by Academician V. AVDUYEVSKY, A. EVICH, Cand. Sc. (Tech.)
Almost thirty years ago mankind reached out beyond the confines of the Earth, conquered zero gravity, and planted its first technological seeds in space. However, at present there is much talk about a specific side of space exploration-on using its properties for preparation of different products. Problems of space technology are coming to the fore.
The history of manned orbital flights covers a span of nearly three decades. During all of these years the mere fact of human presence in space has been in the focus of public attention. In recent time, however, the emphasis has been shifting to one specific aspect of space research-using the properties of space environment for manufacturing various products. Problems of space technology are high on our agenda now.
Both here and in the United States technological activities in zero gravity have reached a scale and diversity which are beginning to rival the traditional technologies here on earth. Being produced in orbital flight today are semiconductor crystals, glass and alloys and space environment is also used for assembly and repair operations of various kinds, spray-coating and testing of materials, and equipment. The results of such tests and experiments conducted on board the Soviet manned and unmanned spacecraft are geared to both scientific and economic applications. They are also having a visible impact on the appearance and technical level of aerospace industry products.
What we call the technological environment of an orbital flight possesses some truly unique characteristics, including long periods of zero gravity, deep vacuum, intense solar radiation, fluxes of charged particles and sharp changes of temperature. Any and all of these factors can have a revolutionary effect on our technological development to say nothing of some selective combinations of these factors.
Not all of these factors of space environment receive equal measure of attention on the part of our technical experts. The pride of place belongs to solar rays. Transformed into electricity, they power all of the onboard systems and equipment, including furnaces for growing crystals and units for spray-coating in vacuum. From the remaining "menue" of space "benefits" experts have been mostly focusing on zero gravity with space vacuum being in the second place and all the other factors still awaiting their turn, so to speak.
And this is only natural because our traditional "earthly" technologies took quite some time to mature and attain their present level.
Space technology was born in 1969. Circling the Earth on board Soyuz-6, cosmonaut Valeriy Kubasov welded parts using a low-pressure plasma arc and a melting electrode, and cut metal with an electron beam. He was the first to test basic metallurgical processes in space - the smelting of metals, molding, chilling, and crystallization, thus demonstrating that technological operations can be conducted under conditions of weightlessness and vacuum. It was also established that these processes occur differently in space than on Earth because of the predominant role of surface tension, diffusion, capillary effects, and other intermolecular interactions.
This was 20 years ago. Since then our space efforts have scored many achievements. Experiments conducted by the crews of the first Soviet Salyuts, the American Skylab and during the Soviet-American Soyuz-Apollo Test Project led experts to draw optimistic conclusions: products made in space can be superior in many
respects to those produced on Earth and can enjoy vast economic and research advantages.
There were also some dashed hopes. For example, some homogenous alloys made on Earth lost their homogeneity after remelting and crystallization in space with clusters of certain fractions of material forming in them. The Skylab crew failed to achieve the required properties of crystals of gallium antimonide. Crystals grown from solutions on board Salyut- 5 were found to contain more gaseous-liquid inclusions than those produced on the ground. All these surprises attested to the fact that different substances behave differently in phase transformations in space and not always the way we expected them to on the strength of our earthbound theories and experience. The obvious conclusion was that we had to work out the fundamentals of a new branch of physics - "the physics of microgravity." Serious studies were launched of the processes of heat and mass transfer in space conditions.
We also learned another lesson. Setbacks of all sorts can in no way discredit the central idea of space-processing of materials. Like our conventional technology, it will have to traverse a difficult and winding road, but will do that much faster. Within only two decades we covered the road from the first metal smelts molded in space and the first manmade crystals to what becomes a well- established industrial production of semiconductors and optical glass, homogeneous alloys, pharmaceuticals and vaccines.
A large amount of experimental work was carried from 1977 to 1981 by the successive crews of the Salyut-6 space station which included specially trained spacemen from other countries. Specialists from 11 countries - Bulgaria, Cuba, Czechoslovakia, France, the German Democratic Republic, Hungary, Mongolia, Poland, Romania, Vietnam and the Soviet Union - tried to make the most effective use of space environment to help reach technological and production objectives. It should be stressed that a comprehensive research program of this kind launched by international efforts was something unprecedented. Using the Kristall and Splav materials processing devices the Salyut-6 crews conducted close to 200 smelts of metal, produced some 300 semiconductor samples, alloys and glasses, including over 50 using internationally designed technologies.
For the first time ever the cosmonauts grew comparatively large tri- component crystals of cadmium, mercury and tellurium crystals. Crystals of this size cannot be made on Earth because of a rapid phase separation of the melt. Such triple crystals are used in the production of infrared-sensitive semiconductors (the range of "vision" of such devices extends from 1 to 30 mcm. Other crystals were grown that proved far superior to their earthly analogs. They have more orderly inner structure, greater purity and size. And the key to all these achievements is zero gravity.
The density of crystal lattice defects of germanium and indium antimonide crystals grown in microgravity is one hundred to one thousand times less than in crystals produced on Earth. What is more, they boast better electrophysical parameters, and electronic devices fitted with such semiconductors perform better. Salyut-6 cosmonauts also tried different methods of making crystals that are well known on Earth, including directional crystallization from melt, chemical gas transport and sublimation. They were able to produce strip-shaped and spherical crystals and fine crystal layers upon a base.
