The growth of homogeneous crystals of solid solutions of A2B6 and A3B5 compounds is considered one of the promising areas of space materials science. This method has already been used to grow crystals in space.

However, even here, in some cases, a large inhomogeneity of the properties of the grown crystals was observed. Currently, research in this direction continues abroad. In particular, an extensive program of theoretical research and ground-based experiments is being carried out in Japan to prepare space experiments to obtain homogeneous In1-xGaxAs and Cd1-xZnxTe crystals on the Japanese ISS module. Similar experiments are planned by European scientists under the MAP program. Therefore, the planned VAMPIR experiment corresponds to the latest trends in space materials science.

INTRODUCTION

Today, many achievements of astronautics are widely used in various branches of the national economy. The use of artificial Earth satellites for the needs of communications, television, meteorology, cartography, navigation, for the study of natural resources, in the interests of geology, agriculture, forestry, and fisheries has firmly entered the daily activities of mankind. However, the continuous improvement of space facilities opens up more and more new possibilities for their application in the national economy and science. One of the promising areas of cosmonautics is the production of new materials in osmosis. A practical solution to this important scientific and technical problem has become possible in recent years thanks to the successes achieved in the creation of long-term manned orbital stations and transport vehicles designed to deliver astronauts to these stations and return to Earth along with the necessary consumables (photographic film, fuel, food supplies and etc.).

Research in the field of the production of materials in space is due to the desire to use in technological processes the unusual conditions created during the movement of spacecraft in near-Earth orbits: first of all, a long state of weightlessness, as well as the surrounding deep vacuum, high and low temperatures and cosmic radiation.

Under conditions of weightlessness, a number of known physical processes proceed differently than under the earthly conditions familiar to us (under the influence of gravity). Thus, in weightlessness there is no Archimedes force, which under ordinary terrestrial conditions causes the stratification of liquid substances with different densities, natural convection is weakened, which under terrestrial conditions leads to mixing of layers of liquids and gases with different temperatures. This opens up fundamental possibilities both for obtaining qualitatively new materials in zero gravity and for improving the properties of existing materials.

In weightlessness, containerless retention of liquid metal in space is possible, thanks to which it is possible to avoid its contamination due to the ingress of impurities from the walls of the container and to obtain ultrapure substances as a result. In weightlessness, the behavior of liquids is determined by surface tension forces, and this must be taken into account even when performing such common technological processes as welding, soldering, melting, etc.

In the USSR, the first technological experiments were carried out in 1969. On board the Soyuz-6 manned spacecraft in conditions of prolonged weightlessness, the USSR pilot-cosmonaut V.N. E. O. Paton of the Academy of Sciences of the Ukrainian SSR, worked out various methods of welding metals. The practical possibility of performing various welding operations in space conditions was confirmed. Technological experiments were carried out in 1975 during the flight of the Salyut-4 orbital station, as well as during the joint flight of the Soyuz and Apollo spacecraft. Some technological experiments were carried out on vertically launched high-altitude rockets during their passive (with disabled engines) flight in the upper layers of the atmosphere (in this case, the state of weightlessness is ensured for a short time - about ten minutes).

A new step towards the creation of the scientific foundations of space production was made during the flight of the Salyut-5 orbital scientific station, when the USSR pilot-cosmonauts B.V. Voltov, V.M. Zholobov, V.V. Gorbato and Yu.N. Glazkov carried out a cycle of technological experiments using a set of instruments "Crystal", "Flow", "Sphere", "Diffusion" and "Reaction".

Space technology research is also being carried out in the United States and other countries. Various technological experiments were carried out on the Apollo 14, -16, -17 spacecraft, at the Skylab orbital station, during the launch of the Black Brant high-altitude rockets.

This brochure provides an overview of the current state of research in the field of space technology and space production. It tells about promising areas of space production, such as obtaining metals, semiconductor materials, optical glass, ceramics, biomedical preparations, etc.

Physical conditions on board spacecraft

During the flight of spacecraft in near-Earth orbits, conditions arise on board that a person usually does not encounter on Earth. The first of these is prolonged weightlessness.

As you know, the weight of a body is the force with which it acts on a support. If both the body and the support move freely under the action of gravity with the same acceleration, i.e., fall freely, then the weight of the body disappears. This property of freely falling bodies was established by Galileo. He wrote: “We feel a load on our shoulders when we try to prevent its free fall. But if we begin to move down with the same speed as the load lying on our back, then how can it press and burden us? It is as if we wanted to hit with a spear someone who runs ahead of us with the same speed with which the spear moves.

When a spacecraft moves in Earth orbit, it is in free fall. The device falls all the time, but cannot reach the Earth's surface, because such a speed is given to it, which makes it endlessly rotate around it (Fig. 1). This is the so-called first cosmic velocity (7.8 km/s). Naturally, all objects on board the apparatus lose their weight, in other words, a state of weightlessness sets in.

Rice. 1. The emergence of weightlessness on a spacecraft

The state of weightlessness can also be reproduced on Earth, but only for short periods of time. To do this, for example, weightlessness towers are used - high structures, inside which a research container falls freely. The same condition occurs on board aircraft flying with the engines switched off along special elliptical trajectories. In towers, the state of weightlessness lasts a few seconds, on airplanes - tens of seconds. On board the spacecraft, this state can continue for an arbitrarily long time.

This state of total weightlessness is an idealization of the conditions that actually exist during space flight. In fact, this state is violated due to various small accelerations acting on the spacecraft during orbital flight. In accordance with Newton's 2nd law, the appearance of such accelerations means that small body forces begin to act on all objects on the spacecraft, and, consequently, the state of weightlessness is violated.

The small accelerations acting on the spacecraft can be divided into two groups. The first group includes accelerations associated with a change in the speed of the apparatus itself. For example, due to the resistance of the upper layers of the atmosphere, when the apparatus moves at an altitude of about 200 km, it experiences an acceleration of the order of 10 -5 g 0 (g 0 is the acceleration of gravity near the Earth's surface, equal to 981 cm / s 2). When the engines are turned on on the spacecraft to transfer it to a new orbit, it also experiences the effect of accelerations.

The second group includes accelerations associated with a change in the orientation of the spacecraft in space or with displacements of mass on board. These accelerations occur during the operation of the engines of the orientation system, during the movements of cosmonauts, etc. Usually, the value of the accelerations created by the engines of orientation is 10 -6 - 10 -4 g 0 . Accelerations arising due to different activities of astronauts lie in the range 10 -5 - 10 -3 g 0 .

When talking about weightlessness, the authors of some popular articles on space technology use the terms "microgravity", "world without gravity" and even "gravitational silence". Since in the state of weightlessness there is no weight, but there are gravitational forces, these terms should be recognized as erroneous.

Let us now consider other conditions that exist on board spacecraft during their flight around the Earth. First of all, it is a deep vacuum. The pressure of the upper atmosphere at an altitude of 200 km is about 10–6 mm Hg. Art., and at an altitude of 300 km - about 10 -8 mm Hg. Art. Such a vacuum can also be obtained on Earth. However, open space can be likened to a vacuum pump of enormous capacity, capable of very quickly pumping out gas from any container of a spacecraft (for this, it is enough to depressurize it). In this case, however, it is necessary to take into account the action of some factors that lead to a deterioration of the vacuum near the spacecraft: gas leakage from its internal parts, destruction of its shells under the action of solar radiation, pollution of the surrounding space due to the operation of engines of orientation and correction systems.

A typical scheme of the technological process for the production of any material is that energy is supplied to the initial raw material, which ensures the passage of certain phase transformations or chemical reactions, which lead to the desired product. The most natural source of energy for materials processing in space is the Sun. In near-Earth orbit, the energy density of solar radiation is about 1.4 kW/m 2 , and 97% of this value is in the wavelength range from 3 × 10 3 to 2 × 10 4 ?. However, the direct use of solar energy for heating materials is associated with a number of difficulties. First, solar energy cannot be used in the darkened section of the spacecraft's trajectory. Secondly, it is required to provide a constant orientation of radiation receivers to the Sun. And this, in turn, complicates the operation of the spacecraft attitude control system and can lead to an undesirable increase in accelerations that violate the state of weightlessness.

As for other conditions that can be implemented on board spacecraft (low temperatures, the use of a hard component of solar radiation, etc.), their use in the interests of space production is not currently envisaged.

The behavior of matter in weightlessness

Aggregate and phase states of matter. When considering the features of the behavior of matter in space conditions, such concepts as aggregate and phase states, phase and components are often used. Let's define these concepts.

Aggregate states of matter differ in the nature of the thermal motion of molecules or atoms. Usually they talk about three states of aggregation - gaseous, solid and liquid. In gases, the molecules are almost not bound by attractive forces and move freely, filling the entire vessel. The structure of crystalline solids is characterized by high orderliness - the atoms are located at the nodes of the crystal lattice, near which they perform only thermal vibrations. As a result, crystalline bodies have a strictly limited shape, and when you try to somehow change it, significant elastic forces arise that counteract such a change.

Along with crystals, another kind of solids is also known - amorphous bodies. The main feature of the internal structure of amorphous solids is the lack of complete order: only in the arrangement of neighboring atoms is order observed, which is replaced by a chaotic arrangement of them relative to each other at greater distances. The most important example of an amorphous state is glass.

The same property - short-range order in the arrangement of neighboring atoms - is possessed by a substance in a liquid state of aggregation. For this reason, a change in the volume of a liquid does not cause the appearance of significant elastic forces in it, and under normal conditions, the liquid takes the shape of the vessel in which it is located.

If a substance consists of several components (chemical elements or compounds), then its properties depend on the relative concentration of these components, as well as on temperature, pressure and other parameters. To characterize the final product resulting from such a combination of components, the concept of a phase is used. If the substance under consideration consists of homogeneous parts bordering each other, the physical or chemical properties of which are different, then such parts are called phases. For example, a mixture of ice and water is a two-phase system, and water in which air is dissolved is a single-phase system, because in this case there is no interface between the components.

Phase state - a concept based on the structural representation of the term "phase". The phase state of a substance is determined only by the nature of the mutual arrangement of atoms or molecules, and not by their relative motion. The presence of long-range order (complete order) corresponds to the crystalline phase state, short-range order - to an amorphous phase state, the complete absence of order - to the gaseous phase state.

The phase state does not necessarily coincide with the state of aggregation. For example, an amorphous phase state corresponds to an ordinary liquid state of aggregation and a solid glassy state. The solid state of aggregation corresponds to two phases - crystalline and amorphous (glassy).

