Статьи журнала - Siberian Aerospace Journal
Все статьи: 352
Статья научная
High complexity and cost of developing flying models necessitate the use of such design and production techniques that would ensure the best flight technical and technological characteristics of the model also would raise of it operation effectiveness. These techniques include the experimental control method of flying model’s mass-inertia asymmetry parameters during final assembly of the model. Solution of the problem of optimization the process of bringing parameters of mass-inertia asymmetry of the conical flying model to specified standards is considered in the article. The only correction plane is designed to be positioned close to cone face, away from the center mass of the flying model. The flying model as a component of prefabricated rotor is being balanced in dynamic mode on a low-frequency dynamic vertical stand, which based on gas bearings. Before balancing experiment the weigh, longitudinal center of mass and inertia moments of the flying model have to be controlled with use of another measurement equipment. As a criterion of optimization is sorted the reaching of minimum of the angle of deviation of principal longitudinal centroidal axis of inertia from geometrical axis of the flying model. But simultaneously the pre-set standard of center-mass shift from the geometrical axis must be ensured. Balancing algorithm, easy-to-realized by modern computers, is presented. Numerical illustration of balancing is given. The algorithm enables omitting intermediate steps of balancing, reducing them to one step (as a rule), and shortening the balancing time, as well. In one step of balancing the engineering model permits either bringing parameters of mass-inertia asymmetry of the flying model to specified standards, or diagnosing impossibility of attaining the specified standards with available design of flying model. The algorithm and balancing method are experimentally tested at newly-designed vertical dynamic stand on conical gas bearings. It’s high precision and efficiency are corroborated.
Бесплатно
Elastic-plastic problem in the case of inhomogeneous plasticity under complex shear conditions
Статья научная
In this research, the authors solved a two-dimensional elastic-plastic problem of the stress state under com-plex shear conditions in the body weakened by a hole that is bounded by a piecewise smooth contour. The stress state of a complex shear occurs in a cylindrical body of infinite length under the action of loads directed along the cylinder generators and constant along the generators. At the same time, with a sufficiently large load, both elastic and plastic zones appear in the body. As in any problem of this kind, it is necessary to find a previously unknown boundary separating the elastic and plastic zones. Finding such a boundary is not an easy task, but the specificity of elastic-plastic problems of complex shear is that solving such problems is easier than solving simi-lar elastic problems. Apparently, for the first time this fact was noted by G. P. Cherepanov. A lot of research is devoted to elastic-plastic problems of complex shear in the case of homogeneous and iso-tropic plasticity. All articles that solve complex shear problems essentially use the representation of stresses and displacements in the elastic zone in a complex form. In this research, the problems of complex shear are solved using conservation laws. It is assumed that the yield strength is a function of the coordinates of the point where the stress state is being studied. It is known that the elastic properties of structural materials can be homogene-ous and isotropic, while their yield point and strength are inhomogeneous. This situation is observed, for exam-ple, in the case of neutron bombardment of structural materials. This research will examine exactly this situa-tion. The article presents conservation laws for equations describing a complex shear. It was assumed that the components of the conserved current depend on the components of the stress tensor and coordinates. The com-ponents of the stress tensor are included in them linearly. The problem of finding the components of the con-served current was reduced to the Cauchy-Riemann system. The solution of this system allowed us to reduce the calculations of the stress tensor components to a curvilinear integral along the contour of the hole and thus find the boundary between the elastic and plastic areas.
Бесплатно
Elastic-plastic torsion of a two-layer rod
Статья научная
We study the elastic-plastic torsion of a two-layer rod under the action of torque in this article. It is as-sumed that the rod consists of two layers. Each layer has its own elastic properties, but the plastic proper-ties of both layers are the same. The contact boundary of the layers is located along the ох axis. The lateral boundary of the rod is stress-free, displacements and stresses are continuous at the interface. The compo-nents of the stress tensor at a point are calculated using contour integrals derived from conservation laws calculated along the lateral boundary. Next, the second invariant of the stress tensor is compared with the yield strength. At those points where the yield point is reached, the plastic state is realized, in the rest – elastic. This allows you to build a boundary between the plastic and elastic regions. This technique pro-vides a way to calculate elastic-plastic boundaries for the main rolling profiles of rods. This is supposed to be done in subsequent works. We remind you that earlier, with the help of conservation laws, the main boundary value problems for a plastic two-dimensional medium, elastic-plastic torsion of isotropic rods and elastic media for bodies of finite dimensions were solved.
