Mathematical Modeling Methods in Designing Onboard Laser-Ranging Systems of Spacecraft

To perform rendezvous and docking of spacecraft (SC), it is necessary to detect and measure the coordinates of a passive space vehicle (SV) using the onboard aids of an active SV. For this purpose, in addition to radio engineering systems, laser-ranging systems (LRS) are used. A designing process of the onboard LRS for promising spacecraft is currently becoming more complicated and requires taking into account a lot of factors.The authors have developed the PC software to assess capabilities of onboard pulse LRS of spacecraft when working on the nearby or distant space objects that have a diffusely scattering surface, as well as are equipped with the corner reflectors. The software also allows us to calculate the LRS parameters, which, according to GOST R 50723-94, ensure eye-safety in the spectral range of 0.81 ... 1.5 microns in case of accidental irradiation.The energy of the intensifier pulse and the divergence of a sensing beam determine the LRS range and the distance of eye-safe observation, which are the most important indicators to characterize the onboard LRS capabilities. To ensure the best LRS range and safety characteristics simultaneously, it is necessary to solve the problem of multi-criteria optimization.The paper solves the problem of multi-criteria optimization for the maximum LRS range and the eye-safe observation distance by Pareto sets the use of which allows us to avoid uncertainty in choosing a significance of criteria.The results obtained show that the proposed methods can be successfully applied in designing onboard LRS of spacecraft.

Odd Mathieu Functions Application to Synthesize a Multi-element Radiator Flat-topped Radiation Pattern

The paper studies synthesizing capabilities of a flat-topped radiation pattern when using the expansion of the target radiation pattern into a series in terms of odd Mathieu functions. As parameters for comparing the target and synthesized radiation patterns, we used a main-lobe width at a level of -1 dB and an irregularity of the top of the main-lobe of the radiation pattern. The sector-shaped radiation pattern has been synthesized for linear radiators of various lengths. The convergence of the coefficients of the Mathieu series in the synthesis of the sector-shaped radiation pattern has been estimated. It is shown that the use of piecewise-linear approximation of the target radiation pattern in the synthesis using a series expansion into odd Mathieu functions allows us to improve the quality of the radiation pattern formed.The task that involved finding the amplitude-phase distribution for a linear emitter with a length of 3λ, 4λ and 5λ (λ is operation wavelength) for a target radiation pattern was solved. The target amplitude distribution has the following electrical characteristics: the main-lobe width is 37.5° at a level of -1 dB and the side lobe level (SLL) is -20 dB. The synthesis procedure was performed for two cases. In the first case, the target radiation pattern is represented by a piecewise constant function with a given width. In the second case, the target pattern was specified using piecewise linear approximation of the top and slopes of the main lobe.Comparison of the radiation patterns obtained shows that in the first case, the main-lobe width of the radiation pattern at a level of -1 dB is 34°, the SLL varies from -15.6 to -17 dB, and the irregularity of the main-lobe top of the radiation pattern lies within 0.9 ... 1.2 dB. In the second case, the main-lobe width of the antenna radiation pattern at a level of -1 dB is 36.5°, the SLL is -17.5 dB, and the irregularity of the main-lobe top is 0.4 dB at most. When used, the considered under consideration enables us to obtain both the synthesized patterns for linear radiators of various lengths, and the corresponding amplitude-phase distributions and coefficients of the Mathieu series. An estimate of the convergence of the Mathieu series shows that the use of linear approximation of the target radiation pattern in some cases allows up to 2.7-fold increase in acceleration of the convergence of the Mathieu series. The accuracy of reproducing the sector-shaped pattern by the synthesis method using the expansion into odd Mathieu functions gives good results when synthesizing the amplitude-phase distribution for the linear radiators with an electric length of 5λ or more.