Rice. 2. Diagramp-t equilibrium of a one-component system

The transition of a substance from one phase state to another is called a phase transition, or transformation. If two or more different phases of a substance at a given temperature and pressure exist simultaneously, in contact with each other, then they speak of phase equilibrium. On fig. As an example, Figure 2 shows the phase equilibrium diagram of a one-component system plotted in the coordinates pressure ( R) - temperature ( T). Here is the isobar (i.e., a straight line of constant pressure) ah corresponds to direct transitions solid - liquid (melting and solidification) and liquid - gas (evaporation and condensation), isobar s-s- transition solid - gas (sublimation), and the isobar in-in- the coexistence of all three phases in the so-called triple point, at certain values R and T.

Effect of weightlessness on liquid. How does gravity affect the behavior of matter in various states of aggregation? In solids, atoms and molecules are arranged in a strictly defined order, and the force of gravity cannot have a significant effect on the processes occurring in this state.

This force can affect processes in gases more significantly. It is known, for example, that under conditions of uneven heating of various layers of gas in the atmosphere, free convection arises under the action of gravity, i.e., an ordered exchange of gas between these layers. Under weightless conditions, this effect may not occur.

But the gravitational force has a particularly strong effect on the liquid. During the transition to weightlessness in the liquid, the Archimedes force, which acts on components of different densities and leads to their separation, disappears, the nature of convection flows changes, the relative role of intermolecular interactions in the liquid increases, and it becomes possible to freely retain it outside the vessel (the phenomenon of levitation). For these reasons, let us consider in more detail the processes occurring in a liquid.

As in a gas, molecules in a liquid do not maintain a constant position, but move from place to place due to thermal energy. If at any point in the liquid particles of the same type predominate, then due to more frequent collisions with each other, they gradually move into a zone where their concentration is lower. This process is called diffusion. Due to diffusion over time t particles are displaced by a distance X = (2Dt) 1/2 , where D- diffusion coefficient. If we consider particles as spheres with a radius r, then D = W · (?? r) -one . Here W- thermal energy of particles, ? is the viscosity of a liquid, which is highly dependent on its temperature. When the liquid is cooled, the viscosity increases and, accordingly, the diffusion processes slow down.

If the change in the concentration of particles of the same type at a distance ? x inside the liquid is ? With, then the number of particles must pass through a unit area in 1 s I = - D? c/? x.

A liquid may contain several components at the same time. If the content of one of the components is low, then this component is considered as an impurity. If at the initial moment the impurity is distributed unevenly in the liquid, then diffusion processes in the liquid lead to the establishment of a uniform distribution (homogenization).

In some cases, the liquid may contain components of different densities. On Earth, under the action of the Archimedes force, these components are gradually separated (for example, cream and skim milk are formed from milk). In weightlessness, this separation does not exist, and after the solidification of such liquids, substances with unique properties can be obtained. The liquid may also contain phases that are immiscible with each other, such as kerosene and water. On Earth, clear boundaries are formed between them. In weightlessness, by mixing, one can obtain a stable mixture consisting of small drops of one or the other phase. After hardening, homogeneous composite materials, foam metals, etc. can be obtained from such mixtures of different phases.

The appearance of interfaces between different phases in a liquid is associated with the presence of a surface tension force, or capillary force, which arises due to the interaction between liquid molecules. Surface tension can be likened to the force that returns a string to its original state when a player tries to pull it aside. It is the force of surface tension that causes drops to fall from a poorly closed tap, and not a thin trickle of water. But on Earth, these drops are small: the force of gravity is much greater than the forces of surface tension and breaks too large of them into pieces. In weightlessness, nothing can prevent the formation of very large drops, and a liquid body, left to itself, will take on a spherical shape.

In fact, on board the spacecraft, due to various kinds of small accelerations, the state of weightlessness is violated. If a r- the radius of the sphere, the shape of which is taken by the liquid, then the capillary force acting on it is approximately equal to? r, where? - coefficient of surface tension. The magnitude of the inertial body forces acting on the liquid is equal to? gr 3 where? is the density of the liquid, g- small acceleration. Obviously surface tension effects will play a major role when? (? gr 2) –1 > 1. This condition determines the possibility of obtaining, in a state close to weightlessness, liquid spheres with a radius r. Such liquid spheres on board spacecraft can be in a free-floating state, when vessels are not needed to hold them. If it is a liquid melt, then when it solidifies on the Earth, harmful impurities come from the walls of the vessel. In space, you can do without a vessel and, therefore, get more pure substances.

Heat and mass transfer in weightlessness. The transition to weightlessness also has a significant effect on the processes of heat and mass transfer in liquids and gases. Heat can be transferred by conduction, convection, or radiation, or any combination of these mechanisms. Thermal conductivity is the process of transferring heat from a zone with a higher temperature to a zone where the temperature is lower, by diffusion of medium molecules between these zones. For this reason, the thermal conductivity coefficient is proportional to the diffusion coefficient.

Heat transfer by radiation is typical mainly for solid and liquid bodies and occurs at sufficiently high temperatures. The processes of radiant heat transfer and thermal conductivity do not depend on gravity or on small body forces acting on board spacecraft.

Another thing is convective heat transfer. Convection is the transfer of heat in a liquid or gaseous medium by macroscopic movement of the substance of this medium. The simplest example of convection has already been cited above - free (or natural) convection arising from uneven temperature distribution in a medium subject to the action of mass forces (for example, gravity or inertial forces caused by small accelerations on board the spacecraft). Everyone can easily observe this phenomenon at home in any boilers, when layers of liquid having a higher temperature and, as a result, a lower density will float up and carry heat with them, and in their place, on the hot bottom of the boiler, more cold and dense layers.

The relative role of heat transfer due to free convection and thermal conductivity is determined by the Rayleigh number:

Here g is the acceleration acting on the system, L is the characteristic size of the system, ? - coefficient of volumetric expansion, ? T- temperature difference in the environment, ? - coefficient of thermal conductivity, ? - viscosity of the medium. Hence it follows that under conditions approaching weightlessness ( g -> 0), Ra-> 0, and, consequently, the role of convection leading to efficient mixing of the medium can be neglected.

This conclusion has a double meaning. First, the contribution of convection to heat transfer processes decreases, and heat transfer is carried out by a slower heat conduction process. Secondly, the exclusion of convection currents in the medium leads to the fact that the main role in mass transfer will be played not by macroscopic displacements of matter, but by diffusion processes. And this, in turn, opens up the possibility of obtaining substances in which the distribution of impurities will be much more uniform than on Earth.

In addition to free convection, there are a number of other convection effects, some of which depend on body forces, while others do not. Forced convection is also known, which occurs under the influence of some external factor (for example, a stirrer, pump, etc.). In space conditions, this type of convection is used to ensure the required rate of heat removal from operating units.

As an example of convection that does not depend on body forces, let us point out thermocapillary convection, which is expressed in the fact that waves can arise and propagate at the boundary of the liquid phase. Capillary waves are caused by temperature drops, due to the presence of which the value of the surface tension coefficient is not constant along the surface. This type of convection flow obviously does not depend on the value of g and can lead to a deterioration in the homogeneity of materials obtained in space conditions. A way to compensate for the detrimental effects of this effect is to reduce the actual temperature differences along the interface.

Spacecraft and special equipment for space production

Equipment for space experiments. Speaking about the problem of production of new materials in space, they usually mean five areas of research and development:

1. Space metallurgy.

2. Semiconductor materials.

3. Glass and ceramics.

4. Medico-biological preparations.

5. Study of physical effects in weightlessness.

The first four directions are directly aimed at obtaining new or improved materials and products on board spacecraft (SC). The task of the fifth direction is to develop the science of the behavior of matter in space conditions in order to create the theoretical foundations of space production.

Conducting research in all these areas requires the development of special on-board installations. Therefore, before proceeding to the analysis of specific areas, it is advisable to consider how things stand with the creation of special equipment for space experiments. At the same time, in this section, we restrict ourselves to consideration of the most universal types of installations that can be used to solve a number of different problems. It is more convenient to talk about those experimental facilities that have a narrower purpose or are designed to carry out specific studies by discussing these studies themselves.

For all practical directions, with the exception of obtaining biological preparations, the basic scheme of the production process is as follows. The initial material (raw material) is subjected to heat treatment on board the spacecraft, melts or evaporates. Then it hardens. Since this process takes place under weightless conditions, an improvement in the characteristics of the final product can be expected, in accordance with the analysis performed in the previous chapter. For these reasons, the main option for processing equipment for the processing of inorganic materials is heating installations of various types.

The heat of exothermic reactions can be used to heat the starting material. A typical heater of this type consists of a cylindrical cartridge filled with a mixture of chemicals and an ampule with the test material, which is placed along the axis of the cartridge. A low-power electrical impulse is usually used to initiate a chemical reaction. The advantage of such installations is that in them relatively high temperatures can be obtained in relatively short times (seconds or tens of seconds). Therefore, such heating installations are used primarily in cases where the duration of the state of weightlessness is limited.

Another kind of heating devices for material processing are electric heating furnaces. Several structurally different variants of such furnaces are known. The temperature of 1200–2400 °C is maintained in the working zone of the isothermal furnace. To reduce energy consumption, this area is surrounded by multi-foil insulation made from special materials.

To grow crystals, it is necessary that the furnace has a zone with a temperature difference. On fig. 3 shows one of the possible schemes of installations of this type. An ampoule containing the test substance is pulled through the zone with a temperature difference. At the point where the melting point is reached, the raw material melts, and when the molten material enters the region of lower temperatures, it begins to crystallize. The existing installations of this type provide a temperature of 1050–1150 °C, in the designed installations it is supposed to raise it to 2000 °C.

Rice. Fig. 3. Scheme of growing single crystals from a melt (1 - melt; 2 - seed crystal; 3 - pulling and rotation mechanisms; 4 - rod; 5 - crucible; 6 - inductor for heating the melt)

The disadvantage of installations like the one shown in Fig. 3 is that from the walls of the ampoule (crucible) impurities can enter the melt, polluting the resulting material and degrading its quality. On fig. 4 shows a diagram of an electric furnace in which the zone melting method is used, which makes it possible to partially eliminate this disadvantage. In this installation, the substance is also subjected to remelting in the zone with a temperature difference, but at the same time it does not come into direct contact with the walls of the ampoule. Heating can be carried out using high-frequency currents, sources of infrared radiation or arc light sources equipped with focusing mirrors, etc. In the latter case, the ampoule is made of a transparent material, such as quartz. The zone melting method also makes it possible to obtain higher temperatures. The molten substance does not touch the walls of the crucible and is held by surface tension forces. Therefore, the maximum dimensions of the zone are determined from the condition of the balance of the mass forces acting on the melt and the forces of surface tension. The mass forces on board the spacecraft, due to small accelerations, are much less than the force of gravity. This means that the dimensions of the molten zone under space conditions and, accordingly, the dimensions of the crystals obtained in such facilities can be much larger than on Earth.