Бесплатно
Статья научная
Cation-substituted solid solutions YbXMn1-XS were prepared by the melt method from polycrystalline sulfide powders. The synthesized samples are antiferromagnetic semiconductors and, according to the results of X-ray structural analysis, have an FCC structure of the NaCl type. Structural, electrical, optical, and acoustic properties of the chalcogenide system YbXMn1-XS were studied in the temperature range 80–500 K. The effect of variable valence elements on the electronic structure of cationic substitution of manganese sulfide has been studied. The change in the electronic structure in the YbXMn1-XS system occurs due to the electron-phonon interaction. Samples with variable valence have anomalous compressibility, which is confirmed by the data on the thermal expansion coefficient and the change in the attenuation coefficient. As a result of inelastic interaction with d- electrons, the density of states at the Fermi level changes, this is reflected in the temperature dependence of the conductivity. The positions of the f-level and two electronic transitions were determined from the IR spectra. A zone of temperatures and concentrations was found, where a correlation of structural, electrical, optical and acoustic properties is observed. To explain the experimental results, the electronic structure of the semiconductor is considered and a model is proposed that qualitatively describes the experiment.
Бесплатно
Electrooptical response of the films of polymer dispersed nematic with conical boundary conditions
Статья научная
The electrooptic response of films of polymer dispersed nematic under conical boundary conditions has been investigated. An axial-bipolar director configuration is formed in nematic droplets. It has been shown that initially, the orientation of droplet’s bipolar axes is chaotic both in the sample plane and relative to the normal to the substrates. The applied voltage U orients the droplet’s bipolar axes parallel to the electric field and the reorientation process is threshold only when the bipolar axis is initially orthogonal to the substrate normal. Accordingly, the samples strongly scatter light in the initial state, and the optical response to an electric field is thresholdless. The samples with a film thickness of 5, 10, 20 and 30 μm have been studied. All the samples under study are characterized by a high transmittance and contrast ratio, which for a 30 μm sample are equal to 84 % and 5536, respectively, and achieved at U = 12 V. The results obtained are relevant for use in low-power optoelectronic devices required for the development of energy-saving technologies in aerospace engineering.
Бесплатно
Energy saving simulation test complex for spacecraft power supplies full-scale electrical tests
Статья научная
The aim of this paper is to describe an energy saving automatized simulation test complex used for spacecraft power supplies full-scale electrical ground-based tests. The complex allows you to simulate the operation of solar array, lithium- ion-battery and spacecraft payload. The distinctive features of the test complex are a continuous and impulse control methods combination with an improved dynamic accuracy, and recuperation of consumed energy into its internal DC network for the better energy efficiency. Test complex operational time from uninterruptible power supply accumulator batteries is significantly increased due to the recuperation of excess power into the test complex internal DC network. The results are experimentally proved. The authors of the paper analyzed dynamic accuracy improvement and energy saving during ground-based spacecraft power system electrical tests. The process of ground-based spacecraft electrical testing includs the following tasks: – the accurate simulation of static and dynamic characteristics of spacecraft power system energy sources and loads; – the utilization of energy produced by power system under load and during spacecraft battery charge simulation. The paper deals with the description of energy saving automatized simulation test complex (ESAST) including complex subsystems structure and experimental study of the test complex characteristics. Commercially available simulation test complexes usually use continuous or impulse control methods. The continuous control methods decrease energy efficiency, as the most part of energy is dissipated on the regulator, which requires massive heat sink, increasing weight and size. It makes difficult to produce high-power test complexes. The impulse control methods provide better energy efficiency, but limit dynamics and real devices fast response reproduction accuracy. The paper describes the combination of continuous and impulse control methods with the aim of taking the advantages of both. The energy consumed by the test complex can be utilized either by the heat dissipation in the environment or by the recuperation into industrial AC grid. The heat dissipation reduces the energy efficiency, increases the testing room temperature (in case of high-power spacecraft power system) and an air conditioning system. The recuperation into AC grid is free of specified disadvantages, but it requires the recuperated excess energy parameters matching with AC grid requirements through the network of grid-tied inverters, which leads to the increase of weight and size of the test complex. Moreover, the recuperation into AC grid is difficult during grid emergency shutdown, which can result in long test failure. The paper describes the method of excess energy recuperation into the complex internal DC network. The method significantly reduced test complex energy consumption, which in case of powering test complex from uninterruptible power supply (UPS) notably increase operating time from UPS accumulator batteries during AC grid emergency shutdown. In conclusion the main advantages of ESAST are given: – more than twice wattage reduction of test complex main power supply; – the ability to work during AC grid emergency shutdown with increased operating time from UPS; – the significant reducing of ESAST main parts weight and size.
