Том 20, № 1 (2019)

The features and capabilities of remote sensing of earth covers by means of signals of navigation satellites are pre- sented. The methods of reflectometry of the surfaces of earth covers and radioscopy of forest canopy are described. The options for using the signals of GLONASS, GPS systems are considered. Test measurements of interference diagrams were carried out on 5 test platforms from heterogeneous soil surfaces: salt marshes and asphalt; water surfaces of sa- line and freshwater bodies in summer, including ice cover of small thickness in the period of autumn freeze-up. The method of radioscopy helped obtain the data on the spatial and temporal characteristics of attenuated signals of the GLONASS and GPS satellites in the pine forest. Estimates of the linear attenuation coefficients of the signals passing through a forest canopy with a coordinate reference were made. The results obtained are the basis for the development of methods and technologies for continuous monitoring of the characteristics and state of earth covers by means of sig- nals of navigation satellites for solving a wide range of applied tasks.

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 good- ness 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 pre- sented.

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 frame- work 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 near- earth 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 liquid- propellant rocket engine and an electric jet engine, taking into account the chosen trajectory and the model of the Earth’s radiation belt.

A mathematical model of the aircraft avionics thermal state describing the heat exchange of the onboard equipment housing with a honeycomb structure made of a carbon fiber composite, the process of heat transfer of the onboard equipment elements and the air is developed. The considered heat transfer process in a heterogeneous medium is de- scribed by the boundary value problem for the heat equation with boundary conditions of the third kind. To solve the direct problem of the onboard equipment housing with a honeycomb structure thermal state, the Monte- Carlo method on the basis of the probabilistic representation of the solution in the form of an expectation of the functional of the dif- fusion process is used. The inverse problem of the honeycomb structure heat exchange is solved by minimizing the func- tion of the squared residuals weighted sum using an iterative stochastic quasigradient algorithm. The developed mathematical model of the onboard equipment in the unpressurized compartment thermal state is used for optimizing the temperature and airflow of the thermal control system of the blown onboard equipment in the unpressurized com- partment of the aircraft.

A method of synthesizing a digital controller for a solar energy conversion channel in a power supply system of a spacecraft is presented. The method is based on the initial functional diagram of the pulse converter and the method of switching discontinuous functions. In accordance with the technique, which is formally presented in the form of eight consecutively executed items, a block diagram of the shunt converter has been developed in the basis of switching func- tions, which is taken as an example for testing the technique. The shunt converter is one of the three energy conversion channels in modern power supply systems of a spacecraft. The block diagram showed that all nonlinearity of the system can be reduced to nonlinearities of two multiplication links and nonlinearity of a pulse-width modulator. The possibility and acceptability of joint linearization of each of the specified nonlinear multipliers with a pulse-width modulator at the selected operating point is shown. A linearized block diagram of the control object was obtained, after which the trans- formation and simplification of the block diagram to a convenient form for calculation was carried out. Using the trans- fer functions of the linearized block diagram, the logarithmic frequency characteristics were calculated analytically and the results of their comparison with the frequency characteristics obtained experimentally on a simulation model, which confirmed their identity in the working frequency domain, were presented. At the same time, the specified simulation model of a shunt pulse converter, built in the Simulink package of the Matlab design environment, took into account all the mentioned nonlinearities of the real converter. According to the obtained logarithmic characteristics, a classical synthesis of the analogue prototype correcting section was produced. The transition from the analog correcting section of the prototype to the implementation of the digital correcting section is shown. Simulation modeling of a closed-loop power supply system with a synthesized analog controller, in its mode of operation from a solar battery, confirmed the correctness of the methodology and the achievement of the goals. The results of the work are intended to create a new onboard energy conversion equipment for power supply systems of high-potential spacecrafts. The scope of application of the project results is space instrumentation.

The inelastic electron scattering cross-section spectra of FeSi silicide were calculated from the experimental re- flected electron energy loss spectra as the product of the average inelastic mean free path and the differential cross section of the inelastic electron scattering. To inelastic electron scattering cross-section spectra study, factor analysis was used. This method allowed us to quantitatively separate the surface and bulk contributions to the spectra, and de- termine the energy of the bulk plasmon more accurately than it is possible using traditional methods. Inelastic electron scattering cross-section spectra (Kλ-spectra) are the products of the average inelastic mean free path λ and the differential inelastic scattering cross-section K (E0, E0 - E), where E0 and E are the energies of the pri- mary and reflected electrons, respectively. The advantage of inelastic electron scattering cross section spectroscopy is that, unlike the reflected electron energy loss spectra, the Kλ-spectra exclude losses due to multiple excitations, and the intensities are determined in absolute units. These spectra are also more sensitive to changes in the energy of the pri- mary electrons and the angle of emission. Inelastic electron scattering cross-section spectroscopy allows to determine the element composition with much greater accuracy than the traditional method of reflected electron energy loss spec- troscopy. In this work, factor analysis is used to study the inelastic electron scattering cross section spectra of the FeSi sili- cide. This method allowed to solve the actual problem of separating spectra into contributions of a different origin, quantify them and determine the energies of a bulk plasmon more accurately compared with traditional methods. The study of electron energy loss processes by isolating contributions of different origin in the inelastic electron scattering cross section spectra is one of the urgent problems of electron spectroscopy, which can be used to assess the effect of surface excitations in REELS, XPS and AES.

Bismuth-substituted ferrite garnets possess magneto-optical (MO) properties and are used as spatial light modula- tors and indicators. The paper studies the influence of magnetic and electric fields on the structural characteristics of thin epitaxial films of bismuth-neodymium ferrite garnet (Bi: NIG) deposited on glass and gallium gadolinium garnet (GGG) substrates. Dynamic properties of polarization, relaxation in a magnetic and electric field are considered, which is an important task for getting a deep insight into the mechanisms of electromagnetic phenomena in solids. Dependence of the magnetostriction coefficient on the magnetic field and dependence of a relative change in the length of the film on the electric field at different temperatures are obtained. A change in the sign of magnetostriction constants with respect to temperature was found. The electric polarization in a periodically applied electric field of 400 V / cm with a frequency of 10 MHz is determined for various magnetic field orientations of 12 kOe and in the absence of a magnetic field. Anisotropy of polarization in a magnetic field and a functional dependence of the polariza- tion relaxation on time are found. These materials can be used as sensors of the magnetic field in a spacecraft.