Rice. 4. Zone melting method (1 - melted zone; 2 - inductor; 3 - furnace wall; 4 - ampoule; 5 - rod of the test substance; 6 - mechanism for pulling and rotating the rod)

On fig. Figure 5 shows a scheme for growing crystals from the vapor phase. The ampoule is placed in a furnace with a temperature difference in such a way that the source material is in the hot zone. Mass transfer is carried out in the vapor phase, and at the cold end of the ampoule, it condenses to form crystals. Vapor-phase methods are used, for example, to obtain epitaxial films, which are widely used in electrical engineering.

Epitaxy is the deposition of single-crystal films on a single-crystal substrate. The epitaxial film, as it were, repeats the structure of the substrate and is something like a two-dimensional crystal. Its perfection is determined, in particular, by the processes of convection in the vapor phase. Convection leads to uncontrolled conditions on the surface of the growing layer and ultimately to lattice defects. In space, one can count on limiting the role of convection and, accordingly, on improving the quality of the materials obtained.

Rice. 5. Scheme of growing crystals from the vapor phase

Earlier it was noted that containerless containment of liquids is possible in space conditions. Installations in which this process is carried out are called levitators. Since accelerations of the order of 10–5 - 10–4 g 0 act on board the spacecraft, measures must be taken in levitators to keep the free floating liquid in the center of the working chamber. Ultrasonic fields, aerodynamic confinement or an alternating electromagnetic field can be used for this purpose. The latter method is suitable only for conductive materials and is not suitable, for example, for working with glass. Materials can be heated in a levitator using optical heaters, high-frequency currents, electron beams, etc. Installations of this type are obviously very complex, but they make it possible to practically realize such an important advantage of the production of materials in space as their containerless processing. Levitators of various types are currently under development.

Experiments in the field of space technology. The first technological space experiments were carried out in 1969 in the Soviet Union. For this purpose, at the Institute of Electric Welding named after E. O. Paton developed a special installation "Volcano", designed to study and refine the methods of welding and cutting metals on board spacecraft. The Vulkan installation was placed aboard the Soyuz-6 spacecraft, and on October 16, 1969, the ship's crew, Soviet cosmonauts G.S. Shonin and V.N. Kubasov, successfully tested it.

In 1973–1974 a series of technological experiments was carried out on the American space station "Skylab". To carry out these experiments, a special material processing facility was developed in the USA. This setup included a vacuum chamber, an electron gun for melting samples, an electric heating furnace, and other equipment. The universal furnace developed for the Skylab station provided a maximum temperature of 1050 °C and allowed operation in various temperature conditions (constant high temperature, temperature drop along the length of the ampoule, programmed cooling). The studied samples were placed in ampoules, which were installed in the oven by the cosmonauts.

The next step in the development of work in the field of technological experiments in space was the joint Soviet-American program "Soyuz" - "Apollo" (ASTP). During the flight of these ships in July 1975, a number of new technological experiments were carried out using a modified electric furnace and installations for researching methods for obtaining pure biomedical preparations.

Conducting technological experiments was also included in the research program on the Soviet space station Salyut-5. For this purpose, a special set of instruments was developed - "Crystal", "Diffusion", "Flow", "Sphere", "Reaction" (Fig. 6), designed to study a wide range of issues in the field of sciences about matter in space, as well as for testing soldering methods in space conditions.

Technological experiments with these devices were successfully carried out in July - August 1976 by the USSR pilot-cosmonauts B. V. Voltov and V. M. Zholobov and in February 1977 by V. V. Gorbatko Yu. N. Glazkov.

Along with the research carried out aboard manned space stations and ships, both in the Soviet Union and in the United States, technological experiments were carried out automatically during high-altitude rocket launches.

A distinctive feature of these experiments is the relatively limited duration of the state of weightlessness (5–7 minutes on American rockets, about 10 minutes on Soviet ones). Therefore, to carry out such experiments in the Soviet Union, installations have been developed in which the heat of exothermic reactions is used to melt the samples.

On American high-altitude rockets, an electric ampoule furnace is used, which cannot provide such a rapid heating of the blanks and which therefore has to be turned on in advance, before the rocket launch.

Research on high-altitude rockets allows space experiments to be carried out more quickly and with simpler equipment, and therefore they should be considered as a useful addition to work on space stations and ships.

Rice. Fig. 6. Devices for carrying out technological experiments at the Salyut-5 station (a - the Crystal device; b - the Reaction device)

Space vehicles and technological modules. The prospect for the development of work in the field of materials processing technology in space is that from experimental research there will be a gradual transition to semi-industrial production on board a spacecraft of some materials, and then to production on an industrial scale. According to foreign estimates, it can be expected that by 1990 the cargo flow of space products, as well as the necessary equipment, will reach several tens of tons per year.

The creation in the USSR of the Salyut long-term orbital station and an economical system for its transport support with the help of Soyuz manned spacecraft and Progress automatic spacecraft opens up new great opportunities for conducting technological experiments, testing the necessary equipment, as well as analyzing technological processes in conditions of prolonged weightlessness .

The development and improvement of orbital manned complexes designed to solve problems of a scientific and applied nature, as you know, is the main direction in the development of domestic cosmonautics. One of the main tasks is connected with the development of the sciences of the behavior of matter under conditions of weightlessness and with meeting the needs of the production of materials in space.

Within the framework of this program, the longest flight in the history of cosmonautics of the Salyut-6 - Soyuz orbital research complex, which lasted 96 days and was successfully completed on March 16, 1978, was carried out in the Soviet Union. On board this complex, the USSR pilot-cosmonauts Yu V. Romanenko, G. M. Grechko, A. A. Gubarev and the pilot-cosmonaut of Czechoslovakia V. Remek carried out important new technological experiments.

In the future, as cargo flows increase, the means of supplying orbital scientific complexes will be improved. New cargo ships will appear to deliver equipment, instruments and blanks from various materials to orbital complexes. Products and materials obtained in space will be delivered into space and returned to Earth using reusable spacecraft. Orbital complexes will include specialized technological modules.

Some technological operations in space, such as obtaining materials of ultra-high purity, require the provision of a deep vacuum. For this purpose, in combination with DOS, it is possible to use the so-called molecular screen, which, using a special rod, is placed at a distance of about 100 m from the ship. Screen diameter - 3 m.

Since the velocities of the thermal motion of the molecules of the residual gas are less than the speed of the forward motion of the spacecraft along with the screen in orbit (8 km/s), a zone of increased rarefaction will appear behind the screen. The pressure of the residual gas in this zone will be about 10–13 - 10–14 mm Hg. Art.

The development of transport spacecraft capable of providing cost-effective transportation, the creation of long-term orbital stations of the type of the Soviet Salyut space stations open the way to the construction of operating factories in space for the production of pure materials.

According to experts, such space factories will start operating in the 1990s.

Study of the physical foundations of space production

Processes of heat and mass transfer. Elucidation of the features of the processes of heat and mass transfer under conditions close to weightlessness is necessary for the optimal organization of the production of new materials in space. In order to study these features, both theoretical and experimental studies are carried out.

One such experiment was carried out on the Salyut-5 space station by cosmonauts V. V. Gorbatko and Yu.

These studies at the Salyut-5 station were carried out using a special Diffusion device - the device was a cylindrical electric furnace containing two quartz ampoules inside, each of which was partially filled with dibenzyl and partially with tolane. These organic substances have different densities and are in a crystalline state at room temperature. The ampoules in a cylindrical electric furnace were arranged in such a way that a small mass force, which arose due to the aerodynamic deceleration of the station, was directed along their axis.

After turning on the device, both substances melted, and the process of their mutual diffusion through the interface between the melts continued for three days. The temperature along the length of the ampoules was maintained constant. After turning off the device, cooling and solidification of the alloy occurred, the structure of which had a polycrystalline character.

To compare the results of the space experiment with the theory, a computer calculation was made of the mass transfer process for conditions corresponding to the experiment with the Diffusion device. The calculation showed that since the temperature along the length of the ampoule remained constant during the experiment, there should be no thermal convection, and the concentration convection that occurs at the interface between liquids had a noticeable effect on the mass transfer only at the initial stage of the experiment. In other words, according to the calculations performed, the main contribution to the mass transfer under the studied conditions should have come from purely diffusion processes.

After the experiment was carried out and the astronauts returned to Earth, the ampoules delivered from space were carefully studied in the laboratory. Studies of the distribution of the substance along the length of the ampoule made it possible to determine the value of the diffusion coefficient. For comparison, control experiments were performed on Earth with the same ampoules. It turned out that the value of the diffusion coefficient determined under space conditions for an alloy of dibenzyl with tolane is close to theoretical knowledge (about 9.5 10–6 cm/s 2) and somewhat exceeds the value obtained in control experiments on Earth, but this discrepancy is within the error of the method. It should also be noted that on Earth there is no way to accurately reproduce the nature of those microaccelerations that acted on the melt in space.

An experiment similar in design was also staged on the Skylab space station. In contrast to the studies carried out at the Salyut-5 station, American scientists did not study the mutual diffusion of two different substances, but a simpler case - the process of self-diffusion. For this purpose, a disk made from the radioactive zinc isotope Zn 65 was inserted into a zinc cylindrical rod. When heated, the rod melted, a temperature difference was established along it, as a result of which the process of diffusion of the radioactive isotope into the base material (self-diffusion) began. Assuming that under space conditions the effect of convection on mass transfer can be neglected and the diffusion process plays the main role there, the distribution of the radioactive isotope along the length of the rod was calculated. The calculation results are in good agreement with the data of the space experiment (Fig. 7). In control experiments carried out with similar samples on Earth, the effective diffusion coefficient of radioactive zinc due to convection turned out to be 50 times higher than for space conditions.

Rice. Fig. 7. Distribution of radioactive zinc along the sample (o and? - experiments on Earth for two positions of the sample, solid line - calculation and experiments in space)

This experiment, as well as the experiment with the "Diffusion" device, showed that for the studied conditions, the influence of convection on the mass transfer in the melt can be neglected and that the diffusion transfer process plays the main role. This conclusion confirms the possibility of obtaining in space crystalline materials with a homogeneous structure, which, under terrestrial conditions, is disturbed, in particular, by convection currents. However, it is not always possible to realize this possibility in practice and ensure the production of materials with a more uniform distribution of impurities in space.

Let us consider as an example the "Universal Furnace" experiment, staged during the joint flight of the "Soyuz" and "Apollo" spacecraft. In the course of this experiment, the possibility of obtaining homogeneous single crystals of germanium containing impurities of silicon (0.5% by weight) and antimony (hundredths of a percent) was studied. The cylindrical sample was heated to the melting temperature, except for the cold end, which was supposed to be used as a “seed” during crystallization. The sample was kept at the maximum temperature for 1 h, after which it was cooled for 5 h at a rate of 0.6 deg/min, and then the furnace was uncontrollably cooled to complete cooling (Fig. 8).