Information-Measuring Complex to Detect High Frequency Gravitational Waves

The gravitational waves predicted by the general theory of relativity and detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) have typical frequencies in the range of 30 ... 300 Hz. Current theories of gravity predict the existence of high-frequency gravitational waves with frequencies of 10 ... 100 MHz, including those of cosmological origin, induced by quantum fluctuations of the scalar field at the stage of cosmological inflation in the early Universe.Multi-beam optical resonators, in particular the Fabry-Perot interferometers, can be used to detect high-frequency gravitational waves. When using multi-beam optical resonators, it is possible to use the phenomenon of low-frequency optical resonance, which allows us to have a selective response to the gravitational wave effect. The gravitational-optical resonance in a multi-beam interferometer occurs if the condition is fulfilled that an integer number of half-waves of gravitational radiation is along the length of the resonator.The use of a multi-beam interferometer to detect high-frequency gravitational waves does not require the creation of a complex system for decoupling mirrors used for gravitational antennas operating in the low-frequency part of the spectrum. This is due to the fact that the frequency of mechanical vibrations of the interferometer mirrors is significantly less than the frequency of the gravitational wave.The paper considers possible optical schemes of a high-frequency gravitational antenna: based on the traditional Michelson interferometer, in the arms of which two Fabry-Perot interferometers are available, and on the basis of the Mach-Zehnder optical scheme, where Fabry-Perot interferometers can be made in the form of two perpendicular arms, with reflecting mirrors at the bend of the beam. The advantage of the second scheme is that three photo-detectors, one being main and two others being auxiliary, can be used, and there is a possibility to detect radiation transmitted by Fabry-Perot interferometers.To prove that detection of high-frequency gravitational waves is possible, a potential sensitivity of the high-frequency gravitational antenna has been estimated in the paper.

Acousto-optic Light Pulse Shaper for Measuring the Parameters of Photo-detectors

The paper emphasizes that intensive utilization of the optical range increases the need for the development of new optoelectronic devices. Accordingly, there is a growth in the need for effective methods and tools to study photoelectric properties of semiconductor materials, including photo-detectors.In the paper we have analyzed the well-known methods and tools for measuring the photo-detector parameters, defined the restrictions in their applications, and proved that it is relevant to create a measuring system, the parameters of which are easily adapted to the study of photoelectric characteristics of a wide range of semiconductor materials, including photo-detectors.The scheme and principle of operation of the acousto-optic processor and the features of the photo-elastic effect are discussed, and it is proved that they can be used to form a light pulse of required duration and power. The expressions obtained for calculating the response at the acousto-optic processor output enable us to estimate separately the effects of time of crossing the optical beam by the elastic wave packet and the photo-detector inertia.The capability to determine the time of crossing the optical beam by the elastic wave packet and taking it into account as a device error has been substantiated. The proposed formulas have been tested and by numerical analysis based on the datasheet specifications of the FD-24K photodiode, the effectiveness of the obtained expressions has been convincingly proven.The inertia parameters of a particular sample of the FD-24K photodiode are experimentally studied. The emphasis is upon measuring the rise time of the transient response of the object under study. The exact rise time value of the transient response of the experimental FD-24K sample was approximately 7 μs, which is less than that indicated (≤10 μs) in the product certificate. In real life, such a measurement is necessary when selecting the photodiode pairs with identical parameters.By comparing the results of numerical analysis and experimental studies, it has been convincingly proven that the features of the photo-elastic effect can be used to construct a light pulse shaper with the required parameters.

Research of the Possibilities of Matching the Multi-element Receiving-Transmitting Irradiator Aperture

Currently, aperture antennas with spatial excitation, such as reflector antennas and phased array antennas, are widely used in radar. The composition of such an antenna includes an irradiator, which can be made in the form of a small-element array of radiators to form a set of necessary radiation patterns. Monopulse irradiators are often used, which form both total and difference directional patterns. When performing an irradiator based on waveguide parts, radiators in the form of horns or open ends of waveguides are installed in its aperture. Waveguide irradiators with four and twelve horns are widely used. One of the main electrical characteristics of such an irradiator when used as part of a receiving-transmitting antenna is the isolation of the transmitting and receiving paths. Matching the aperture of the transmitting and receiving irradiator has a significant effect on the isolation of its waveguide channels. With small transverse dimensions of the radiators in the form of open ends of waveguides, it is not possible to obtain high isolation of waveguide channels without the use of additional matching elements. The task of research the effect of matching the aperture of a waveguide multi-element irradiator on the isolation of its transmitting and receiving channels, as well as the ways of matching its radiators, is set.The article considers a four-horn irradiator, the aperture of which contains radiators in the form of open ends of a square waveguide. Each radiator has the radius rounding required for the manufacture of the product using the available technological processes. To match the emitter, a dielectric plate is installed inside it. During the research the thickness of the plate and its location relative to the aperture plane changed. The characteristics of matching the radiators with a plate made of teflon, polyethylene and ST-4 material based on polymers filled with titanium dioxide are presented.The proposed method of matching the opening of a multi-element irradiator with a transverse emitter size of 0,68λ (λ is the wavelength in free space corresponding to the average frequency of the operating band) makes it possible to improve the isolation of the receiving and transmitting waveguide channels by at least 4 dB in the frequency band of up to 3%.