Бесплатно
Статья научная
Currently, in the field of engine building, development of three-component propulsion systems (PS) is a very promising task. Liquid-propellant rocket engines (LPRE) operating at the initial stage of launching a launch vehicle (LV) on liquid oxygen + kerosene fuel and at high-altitude launch sites using cryogenic fuel (liquid oxygen + liquid hydrogen) are in particular interest. LPRE that use three-component fuel have a high pressure level in a combustion chamber (CC) (up to 30 MPa) and temperatures (up to 4000 K). In this regard, arise questions related to reliable cooling of such engines, as well as ensuring minimal hydraulic fluid losses in a cooling passage in order to further use re-frigerant as a working fluid for driving the turbine of a booster turbo pump unit (BTP). The object of research is a two-mode single-chamber three-component liquid-propellant rocket engine, made in a closed circuit with generator gas afterburning. Oxidizing agent is liquid oxygen, fuel is RG-1 kerosene and liquid hydrogen. Cooling of the chamber is combined: it consists of regenerative and internal. Regenerative cooling passage is formed by longitudinal integral-machined fins. Hipercritical hydrogen is used as an engine coolant. Internal cooling includes a tantalum coating applied to a fire wall of the chamber in a critical section. The article examines the problems of organizing cooling system (CS) and implementation of effective heat removal from a firing wall of a three-component rocket engine. Basing on existing liquid-propellant engine cooling systems, optimal circuit solutions and measures to remove thermal load in the most stressed places are proposed. A mathematical model has been developed for calculating a CS of a three-component LPRE. The results of the design calculation of cooling using several calculation methods are presented.
Бесплатно
Статья научная
The reliability of ring current-collecting devices during a given service life plays a decisive role in the operation of power supply systems of various equipment and largely depends on the strength and reliability of all its components, in particular, contact rings. One of the most important characteristics of ring current collectors is the contact resistance, which is reduced by using non-ferrous and precious materials with low resistance, while increasing the downforce between the rings of the current collector. With an increase in the compression force F of the contact ring, the resistance of the contacts decreases to a certain minimum value and practically does not decrease with further growth of the force. The dependence of the contact resistance on the compression force has the form of a power function, the coefficients of which are determined experimentally. However, the operability of the contact rings in such severe conditions can be ensured in the case of low speeds and a small number of loading cycles by using the low-cycle fatigue area on the Weller curve. Having determined the coefficients of the equation of the inclined section on the Weller curve in the area of low-cycle fatigue, it is possible to determine the number of permissible loading cycles at a given stress level or solve the inverse problem of determining the permissible stress level if the number of loading cycles is known. To substantiate the correctness of the selected compressive force and the corresponding stresses, methods for calculating the fatigue margin coefficient, as well as a method for calculating the reliability of the ring material, are proposed. Reliability is estimated by the Gauss curve and is numerically expressed in the form of the probability of failure-free operation and the probability of failure, for which the corresponding theoretical dependencies are obtained. According to the proposed methods, calculations of the rings of the current-collection device used in EXPRESS-type spacecraft were performed, which showed the operability of the methods and allowed to ensure the required service life of the contact rings and their reliability. A very simple analytical formulation of the methods allows us to solve both verification and design calculations of rings, depending on the task at hand.
