexible bearing surfaces. The rigid supporting structure of the SB is made in the form of a wing, on which FEPs are superimposed, it has high resonant frequencies and small deflections of the panels. The specific power of such SBs is 20-40 W / kg of construction. Flexible solar panels have a substrate with zero bending stiffness, deployed and held in position using folding masts, beams or pantographs. The design of SB with a flexible bearing surface can be of two types: rolled or rolled, folding or packaged. Specific power - 40-80 W / kg. The main contribution to the SB mass comes from FEPs. Therefore, the task of reducing their thickness and increasing the efficiency is an urgent task. The most promising in this regard are ultrathin PVCs (up to 50 μm), the use of large PVCs. An increase in specific power up to 200W/kg is expected. 54 Copyright JSC Central Design Bureau BIBCOM & OOO Agency Kniga-Service To obtain the required voltage and current, solar cells have to be connected in series and in parallel. In solar batteries of the old type, up to several hundred thousand elements were connected. This led to a large weight of the connecting wires, but with a failure of up to 80% of the solar cell, the battery continued to work. The currently used solar cells are large and create a current of up to 6A per cell. To obtain a voltage of 27 V and a current of 200A, it is necessary to connect 54-55 elements in series and 34 branches in parallel. Thus, the solar battery contains only 1870 elements. When electrically connecting solar cells, a dilemma arises: to make all connections (both serial and parallel) - we get high reliability of the SB, but a large mass, if we connect all 54-55 solar cells in series and connect these "branches" in parallel - we get the minimum mass, but also low reliability, and short service life. The second problem: when using SB, the interaction of the current flowing through the connecting wires of the SB and the Earth's magnetic field leads to the appearance of a force and moment, which causes the spacecraft to turn. The third problem is related to the static electrification of SB panels. The gradual accumulation of a charge of static electricity on the surface of the SB can cause breakdown and damage to the solar cell. To eliminate this phenomenon, conductive films are glued on the SB panels (decrease in efficiency). 5.3 Space photovoltaic converters and solar batteries Increasing requirements for spacecraft (SC) onboard systems lead to the need to create solar batteries (SB) with higher energy and operational characteristics with an extended service life. The most promising way to solve these problems is the creation of solar cells based on photoelectric converters from gallium arsenide and related compounds. Solar photovoltaic converters (SCs) based on gallium arsenide provide a significant increase in efficiency, specific energy output and radiation resistance of space SCs compared to silicon-based batteries. PV cells based on AsGa provide: FEP. Improving radiation resistance, providing an increase in the service life of the SB up to 15 years in geostationary orbits. Ability to work at high degrees of solar radiation concentration while increasing the efficiency up to 30-35%. Over the past decades, a large domestic and foreign experience has been accumulated in the operation of space solar cells and solar cells based on GaAs and compounds. It is shown that GaAs-PVC provide an increase in efficiency, specific energy output, radiation resistance and other parameters compared to silicon SBs. The high absorption coefficient of solar radiation in gallium arsenide makes it possible to maintain high efficiency with a decrease in the thickness of the solar cell structure to less than 10 μm, which reduces the consumption of gallium arsenide by more than an order of magnitude and, as a result, reduces the weight of solar cells by 2–3 times. In such thin-film solar cells with an active region thickness of about 5 μm, it is possible to achieve high two-way sensitivity and increase the energy output in space by 20-25% due to the use of the Earth's al-bedo. PV cells from GaAs, along with an increase in efficiency, also provide an improvement in radiation resistance, which approximately doubles the service life of space SBs. As shown by long-term studies on the degradation of space satellites under the action of radiation exposure, the degree of degradation significantly depends on the parameters of the orbit of the spacecraft (SC). For low-orbit spacecraft (770 km), the degradation of SBs based on silicon and GaAs-GaAlAs is 15% and 5%, respectively, during 5 years of spacecraft stay in orbit. For spacecraft in geostationary orbits, degradation is 31% (Si) and 16% (GaAs) during 15 years in orbit. For radiation hazardous orbits (7400 km at an inclination angle of 50°), degradation is 49% (Si) and 22% (GaAs) over a 5 year orbit. Therefore, the use of batteries based on GaAs for spacecraft power supply provides a significant economic effect compared to silicon-based SBs, despite the higher cost of such SBs. An extremely important advantage of GaAs solar cells is their ability to efficiently convert 100-1000-fold concentrated solar radiation. This makes it possible to reduce the consumption of GaAs semiconductor materials in proportion to the degree of concentration and, consequently, to significantly reduce the cost of "solar" electricity. Additional advantages in the transition to concentrator SBs in space are: the possibility of organizing the protection of the photoconverter by structural elements of the concentrating system from ionizing radiation; the possibility of choosing the thermal mode of the solar cell, which provides thermal annealing of radiation defects; improving the radiation resistance of solar cells operating at an increased photocurrent density due to photon and injection "annealing" of radiation defects. In cascade solar cells, a significant increase in efficiency up to 25-27% and up to values ​​of the order of 30-35% with concentrated irradiation can be achieved. In recent years, AlGaAs / GaAs solar cells have been created at the A.F. Ioffe Physicotechnical Institute, in which, due to improved photosensitivity in the "violet" region of the spectrum, efficiency values ​​​​of 23-25% are achieved, close to the theoretical limit for a solar cell with one p-n junction . The addition of narrow-gap materials based on InP/InGaAs and AlGaSb/GaSb to these PV cells made it possible to create mechanically coupled cascade PV cells with an efficiency of up to 28%, which not only have high efficiency, but also increased radiation resistance, which will make it possible to create space SCs with an increased resource on their basis. work. 5.4. Solar cells manufactured by "Solar Wind" plant 57 Copyright JSC Central Design Bureau "BIBKOM" & LLC "Agency Book-Service" Pic. 5.5 Appearance of solar cells manufactured by the Solnechny Veter plant The Solnechny Veter plant (Krasnodar) produces photovoltaic cells based on single-crystal silicon, both p-type and n-type, using its own technology (Fig. 5.6), which provides high parameters elements and a wide range of applications at a relatively low price. The elements have a structure: Fig. 5.6. FEP structure 1 - texture with antireflection coating 2 - n+ (p+) - Si , 3 - p (n) - Si , 4 - p+ (n+) - Si , 5 - metal, 6 - sunlight. All elements, both n- and p-type, are transparent to the infrared region of the spectrum, which leads to less heating of the elements in the sun and, accordingly, an increase in their efficiency (Fig. 5.7). 58 1-sunlight 2-infra-red rays 5.7. Solar cells with a structure that transmits the red part of the spectrum The company "Solar Wind" was one of the first in the world to start the industrial production of solar cells with two-sided sensitivity on p- and n-type silicon. The company produces various modifications of elements based on a pseudo-square (Fig. 5.5) with dimensions: 103.5x103.5 mm, 125x125 mm, 156x156 mm, as well as their parts. Typical current-voltage characteristics: for example 1 2 Fig. 5.8. The current-voltage characteristics of the FEP solar cell 125x125 made of silicon with low (pos.2) and high (pos.1) resistivity are shown in Fig.5.8 Table. Electrical characteristics of solar cells: Dia- Current Power Size, Max Voltage - Max meter, KZ, XX, V ost, V mm e.g., V current, A A mm t 59 Copyright JSC Central Design Bureau BIBCOM & LLC Agency Book -Service» 85x85 100 102.8x102.8 135 103.5x103.5 125 125x125 150 2.1 2.4 3.2 3.6 3.2 3.6 4.6 5.2 0.59 0.61 - 0.59 0.61 - 0.59 0.6 1 - 0.59 0.61 - 0.49 1.85 - 0.9 2.14 1.05 0.49 2.9 - 1.4 3.3 1.6 - 0.49 2.9 - 1.4 3.3 1.6 - 0.49 4.1 - 2.0 4.7 2.3 - At present, pseudo-square photovoltaic cells are mainly produced with side sizes from 100 to 175 mm. Separate photovoltaic modules with peak power from 5 to 160 W are available for sale. Higher power modules (up to 200 W) are made to order. All modules have a clear glass cover and a durable aluminum frame. In solar panels with a protective coating of ordinary glass, photovoltaic cells are used with an efficiency of 12% or more (13-16% on average). 