Investigation of Aerosol Inhomogeneities Parameters in Planetary Boundary Layer in UV-A Spectral Region

For today necessity of atmosphere wind remote sensing for wide pool of applications require development of new measurement methods and improvement of already existing.Currently doppler methods for wind speed measuring have largest sensing range. Correlation-based methods are provide lower sensing range for wind speed measurement. However, doppler-based lidar are expensive in opposite to simply designed correlation lidars that additionally allows to measure wind profile along sensing direction.Development of wind correlation lidars required knowledge of atmosphere aerosol inhomogeneities parameters.The most experimental research till now in this area are related to visible spectral range.One of the perspective eye-safety spectral range for wind lidar is UV spectral region. There not so much experimental research works of aerosol inhomogeneities parameters in UV.This paper is related to field experiments of aerosol inhomogeneities parameters in planetary boundary layer on 0.355 um operating wavelength.Block diagram and parameters of lidar with 0.355 operating wavelength is shown. Process of experiments is described. Typical atmosphere backscattering echo-signal for single laser pulse is demonstrated.Procedures if lidar signals processing are described, example of two-dimensional field of relative fluctuations of volume backscattering coefficient for different atmosphere conditions is shown.Results of measurement data processing shown that in planetary boundary layer average contrast of aerosol inhomogeneities in most cases has values in range 0,4% – 10 % (in case of snow up to 25%), and size in range 1,5 – 20 m. Dependency of observation number of aerosol inhomogeneities by range z from lidar to backscattering volume is descending with 1/z manner that the same for dependency for signal-noise ratio SNR(z).

Glycerin-containing Working Fluids for Hydraulic Drives for Special Purposes

The cavitation properties of a liquid must be taken into account in the engineering design of hydraulic machines and devices for hydraulic automation in cases when in their working process the absolute pressure in the liquid may drop below atmospheric, and the liquid is in a rarefied state for a certain time. Cold boiling, which occurs at a relatively low temperature and reduced absolute pressure inside or on the surface of the liquid, is considered as hydrostatic cavitation, if the liquid is stationary, or as hydrodynamic cavitation, if the liquid enters conditions under which the velocity head sharply increases in the flow section and the absolute pressure.In accordance with the theory of cavitation, the first phase of cavitation occurs when the absolute pressure in the degassed liquid drops to the value of the saturated vapor pressure and the air dissolved in the liquid, leaving the intermolecular space, turns into microbubbles of undissolved air and becomes a generator of cavitation "nuclei". Of practical interest is a quantitative assessment of the value of the minimum permissible absolute pressure in a real, partially or completely degassed liquid, at which hydrostatic cavitation occurs.Since the pressure of saturated vapor of a liquid is, to a certain extent, associated with the forces of intermolecular interaction, it is necessary to have information on the cavitation properties of technical solutions, including the solution of air in a liquid, since a solute can weaken intermolecular bonds and affect the value of the pressure of saturated vapors of the solvent. The article describes an experiment carried out by the authors to evacuate liquids. During the experiment, evacuation of various liquids was carried out using a developed hydraulic vacuum pump with a pneumatic drive.The article presents the technologies of hydrostatic and hydrodynamic degassing of liquids used in the experiment.As a result of experimental studies of the cavitation properties of pure glycerin and glycerin in the form of a 49/51% solution in water, mineral oil and aviation kerosene, quantitative estimates of the permissible absolute pressure in the considered technical fluids and solutions were obtained, its dependence on the saturated vapor pressure, the influence of the degree of hydrodynamic degassing the liquid, and the amount of dissolved substance in it on the strength of the liquid to rupture.In the process of studying the cavitation properties of solutions, it was found that the level of permissible absolute pressure in the solution is greater than that of the solvent. It has been suggested that dissolved solid, liquid or gaseous substances weaken the intermolecular bonds of the solvent and increase the pressure of its saturated vapor.On the basis of the experimental studies, a method for determining the highest rarefaction in solvents and in glycerol solutions has been developed. In addition, a comparative assessment of the cavitation properties of the considered technical fluids is given.