Rice. 8. Cartridge for the experiment "Universal Furnace" (1 - graphite heating block; 2 - graphite thermal insert; 3 - stainless steel shell; 4 - insulation; 5 - locking mechanism; 6 - heat removal unit; 7 - copper thermal insert)

An analysis of the samples delivered to Earth showed that, contrary to expectations, after remelting and solidification under conditions close to weightlessness, the distribution of impurities in the cross section of the sample became less uniform. In this case, the lighter impurity (silicon) shifted in one direction along the sample diameter, while the heavier one (antimony) moved in the opposite direction. Such a redistribution of impurities in the sample may be due to the fact that it was precisely along the ampoule diameter that small accelerations acted during the experiment, due to the operation of the engines of the ship's orientation and stabilization system. However, the specific mechanism of the processes that led to the deterioration of the homogeneity of the impurity distribution in this experiment has not yet been unambiguously established.

It is possible that for the range of accelerations that were observed aboard the Apollo spacecraft during the Universal Furnace experiment, the convection currents were especially intense. Calculations of heat and mass transfer processes carried out by Soviet scientists with the help of computers for the conditions corresponding to this experiment confirmed this possibility. In this case, the redistribution of impurities in the melt and the deterioration of the homogeneity of the sample after its recrystallization in space should be associated precisely with the convection currents that have arisen in the melt. But there are other possible explanations for the results of the "Universal Furnace" experiment.

The considered experiments showed that for the correct organization of mass transfer processes in space it is necessary to provide such conditions when convection effects can be neglected. Otherwise, depending on the specific conditions, both an increase and a deterioration in the uniformity of the distribution of impurities in the materials under study are possible.

If in the given examples it was necessary to analyze the possible influence on the processes of heat and mass transfer of natural convection, which depends on the magnitude of the small acceleration acting on the spacecraft, then in other cases, convection effects that do not depend on accelerations should be taken into account. Let us point out as an example thermocapillary convection, which in some cases can also be the reason for the deterioration of the structure of material obtained in space.

For example, in zone melting used to grow crystals, there is an interface between the liquid and the saturated vapor above it. The temperature can change along this surface, and since the surface tension depends on it, a convection flow can occur under these conditions. When the temperature drop begins to exceed a certain critical value, convection currents appear in the melt, which are oscillatory in nature and lead to an uneven flow of impurities into the crystallization zone. As a result, the impurity inside the crystal will also be distributed inhomogeneously (banding phenomenon). Compared to free convection, the intensity of which depends on the level of acceleration on the spacecraft, overcoming thermocapillary flows requires other measures (limiting the magnitude of temperature drops, etc.).

The above experimental and theoretical studies of the processes of matter transfer under conditions close to weightlessness were related to melts. However, under these conditions, and for the gaseous state of matter, the processes of transfer may have their own characteristics. Let us also cite as an example an experiment at the Skylab station, in which the growth of semiconductor crystals - germanium selenide and telluride - from the gas phase was studied. This method is based on the fact that at the hot end of a sealed ampoule, a substance in the gas phase (germanium iodide) reacts with the surface of a solid source material, and then diffuses towards the cold end of the ampoule under the action of a temperature difference. There, in the colder zone, vapors condense on the seed crystal and the desired crystals are formed. It was expected that the mass transfer rate of the product in the gas phase would be determined by purely diffusion processes. Under terrestrial conditions, this speed increases significantly due to convection. This experiment showed that the actual rate of mass transfer in space conditions is lower than that observed on Earth, but higher than the value calculated in a purely diffusion approximation.

Similar results were also obtained in an experiment carried out during the joint flight of the Soyuz and Apollo spacecraft. This discrepancy in diffusion transfer rates can be associated with the features of chemical reactions in the gaseous state, which are not taken into account in the existing calculation methods.

Fluid mechanics. Considering fluid mechanics in zero gravity as one of the sections of the theoretical foundations of space production, it is necessary to study the issues of surface tension and wetting, capillary effects, the stability of fluid forms and the behavior of inclusions contained in it - gas bubbles, solid particles, etc. For a qualitative study of these issues it is convenient to conduct experiments on board spacecraft using water and aqueous solutions.

A series of similar demonstration experiments was carried out, for example, on the American space station Skylab. The behavior of free-floating water spheres, their vibrations caused by the push of a syringe, and the collapse of the spheres during rotation were studied by the method of filming. The influence of surface tension on the damping of vibrations of a liquid and on its interaction with a solid surface was studied by adding a soap solution to the liquid, which led to a change in the surface tension coefficient.

Another experimental setup, used at the Skylab station for demonstration experiments on fluid mechanics, made it possible to simulate the behavior of the floating zone. In this installation, between two rods that could be moved apart and rotated independently of each other, a liquid bridge was created with different surface tension coefficients (due to the addition of a soap solution to the water). This setup was used to study the stability of the liquid zone with respect to the rotation and displacement of the rods with a change in the value of the surface tension coefficient.

The next task of fluid mechanics is to study the behavior of gas and other inclusions. The importance of these studies was pointed out back in 1969 by Soviet scientists who carried out the first welding experiments on the Soyuz-6 spacecraft and noted the appearance of gas inclusions in the welds. On Earth, bubbles are removed from the liquid under the action of the Archimedes force, this does not happen in space. In some cases, such inclusions can lead to a deterioration in the quality of the material. To control the dynamics of gaseous and other inclusions in liquids, Soviet scientists proposed the use of ultrasonic vibrations of liquids and carried out experiments on board a flying laboratory under conditions of short-term weightlessness, which confirmed the promise of this method.

Given the importance of research in the field of fluid mechanics, the corresponding experiments were also included in the program of experiments at the Salyut-5 station. The purpose of these experiments was to investigate the motion of a liquid under the action of capillary forces alone and to obtain qualitative data on the behavior of bubbles in a liquid under conditions close to weightlessness. The experiments were carried out by cosmonauts B.V. Voltov and V.M. Zholobov using Potok and Reaktiya instruments.

The Potok device was a rectangular parallelepiped made of transparent plexiglass and containing two cavities inside, the inner surface of one of which is wetted by water, and the other is not. The spherical cavities are interconnected by capillary and drainage channels equipped with shut-off valves. Before the start of the experiment, the valves were opened, and under the action of surface tension forces, an aqueous solution flowed from a cavity initially filled with liquid with non-wetted walls into a cavity, the walls of which were wetted with water. Through the drainage channel, the air pressure between the cavities was equalized. When testing the instrument in a flying laboratory, the process of fluid flow from one cavity to another was recorded using filming.

When testing the device at the Salyut-5 station, the resistance of a gas bubble in a liquid to mechanical stress was studied. When the device was vigorously shaken, the gas bubble in the liquid-filled cavity broke into a large number (about 100) of small bubbles. Subsequently, these bubbles gradually merged into one large one, but the duration of this process was significant - about two days.

Rice. 9. Scheme of the location of the tube and coupling in the device "Reaction".

The Reaktiya device consisted of a body and two containers with cylindrical exo-packets, inside each of which there was a stainless steel tube with a coupling put on it (Fig. 9). Manganese-nickel solder was placed in the gap between the tube and the sleeve, which melted during the experiment, spread along the gap, and solidified upon cooling and provided strong soldered joints between the sleeve and the tube. As the study of soldered samples delivered to Earth showed, the liquid solder wetted the surfaces and flowed through the capillary gap formed between the inner surface of the coupling and the tube, from the larger annular cavity to the smaller annular cavity (Fig. 10).

Thus, using the "Reaction" device, the possibility of liquid overflow under the action of surface tension forces was demonstrated. This method of fluid flow control can be useful in practice, for example, for the production of molded products of complex shape in space. Similar experiments to study the spreading of liquid metal (tin) along copper molds of complex shape under the action of surface tension forces were also carried out during the launch of a high-altitude rocket in the USSR in March 1976.

Rice. 10. Transverse (a) and longitudinal (b) sections of a solder joint in the Reaction device

crystallization processes. The most important process of obtaining materials in space conditions is their crystallization. Single crystals can be obtained from solutions, melts, or from the vapor phase. The features of all three methods of obtaining crystals were studied on various spacecraft. Let us consider as an example the crystal growth experiments performed at the Salyut-5 station, as well as during the joint flight of the Soyuz and Apollo spacecraft.

At the Salyut-5 station, the features of crystal growth from aqueous solutions were studied. The main distinguishing feature of such experiments in space is the absence of convection in the liquid, which leads to fluctuations in the growth rate and composition of the crystal. From this point of view, the quality of crystals obtained in space should be higher. But on the other hand, under cosmic conditions, the Archimedes force does not act on gas bubbles in a liquid, and these bubbles can be captured by growing crystal faces.

The study of these processes at the Salyut-5 station was carried out using the Kristall device. It was a thermostat with three crystallizers, in each of which crystals of potassium alum were grown from their aqueous solution (see Fig. 6). Potassium alum was chosen as the material under study, since their properties and features of growth on Earth are well studied. In order to induce the crystallization process, a piece of a crystal (“seed”) was introduced into each of the solutions. On its faces, the growth of the crystal began, the material of which, due to diffusion, came from the solution. On fig. 11 shows samples of potassium alum crystals grown on the Salyut-5 orbital station.

The experiment with crystallizer No. 1 lasted for 24 days (from July 14 to August 8, 1976). The first expedition to the Salyut-5 station - cosmonauts B.V. Volynov and V.M. Zholobov - delivered crystals from this crystallizer to Earth, which grew not only on the "seed", but also in the volume of the crystallizer (mass, or volume , crystallization). The experiment with crystallizer No. 2 lasted 185 days (from August 9, 1976 to February 11, 1977). Most of this experiment took place while the Salyut-5 station was in unmanned controlled mode. The second expedition - cosmonauts V. V. Gorbatko and Yu. N. Glazkov - delivered to Earth a large number of crystals obtained during mass crystallization. An interesting phenomenon was noted - the fusion of individual crystals into chains ("necklaces"). The experiment in the crystallizer No. 3 was carried out for 11 days. A crystal that grew on a "seed" was delivered to Earth; there was no mass crystallization in this crystallizer (see Fig. 11).

The study of crystals grown in crystallizer No. 1 showed that "cosmic" crystals differ from those grown on Earth both in the external faceting of crystals (those crystal faces that are usually poorly developed in terrestrial samples are well developed) and in the internal structure (cosmic samples contain an increased amount of gas-liquid inclusions). The study of crystals obtained by mass crystallization in the crystallizer No. 2 showed that they also contain gas-liquid inclusions. Intergrowths of four to five individual crystals are observed. For a crystal grown in mold No. 3, the alternation of zones containing gas inclusions with zones free of inclusions is typical.