6. Secondary sources of electricity Secondary sources convert voltage of one magnitude and frequency into voltage of another magnitude and frequency. To ensure the operation of various on-board equipment, it is necessary to have several voltages. It is most convenient to get them using alternating voltage, so there is a DC-to-AC converter 500 (1000) Hz, 40V on board. There are 2 conversion methods: dynamic and static converters. A dynamic converter is a connection in one machine of a DC motor and an alternator. The voltage and frequency regulator of such a machine is a complex device and makes up about half the mass of the converter itself. Disadvantages: 1. does not work in a vacuum, 2. creates great interference with electronic equipment, 3. creates vibrations, 4. requires constant maintenance, 5. large flight weight , 6. low efficiency, 7. insufficiently high reliability. At present, reliable static transistor DC-to-AC converters (inverters) with a power of several kilowatts have been created for spacecraft, surpassing electric machine converters in terms of basic parameters. The efficiency of transistor converters can reach 60-70%. Compared to electric machines, static converters have the following advantages: the time to reach the operating mode is 5-10 times less and is a fraction of a second; starting currents are several times less; better quality of transient processes; there are no acoustic noises generated during the operation of the converter; long service life, small weight and dimensions. Strict requirements are imposed on them: frequency instability is not worse than 10-4, the voltage amplitude deviation is not more than ±5%, the shape of the alternating voltage must differ from the harmonic one by no more than a few%. The use of silicon transistors allows you to create converters operating at temperatures up to 80-1000C. Semiconductor devices operate in converters in the key mode. This mode allows relatively small power devices to control a sufficiently large load power. It is possible to further improve the output characteristics of static converters due to the use of additional filters, an increase in the number of conversion stages, etc. practically little effect on the increase in their dimensions and weight in comparison with electric machine converters. The technical characteristics of the converter are given in Table 1. The device is designed to power special equipment with alternating current of a stabilized frequency of 500 Hz and a stabilized voltage of 40 V. Table 1 No. 1 2 3 4 5 6 7 8 9 Supply voltage, V 27 + 4 -3 voltage, Hz Output voltage, V: single-phase three-phase Nonlinear distortion factor, % for single-phase output for three-phase output Output power, VA: single-phase output of three-phase output Load power factor: single-phase (inductive) three-phase (inductive or capacitive) Efficiency, not less Weight , kg, no more than Service life, hour 6.1. Block diagram of the converter 62 Numerical value Parameter name 500 40+1.2 –1.2 40+2 -2 5 10 0…65 0…115 0.7 0.8…1 0.62 12.5 1000 -Service» The principle of building a static converter is based on the division of functions between individual elements. On fig. 6.1. the functional diagram of the static converter is given. It consists of the following blocks: 1 - quartz master oscillator; 2 - preamplifier; 3 - phase splitter; 4 - preamplifier; 5 - three-phase voltage power amplifier; 6 - filter output three-phase voltage; 7 - relay; 8 - three-phase output voltage regulator; 9 - delay circuit; 10 - single-phase voltage power amplifier; 11 - filter output single-phase voltage; 12 - diode adder; 13 - single-phase output voltage regulator; 14 - three-phase output; 15 - single-phase output. Quartz master oscillator 1 (Fig. 6.1.) is designed to generate an alternating voltage of a stable frequency. It includes (see the block diagram of Fig. 6.2) a quartz exciter 1, a buffer-former 1 2 7 3 4 5 6 14 8 15 9 10 11 63 12 13 Service» Fig.6.1. Block diagram of a static converter 2, blocks of frequency dividers 3 and output amplifier 4. Quartz exciter 1 (CCG) provides a given stability of the output voltage of the quartz master oscillator in frequency. At the output of the quartz exciter, arbitrary-shaped pulses are formed with a repetition rate of 24 kHz, which are fed to the input of the buffer stage. The buffer stage 2 (Fig. 6.2) decouples the quartz exciter from the frequency divider and generates pulses with a steep leading edge to start the frequency dividers. The frequency divider block 3 consists of four trigger frequency dividers with a common division factor of 16. From the output of the frequency divider block, rectangular 2 1 24 kHz 3 24 kHz 4 1.5 kHz 1.5 kHz 6.2. Block diagram of the master crystal oscillator. 1 - quartz exciter, 2 - buffer stage, 3 - frequency divider unit, 4 - output amplifier. pulses with a repetition rate of 1.5 kHz are fed to the input of the output amplifier 4, where they are amplified in power and fed to the input of the phase splitter 3 (Fig. 6.1.). Preamplifier 2 (see Fig.6.1) serves to amplify the output voltage of the quartz master oscillator and eliminates the response of the phase splitter input to the output of the CCG. The preamplifier works in key mode. Phase splitter 3 (Fig. 6.1) is designed to obtain three rectangular voltages with a frequency of 500 Hz, phase shifted by 120 degrees. The frequency stability of the phase splitter is ensured by its synchronization from a quartz master oscillator. Preamplifier 4 (Fig. 6.1.) is designed to amplify the signal of the phase splitter in terms of power and eliminate the effect of changing the load of the device on the accuracy of the phase shift angle and the stability of the synchronization of the phase splitter. It is a divider by 3. Power amplifiers 5, 10 are designed to amplify the power of single-phase and three-phase voltages. A three-phase power amplifier consists of three transistorized amplifiers, made according to a push-pull circuit with a transformer output. The transistors operate in the key mode, the output windings of the transformers are connected in a "triangle" scheme. The power amplifier transistors are triggered by rectangular pulses. The output single-phase 11 and three-phase voltage filters 6 convert rectangular voltages of power amplifiers into sinusoidal ones. They consist of chokes and capacitors, which form a series oscillatory circuit. This circuit is tuned to resonance with the fundamental harmonic. Single-phase 13 and three-phase voltage regulators 8 are designed to stabilize the output single-phase and three-phase voltages by influencing the supply voltages of single-phase and three-phase power amplifiers. They are made on a bridge scheme. When creating such a converter, all these requirements are divided into various elements. The source of oscillations is a quartz oscillator, which generates oscillations of arbitrary shape, but with a stable frequency of 24 kHz. The instability is 10-4…10-6%. Since it is impossible to make quartz at a frequency of 500 Hz and in order to reduce weight, a quartz oscillator generates a frequency of 24 kHz. Then this frequency is divided by 16 times. 65 Copyright JSC "Central Design Bureau" BIBCOM " & LLC "Agency Book-Service" From the output of the divider we get a rectangular voltage with a frequency of 1500 Hz. With the help of a phase splitter, the voltage is divided by 3 times and shifted by 120º, we get a three-phase voltage of a rectangular shape. Three pre-amplifiers bring this voltage to the desired value needed to drive the power amplifiers. Three power amplifiers provide the necessary output power, and after the filters we get a sinusoidal voltage. The voltage meter determines the voltage deviation from the set value and controls the voltage regulator. If the measured voltage goes beyond the specified value, the control and signaling system (SCIS) turns off this converter and turns on the backup one. In addition, a signal from a quartz oscillator gets to the SCIS. In general, 2 quartz oscillators are used as part of a static converter. If one of them fails, then the SKIS turns on the other. All processes in this converter occur with rectangular voltages, that is, the transistors operate in a key mode, have two states - on or off. This mode is characterized by the fact that the power dissipated by the transistors is small. This leads to an increase in efficiency, a decrease in radiators, and a reduction in the weight of the entire converter. In addition, by filtering from a rectangular voltage, you can get harmonic with much less distortion. 6.2. Ways to improve the reliability of a static converter As a rule, the converter is a source for powering vital systems, and the existence of a spacecraft depends on its reliability. Increasing the reliability of a static converter is one of the first tasks in its design. There are 3 ways to improve reliability: 1. redundancy of the entire product, 2. redundancy of individual units, 3. redundancy of only unreliable elements (transistors). 