Vol 18, No 1 (2019)

In order to conduct experiments to study convection under microgravity it is proposed to use the “Progress” cargo transportation spacecraft. This is due to the fact that the microgravity environment onboard the Russian Segment (RS) of the ISS is not favorable, since the ISS center of mass is in the US segment, while many onboard systems generating micro-accelerations are installed in the ISS RS. There is no crew and no life support systems onboard the cargo spacecraft and micro-accelerations in it are significantly lower than those in the ISS RS. Passive modes of the cargo spacecraft attitude control are particularly favorable for carrying out microgravity experiments in space. In the course of a series of experiments conducted onboard a cargo spacecraft to find the minimal level of residual micro-accelerations, the gravity orientation mode turned out to be the most suitable one. It is planned to conduct an experiment to study convective isothermal currents using the Dakon-P scientific gear specifically developed for this purpose onboard “Progress” spacecraft in free flight in the gravity orientation mode.

А method based on comparing oscilloscope patterns of operational parameters with reference curves is one of the most promising methods of diagnosing hydraulic systems among the existing ones. Its implementation does not allow accurate localization of the faulty unit in the system and quantitative estimation of the magnitude of the fault. To eliminate these shortcomings, it is advisable to use simulation models of hydraulic units, taking into account typical faults of a hydraulic system. Their use makes it possible to evaluate the effect of a particular malfunction on the change of dynamic parameters at the stage of mathematical modeling. As a result of the analysis of statistical information and literary sources, characteristic faults of hydraulic systems are identified. Their causes and the impact on the operation of hydraulic units are examined. Simulation models of units taking into account typical faults are described in the Matlab / Simscape software package. They are implemented using a typical hydraulic system as an example. Dynamic characteristics of a hydraulic system in a healthy condition and those of a system with one of the characteristic faults are compared.

The article is devoted to the problem of ensuring the operability of air-fuel lubrication and cooling systems for gas turbine engine (GTE) rotor bearings. The paper considers one of the advanced designs of a GTE in which an air-fuel mixture obtained in a special mixer is fed to a bearing installed in the turbine support and then through a hollow shaft to the bearing of the compressor support and then directed to the engine input.  It is difficult to implement such a GTE scheme because of the necessity to ensure the operability of bearings lubricated with an air-fuel mixture for a predetermined period of time. It is impossible to determine the thermal state of the bearings and the friction regime in them with sufficient accuracy. The solution of the problems requires carrying out experimental work to determine the coefficients of friction and convective heat transfer in the bearings, as well as their full service life under various operating conditions and parameters of the air-fuel mixture blown through the bearings. The paper presents the results of testing a 45-126205РЯ radial thrust bearing lubricated with an air-fuel mixture, МС-8П oil and a non-lubricated bearing of the same kind. The operability of the GTE rotor bearings lubricated with the air-fuel mixture is analyzed, the area of efficient application of the gas turbine engine with an air-fuel lubrication system is determined.

In this paper, the criteria for determining the composition and physicochemical properties of aviation kerosene were formulated. The data on the physicochemical properties of known kerosene surrogates were systematized and classified. The main classes of individual chemical components of aviation kerosene were determined, and the main representatives of these classes which were used in the preparation of surrogates, were investigated. Four- and six-component kerosene substitutes are proposed. The physical properties of the developed surrogates were validated according to the flow characteristics and the spray angle of the flame of a centrifugal fuel nozzle. The dependence of the flame speed on the composition of the mixture of developed kerosene surrogates was determined. The results of determining the composition of combustion products during the combustion of TS-1 brand aviation kerosene and its surrogates in a model combustion chamber were compared.

The natural and “man-made” space environment generates serious risks for the implementation of space missions, both automatic and human. The main natural and technogenic risk factors that limit or pose a threat to the implementation of space-based automatic and manned space missions in the near-Earth space are cosmic radiation and space debris. In the upper layers of the atmosphere, natural transient electromagnetic phenomena associated with significant energy release are also risk factors for suborbital flights. It is planned to create a system of spacecraft in the proposed “Universat-SOCRAT” project that makes it possible, in a mode close to real-time, to determine the radiation conditions in a significant part of the area of trapped radiation, up to the orbits of global navigation satellite systems or the geostationary orbit. It is also planned to create a space segment of monitoring space debris and electromagnetic transients in the upper atmosphere. Monitoring of space debris will allow all-weather and global tracking of near-Earth objects and, thereby, increase the efficiency of analyzing data and making necessary decisions.  In some cases it will improve the accuracy of determining the coordinates of objects for their subsequent cataloging. Successful realization of the project will make it possible to create a space system for monitoring and preventing space hazards for both ongoing and planned space missions for the first time in the world.