Rice. Fig. 11. Potassium alum crystals grown at the Salyut-5 station (a - samples from mold No. 1; b - from mold No. 2; c - from mold No. 3)

Studies of crystals delivered from space also showed that they do not show banding, which is characteristic of terrestrial conditions and indicates fluctuations in the growth rate. This result may be due to the absence of convection in the solution under space conditions.

The source of gas-liquid inclusions in crystals is obviously gas bubbles dissolved in the liquid and released at the crystallization front. The gas bubbles are captured by the growing crystal and cause the liquid solution to be entrained. Using degassed solutions in subsequent experiments, it will be possible to grow crystals in space that do not contain such inclusions. The intergrowths of crystals observed in crystallizer No. 2, in which the crystallization process lasted for about half a year, are apparently due to the mutual attraction of crystals growing in the liquid volume for a long time.

The features of the growth of crystals from the melt were also studied using germanium as an example, also in an experiment conducted during the flight of the Soyuz-Apollo spacecraft. The test samples were placed in ampoules, which were installed in an electric furnace, where germanium was subjected to partial melting followed by solidification in the programmed cooling mode at a rate of 2.4 deg/min. To experimentally determine the crystal growth rate, marks of the interface were made every four seconds by passing short pulses of electric current through the melt. During the post-flight processing of the samples, these marks were revealed, and the crystal growth rate was measured from them, which at the end of the cooling period was about 10–3 cm/s. In control experiments set up on Earth, this speed turned out to be approximately the same. This result means that, both in space and on Earth, heat transfer in the melt was determined for this case mainly by thermal conductivity, while the role of convection is negligibly small. Crystals obtained in space were much larger than those grown on Earth in the same setup.

In the experiment, which was also carried out as part of the Soyuz-Apollo program, the growth of crystals from the vapor phase was studied. Crystals of the germanium - selenium - tellurium type grew in sealed ampoules, which were placed in a zone with a temperature difference in an electric heating furnace. The experiment showed that the crystals delivered from space are more perfect than the control samples obtained on Earth (higher homogeneity, fewer crystal lattice defects, etc.). At the same time, it was found that, contrary to theoretical expectations, the mass transfer rate exceeds the value calculated in a purely diffusion approximation, but is lower than the value obtained in control experiments on Earth, where convection played a significant role. This result still requires a theoretical explanation.

Thus, experiments performed in space on growing crystals from solutions, melts, and from the vapor phase have shown that under space conditions it is possible to obtain crystalline materials with higher perfection and uniformity. At the same time, it has been established that a number of experimentally observed features of crystal growth in weightlessness have not yet received the necessary theoretical coverage and require further investigation.

Containerless solidification in weightlessness. The processes of shaping of liquid bodies and their solidification under conditions when they are not affected by the force of weight have their own characteristics. First, the liquid, left to itself under these conditions, tends, as is known, to take the form of a ball. However, in reality, when a liquid solidifies, a number of effects arise that complicate the spheroidization process: free fluctuations of the volume of the liquid, different cooling rates of the liquid on the surface and in the volume, etc. Secondly, the processes of solidification and crystallization of such a liquid in weightlessness can also proceed according to -other. First of all, this concerns convection, which, under terrestrial conditions, smooths out temperature fluctuations in the melt and contributes to the stability of the crystallization process. Third, in the case of multicomponent alloys, the absence of gravity can affect the redistribution of components inside the liquid, and thus the homogeneity of the sample.

The totality of these issues was investigated in experiments at the Skylab station, as well as in an experiment with the Sphere device at the Salyut-5 station. In the first of these experiments, blanks of pure nickel or its alloys were melted by an electron beam and then cooled by floating freely in a vacuum chamber aboard the Skylab station. Ground studies of the obtained samples showed that the deviation of their shape from spherical is about 1%, and the samples prepared from alloys contain internal pores. The purpose of another experiment was to obtain in weightlessness materials with uniform porosity by remelting silver grids. American scientists failed to obtain such materials, but when melting thin silver meshes in ampoules, spheroidization of liquid silver drops was observed. Ground studies of that part of the hardened drops, which had no contact with the walls of the ampoule during cooling, showed that their shape is far from perfect. The surface of the samples is covered with a grid of grooves, and there are shrinkage cavities in their volume. The internal structure of the samples had a cellular character. It can be assumed that it was cellular solidification and the formation of shells that prevented the formation of more regular spheres under conditions close to weightlessness.

In order to obtain new information about the processes accompanying containerless solidification of liquid metal at the Salyut-5 station, an experiment was set up with the Sfera device. Wood's eutectic alloy was chosen as the test substance, which has a minimum melting point (about 70 °C) and therefore allows minimizing power consumption (10 W). The chemical composition of the investigated alloy (by weight): bismuth - 40, lead - 40, cadmium - 10, tin - 10%. The "Sphere" device was an electric heater, inside which the investigated workpiece weighing 0.25 g was melted, which was then pushed into a lavsan bag using a rod. Inside this bag, the casting cooled and solidified without coming into contact with the walls. The time during which the preform placed in the heater was heated to the melting point was 30 s on Earth. In weightlessness, the contact between the workpiece and the walls of the heater should worsen; therefore, the heating time of the sample was increased to 2 min.

The sample delivered to Earth after the completion of the experiments had an ellipsoidal shape, and its surface was covered with randomly arranged fibers (according to cosmonaut V. M. Zholobov, the sample looked like a hedgehog). As the analysis showed, the internal structure of the sample also changed significantly due to remelting in space: the uniform distribution of the alloy components over the volume was disturbed, needle-shaped crystals with different chemical composition formed, etc. curing under containerless containment conditions. Attempts to select under laboratory conditions such a thermal regime for processing a workpiece from Wood's alloy, which would lead to a similar structure of the casting, did not give a positive result, obviously, because it is impossible to reproduce containerless sample retention on Earth.

Thus, the studies carried out to date in the field of the physical foundations of space production, including experiments carried out on various spacecraft, have confirmed the correctness of the general ideas about the features of physical processes in weightlessness and provided direct experimental evidence of the possibility of obtaining materials with improved characteristics in space. At the same time, the experiments showed the insufficiency of the existing quantitative theories of these processes and revealed the need for special studies aimed at developing the theoretical foundations for the production of new materials in space.

space metallurgy

Metallurgy deals with the production of metals and with processes that give metal alloys the necessary properties by changing their composition and structure. Metallurgy includes the processes of cleaning metals from unwanted impurities, the production of metals and alloys, heat treatment of metals, casting, coating on the surface of products, etc. Most of these processes include phase transitions to liquid or gaseous states, for which the influence of the mass forces on the composition and structure of the final material can be significant. Therefore, the transfer of metallurgical processes into space opens up fundamental possibilities for the production of materials with improved characteristics, as well as materials that cannot be obtained on Earth.

Metallurgical processes in space conditions can be used to solve the following problems.

1. Preparation of alloys in which there is no segregation due to the Archimedes force (obtaining composite materials, alloys of high homogeneity and purity, foam metals).

2. Preparation of alloys in the absence of convection currents (defect-free single crystals, improved eutectics and magnetic materials).

3. Gravity-free casting (preparation of films, wire, cast products of complex shape).

4. Crucibleless melting of metals and alloys (purification of metals and alloys, their homogeneous solidification).

5. Development of methods for obtaining permanent joints on space vehicles (welding, soldering, etc.).

Let us briefly consider the state of research aimed at obtaining materials in space by metallurgical methods.

Defect-free crystals and alloys. For the production of alloys, the initial components can be prepared both in the liquid and in the gaseous (vapor) phase, followed by crystallization. In weightlessness, due to the absence of phase separation, arbitrary combinations of components in any state can be specified. It is possible, in particular, to obtain a direct transition from the vapor phase to the solid, bypassing the melt. Materials obtained by evaporation and condensation have a finer structure, which is usually difficult to obtain in the processes of melting and solidification (melting in space conditions can be considered as a purification method). In this case, the following effects are possible in the melt: evaporation of a more volatile component, destruction of chemical compounds (oxides, nitrides, etc.).

The most important process for producing alloys is solidification. This process significantly affects the structure of the metal. During solidification, various defects can occur in the metal structure: heterogeneity of the alloy in chemical composition, porosity, etc. The presence of temperature and concentration drops in the melt can lead to convection. If the melt solidifies under conditions of temperature fluctuations, then local fluctuations in the crystal growth rate occur, which can lead to such a defect as a banded crystal structure. To overcome this structural defect, measures are needed to reduce convection.

Under space conditions, the possibility of preparing homogeneous mixtures consisting of components with different densities and with different melting points opens up. On Earth, such mixtures cannot be stable due to the Archimedes force. A special class of alloys of this type are magnetic materials, including new superconductors.

It was previously noted that one of the advantages of the zone melting method in space conditions is that it is possible to obtain single crystals of larger sizes than on Earth. The absence of gravity also makes it possible to organize the processes of directed crystallization in a new way. In this way, whiskers of great length (“whiskers”, or “whiskers”) with increased strength can be obtained.

Let us consider experiments in which the practical possibilities of space metallurgy were investigated. So, in an experiment at the Skylab station, alloys were obtained from components that are poorly mixed under terrestrial conditions. In three ampoules blanks of gold-germanium, lead-zinc-antimony, lead-tin-indium alloys were placed. Under space conditions, the samples were remelted for several hours, kept at a temperature above the melting point, and then cooled. The samples delivered to Earth have unique properties: the homogeneity of materials turned out to be higher than that of the control samples obtained on Earth, and the alloy of gold with germanium turned out to be superconducting at a temperature of about 1.5 K. Analogous mixtures obtained from a melt on Earth do not possess this property. , apparently due to the lack of homogeneity.

Within the framework of the Soviet-American ASTP program, such an experiment was carried out, the purpose of which was to study the possibility of obtaining magnetic materials with improved characteristics. Alloys of manganese-bismuth and copper-cobalt-cerium were chosen for research. The maximum temperature of 1075 °C was maintained in the working zone of the electric furnace for 0.75 h, and then the furnace cooled down for 10.5 h. Solidification took place during the sleep period of the astronauts in order to reduce the undesirable impact of vibrations during their movements inside the station. The most important result of this experiment is that the samples of the first type, hardened on board the spacecraft, have a coercive force that is 60% higher than that of the control samples obtained on Earth.