66 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service As a rule, two converters are installed on board: the main and the backup. Switching from one to another occurs automatically with the help of SKIS. The use of redundant units as part of one device can significantly increase its reliability. However, such redundancy is associated with the difficulty of determining the failed unit, disconnecting the faulty unit and turning on the backup one, since the switching elements themselves may turn out to be less reliable. In the considered converter, only the crystal oscillator is reserved. Redundancy of unreliable elements is the most common and rational, since the mass of the device increases by a small amount, and the probability of failure decreases significantly. 7. Power distribution systems The power distribution system includes: electrical wires, assembly and installation equipment, distribution devices, switching equipment, anti-interference and static electricity protection devices, control devices for the operation of sources and consumers. By purpose and the number of incoming elements, the electrical energy distribution system is the most important component of the spacecraft electrical equipment and determines to a large extent its technical and operational performance. The importance and complexity of the functions performed by the electric power distribution system, as well as the specificity of its operating conditions, impose high requirements on this system, the fulfillment of which should guarantee the reliability and non-failure supply of electricity to spacecraft consumers. There are 3 types of distribution systems: centralized, decentralized and combined. The centralized spacecraft power supply system is characterized by the fact that all sources are connected to one switchgear (Fig. 7.1), called the central switchgear (CRU). On fig. 7.1 two sources of electrical energy I1 and I2 through fuses F1 and F2 are connected to the central switchgear with the help of switches B1 and B2. All Pi consumers are fed by the CIA. The advantage of such a system is that power supply is possible as long as at least one source of electricity is in operation. The disadvantages of centralized distribution are much greater. 1. Poor quality of electricity, determined by the fact that consumers are switched on and off all the time. Hence the voltage surges. 2. Heavy electrical network, since it is necessary to pull wires from all sources to the CIA, then from the CIA to all consumers. 3. If the CIA fails, all consumers are de-energized. CIA F1 B1 I1 F2 P1 B2 I2 P2 Fig. 7.1. Centralized power supply system Decentralized electricity ideally assumes that RU1 has a source I1 F1 B1 I2 B2 for distribution that each consumer has his own electricity. to RU2 68 to p o r F2 Fig.7.2. Decentralized power supply system of spacecraft Copyright JSC Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" In reality, in a decentralized distribution system, one source serves its own group of consumers (Fig. 7.2) through its own distribution devices. The advantages of such a system are somewhat better quality of electricity (fewer consumers, less power surges) and a reduction in the weight of the network (the source and consumers are located nearby). There is only one drawback in this system, but more significant - if the source fails, all consumers of its group remain without power. Such a system is mainly used in accompanying experiments, when this group of instruments is powered by a separate source not connected to the common spacecraft network. The considered distribution systems are limiting. In practice, such systems are never used. Real systems are usually intermediate. Combined distribution of electricity F1 V1 RU 1 P1 I1 V4 V5 V3 P3 F2 I2 P2 V2 RU 2 P4 Fig. 7.3. Combined Electricity Distribution System 69 Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" Let's consider a combined electric power distribution system (Fig. 7.3.) based on two sources. Each source of electrical energy has in its circuit protective equipment, a switching device and a switchgear (for example, for source I1, protection F1 and switchgear RU1). Most often, an ordinary bus is used as a switchgear. Each bus has its own consumer group. During normal operation, the distribution system can operate as a decentralized one (B1 and B2 are turned on) and as a centralized one (B3 is additionally turned on). The last mode occurs, for example, when the consumer connected to the switchgear does not have enough electricity from the source I1. Switches B4 and B5 are necessary in emergency situations. If one of the sources fails, it is switched off, and the switchgears receive electricity from one source. For example, the source I1 is out of order, B1 and B4 are turned off, and RU1 can be powered through B3 or B5. In the event of a switchgear failure, this switchgear is switched off, and both sources work for the second device. For example, RU2 failed. B2, B3 and B4 are off, B1 and B5 are on. Thus, in the combined distribution system, full redundancy of both sources and switchgear is provided. How to deal with consumers who are connected to a switchgear that has failed? Consumers are divided into four groups (in Fig. 7.3, consumer protection and switching equipment is conventionally not shown). Group P1 consumers do not affect the continuation of the flight and serve to ensure, for example, the comfort of the crew members (lighting, heating, etc.). They are distributed between the switchgear and connected to us using one line. Consumers of group P2 can be connected to one or another switchgear. Consumers of the P3 group are permanently connected to both switchgear, the wires from each switchgear go to the consumer in different cables, and, as a rule, on different sides of the spacecraft. In addition, these consumers are directly connected to some source. 70 Copyright JSC Central Design Bureau BIBCOM & OOO Agency Kniga-Service Consumers of P4 group, in addition to those specified for P3 group, have their own "super-emergency" source. These are mostly pyrotechnics. For example, it is impossible to carry out the descent of the descent vehicle without separating it from the instrument-aggregate compartment. Thus, the system has high reliability and flexibility. In reality, there are several such systems on board the spacecraft (a direct current system of primary sources of electricity, an alternating current system, a system of buffer sources), which differ in the number of consumers, their degree of importance for the reliability of the spacecraft, etc. 8. Electric network Electric networks are subject to a number of specific requirements. 1) Ensuring a reliable and uninterrupted supply of electricity to consumers in any operating conditions. This task is solved by joint construction of the network configuration, distribution and protection systems. 2) Ensuring high quality of electricity received by consumers. This is because many consumers are critical to the amount of voltage (especially reduction) or frequency. 3) Ensuring the protection of equipment from interference arising from the operation of electrical equipment and static electricity. The propagation of interference is possible in two ways. Directly from the source, interference propagates through the wires of the network. To protect against this kind of interference, filters are installed in the network that limit the propagation of interference through the network. The second way of interference is the magnetic and electric fields that exist inside the spacecraft. From an electrical point of view, network wires have capacitance and inductance, so the fields induce interference EMF in them (in some cases, the magnitude of interference pulses can reach large values). Particular attention should be paid to static atmospheric electricity. Given the high speed of the spacecraft, and despite the small number of charges, the potential on parts of the spacecraft body can reach large values. Therefore, parts of the construction of SC 71 Copyright OJSC "Central Design Bureau" BIBCOM " & LLC "Agency Kniga-Service" must be electrically connected not only through contact, but with the help of special metallization busbars. The Earth's atmosphere has its own potential, which changes with height. This must be taken into account when maneuvering the spacecraft. The type of electrical network is determined by the type of aircraft, its purpose, and the specific requirements for the power supply system. The electrical network is classified according to its purpose, the main electrical parameters of the power supply system, the type of current, voltage, frequency, network configuration, etc. By purpose, networks are divided into supply (main) and distribution (secondary distribution). The part of the electrical network from the energy source to the switchgear, as well as the sections between the switchgears, is called nutritional. The distribution network is used to transmit and distribute electrical energy from the switchgear to consumers. The section of the distribution network that feeds a group of consumers from the switchgear through a common protection apparatus is called a feeder. According to the main electrical parameters, the networks are divided into DC networks (27 V), three-phase networks (40 V, 500 or 1000 Hz) and single-phase AC networks (40 V, 500 Hz). DC networks are used, as a rule, in primary systems. According to the power transmission system, networks are divided into two-wire ungrounded, two-wire grounded and single-wire networks of direct and single-phase alternating current and three- and four-wire networks for three-phase circuits. A two-wire ungrounded (Fig. 8.1. pos. 1) network has an important advantage - when one of the wires is closed to the case, the network continues to function, but the network is heavy (two wires - direct "plus" and reverse "minus"). Typically, the network uses a battery as a buffer, which has a low internal resistance, so the level of interference in the network (between the wires) is small. The main interference occurs between the network and the case, their level is quite high. Switching and protective equipment is included in one positive wire. The two-wire grounded network is connected to the spacecraft body at one point. It is also heavy, but the level of interference in it is much lower. A significant drawback of this network is that when the positive wire is shorted to the body, the network de-energizes the consumer. 