Бесплатно
Статья научная
Heterogeneous energy sources and homogeneous energy sources with different characteristics are frequently used in autonomous power supply systems. Solar batteries are widely used as primary energy sources for on-board power supply systems of spacecrafts, unmanned and manned aircrafts. Renewable energy sources such as solar, wind, geothermal and hydro energy, serve as primary energy sources of terrestrial autonomous power supply systems. Matching primary energy sources with different characteristics and operating conditions within a unified power supply system leads to problems connected with the power control of energy sources, which determines the relevance of the considered problems. The main aim of the study is to develop a combination of primary energy sources and control techniques which allow using primary energy sources with different characteristics and operating conditions in unified autonomous power supply system. The objectives of the study are to create the simulation model of a power supply system using MATLAB/Simulink software; to develop and test control algorithms for primary energy source controllers that would allow to maintain the needed battery charging current; to develop and test control algorithms for primary energy source controllers that would allow the primary energy sources to operate in the maximum power point tracking mode and to minimize the maximum power point search time. Methods used in the study: the simulation of a power supply system using MATLAB 7.9 Simulink software. Results: the simulation model of a power supply system including two primary energy sources with different characteristics is designed. In the case of excess power generating by the primary energy source, its controller operates in the battery charging mode. When the primary source power shortage occurs, its controller operates in the maximum power point tracking mode. The proposed power supply system structure allows controlling two energy sources independently, thus the primary energy source controllers can operate in different modes. This provides flexibility of the power supply system. The use of fuzzy logic control algorithm increases the accuracy and search speed of the maximum power point tracking algorithm. Simulation results confirmed the efficiency of the proposed solar controller operation algorithms in all modes stated above. The efficiency of controller operation modes selection algorithm was confirmed in different operating conditions. The proposed algorithms allow implementing the effective control of primary power sources depending on power supply system operating conditions.
Бесплатно
Ensuring the thermal regime of spacecraft structures
Статья научная
The main requirement for the smooth operation of the spacecraft is its stable thermal regime. A particularly difficult task is to ensure a stable temperature control system of the device, taking into account strict restrictions on energy and mass costs for temperature control devices. These tasks need to be solved at every stage of the creation of satellites. At each stage, thermal calculations are carried out with the choice of optimal thermophysical parameters. This amount of work is about a tenth of all work with the satellite. The need for theoretical and experimental refinement of calculation methods is an urgent task that will significantly reduce the material and time costs of designing, testing and fine-tuning the device. Therefore, the calculation and analysis of the thermal regimes of spacecraft is an important stage in the design of satellites. Ground thermal vacuum tests are very costly, both in time and financially. The essence of the concept is to conduct only stationary thermal modes under conditions of maximum and minimum thermal loads on the satellite as a whole and its individual external elements, followed by ensuring convergence of test results with calculated results. And the confirmation of intermediate requirements to ensure the specified thermal conditions is carried out by calculation. The article considers the tasks of ensuring the thermal regime of spacecraft structures. Classification of devices used to ensure the thermal regime. Ground-based testing of the thermal regime of communication satellites during thermal vacuum tests. Ensuring the thermal regime of the communication spacecraft during ground-based electrical tests. Thermal regime of spacecraft structures during transportation from the manufacturer to the technical position.
Бесплатно
Equilibrium distribution of defects in cadmium telluride before exposure to external factors
Статья научная
The reliability of electronic equipment, including in the aerospace industry, both under normal and extreme conditions, is associated with the degradation of materials due to the formation and development of a defective network. Cadmium telluride is one of the semiconductors that is actively used in the creation of solar cells and modern microelectronic devices. In this paper, the model of the point defects distribution in cadmium telluride before exposure to any ionizing radiation is proposed, that made it possible to calculate the effective thermal activation energy of a Frenkel pair equal to 1.37 eV. Studies of the features of the defects formation and evolution using modeling methods in cadmium telluride, in the future, will improve the quality of its technological use, saving financial resources and increasing the reliability of products.