Composite materials. Composite materials, or composites, are artificially created materials that consist of a main binder and a durable reinforcing filler. Examples include the combination of aluminum (bonding material) with steel prepared in the form of filaments (reinforcing material). This also includes foam metals, i.e., metals, the volume of which contains a large number of evenly distributed gas bubbles. Compared with the components that form them, composite materials have new properties - increased strength with a lower specific gravity. An attempt to obtain composites with a base in a liquid state under terrestrial conditions leads to material delamination. The preparation of composites in space conditions can provide a more uniform distribution of the reinforcing filler.

An experiment was also set up at the Skylab station, the purpose of which was to obtain composite materials reinforced with silicon carbide "whiskers" (specific gravity 3.1). Silver (specific gravity 9.4) was chosen as the main (matrix) material. Composite materials with a metal base reinforced with "whiskers" are of practical interest due to their high strength. The technique for their production is based on successive processes of mixing, pressing and sintering.

When conducting a space experiment, the particle sizes of silver powder were ~ 0.5 mm, the diameter of the silicon carbide whiskers was ~ 0.1 μm, and the average length was ~ 10 μm. The quartz tube that housed the sample had a graphite-quartz piston with a spring to compress the sample after melting in order to extrude voids from the melt. A study of space-delivered composite materials showed that, compared with control samples, they have a much more uniform structure and higher hardness. In the case of materials obtained on Earth, structural stratification is clearly visible, and the “whiskers” float up.

Eutectics. A eutectic is a thin mixture of solids that crystallizes simultaneously at a temperature below the melting point of any of the components or any other mixtures of these components. The temperature at which such a melt crystallizes is called the eutectic temperature. Alloys of this type are often formed from components that are very different from each other (for example, Wood's eutectic alloy includes bismuth, lead, tin, cadmium). Eutectic materials are widely used in science and technology: they are used for the manufacture of gas turbine blades, as superconducting and special optical materials.

For the preparation of eutectics, the method of directional solidification is usually used, i.e., solidification in one given direction. The application of this method in space conditions is of undoubted interest, because due to the absence of convection, the homogeneity of the material can be improved, and by eliminating the contact of the melt with the walls, it is possible to obtain oxide-free materials that will have useful optical properties.

A variety of eutectics are two-phase systems such as "whiskers". These are acicular single crystals with a very perfect structure, the strength of which, due to the absence of foreign inclusions, approaches the theoretically possible. In weightlessness, such materials can be grown and introduced into liquid metal by composite casting methods. Another type of eutectics is thin epitaxial films. Such films are widely used in the manufacture of transistors by depositing a material on a solid base - a substrate from a liquid or vapor phase. The manifestation of convection in a liquid or gas leads to a distortion of the lattice of epitaxial films, to the appearance of unwanted inclusions and other structural defects in them.

A number of experiments were carried out under space conditions to study eutectic alloys. For example, in one experiment at the Skylab station, the effect of weightlessness on the structure of a copper-aluminum alloy during directional solidification was investigated. In samples delivered from space, the number of defects decreased by 12–20%. In another experiment at the Skylab station and MA 131 during the joint flight of the Soyuz and Apollo spacecraft, the production of two-phase halide eutectics (NaCl-NaF in the first case and NaCl-LiF in the second) was studied. During the solidification of such a eutectic, one of the phases (NaF or LiF) can form filaments embedded in the other phase as a matrix material.

Such eutectics can be used as optical fibers for the infrared region of the spectrum. Filamentous eutectics produced on Earth have a large number of defects, the occurrence of which is associated with oscillatory convection movements in the liquid. The structure of halide eutectics obtained in space turned out to be more perfect, which led to an improvement in their technical characteristics. Thus, the light transmission coefficient for the sample of the first type increased by 40 times, and of the second type - by 2 times in comparison with similar samples grown on Earth.

Technology for obtaining permanent connections. As noted above, the world's first work in this area was carried out in the Soviet Union in 1969 on the Soyuz-6 spacecraft. On the Soviet space station Salyut-5, cosmonauts B. V. Volynov and V. M. Zholobov continued research in this direction, successfully carrying out experiments on soldering metals using the Reaction device. The “Reaction” device (see Fig. 6) and the exocontainer placed in it were not hermetic by design, and therefore, to simulate soldering conditions in outer space, air was evacuated in advance from the sealed area between the sleeve and the tube (see Fig. 9). The tube and coupling were made of stainless steel, and to create capillary gaps between them, knurling with a depth of 0.25 mm was made on the surface of the tube. High-temperature manganese-nickel solder (soldering temperature 1200–1220 °C) was chosen as the solder, which is characterized by high mechanical properties and good corrosion resistance.

Ground-based metallographic studies and tests of welds (for vacuum tightness, for mechanical strength in a tensile tester with an internal pressure of up to 500 atm) have shown that solder joints obtained in space are not inferior in quality to those obtained in terrestrial conditions, and surpass them in a number of indicators. In particular, a uniform filling of the gaps with solder is observed, and the metal microstructure is more uniform (see Fig. 10).

The results of testing various methods of welding and soldering on board spacecraft confirm that these methods of obtaining permanent joints will find wide application when performing mounting and assembly work on promising space objects.

semiconductor materials

Semiconductors - substances that have electronic conductivity, and in terms of electrical conductivity occupy an intermediate position between good conductors (metals) and insulators (dielectrics). Typical semiconductors are, for example, germanium and silicon. The electrical conductivity of semiconductors is highly dependent on temperature. Under the action of light, the electrical conductivity of some semiconductors increases; such materials are sometimes referred to as photoconductors. The properties of semiconductors are also very sensitive to the perfection of their crystal lattice and to the presence of impurities. In some cases, the presence of an impurity in the smallest concentration (for example, 10 -6 or 10 -7) is the decisive factor that determines the electrical properties of the semiconductor. These unique qualities of semiconductor materials ensured their widest use in almost all areas of science and technology.

Manufacturing semiconductor materials in space can provide significant benefits for several reasons. First, the properties of these materials strongly depend on the technology of their preparation, and many undesirable effects are caused by the manifestation of the weight force (convection in the melt, separation of components of different densities, etc.). Second, under space conditions, the uniformity of the dopant distribution in a semiconductor can be significantly improved.

Let us turn to the consideration of specific technological experiments aimed at realizing the indicated advantages of manufacturing semiconductor materials in space.

Growth of single crystals from melts. Defects in semiconductor single crystals during their growth from a melt arise due to the appearance of various types of convection flows in the melt, as well as due to the ingress of undesirable impurities into it. To grow a single crystal from a melt, a temperature difference is necessary, and in this case, thermal convection often occurs on the Earth. Convection currents lead to the appearance of local temperature fluctuations in the liquid, and due to the fact that the solubility of the impurity in the melt depends on the temperature, to an inhomogeneous distribution of the impurity in the growing crystal. This phenomenon, due to convection, is called banding, or microsegregation. Banding is one of the defects in the structure of semiconductor single crystals. Due to the possibility of reducing the role of convection in space, it is expected that single crystals grown onboard a spacecraft will have a more uniform structure.

To assess the effect of convection currents on the phenomenon of segregation, using the example of single crystals of germanium doped with impurities, such an experiment was carried out at the Skylab station. The crystals installed in ampoules were placed in an electric heating furnace, where they were first partially melted, and then, under conditions of an almost constant temperature difference, they cooled and crystallized. Gallium, antimony, and boron were used as dopants in different ampoules. Comparison with control samples obtained by the same method on Earth showed that the segregation of impurities in germanium crystals delivered from space turned out to be several times less. In the case of germanium doped with gallium, the relative uniformity of the resistivity of the material along the length of the sample was also investigated. For terrestrial samples, it was ? ?/? ? 6.4 10 -2, and for space - 0.8 10 -2.

The process of crystallization of gallium-doped germanium was also studied during the launch of a Soviet high-altitude rocket in December 1976. In this experiment, an exothermic heat source was used to heat the samples. A study of the ampoules delivered to Earth showed that the melting front had a fairly flat shape. This result confirmed the promise of using devices of this type c. experiments to obtain semiconductor materials.

In other experiments at the Skylab station, single crystals of indium antimonide were obtained. In the first of them, an indium antimonide rod was installed inside a graphite capsule in such a way that its free end was in a hollow hemisphere. The purpose of the experiment is an attempt to obtain spherical crystals. However, due to the fact that the melt partially adhered to the graphite wall of the cavity, the shape of the obtained crystals turned out to be not spherical, but drop-shaped. However, the crystal structure became more perfect: the dislocation density decreased by a factor of 5–10, and the impurity (selenium) was distributed more evenly than in control samples obtained on Earth.

Another experiment involved remelting and subsequent solidification of samples of indium antimonide contained in three sealed ampoules: one contains pure indium antimonide, the other contains tellurium-doped, and the third contains tin-doped. Studies of the obtained crystals also showed their high homogeneity.

In a number of experiments, the possibility of obtaining semiconductor materials from melts consisting of components that differ greatly in specific gravity was studied. For example, in one experiment carried out during the joint flight of the Soyuz and Apollo spacecraft, the effect of weightlessness on the directional solidification of semiconductor materials was investigated. Pairs of lead-zinc and antimony-aluminum were used. Space samples of the antimony-aluminum alloy turned out to be more homogeneous than those on the earth. In the case of the lead-zinc alloy, complete homogeneity could not be achieved.

Growing single crystals from solutions. If a seed crystal is introduced into a supersaturated solution of the desired substance, then the crystal will grow on it at a constant temperature. This method is used to grow crystals that are used as detectors of sound waves, in optics, etc. A growing crystal is sensitive to any changes in growth conditions: temperature and concentration fluctuations, the appearance of convection currents, the presence of foreign impurities, etc. Changing the excitation conditions convection currents in solution, a different behavior of impurities in weightlessness will affect the features of crystal growth on board spacecraft.

The results of an experimental study of the features of growing potassium alum crystals from their supersaturated aqueous solution, which was carried out at the Salyut-5 station, are presented in the previous chapter.

Growing crystals from the vapor phase. The growth of crystals by the vapor phase method is widely used to obtain epitaxial films of semiconductor materials. A schematic diagram of a device for growing crystals from the vapor phase was shown in fig. 5. Under normal conditions, the method is sensitive to the excitation of convection, which leads to the appearance of defects in the crystal lattice. In addition, there is a tendency to polycrystallization, it is difficult to obtain large crystals by this method on Earth. In space conditions, one can count on limiting the role of convection and improving the quality of the materials obtained, as well as increasing the size of single crystals.

The expected effects were also investigated in the Skylab experiment. The vapor phase crystal growth technique was applied to germanium selenide and germanium telluride. Crystals were obtained, the quality of which turned out to be higher than that of the control samples prepared on Earth. It was possible to obtain flat single crystals of germanium selenide with a size of 4 x 17 mm and a thickness of about 0.1 mm. On Earth, only small crystals with an imperfect structure have been obtained.