72 Copyright JSC Central Design Bureau BIBCOM & LLC Agency Book-Service In a single-wire network (Fig. 8.1, pos. 3), the spacecraft housing is used as a return wire. In this case, the network is almost twice as light, the power quality is higher, since the electrical resistance of the case is much less than the network wire. network I P I P I P R Fig.8.1. Types of networks 1 - two-wire ungrounded network; 2 - two-wire grounded network; 3 - single-wire network. A single-wire network is used in many transport systems and is called "airplane". The processes of undocking are typical for rocket and space technology (RKT). During the slow separation of the spacecraft blocks between them with a single-wire network, an arc will burn, therefore, a single-wire network has not been used in RCT until recently. The Shuttle reusable space system uses a single-wire network, obtaining significant savings in the mass of wires. A three-wire network with a neutral connected to the spacecraft housing allows you to turn on consumers for both phase and line voltage. Depending on the distribution system, networks are classified into centralized, mixed, decentralized and separate. 9. Switching equipment Switching equipment is used to control sources and consumers of electrical energy. It is subdivided into equipment of direct (manual) and remote action. Direct action equipment – ​​pushbuttons, switches, limit and travel switches 73 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service switches – designed for control in low power circuits on manned spacecraft. Switches and switches are of three types: toggle, push and rotary. They serve to close or open circuits for a long time. According to the number of switched circuits, switches and switches can be single-circuit, two- and three-circuit. Limit switches and switches belong to devices of pressure action, only pressing is carried out not by the crew, but by a special device of an electrified mechanism. Limit switches are used for a fixed stop of the mechanism when their output devices reach the extreme positions, blocking, signaling, program control of mechanisms. Limit switches are often used to signal spacecraft docking, separating any blocks, closing hatches and doors. Remote equipment includes electromagnetic (contact, relay) and electronic (non-contact) devices. The basis of the relay is an open magnetic system 1 3 4 (Fig. 9.1.), a movable armature 3, which is under the influence of a magnetic field created by the current of the coil 5. Fig. 9.1. Relay device 1 - magnetic wire 2 - return spring 2 3 - movable armature 5 4 - contact group 5 - winding 1 turns, closing contacts 4. When the power to winding 5 is turned off, spring 2 returns the armature to its original position. In space technology, in connection with the peculiarities of the spacecraft existence environment, in addition to conventional relays, special relays are used. Conventional relays are used in pressurized cabins, because under vacuum conditions, the arc that occurs when the contacts open cannot be extinguished. 74 Copyright OJSC Central Design Bureau BIBCOM & OOO Agency Kniga-Service For operation in a vacuum, special relays are used, placed in a glass flask, or relays using reed switches. 1 2 3 4 Fig. 9.2. Reed switch device 1-glass case, 2 - movable contact, 3 - magnet, 4 - fixed contact. + N 1 2 3 4 9.3. The device of a polarized relay The reed switch is a glass tube (Fig. 9.2.1) filled with neutral gas, in which the contact group 2 and 4 are located. A permanent magnet 3 is attached to one of the contacts. If a magnetic field is created around the reed switch, then contact 2 closes with contact 3. 75 Copyright OJSC "TsKB "BIBCOM" & LLC "Agency Kniga-Service" The switched on state of the considered relays occurs only when current flows through the winding. This is an irrational consumption of electricity and excess heat generation. A relay that maintains one of two positions without current flowing through the windings is called polarized. The polarized relay does not have a return spring, and the movable armature is a permanent magnet (Fig. 9.3, pos. 3). When power is applied to the left winding 1, the magnetic armature is thrown to the left, the magnetic flux created by the armature in the magnetic system 2 keeps the armature in a new position after the power is removed from the winding 1. The force of holding the armature in one of the positions is such that for throwing it to another position over 150g overload required. An example of an electronic switching device is discussed in the "Protective equipment" section. 10. Protective equipment Increasing the reliability of the spacecraft power supply system is achieved by using protective equipment that provides disconnection (isolation) of a faulty element. The selectivity of protection is understood as its ability to isolate the faulty one from all elements of the system and isolate it. The main classification parameter of protection is an electrical parameter: current, voltage and power. The reason for the increase in current can only be a consumer, so you need to protect the network and the source of electricity from a faulty consumer. Source protection is a new challenge compared to terrestrial sources. In flight, a certain amount of energy is taken to perform it. If it is spent irrationally (by feeding a faulty consumer), it may not be enough to complete the tasks of the flight. Voltage protection should be double. Overvoltage leads to the fact that consumers will overheat, since the power released is proportional to the square of the voltage. Semiconductor elements break through increased voltage. The life of most electrical devices is inversely proportional to the square of the voltage. 76 Copyright JSC Central Design Bureau BIBCOM & OOO Agency Kniga-Service Low voltage leads to failure of electronic equipment, electric motors overheat. Despite all the above, voltage protection is practically not used on board the spacecraft. This is due to the fact that the primary sources of electricity used on board, in principle, cannot produce a voltage greater than a certain one, so it makes no sense to install overvoltage protection. At present, there is a tendency to increase the service life of solar panels due to the redundancy of the number of cells, due to the excess voltage at the beginning of operation, so that by the end of operation the voltage generated by the solar battery should be nominal. During the entire period of operation, the voltage is maintained at nominal voltage using an appropriate converter, in the event of a failure of which the voltage may exceed the permissible values. In this case, overvoltage protection is required. Undervoltage protection is not implemented; Power protection is practically not used, but sometimes overheating protection is used. By the number of operations, protection can be: one-time and reusable. Disposable protection (fuses) after operation becomes unusable for further use. With such protection, it is impossible to determine the operating current. It is defined indirectly. A certain percentage is taken from the batch, the operating currents are determined, if they fit into the norms, the batch is recognized as suitable. Due to the inability to determine the true operation current of each device, the tolerance for the device is made large +/- 15%. One-time current protection - fuses. The glass fuse type SP consists of a glass tube 2, stamped metal tips 1 and calibrated wire 3 (Fig. 10.1). The operating current of the fuses Icrit is one and a half of the rated current indicated on the fuse. If the fuse has a current of 2 A, the fuse will operate at a current of 3A (+15%...