The Isparitel (evaporator) device was used to conduct more than 200 spray- coatings of gold, silver, copper and various alloys upon glass, polymer and metals in space vacuum conditions. This technology can be used to repair the shiny gloss of mirror reflectors and lenses without bringing them back to Earth and thus save time and money.
Experiments on board space vehicles confirm that there is no true or absolute zero gravity in them. Microgravity is generated by operating on-board systems and is thousands and millions times smaller than the gravitational pull of the Earth at sea level. Microgravity can be further increased by the crew doing physical exercises. Small as it is, this microgravity generates defects in growing crystals. A special device registers on film the field of densities and velocities in liquids in microgravity conditions. Even the rarified space environment is having a braking effect upon orbiting craft, producing permanent decelerations.
The above experiments gave us an idea of the convection mechanism on the liquid-gas boundary within the volume of the liquid. This first information on "zero-gravity physics" and the materials processing experi-
ments aboard Salyut-6 provided a valuable basis for future technological experiments in space.
The crew of Salyut-7 , which blasted off in 1982, had before them a program of semi- industrial production of new materials. The Korund electric furnace, delivered separately by a Progress-14 space freighter, was fitted with a drum with a set of ampules which were automatically transported into the furnace for heating and them taken out for cooling. The experiment was controlled by a special on-board computer. It was able to produce kilograms of semiconductors, an amount comparable to the practical requirements of our ground-based industries producing microchips, infrared and laser devices. Thus furnaces like Korund can provide an important addition to our ground facilities at no sacrifice in quality.
The first experiments in bioengineering were also started on Salyut-7. Using electrophoresis, the Tauria device separated bone marrow cells of rats, serum albumin and human hemoglobin, and a mixture of proteins. The isolated fractions had a high degree of purity. Further on Tauria was supplemented with another electrophoresis device, called Genom, which was used to produce pharmaceuticals, including some for veterinary use.
The Salyut-7 cosmonauts did a lot of space assembly and dismantling work in EVA (extra-vehicular activity). On one such occasion the cosmonauts mounted an external platform with a 12-meter long arm with instruments on top. Using an electron-beam device called the Unified Manual Instrument, the cosmonauts performed metal welding and soldering operations on some elements of the structure.
Reactivating Salyut- 7 involved minor and also major repairs which called for no small measure of courage in addition to skill. Vladimir Dzhanibekov and Victor Savinykh in 1985 literally gave the Salyut-7 station a second lease of life - one more full year of active service.
An even broader program of technological tasks is being implemented on board the Mir space station which went into orbit on February 20, 1986. Its production and technical facilities are a far cry from its predecessors. Onboard equipment includes a Czechoslovak crystallizer furnace and a modified electric heating unit Korund 1 M. The latter is controlled by its own minicomputer which maintains the temperature in the hot and cool compartments of the furnace with an accuracy of half a degree C. The furnace is fully automated and all the crew have to do is load the capsules into a revolving drum and take them out with the finished products after 6 to 150 hours. The unit is programmed for six technological processes which are used to manufacture ten different materials.
The Mir mission has given new momentum to international cooperation in space technology. A series of material testing experiments has been conducted with the participation of a Syrian and a Bulgarian cosmonauts, including growing multicomponent crystals and smelting different alloys.
Relying on previous experience, the Mir crew conduct regular EVA. A major task accomplished by the crew during Mir's first years in orbit was installing additional solar panels. They added to the original two panels of 38 m 2 a third one which is 10.6 m long and has an area of 24 m 2 , boosting the electricity capacity from 7.7 to 11 kW. The Mir does consume plenty of electricity, with the Korund furnace alone requiring close upon one kilowatt of power to say nothing of the Electron unit which recycles water vapors from the air into hydrogen and oxygen.
A number of impressive operations were conducted by the Mir crew on October 20, 1988. During an EVA cosmonauts Vladimir Titov and Musa Manarov replaced a set of detectors designed and built by Dutch and British experts. Without it one of the station's X- ray telescopes would have been rendered useless.
Mir is being used for putting together large structures in orbit in preparation for making space platforms of the future. During a joint Soviet-French expedition (December 1988) the cosmonauts conducted EVAs to try and open a support frame ofcarboplastic tubes (the Eraexperiment). Inside the Mir they tested a new low-friction articulated joint (the Amadeus experiment). In March 1989 an experiment was conducted in which two large metal structures unfolded all by themselves. They were made of an alloy with "shape memory". The frames were installed on a Progress freighter and the test was observed by the Mir crew.
The first to have been ferried to the Mir was the Kvant astrophysical module. The new modules will be added to it in the near future, one of them a technological unit for the manufacture of high-grade semiconductor materials for microchips. The diverse technological equipment on board the Mir space station will make it possible to continue the search for the optimal regimes of materials processing to obtain materials with improved or unprecedented parameters which cannot be attained here on Earth.
In 1989 the Mir station was used for a commercial venture. This involved growing crystals of protein substances for new medications on a contract with the US Payload Systems Company. Under an earlier contract with the West German Kaiser-Trade Firm technological studies are to be conducted on the Soviet Foton satellite in 1989-1992.
Thus, space technology is confidently reaching out over the national borders to serve mankind.
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