Taking into account these results, during the joint flight of the Soyuz and Apollo spacecraft, such an experiment was carried out. Here, the technique of growing crystals from the vapor phase was applied to more complex systems: germanium-selenium-tellurium and germanium-sulfur-selenium. The samples obtained under space conditions also turned out to be more perfect, and their structure more homogeneous.

Optical glass and ceramics

The influence of conditions close to weightlessness on glass production technology can be different. First, containerless melting can be carried out in weightlessness, thus dramatically reducing the entry of harmful impurities into the material from the walls of the crucible in which glass is melted. Secondly, it is possible to ensure the stability of liquid mixtures, the components of which differ greatly in density. Thirdly, the absence of free convection reduces the probability of the appearance of random crystallization centers and improves uniformity. Fourth, the predominant role of capillary forces can be used to give the liquid melt the necessary shape (fibers, films, etc.) before solidification. The use of these factors makes it possible to count on (obtaining improved or qualitatively new types of glasses, as well as glass products in the process of space production.

On fig. 12 shows how the volume of the molten glass-forming mass changes with temperature. When, as the melt cools, the solidification temperature is reached T m, the further process can develop in two ways. If nuclei are present in the melt (impurities coming from the walls of the crucible, local inhomogeneities in chemical composition, etc.), then crystallization can begin in the volume and the volume will decrease in accordance with the lower curve. If, on the other hand, the formation of crystallization nuclei can be suppressed, and the cooling rate can be made sufficiently large, then the state of a supercooled liquid will first appear, which, when the glass transition temperature is reached, T g passes into glass (upper curve in Fig. 12). In space, the process of crucibleless melting of glass is possible, and the homogeneity of the melt will be higher due to the absence of convection. These advantages open up the possibility of obtaining improved and new types of optical glass on board spacecraft.

Rice. 12. Change in the volume of liquid with temperature during glass melting (T m - crystallization temperature;T g - glass transition temperature. 1 - melt; 2 - supercooled liquid; 3 - glass; 4 - crystal)

At the same time, for the successful development of glass production in space conditions, apparently, a number of technical difficulties will have to be overcome: removal of undesirable gas bubbles from a glassy mass in the absence of buoyancy, ensuring a given cooling rate without natural convection, control of the temperature regime of cooling and the permissible level of random accelerations under conditions of containerless containment of the glassy mass.

All that has been said about the peculiarities of glass production under space conditions also applies to the production of ceramics.

Let us briefly consider some promising areas of space production of glass and ceramics. The purpose of these studies is to explore the possibility of obtaining glasses with improved optical characteristics, with a high melting point, absorbing and reflecting heat, for the manufacture of solid-state lasers that are resistant to chemically active media and retain their properties over long periods of time, semiconductor glasses with "memory" for integrated circuits.

The space production of these glasses can provide a number of advantages. Semiconducting glasses, for example, have a high refractive index in the infrared region. When melting them on Earth, it is difficult to ensure sufficient optical uniformity. Another example is the production of glasses for solid-state lasers containing high-concentration impurities (neodymium, ytterbium, etc.). In space, it is possible to increase the uniformity of the distribution of impurities and at the same time reduce the flow of harmful contaminants from the walls of the container.

Due to the absence of the Archimedes force and the predominant role of capillary forces in conditions close to weightlessness, it is possible to produce glass products consisting of dissimilar raw materials and having a high surface perfection using the containerless method. As an example, consider solid filters, which are a suspension of small transparent particles inside a transparent material, selected in such a way that the refractive indices of these particles and the material coincide for only one wavelength. As a result, light radiation of only this wavelength will pass through the filter without loss, and for all other wavelengths there will be strong scattering and absorption of light due to multiple reflections between particles. In weightlessness, it is possible to achieve a high uniformity of particle distribution in the base material.

Containerless glass production under space conditions can lead to a reduction in the relative number of some of the most common defects. These defects include:

1) crystals, i.e., inclusions that stand out from the glass itself during solidification;

2) foreign inclusions (containerless vitrification is able to drastically reduce their concentration);

3) streaks, i.e. interlayers of one glass in another, which has a different chemical composition (the source of the striations is also to a large extent the inflow of contaminants from the walls of the crucible);

4) bubbles, i.e., gas inclusions, in order to eliminate them under conditions close to weightlessness, the liquid glassy mass may have to be subjected to special processing (rotation, vibration, etc.).

A significant improvement in the material can also be expected in the case of the production of optical fibers in space. Such a light guide is typically a high refractive glass rod surrounded by a lower refractive glass cladding. A large difference between these coefficients ensures low absorption and high transmittance through the light guide.

The quality of a light guide depends on the accuracy of the relationship between the diameters of the rod and the shell, as well as between their refractive indices. If at the interface between the rod and the shell there are inhomogeneities no smaller than the wavelength of light (diameter difference, glass structure defects, refractive index inhomogeneity, etc.), then light energy will be partially scattered and absorbed on them. Glass contamination (with heavy ions, water vapor, etc.) also strongly affects the absorption value. Under space conditions, it is possible to improve the technology for the production of optical fibers by removing unwanted impurities during containerless melting, equalizing diameters due to the predominant role of surface tension forces in the melt.

As an example of promising ceramic materials, the production of which in space can be profitable, we present eutectics that solidify in one direction. With this method, metal threads can be embedded in the ceramic base.

There are also proposals for the production in space of another type of ceramic materials - composite microcircuits. These ceramics are composed of a glassy mass containing suspended particles that determine the electronic characteristics of the materials. Under weightless conditions, one can count on an increase in their homogeneity.

Due to the complexity of the technology for obtaining glass, experimental research on spacecraft in this direction has lagged far behind work in other areas of space production. In March and December 1976, when high-altitude rockets were launched in the USSR, glass melting experiments were carried out for the first time. Using exothermic energy sources, the processes of melting and glass formation were studied under conditions close to weightlessness, using the example of glass with a filler (glass with aluminum), as well as especially strong phosphate glass. A sample of phosphate glass delivered from space partly consists of zones with gas inclusions, and partly - from a zone of homogeneous material. The obtained aluminum-glass alloy has semiconducting properties.

Biomedical products

One of the important tasks associated with the production of biomedical products (vaccines, enzymes, hormones, etc.) is their purification. It is known, for example, that increasing the purity of the vaccines used reduces the likelihood of harmful side effects when they are used, and this, in turn, allows you to increase the dosage and increase the effectiveness of the therapeutic drug.

One of the most common methods for purification and separation of cellular biological material is based on the use of electrophoresis. This phenomenon is observed in dispersed systems, i.e., such systems that consist of two or more phases with a highly developed interface between them, and one of the phases (the dispersed phase) is distributed in the form of small particles - droplets, bubbles, etc. n. - in another phase (dispersion medium). Disperse systems include biological substances. If an external electric field is applied to such a medium, then under its influence, dispersed particles suspended in the liquid begin to move. This is the phenomenon of electrophoresis.

Dispersed particles suspended in a liquid medium come under the action of an electric field in motion, because they have an electric charge. Since different organic molecules have different electrical charges, the speed they acquire in an electric field is different. This difference in speeds is the basis for the method of electrophoretic separation of the necessary fractions from a dispersed medium and purification of biological materials. The scheme of the experimental setup built on the basis of these principles is shown in fig. 13.

Rice. 13. Electrophoresis in a free liquid flow (1 - solution supply; 2 - fraction selection). The separation of fractions is carried out in the direction perpendicular to the flow of the solution between the electrodes

Under terrestrial conditions, the use of electrophoresis to separate the components of a liquid faces several difficulties. Firstly, there is a partial overlap of fractions caused by free convection, as well as thermal convection, due to the occurrence of additional temperature and density drops of the solution due to its heating during the passage of an electric current. For this reason, the amount of current that can be passed through the solution is severely limited in order to prevent undesirable overheating of the liquid. And this means that the productivity of the installation for the separation of biological materials is relatively low. In addition, due to the difference in the densities of the dispersed phase and the dispersion medium, under the action of the Archimedes force, their separation is possible.

Under space conditions, these difficulties can be overcome. First of all, this concerns the ability to limit the role of convection and, consequently, improve the degree of purification and increase the productivity of installations. Another possible advantage of the electrophoretic method under weightless conditions is related to the fact that density does not affect phase separation. Under terrestrial conditions, density depends on viscosity, the value of which can be changed by adding a large number of small molecules or a small amount of large molecules to the solution. In weightlessness, this method of controlling the viscosity of a solution becomes especially convenient due to the absence of the Archimedes force. As a result, it becomes possible to control the viscosity of the medium as independent parameters that are not related to density. Of course, this possibility cannot be realized on Earth.

With the aim of directly verifying these conclusions in space conditions, West German and American scientists carried out a number of experiments carried out at the Skylab station and during the joint flight of the Soyuz and Apollo spacecraft. In an experiment at Skylab, a device was tested in which an undisturbed fluid flow flowed between two plates to which an electric field was applied. Particles were introduced into the solution at one end of the device and removed through holes located at the other end. Under terrestrial conditions, due to mixing convection currents, the distance between the plates could not be made greater than 1–2 mm. In space conditions, it was possible to increase it to 5 - 10 mm. This result confirmed the possibility of increasing the performance of the instrument and improving its resolution.

In the experiment, a device of a similar type was used to separate blood cells and explore the limitations imposed by convection and particle settling. By reducing the influence of convection, it was possible to increase the depth of the chamber and, as a result, increase the productivity of the installation by 6.5 times. The resolving power has increased 1.5 times in comparison with the experiments carried out on Earth.

In another experiment, the possibility of obtaining pure biological preparations under conditions of suppressed convection was also studied using the example of blood and kidney cells, in particular, the task was to isolate urokenase in its pure form. Urokenase is the only enzyme produced in the human body that is able to dissolve the formed blood clots. If it is possible to isolate the enzyme urokenase in its pure form and find out the process of its production by kidney cells, then it will be possible to produce it in sufficient quantities on Earth. Urokenase is an effective means of combating thrombophlebitis and such cardiovascular diseases as heart attack, stroke, etc. According to reports, this experiment was also performed successfully. On the whole, however, much less work has been done so far in the field of electrophoresis than in other areas of space technology research.

Complex technological experiments

For a comprehensive study of the features that arise during the course of physical processes in weightlessness, as well as to identify the relative prospects (for space production) of specific technological processes, it is necessary to move on to conducting mass experimental studies on spacecraft of various types. The current state of research and development in the field of space production, ongoing in the Soviet Union, is characterized precisely by the transition to this stage.