-15%). Icrit =1.5* Inom. This is due to the fact that the consumer is “allowed” to consume current 20% more than the nominal one. Minimum tripping current value Iav.min. = Icrit *0.85= Inom. *0.85*1.5 = 1.275 In, that is, between the maximum allowable current of the consumer and the minimum current of the fuse operation, a gap of 0.075 In for unforeseen 10.1. Glass fuse 1 - stamped metal cap, 2 - glass case, 3 - wire that burns out. Rice. 10.2. Fuse link circumstances (increase in ambient temperature, etc.). To increase the contact of the fuse with the armature, it is made in the form of a “knife” (Fig. 10.2.) For high currents, consumers are characterized by a large inductive current component, which makes it difficult to extinguish the arc. Fuses for such currents have turned caps (to increase the contact area), filling (Fig. 10.3, pos. 4) from a material that releases a large volume of gas when heated. Due to the gas when the wire 3 burns out, the pressure rises, the arc goes out faster. 78 Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service Difficulties arise when protecting consumers with high starting current (Fig. 10.4.). If the fuse is selected for starting current, then it will not work when the current exceeds the rated current. If the protection is selected according to the rated current of the consumer, then the fuse will trip at start-up and such a consumer cannot be turned on. 1 2 3 4 Fig. 10.3. Fuse for high currents 1 - the caps are turned, 2 - the body is made of electric cardboard, 3 - wire, 4 - a material that, when heated, releases a large amount of gas. To protect these consumers, fuses have been created, consisting of two parts: non-inertia and with thermal inertia. Such fuses are called inertial fuses. Spring 5 (Fig. 10.4) does not have thermal inertia and operates at a current exceeding the starting one. Breaking the electrical circuit occurs very quickly, so the arc quickly goes out. The junction of two plates does not have time to warm up at start-up (due to the large mass) before the solder melts. Only if the current exceeds the rated current for a long time does melting occur. Due to the spring 5, the upper plate 6 (Fig. 10.4) begins to slide along the lower one and at the moment of rupture acquires a sufficiently high speed. The arc quickly goes out. 79 Copyright JSC "Central Design Bureau "BIBCOM" & OOO "Agency Book-Service" Pic. 10.4. Inertial fuse 1 - cap, 5 - spring, 6 - element with thermal inertia. Reusable current protection is based on the use of mechanical structures using bimetallic elements (circuit breakers) or on the basis of electronic circuits with thyristors as power elements. Electronic protection in many cases is also switching. Since the resistance of the switched off thyristors is extremely high (leakage current is from tens of microamperes). On fig. 10.5. a diagram explaining the principle of operation of such protection is presented. In the initial state (Fig. 10.5.), Tv and T0 thyristors are turned off, the current through Potr is zero, the capacitor is discharged. When a control voltage is applied to T0, the thyristor turns on and its resistance becomes zero. (Fig. 10.6.). A current equal to the current Cons flows through T0 and through Ri. In the circuit R1 - C - Ri, the capacitor is charged to the mains voltage. If the current Cons exceeds the allowable value, a voltage sufficient to turn on the thyristor is supplied from the US amplifier to the control electrode Tv. Resistance TV P from r R1 c 27V Tv T0 US Ri Fig. 10.5. Scheme of reusable thyristor protection Consumption - consumer R1 - resistor for charging the capacitor Pot p R1 c I P from p Ri Fig.10.6. becomes zero and the capacitor C is discharged through TV, Ri and T0 (resistance TV is 0, Fig. 10.7.). For some time, the capacitor current Ic exceeds the consumer current, the thyristor turns off, the current is de-energized. Since R1 is chosen large enough, the current Tv flowing through it is small enough and Tv turns off. The scheme has returned to its original position. 81 Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Book-Service" Consumption c Icont T0 IC Ri Fig.10.7. Differential F2 F3 current protection. F4 F5 When considering F1 P I1 F2 D1 I2 D2 F3 F1 I1 P I2 10.8. Differential current protection. distribution systems, cases were indicated when the consumer received energy from two or more sources. 82 Copyright OAO Central Design Bureau BIBCOM & LLC Agency Book-Service In fig. 10.8. (upper) shows the inclusion of such a consumer. Sources I1 and I2 are connected with consumer P with their wires. Fuse F1 is connected in series with P. To exclude the possibility of short circuits of wires from sources, there are fuses F2-F3 and F4-F5 at the ends of the wires. The circuit should work as follows. For example, when the wire is closed on the line from the source I1, the fuses F2 and F3 should burn out. The consumer must be powered from the source I2. In fact, the short circuit current flows from I1 and I2. Since the permissible spread of fuse operating currents is high (15%), fuse F4 or F5 may operate, disconnecting the consumer from a working line. And only then fuse F2 will work. The consumer is disconnected from both sources. Protection is not selective. To eliminate this phenomenon, you can apply a circuit with diodes (lower figure). In the case we have considered, the short circuit current will flow only from the source I1. Fuse F2 will work and turn off the emergency section of the circuit. The consumer receives energy from the source I1. Contents The power supply system of the spacecraft onboard complex……………………………………………. 3 1. Structure of the power supply system……………………... 4 2. Classification of primary sources…………………… 6 Chemical current sources……………………………… 3.1. General information about chemical current sources (CIS) 3.2. Silver-zinc batteries…………………… 3.2.1. Main technical and operational characteristics…………………………………………………….. 3.2.2. Arrangement of silver-zinc batteries 3.3.3. The main working characteristics of a silver -cycle battery …………………………………… ... 3.2.4. Characteristics of some industrial silver-zinc batteries…………………….…….. 3.3. Nickel-zinc batteries…………………….….. 3.4. Lithium-ion sealed prismatic and cylindrical batteries and batteries based on them….…. 3.5. Fuel cells………………………………..…….. 3.5.1. Operating principle……………………………. ..… 3.5.2. Classification of fuel cells………… 3.5.3. CVC of the fuel cell……………………… 3.5.4. Liquid fuel cell device. 3.5.5. Fuel cell with ion exchange membrane (IEM)…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. …… … 5. Solar batteries………………………………………… 5.1. Photoelectric converters………………….. 5.2. Solar batteries ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. ………………………………………………. 6. Secondary power sources……………… 6.1. Structural diagram of the converter…………… 6.2. Ways to improve the reliability of a static converter………………………………………………………………………………………………………………………………………………………………………… 7. Power distribution systems…… ……..……….. 8.Electrical network……………………………………………………………………………………………………………………………………………………………… 10. Protective equipment ……………………………………… References………………………………………….. 84 8 8 9 10 11 14 18 21 25 29 29 32 33 35 37 38 42 47 48 54 55 58 61 63 67 68 72 74 77 87 Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Book-Service" Podshivalov, E.I. Ivanov and others; under the general editorship of. D.D. Nevyarovsky V.S. Viktorova. –M.: Energoizdat, 1981.- 223p. 85 Copyright JSC "Central Design Bureau "BIBCOM" & OOO "Agency Book-Service" 2. Tuzov, V.P. Electrotechnical devices of aircraft; Proc. allowance for aviation. non-electric special universities / - M .: Higher. school, 1987. - 152 p. 3. Grilikhes, V.A. Solar energy and space flights / V.A. Grilikhes, P.P. Orlov, L.B. Popov. –M.: Nauka, 1984. - 216 p. 4. Koltun, V.M. Solar cells / V.M. Koltun. – M.: Nauka, 1987. 192 p. 5. Kravets, V. G. Fundamentals of space flight control / V. G. Kravets, V. E. Lyubinsky. - M .: Mashinostroenie, 1983.- 224 p. 5. Space energy systems / V. A. Vanke, L. V. Leskov, A. V. Lukyanov. – M.: Mashinostroenie, 1990. – 144 p. 6. Corliss, W. Energy sources on radioactive isotopes / W. Corliss, D. Harvey, -M .: Mir, 1967.- 414 p. 7. Petrovichev, M.A. Aircraft equipment systems. Laboratory workshop / M.A. Petrovichev, E. I. Davydov. - Samara: Izvvo Sam. state aerospace un-ta, 2004. - 80 p. 8. Thermoelectric generators, http://www.rif.vrn.ru/new/index.html. 9. Nickel-metal hydride batteries. 2006, e-battery.ru 10. Lavrus, V.S. Energy sources / V.S. Lavrus // NiT, 1997 11. Solid oxide fuel cells; collection of scientific and technical articles. - Snezhinsk; Publishing House RFNC - VNIITF, 2003. - 376 p. 12. Solar batteries of JSC "Saturn" in space programs. / http://www.rigel.ru/rigel/akk/index.html 14. Solar cells produced by the Solnechny Veter plant./ [email protected] [email protected] "Kniga-Service Agency" Educational publication Petrovichev Mikhail Aleksandrovich Gurtov Alexander Sergeevich POWER SUPPLY SYSTEM OF THE ONBOARD COMPLEX OF SPACE VEHICLES Tutorial Technical editor A. G. Prokhorov Editorial processing T. Yu. D e p ts o v a Computer Layout T. Yu. D e p t sova Doverstka T. Yu. Format 60x84 1/16. Offset paper. Offset printing. Pech. l. 5.5. Circulation 120 copies. Order. IP-15/2007 Samara State Aerospace University. 34 Moskovskoe shosse, Samara, 443086. Publishing House of the Samara State Aerospace University. 443086 Samara, Moscow highway, 34. 87