Бесплатно
Erosion coefficient in electric contact processing of metals
Статья научная
In the production of rocket and space technology, difficult-to-machine steels and alloys are used by traditional methods. Therefore, electrical methods for processing parts are used that use a variety of thermal effects of an electric current directly in the process of removing a layer of material. In the technology of dimensional electrical processing, the role of electroerosive methods is increasing, which are increasingly used in all branches of mechanical engineering as the most effective, and often, and as the only possible ways of processing parts made of modern high-strength and viscous structural materials. One of the most promising methods of electrical processing of metal blanks is electrocontact. Performance is applied to evaluate the effectiveness of this method. The carried out literary analysis showed that the product of the current strength and the coefficient taking into account the processing mode and the material of the electrodes is used to assess the productivity. Later, this coefficient was called the coefficient of electrical erosion. For metals used in switching equipment, the value of the coefficient is given. However, it cannot be used to calculate the performance of electrical contact processing due to the significant difference in erosion processes occurring in the interelectrode gap. According to the literature data, the erosion coefficient was calculated during electrical contact processing, the results are presented in the table. In several works it is indicated that the erosion coefficient depends on the polarity of the inclusion of the rotating disk electrodes and the workpiece being processed. The data presented are contradictory; therefore, studies were carried out on the influence of the inclusion polarity on the erosion coefficient. With the same grade of the processed material and the rotating disc, the polarity of the inclusion does not matter. It was revealed that for steel grade St.3 the erosion coefficient depends on the voltage on the electrodes and, when approaching the arcing voltage, increases sharply, regardless of the polarity of the inclusion. For stainless steel, a sharp increase in the erosion coefficient is observed only at the straight polarity of the inclusion.
Бесплатно
Статья научная
Technological indicators of electrocontact processing of metals with a vibrating electrode-tool in an electrolyte have been studied quite fully. Knowledge of the erosion coefficient of this processing method will allow us to evaluate the performance of electrocontact processing in advance, at the stage of technological preparation of production. The article presents the methodology of the experiment, describes the installation based on a linear electrodynamic motor, which allows you to create a vibration of the electrode-tool and electrolyte flow in the interelectrode gap. The results of experimental studies are shown in the form of a graph of the dependence of the metal erosion coefficient on the water velocity in the interelectrode gap at various current densities. Based on the results and previous studies, it was assumed that the erosion coefficient depends in direct proportion on the voltage in the interelectrode gap and is inversely proportional to the volumetric heat capacity of the metal and its melting temperature. Based on the theory of electrical contacts and taking into account the features of electrocontact processing in the electrolyte, the definition of voltage in the contact zone has been refined. The theoretical value of the erosion coefficient exceeds the experimental value by two or more times.
Бесплатно
Errors reduction while locating objects of the radio navigation system
Статья научная
The present research considers a method for improving the accuracy of the dead reckoning position of a board station based on signals from the ground-based radio navigation systems. In the radio navigation sys-tem, grounded on the signal emitted by the base fixed stations, the slave fixed stations receive signals deter-mining the moments of their arrival relative to their own time scales. On the other hand, based on the radio frequency emitting signals by the slave fixed stations, the base fixed stations receive signals defining the moments of their arrival relative to their own time scale. According to the measured moments of radio emit-ted signal arrival, time corrections are calculated to the time scales of the slave fixed stations relative to the base fixed station. Since the time correction is calculated for a time of no more than 10 seconds, a random components are excluded due to the variability of the propagation velocity of the surface electromagnetic wave due to the variability of the environmental parameters and the parameters of the near-surface layer of the electromagnetic wave propagation area. If the calculated value of the time correction of the duration of the clock interval of the generated signal is exceeded, the moment correction (up to a clock) of the formation of the modulating code of the signal emitted by the slave fixed station is performed and the calculated value of the time correction is improved by the value of the previously corrected clock duration. The corrected values of the time corrections (pre-coded) are transmitted to each of the slave fixed stations as a part of their navigation signals. The navigation information consumer receives the radio navigation signals emitted by the fixed stations, through decoding, a consumer highlights information about the mismatch of time scales from the signals of the fixed stations and measures the radio navigation parameters with heightened accura-cy due to compensation for the error of the out-of-sync radiation signals of the slave fixed stations of the radio navigation system.