Information-Measuring Complex for Registration High Frequency Gravitational Waves

The information-measuring complex designed to register high-frequency fluctuations of the space-time metric and its main elements are described in paper. The complex is based on a Fabry-Perot interferometer with highly reflective mirrors and a two-meter resonator. A solid-state Nd: YAG laser with a wavelength λ = 1064 nm is used for pumping. To read the signal, an InGaAs receiver DET10N2, with a working spectral range of 500-1700 nm and an active region of 0.8 mm2, is applied. Using the developed complex, experimental studies of signal registration at readout frequencies of 1 MHz and 20 MHz were carried out. The graphs of signal fluctuations in time and the spectra constructed from them are given.

Navigation Support for Monitoring the Underlying Surface From UAV with a Passive Optical Sensor

На сегодняшний день с помощью беспилотных летательных аппаратов (БПЛА) решается широкий круг задач, в том числе мониторинг окружающей среды и обследование зон чрезвычайных ситуаций, при которых выполняется локация различных объектов на подстилающей поверхности и их последующая привязка к географическим координатам.Развитие беспилотных систем в настоящее время тесно связано с оптическими датчиками, используемыми на БПЛА всех типов. Пассивные оптические датчики имеют малые массу и габариты, потребляют небольшую мощность от бортовой сети электропитания, при этом они могут измерять дальности до объектов со сложной конфигурацией и ненормированным коэффициентом отражения поверхности.Цель данной работы – анализ требований к навигационной аппаратуре при измерении дальности монокулярным пассивным оптическим датчиком до статических наземных объектов с борта БПЛА и их последующей привязке к географическим координатам.Выполнены оценки разных вариантов осуществления оптической локации наземных объектов параллаксным методом измерений с оптической и навигационной аппаратурой на борту легких БПЛА малого радиуса действия, мини- и микро-БПЛА. В качестве источников навигационных данных может быть использована аппаратура спутниковой навигации, телекамеры, бесплатформенная инерциальная навигационная система, барометрический высотомер и цифровой компас.При использовании рассматриваемых навигационных датчиков обеспечивается измерение дальностей до 1000 м с относительной погрешностью не более 10 %. При привязке объектов к географическим координатам оценки погрешности как для прямолинейной, так и для сложной траектории полета БПЛА различаются не более чем на 4,1 м для всех типов навигационных датчиков, а позиционная ошибка не превышает 150 м при величине ошибки по высоте не более 40 м.В ранее известных работахоценка измерений выполнялась на малом базисе (уход БИНС не учитывался), а привязка обнаруженных объектов к географическим координатам не выполнялась.Результаты работы могут применяться в разработке навигационных систем различных БПЛА и беспилотных систем мониторинга наземной обстановки.

Analysis of the Possibility of Remote Laser Detection of Propane Leaks

Propane is one of the main components of the wide fraction of light hydrocarbons (WLHF). A large volume of WLHF is transported to petrochemical plants via pipelines. Control of pipelines is carried out by means of in-line pressure sensors. However, they are ineffective for detecting low-intensity leaks.To detect low-intensity propane leaks from pipelines, it is promising to use a remote laser gas analyzer installed on an aircraft.The article is devoted to the analysis of the possibilities of remote laser detection of propane leaks.Based on the data on the absorption of propane and atmospheric gases, the wavelengths of 3370 nm (in the maximum absorption of propane) and 3550 nm (in the spectral region where there is no absorption of propane) were chosen as the sounding wavelengths.It was believed that the monitoring of propane leaks is carried out by a lidar installed on the aircraft in a monostatic sensing scheme. The method of differential absorption with scattering from the earth's surface is used.To detect propane leaks, an information parameter was used, which is equal to the ratio of the power recorded by the receiver at wavelengths of 3370 nm and 3550 nm. The value of the information parameter was calculated for different heights of the propane layer on the earth's surface and different concentrations of propane in the layer.Statistical modeling was performed to quantify the effectiveness of remote detection of propane leaks.In the work, the probability of correct detection of a propane leak (detection of a leak when it is in reality) and the probability of false alarms (detection of a leak when it is not in reality) were calculated.The decision to detect propane leaks was made when the value of the information parameter was less than the threshold.The results of mathematical modeling show that for a propane content in the leak of at least 0.17 % (an order of magnitude less than the concentration limit of flame propagation), the problem of remote detection of propane leaks from the pipeline can be solved with a probability of correct detection of more than 0.999 and a probability of false alarms of less than 0.001 with a thickness of the propane layer on the earth's surface of at least 20 cm.