Rostec
OJSC "Concern "Radioelectronic Technologies"
KRET has developed a new type of battery for operation in space
The development of competitive space technology requires a transition to new types of batteries that meet the requirements of power supply systems for advanced spacecraft.
Today, spacecraft are used to organize communication systems, navigation, television, study weather conditions and natural resources.
Earth, exploration and study of deep space.
One of the main conditions for such devices is precise orientation in space and correction of motion parameters. This significantly increases the requirements for the power supply system of the apparatus. The problems of the power supply of spacecraft, and, first of all, developments to determine new sources of electricity, are of paramount importance at the world level.
Currently, the main sources of electricity for spacecraft are solar and storage batteries.
Solar batteries have reached the physical limit in terms of their characteristics. Their further improvement is possible with the use of new materials, in particular, gallium arsenide. This will increase the power of the solar battery by 2-3 times or reduce its size.
Among batteries for space vehicles, nickel-hydrogen batteries are widely used today. However, the mass-energy characteristics of these batteries reached their maximum (70-80 W*h/kg). Their further improvement is very limited and, moreover, requires large financial costs.
In this regard, at present, the active introduction of lithium-ion batteries (LIA) is taking place in the space technology market.
The performance of lithium-ion batteries is much higher than other types of batteries with a similar life and the number of charge-discharge cycles. The specific energy of lithium-ion batteries can reach 130 or more Wh / kg, and the energy efficiency is 95%.
An important fact is that LIBs of the same size are able to operate safely when they are connected in parallel into groups, thus it is easy to form lithium-ion batteries of various capacities.
One of the main differences between LIB and nickel-hydrogen batteries is the presence of electronic automation units that control and manage the charge-discharge process. They are also responsible for leveling the voltage imbalance of individual LIBs, and ensure the collection and preparation of telemetric information about the main parameters of the battery.
But still, the main advantage of lithium-ion batteries is considered to be weight reduction compared to traditional batteries. According to experts, the use of lithium-ion batteries on telecommunication satellites with a capacity of 15-20 kW will reduce the mass of batteries by 300 kg. Considering that the cost of launching 1 kg of payload into orbit is about 30 thousand dollars, this will significantly reduce financial costs.
One of the leading Russian developers of such accumulator batteries for space vehicles is JSC "Aviation Electronics and Communication Systems" (AVEX), which is part of KRET. The technological process of manufacturing lithium-ion batteries at the enterprise ensures high reliability and cost reduction.