The results of research on increasing the efficiency of a firing test facility for testing thrusters under high-altitude conditions are presented. The increase in efficiency consists in reducing the expansion pressure generated by the ejector and the flow of the active gas (air) consumed by it. Experimental studies were carried out using three versions of gas generators developed by the author which ensure an increase in the energy of the active gas before it is supplied to the ejector. When using the GG-1 gas generator with working media such as air, kerosene and water, the vacuum of less than 1 mm Hg was achieved with the air mass flow rate of 1.1 kg/s (the ejector provides a vacuum of 13 mm Hg with the cool air flow rate of 2 kg/s). However, the design features of the gas generator led to a cumbersome system of supplying working fluids and a complicated start-up sequence. The GG-2 gas generator with air and kerosene as working media failed to provide the temperature of the active gas below 600°C, therefore, to prevent ejector malfunctioning, GG-2 was turned off when the rarefaction reached 13 mm Hg. The air mass flow rate was 1.1 kg/s. The working media of the GG-3 gas generator are air and kerosene or air and natural gas. The design of the GG-3 makes it possible to regulate the temperature of the produced active gas. When working on kerosene, a vacuum of 4 mmHg was reached with the air mass flow rate of 1.5 kg/s. The studies of GG-3 using natural gas as a fuel are going on.

The task of optimizing the space vehicle combined orbital plane change maneuver with the aim of maximizing its final mass is considered in the paper. Burst of power is used for the vehicle’s exit from the initial low earth orbit and subsequent re-entry. Starting from atmospheric entry till the end of the orbital plane change with the entry in the final orbit the angle of attack, the air-path bank angle and the fuel-flow rate are used as controls. Limitations for the angle of attack, fuel-flow rate, adiabatic recovery temperature, longitudinal and vertical load factor are introduced. The successive linearization method is used to determine the optimal control programs. Solving the optimization task is exemplified by a hypothetical space vehicle. The results of modeling space vehicle motion are presented. The changes in the determined “aerodynamic” (angle of attack and air-path bank angle) and “motion” (fuel-flow rate) controls with increasing the angle of orbital plane change are discussed with and without account of the key limitation on the modes of motion – maximum adiabatic recovery heating temperature.

In many industries, the share of small-scale production plants is significant. In these conditions, compared with traditional methods of pressure treatment, pulse pressure treatment methods, one of the varieties of which is gas stamping, are more efficient. However, the known devices of gas stamping provide mainly stamping of thin-walled parts. To expand the technological capabilities of gas stamping, the authors developed a gas stamping device with a piston pressure multiplier, in which heating and deformation of the stamping workpiece is carried out using the energy of combustion of fuel mixtures in the combustion chamber, in the working cylinder and in the cavity of the matrix. This article is devoted to the study of the workflow of this device. Theoretical analysis of the workflow was carried out, and, as a result, a pattern was determined for the variation of the pressure that performs the stamping process in the working cylinder. In particular, it was found that at the final stage of the stamping process, due to the energy of combustion of the fuel mixture, the pressure in the working cylinder increases 1.5...2 times, which allows a significant increase in the thickness of the parts to be stamped. An experimental gas stamping device with a piston pressure multiplier was developed, and experimental studies were carried out. The studies confirmed the main results of the theoretical analysis: the discrepancy between the theoretical and experimental values of the degree of pressure multiplication in the working cylinder does not exceed 11%.

The article presents the results of analyzing the mechanism of failure of working faces of big  roller bearings made of 0,2C2Cr4Ni (E3316 AISI) structural steel. The microstructure was investigated with the help of a METAM LV-31 metallographic microscope. The surface of the bearing rings and rollers was tested for various kinds of defects using a TESCAN Vega SB scanning microscope. The PMT-3 micro-hardness tester was used to measure micro-hardness. Studies show that the microstructure of steel is a fine-needled tempered martensite with chromium carbide inclusions observed near the surface. The depth of the cementation zone was determined on the basis of the measurement results. The value of the depth exceeds the standard established by the manufacturer. The destruction of the bearing roller assembly is characterized by spalling, stratification and cratering. The destruction of the bearing ring is characterized by scouring and indentation caused by metal particles caught up in the ring-roller contact in the process of operation. These defects result in the formation of micro-cracks and, as a result, further spalling and peeling. It is possible to prevent the defects by reducing the depth of the carbonization zone, as well as reducing the surface maximum hardness by changing the mode of final heat treatment.