The Soviet space research program in the field of technology and production provides for such complex experiments, and this will be a new stage in the research and development of Soviet scientists in this field and, in turn, is determined by the successes achieved at the previous stage. In particular, an extensive complex of technological experiments of the most massive nature was carried out quite recently during the launches of high-altitude rockets and during the flight of the Salyut-6 orbital space station with cosmonauts on board. Carried out as part of a single research program, these experiments complemented each other.

On December 27, 1977, a high-altitude rocket was launched in the Soviet Union, which made it possible to simultaneously perform several dozens of diverse technological experiments. For their implementation, a special set of technological devices was developed - SKAT, in which the heat of exothermic chemical reactions was used to heat and melt the substances under study. The samples under study were placed in ampoules, which were installed along the axis of cylindrical heating cells.

The duration of the state of weightlessness in this experiment was about 10 min. Therefore, in order to ensure a sufficiently rapid solidification of the molten substances before the state of weightlessness ceases (when the rocket enters the dense layers of the atmosphere), a special heat release system was used. She worked on the principle of "thermal sponge", based on the removal of heat released into a massive aluminum clip.

The total mass of the SKAT instrumentation set (together with the heat release system) was 137 kg. In different ampoules, depending on the task of the experiment, different temperatures were obtained. The range of maximum temperatures realized using the SKAT equipment was 600–1700°C.

The program of experiments carried out using the SKAT kit included the study of a wide range of substances: composite materials, foam metals, special alloys, and semiconductors. In order to increase the reliability of the results, almost all experiments were duplicated.

Carrying out technological experiments of a complex nature was included in the program of work carried out by Soviet cosmonauts on the Salyut-6 - Soyuz-27 orbital research complex.

January 11, 1978 cosmonauts Yu. V. Romanenko and G. M. Grechko, who arrived at the Salyut-6 station on the Soyuz-26 spacecraft, were joined by the crew of the Soyuz-27 spacecraft - cosmonauts V. A. Dzhanibekov and O. G Makarov, who subsequently returned to Earth with the help of the Soyuz-26 spacecraft. The descent vehicle of the Soyuz-26 spacecraft delivered to Earth materials with the results of research and experiments during the flight of the Salyut-6 orbital station for more than three months.

On January 22, 1978, docking with the manned research complex "Salyut-6" - "Soyuz-27" of the automatic cargo transport vehicle "Progress-1" was carried out. For the first time in the history of cosmonautics, a transport operation was carried out using an automatic spacecraft to deliver equipment, instruments and materials to a manned orbital station to ensure the life of the crew and conduct scientific research and experiments, as well as fuel for refueling propulsion systems.

With the help of Progress-1, equipment was delivered to the Salyut-6 station, which was also designed to carry out a cycle of technological experiments. In particular, it includes the Splav-01 installation, which consists of an ampoule-type electric heating furnace and a small computer designed to automatically control the thermal regime. The inner cavity of the furnace has three zones: with high and low temperatures, and between them - with a temperature difference (maximum temperature is about 1000 °C). The design of the furnace makes it possible to carry out experiments simultaneously with three ampoules filled with test substances.

Starting the preparation of technological experiments, Yu. V. Romanenko and G. M. Grechko placed the furnace in the lock chamber in the working compartment of the Salyut-6 station, through which the crew throws out household waste (the chamber has two hatches - one leads inside station, the other - into the surrounding space). Then the cosmonauts connected the airlock to the control panel installed inside the station through special hermetic connectors. After that, the inner hatch of the chamber was closed and the outer hatch was opened, so that the furnace was in the vacuum of space. Such operating conditions of the furnace were chosen in order to ensure the removal of heat from it by radiation directly into the surrounding outer space.

Having completed the preparation of the equipment, on February 14, 1978, cosmonauts Yu. V. Romanenko and G. M. Grechko began the first technological experiment. At the same time, the station was switched to the drift mode (at which the attitude control system engines are turned off) in order to reduce the effect of small accelerations on the course of the experiment. For the same purpose, a significant part of the experiment was carried out while the cosmonauts were sleeping. The ampoules installed in the electric furnace in the first technological experiment contained copper-indium, aluminum-magnesium and indium antimonide compounds.

On February 16 and 17, the second technological experiment was carried out at the Salyut-6 station, which lasted 31 hours and studied the reactions between solid tungsten and molten aluminum, as well as the process of impregnation of porous molybdenum with liquid gallium. Experts suggest that the latter material may have superconducting properties.

A new stage in the deployment of the program of technological experiments on the Salyut-6 orbital station was associated with the successful flight of the Soyuz-28 spacecraft, piloted by the first international crew consisting of the USSR pilot-cosmonaut A. A. Gubarev and a cosmonaut-researcher, a citizen of Czechoslovakia V. Remeka.

On March 3, 1978, the Soyuz-28 spacecraft was docked with the Salyut-6 - Soyuz-27 orbital complex. Cosmonauts A. A. Gubarev and V. Remek delivered a capsule made at the Institute of Solid State Physics of the Academy of Sciences of Czechoslovakia, which contained two ampoules filled with samples of silver and lead chlorides and monovalent copper chloride, to the orbital research complex. These substances were chosen because they have valuable optical-acoustic properties. Cuprous chloride is a well-known electro-optical material, and silver chloride is widely used in infrared detection equipment. The joint Soviet-Czechoslovak experiment with these substances was called Morava.

Having started this technological experiment on March 4, 1978, the cosmonauts placed both ampoules with the substances under study in the electric furnace of the Splav-01 installation, placing them in a zone with a temperature difference. The maximum operating temperature of the furnace in this experiment was about 500 °C, and the total duration of the recrystallization process of the samples after they were melted reached approximately 40 h. structures of the studied substances in comparison with control samples obtained on the same setup under terrestrial conditions.

During the experiment, the cosmonauts controlled the operation of the computer of the Splav-01 facility, which ensured the maintenance of the specified temperature regime. After the completion of the Morava experiment, the capsule with the substances under study was packed and delivered by A. A. Gubarev and V. Remek to Earth.

The "Morava" experiment marks the beginning of a new area of ​​joint space research by the socialist countries participating in the "Interkosmos" program. Technological experiments are now being added to research in the field of space physics, meteorology, biology, and research on the natural resources of the Earth. In subsequent flights of international crews, technological experiments will be continued. In particular, the Interkosmos program provides for launches in 1978 of Soyuz spacecraft, whose crews will include representatives of the Polish People's Republic and the German Democratic Republic. As part of a unified program of scientific and technological research and experiments on board the orbital scientific complex based on the Salyut-6 station, cosmonauts from the socialist countries will have to perform tasks of increasing volume and complexity.

Prospects for the development of space production

The first technological experiments in space were performed only a few years ago. And although very little time has passed since then, research and space experiments carried out in the USSR and abroad have made it possible to obtain scientific and technical results, on the basis of which it is possible to give a preliminary assessment of the prospects for the production of new materials in space. What are the main conclusions that can be drawn by analyzing the results of experiments carried out to date?

In general, general ideas about the features of physical processes in weightlessness are confirmed, but at the same time, the insufficiency of many theoretical models is revealed and the need for special studies aimed at developing the theoretical foundations of space production is shown. The possibility of obtaining in space semiconductor single crystals, special alloys, composite and other materials with improved characteristics, as well as such substances, which cannot be obtained on Earth, has been experimentally confirmed. The possibility of improving the resolution and increasing the productivity of installations for the electrophoretic separation of biological preparations has been directly confirmed.

These are the most general results of approximately 60 experiments carried out to date on various spacecraft in the USSR and abroad. And although a lot has already been done, there is still more to be done before space production becomes an independent economically efficient branch of the national economy. Let us note the most important tasks that need to be solved in order to ensure the achievement of this goal.

First, it is necessary to move from experiments performed on relatively simple instruments to extensive experimental studies using specialized on-board facilities, which will fully take into account the specific features of work in space and which will allow the maximum use of the advantages associated with these features. . The task of creating such installations is one of the priorities. Secondly, it is necessary to conduct comprehensive studies of the influence of space flight factors - and first of all, weightlessness - on the regularities of physicochemical processes in matter in order to identify the optimal modes of technological processes for obtaining new materials on board spacecraft. Thirdly, it is necessary to ensure the development of the theoretical foundations of space production, including the development of methods for numerical simulation of processes in matter.

The ultimate goal of research in the field of space production is to turn it into a promising industry that provides a sufficiently high technical and economic efficiency. Due to the high cost of space flights, it is profitable to produce in space only unique expensive products, the annual need for which is relatively small (kilograms or tens of kilograms at present, hundreds or thousands of kilograms after the creation of efficient reusable transport spacecraft). Therefore, for the correct determination of the prospects and ways of further development of work in the field of space production, studies of its technical and economic efficiency play an important role.

Consideration is being given to the possibility of producing in space garnet crystals used in computer memory elements in order to improve their characteristics. The demand for these crystals in the 1980s, according to foreign data, will be characterized by a cost of more than $1 billion. If a part of these needs is covered by space production, this will also provide tangible cost savings. If it is possible to organize the production of certain materials in space, for example, new superconducting alloys with an increased critical temperature or optical glass for high-power lasers, this will literally revolutionize entire branches of technology.

Special attention deserves research aimed at organizing the production in space of new or improved biomedical and pharmaceutical preparations. Successful experiments on obtaining the enzyme urokenase, carried out during the flight of the Soyuz-Apollo spacecraft, indicate that new important results can be expected in this direction. Continued work in this important area can make a tangible contribution to the development of health care and provide a significant economic effect. According to foreign experts, by the year 2000 up to 30 tons of biological preparations (enzymes, vaccines, etc.) with a total cost of about $17 billion will be produced in space annually.

Advances in rocket and space technology have armed man with a new factor that he can use in his production activities - a long state of weightlessness. Is it possible to doubt that our contemporaries - scientists, engineers, designers, technologists - will be able to put this factor at the service of mankind? The entire experience of the history of science and technology indicates that this will definitely happen.

However, one should not think that such a conclusion automatically opens cloudless prospects for the future development of space production. On the contrary, it implies the need for more in-depth studies on the entire problem, carried out within the framework of a single program of a comprehensive nature. There is no doubt that it is precisely this approach that will ensure the rapid development of a new area of ​​human activity in outer space - the production of new materials in outer space.

Literature

Grishin S. D., Pimenov L. V. The path to the factories in orbits. - Izvestia, 1976, August 12.

Avduevskiy V. S., Grishin S. D., Pimenov L. V. To the orbital factories of the future. - Pravda, 1977, February 20.

Belyakov I. T., Borisov Yu. D. Technology in space. - "Engineering", 1974.

Weightlessness. Physical phenomena and biological effects. M., Mir, 1964.

Khaikin S. E. Forces of inertia and weightlessness. M., "Nauka", 1967 (()

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An integrated circuit is an electronic device, the elements of which are inseparably connected structurally and electrically interconnected.