POWER SOURCES OF SPACE VEHICLES
prof. Lukyanenko Mikhail Vasilievich
head Department of Automatic Control Systems, Siberian State Aerospace University named after Academician M.F. Reshetnev

The study and exploration of outer space require the development and creation of spacecraft for various purposes. At present, unmanned space vehicles are most widely used for the formation of a global communication system, television, navigation and geodesy, information transmission, the study of weather conditions and natural resources of the Earth, as well as deep space exploration. To create them, it is necessary to meet very strict requirements for the accuracy of the orientation of the apparatus in space and the correction of orbital parameters, and this requires an increase in the power supply of spacecraft.
One of the most important onboard systems of any spacecraft, which primarily determines its performance characteristics, reliability, service life and economic efficiency, is the power supply system. Therefore, the problems of development, research and creation of spacecraft power supply systems are of paramount importance, and their solution will allow reaching the world level in terms of specific mass indicators and the period of active existence.
Over the past decade, leading world firms have made an impulse to increase the power-to-weight ratio of spacecraft, which makes it possible, with the same restrictions on the mass of vehicles imposed by existing carriers, to continuously increase the payload power. Such achievements were made possible thanks to the efforts made by the developers of all components of the onboard power supply systems, and above all, power sources.
The main sources of electricity for spacecraft are currently solar and storage batteries.
Solar cells with silicon single-crystal photoelectric converters have reached their physical limit in terms of mass-specific characteristics. Further progress in the development of solar batteries is possible with the use of photovoltaic converters based on new materials, in particular, gallium arsenide. Three-stage gallium arsenide photovoltaic converters are already used on the US platform HS-702, on the European Spacebus-400, etc., which has more than doubled the power of the solar battery. Despite the higher cost of photovoltaic converters made of gallium arsenide, their use will increase the power of the solar battery by 2-3 times or, at the same power, reduce the area of ​​the solar battery, respectively, compared to silicon photovoltaic converters.
In geostationary orbit, the use of photoelectric converters based on gallium arsenide makes it possible to provide a specific power of a solar battery of 302 W/m2 at the beginning of operation and 230 W/m2 at the end of its active life (10-15 years).
The development of four-stage gallium arsenide photovoltaic converters with an efficiency of about 40% will enable the specific power of a solar battery to be up to 460 W/m2 at the beginning of operation and 370 W/m2 at the end of its active life. In the short term, we should expect a significant improvement in the mass-specific characteristics of solar batteries.
At present, accumulators based on the nickel-hydrogen electrochemical system are widely used on spacecraft, however, the energy-mass characteristics of these accumulators have reached their limit (70–80 W h/kg). The possibility of further improvement of the specific characteristics of nickel-hydrogen batteries is very limited and requires large financial costs.
To create competitive space technology, it was necessary to switch to new types of electrochemical power sources suitable for use as part of the power supply system for advanced spacecraft.
Lithium-ion batteries are currently being actively introduced into the space technology market. This is due to the fact that lithium-ion batteries have a higher energy density compared to nickel-hydrogen batteries.
The main advantage of a lithium-ion battery is the reduction in mass due to the higher energy-to-mass ratio. The energy-to-weight ratio of lithium-ion batteries is higher (125 Wh/kg) compared to the maximum achieved for nickel-hydrogen batteries (80 Wh/kg).
The main advantages of lithium-ion batteries are:
- reduction in battery mass due to a higher energy-to-mass ratio (weight reduction for a battery is ~40%);
- low heat generation and high energy efficiency (charge-discharge cycle) with very low self-discharge, which provides the simplest control during launch, transfer orbit and normal operation;
- a more technological process for manufacturing lithium-ion batteries compared to nickel-hydrogen batteries, which allows for good repeatability of characteristics, high reliability and cost reduction.
According to SAFT (France) experts, the use of lithium-ion batteries on telecommunication satellites with a capacity of 15-20 kW will reduce the mass of batteries by 300 kg (the cost of putting 1 kg of payload into orbit is ~$30,000).
The main characteristics of the lithium-ion battery VES140 (developed by SAFT): guaranteed capacity 39 Ah, average voltage 3.6 V, voltage at the end of charge 4.1 V, energy 140 Wh, specific energy 126 Wh/kg , weight 1.11 kg, height 250 mm and diameter 54 mm. The VES140 battery is space qualified.
In Russia today JSC "Saturn" (Krasnodar) has developed and manufactured a lithium-ion battery LIGP-120. The main characteristics of the LIGP-120 battery: nominal capacity 120 Ah, average voltage 3.64 V, specific energy 160 W * h / kg, weight 2.95 kg, height 260 mm, width 104.6 mm and depth 44.1 mm. The battery has a prismatic shape, which gives significant advantages in terms of specific volumetric energy of the battery compared to SAFT batteries. By varying the geometric dimensions of the electrode, it is possible to obtain a battery of various capacities. This design provides the highest specific-volume characteristics of the battery and allows you to arrange the battery pack, providing optimal thermal conditions.
Modern spacecraft power supply systems are a complex complex of power sources, converters and distribution devices, combined into an automatic control system and designed to power onboard loads. Secondary power supplies are an energy-converting complex consisting of a certain number of identical pulse voltage converters operating for a common load. In the traditional version, as pulse voltage converters, classical converters with a rectangular shape of current and voltage of a key element and control by means of pulse-width modulation are used.
To improve the technical and economic indicators of the spacecraft power supply system, such as specific power, efficiency, speed, electromagnetic compatibility, we proposed to use quasi-resonant voltage converters. The operation modes of two quasi-resonant series-type voltage converters connected in parallel with switching of an electronic key at zero current values ​​and a frequency-pulse control law were studied. According to the results of modeling and research of the characteristics of prototypes of quasi-resonant voltage converters, the advantages of this type of converters were confirmed.
The results obtained allow us to conclude that the proposed quasi-resonant voltage converters will find wide application in power supply systems of digital and telecommunication systems, instrumentation, technological equipment, automation and telemechanics systems, security systems, etc.
Actual problems are the study of the features of the functioning of space power sources, the development of their mathematical models and the study of energy and dynamic modes.
For these purposes, we have developed and manufactured unique equipment for the study of spacecraft power supply systems, which allows us to automatically perform versatile tests of onboard power sources (solar and storage batteries) and power supply systems in general.
In addition, an automated workstation for studying the energy-thermal regimes of lithium-ion batteries and battery modules and a hardware complex for studying the energy and dynamic characteristics of gallium arsenide solar cells were developed and manufactured.
An important aspect of the work is also the creation and research of alternative sources of electricity for space vehicles. We have carried out studies of a flywheel energy storage device, which is a super flywheel combined with an electric machine. A flywheel rotating in a vacuum on magnetic bearings has an efficiency of 100%. A two-rotor flywheel energy storage device has a property that allows realizing a triaxial angular orientation. In this case, the power gyroscope (gyrodin), as an independent separate subsystem, can be excluded, i.e. flywheel energy storage combines the functions of energy storage and power gyroscope.
Researches of electrodynamic tether systems as a source of electric power of a spacecraft have been carried out. To date, a mathematical model of an electrodynamic cable system has been developed to calculate the maximum power; dependences of energy characteristics on orbit parameters and tether length were determined; a method was developed for determining the parameters of a tether system that ensure the generation of a given power; the parameters of the orbit (altitude and inclination) were determined, at which the most efficient use of tether systems in the power generation mode is achieved; the possibilities of the cable system during operation in the traction mode were investigated.