Бесплатно
Estimation of measurement errors of navigation and landing parameters using pseudosatellites
Статья научная
At the moment, a significant number of regional airfields do not have sufficient space for ground navigation equipment, this can lead to undesirable consequences when landing an aircraft with a weak visual contact of the crew with the runwaу. The pseudo-satellite system is able to improve flight safety at the landing stage in difficult meteorological conditions at regional airfields without using ILS (indicator on the windshield), after evaluating errors in navigation and landing parameters. The pseudo-satellite system can be used to improve flight safety at the landing stage in difficult meteorological conditions at regional airfields. This system consists of a control and correction station and pseudo satellites that operate in certain frequency ranges. When using this system, the PNP-72 scheduled navigation device is installed on the aircraft, which provides basic navigation information with a given accuracy. This allows pilots to use more accurate information and perform a safe approach and landing of the aircraft on the runway, even with weak visual contact with it. Thus, the use of a pseudo-satellite system at regional airfields can significantly improve flight safety at the landing stage, especially in difficult meteorological conditions when the use of ILS is impossible. The use of a pseudo-satellite system can also help solve the problem of an insufficient number of ground navigation aids at regional airfields. This will allow for a more accurate determination of the aircraft's location and improve the quality of navigation information provided to the crew. The use of pseudo-satellites could be an alternative to expensive and complex ILS systems, especially at small airfields where the installation of such systems may be impractical or not economically viable. However, for the successful implementation and operation of the pseudo-satellite system, additional research and testing is necessary to determine the optimal parameters of the system, as well as to develop appropriate regulatory documents and procedures to ensure flight safety.
Бесплатно
Статья научная
A lot of sets of subjects and objects in biology, industry, management can be divided into a number of classes, each of which corresponds to a certain distribution component. When analyzing a mixture of distributions, it is necessary to estimate its parameters (task 1) and to assess the correspondence of empirical and theoretical distribution functions (task 2). To solve the first problem, numerical algorithms that implement the method of moments and the maximum likelihood method are used. In this paper, the problem of estimating the distribution parameters is solved by minimizing the goodness measure by the Quasi-Newton method. The second problem is solved by comparing the empirical and theoretical distribution functions by one or several statistical goodness measures. Statistics of the distribution of these measures depends on the sample size, the method of forming data and estimating distribution parameters. The paper examines the goodness measure between Frocini and omega-square (Kramer – Mises – Smirnov). The evaluation of the statistics of the goodness measure was carried out by the simulation method based on the results of 50000 statistical tests. In each of the tests, the distribution parameters were estimated by minimizing the calculated value of the corresponding goodness measure. The results of simulation modeling allow estimating the statistics of the parameters of a mixture of distributions. The results of solving the considered problems for a mixture of two normal distributions of size 240 are presented.
Бесплатно
Статья научная
Transport operations that ensure the change of the orbit of a spacecraft or its transfer to the departure trajectory are an integral part of almost all space missions. Increasing requirements for the efficiency of transporting spacecraft form the need to search for possible ways to increase this efficiency and assess the characteristics associated with the proposed methods. Current boosters and interorbital tugs, as a rule, use a chemically powered cruise engine, although solutions with the use of an electric jet engine are becoming more common. Due to the high rate of the outflow of working fluid which is much higher than that of combustion products in a chemical engine, the efficiency of use of the substance mass by an electric jet engine significantly exceeds this indicator for a chemical engine. However, the low thrust provided by the electric jet engine leads to high duration of the transport operation and, as a result, to considerable time of exposure to the outer space factors, in particular, radiation. Therefore, the use of the electric jet engine only does not always meet the requirements for the mission. One of the promising ways to increase the efficiency of transport operations is the combination of the traditional chemical and electric jet engines in the propulsion system. Various aspects of the use of such an integrated propulsion system (IPS) consisting of a solar electric jet system and “Fregat” booster were considered, for example, in the framework of “Dvina TM” research project. Unlike a chemical engine, in which energy is released from chemical bonds, the energy for accelerating the working fluid by an electric jet engine is supplied from outside. Solar batteries are the most widespread energy source in nearearth orbits, where the amount of solar radiation is sufficient to meet the energy needs of a spacecraft. Solar batteries are sensitive to radiation, damage accumulates in their internal structure and their characteristics degrade. Therefore, there is a need to account for the radiation dose accumulated during the execution of the transport operation and to evaluate the reduction in the efficiency of solar batteries. Uneven irradiation intensity in the radiation belts formed by the Earth’s magnetic field (Van Allen belts) can be taken into account if the assessment of the radiation intensity at the trajectory points of the maneuver is made using the Earth radiation belt model. The paper proposes a method that allows taking into account the effect of ionizing radiation on the degradation of solar batteries when performing a transport operation using an integrated propulsion system based on a liquidpropellant rocket engine and an electric jet engine, taking into account the chosen trajectory and the model of the Earth’s radiation belt.