6 solar panels are clearly visible, rigidly fixed to the body. To maximize the power of such an installation, a constant orientation of the body of the apparatus to the Sun is necessary, which required the development of an original attitude control system.

Spacecraft power supply system (power supply system, BOT) - the spacecraft system, which provides power to other systems, is one of the most important systems, in many ways it determines the geometry of spacecraft, design, mass, and active life. The failure of the power supply system leads to the failure of the entire apparatus.

The power supply system usually includes: a primary and secondary source of electricity, converters, chargers and control automation.

System Settings

The required power of the power plant of the apparatus is constantly growing as new tasks are mastered. So the first artificial satellite of the Earth (1957) had a power plant with a power of about 40 W, the Molniya-1 + device (1967) had a power plant with a power of 460 W, the communications satellite Yahsat 1B (2011) - 12 kW.

Today, most of the onboard equipment of foreign-made spacecraft is powered by a constant voltage of 50 or 100 volts. If it is necessary to provide the consumer with an alternating voltage or a constant non-standard value, static semiconductor converters are used.

Primary Energy Sources

Various energy generators are used as primary sources:

• , in particular:

The composition of the primary source includes not only the actual generator of electricity, but also the systems serving it, for example, the solar array orientation system.

Often, energy sources combine, for example, a solar battery with a chemical battery.

Solar panels

To date, solar panels are considered one of the most reliable and well-established options for providing spacecraft with energy.

The radiation power of the Sun in the Earth's orbit is 1367 W / m². This allows you to get about 130 W per 1 m² of the surface of solar panels (with an efficiency of 8 ... 13%). Solar panels are located either on the outer surface of the apparatus or on drop-down rigid panels. To maximize the energy given off by batteries, the perpendicular to their surface should be directed to the Sun with an accuracy of 10…15˚. In the case of rigid panels, this is achieved either by the orientation of the spacecraft itself or by a specialized autonomous electromechanical solar array orientation system, while the panels are movable relative to the body of the apparatus. On some satellites, non-orientable batteries are used, placing them on the surface so that the necessary power is provided at any position of the device.

Solar panels degrade over time due to the following factors:

• meteor erosion, which reduces the optical properties of the surface of photoelectric converters;
• radiation that lowers the photovoltage, especially during solar flares and when flying in the Earth's radiation belt;
• thermal shocks due to deep cooling of the structure in the shaded parts of the orbit, heating in the illuminated parts and vice versa. This phenomenon destroys the fastening of individual battery cells, the connections between them.

There are a number of measures to protect batteries from these phenomena. The time of effective operation of solar batteries is several years; this is one of the limiting factors that determine the time of active existence of a spacecraft.

When the batteries are shaded as a result of maneuvers or entering the shadow of the planet, the generation of energy by photoelectric converters stops, so the power supply system is supplemented with chemical batteries (buffer chemical batteries).

Rechargeable batteries

The most common in space technology are nickel-cadmium batteries, as they provide the largest number of charge-discharge cycles and have the best overcharge resistance. These factors come to the fore when the service life of the device is more than a year. Another important characteristic of a chemical battery is the specific energy, which determines the weight and size characteristics of the battery. Another important characteristic is reliability, since redundancy of chemical batteries is highly undesirable due to their high mass. Batteries used in space technology, as a rule, are hermetically sealed; tightness is usually achieved with cermet seals. Batteries also have the following requirements:

• high specific weight and size characteristics;
• high electrical characteristics;
• wide operating temperature range;
• Possibility of charging with low currents;
• low self-discharge currents.

In addition to the main function, the battery can play the role of a voltage regulator of the on-board network, since in the operating temperature range its voltage changes little when the load current changes.

fuel cells

This type of power source was first used on the Gemini spacecraft in 1966. Fuel cells have high weight and size characteristics and power density compared to a pair of solar batteries and a chemical battery, are resistant to overloads, have a stable voltage, and are silent. However, they require a supply of fuel, therefore they are used on vehicles with a period of stay in space from several days to 1-2 months.

Mostly hydrogen-oxygen fuel cells are used, since hydrogen provides the highest calorific value, and, in addition, the water formed as a result of the reaction can be used in manned spacecraft. To ensure the normal operation of fuel cells, it is necessary to ensure the removal of water and heat formed as a result of the reaction. Another limiting factor is the relatively high cost of liquid hydrogen and oxygen, the complexity of their storage.