Бесплатно
Estimation of the number of aperiodic words
Статья научная
In 1902 W. Burnside raised the issue of local finiteness of groups, all elements of which are of finite order. The first negative answer was obtained in 1968 in the article by by P.S. Novikov and S.I. Adian. Finiteness of the free Burnside group of period n was established for n = 2, n = 3 (W. Burnside), n = 4 (W. Burnside, I. N. Sanov), n = 6 (M. Hall). The proof of infinity of this group for odd n ≥ 4381 was given in the article by P. S. Novikov and S. I. Adian (1967); for odd n ≥ 665 in the monograph by S. I. Adian (1975). In relation with these results we consider the set of m-aperiodic words. Word is called l-aperiodic if there are no non-empty subwords of the form Yl in it. In the monograph by S. I. Adian (1975) the proof of S. E. Arshon (1937) of the fact that in the two-letters alphabet there is an infinite set of arbitrarily long 3-aperiodic words was shown. In the A.Yu. Olshansky’s monograph (1989) the theorem on the infinity of the set of 6-aperiodic words was proved, and a lower bound function for the number of words of a given length was obtained. Our aim is to get an estimate for the function ()fn of the number of m-aperiodic words of the length n in the two-letters alphabet. The results can be applied when encoding information in space communications.
Бесплатно
Статья научная
The article discusses the prospects of utilization of aerodynamic control to maintain the formation of nanosatellites of the CubeSat class. The purpose of this work is to estimate the limits of the application of active aerodynamic control to stabilize the relative motion of two CubeSat 3U satellites in a sunsynchronous orbit with a height of 570 km. A review of theoretical information about aerodynamic forces acting on artificial Earth satellites is carried out, within the framework of which models of the Earth's upper atmosphere are considered. Aspects of creating a differential drag force for nanosatellites as an active control actuating mechanism are considered. To study the orbital motion of satellites under the action of aerodynamic control using the General Mission Analysis Tool program, a group flight of two spacecraft was simulated taking into account the factors causing orbital disturbances. Based on the results of experiments, the dynamics of the inter-satellite distance was studied, and a conclusion was made about the possibility of using an aerodynamic differential force to achieve a stable relative motion.
Бесплатно
Статья научная
The prospects for the development of space technology are currently closely connected with the creation of fundamentally new large-sized space structures. When designing large-sized systems, the scheme of which allows for automatic configuration change of the structure, it is necessary to take into account shock loads. They inevitably arise when fixing the working state of the structure in orbit upon completion of the process of its opening. To ensure smooth, reliable and shock-free opening of large-sized space structures, it is proposed to use force drives with active elements made of titanium nickelide material with a shape memory effect. The proposed shape memory force actuator uses an active element in the form of a wire made of titanium nickelide material which is heated during opera-tion by passing an electric current through it. One of the main parameters for the opening drive of large-sized structures is its deformation-force characteristic. Experimental studies aimed at studying this characteristic of the active element of the actuator were carried out in the work. The study of the force-deformation characteristics was carried out under two types of loading: in one, the force changed during the test, and in the other it remained constant. It is worth noting that the amount of deformation that an active element can produce is directly related to the magnitude and nature of the resistance force applied to it. In the experiment, the active element demonstrated sufficient displacement under significant load. The experimental data obtained show the fundamental possibility of using active elements made of a material with a shape memory effect in the opening drives of large-sized space structures. The obtained characteristic will play an important role in the development of a mathematical model of the functioning of an active element made of a material with a shape memory effect for the opening of a space structure with transformable configuration.
Бесплатно
