The object of this study is the process of disposing of the upper stage body of a launch vehicle made of polyolefins by burning in the dense layers of the Earth’s atmosphere during removal from Earth orbit. The task addressed was to determine the possibility of disposal of the upper stage bodies of launch vehicles made of polyolefins during deorbiting. The mathematical model built makes it possible to take into account the effect of ballistic and aerothermodynamic aspects at the same time. The application of this model makes it possible to estimate the degree of disposal of the upper stage bodies of launch vehicles made of polyolefins in the Earth’s atmosphere at the stage of scientific research. In turn, this makes it possible to rationally choose the design parameters of materials for launch vehicle bodies, taking into account the disposal phase in the dense layers of the atmosphere, as well as rationally select the initial parameters for deorbiting orbits. This makes it possible to maximize the level of disposal and minimize the probability of debris falling on uninhabited areas of the Earth. The results of the study showed that launch vehicle bodies made of polymer materials such as polyethylene and polypropylene could burn up in the atmospheric part of the trajectory by 90–100 %, depending on the mass-dimensional characteristics and the type of orbit. In turn, increasing the ellipticity of the orbit makes it possible to increase the steepness of the entry of the upper body of the launch vehicle into the dense layers of the atmosphere, and hence, to increase the heat flows that contribute to the combustion of the body. With this in mind, methodological recommendations have been compiled for choosing orbits of the necessary ellipticity, taking into account the place of fall of fragments of the upper bodies of carrier rockets that did not burn up in the atmosphere
The goal of this article is to theoretically substantiate the applicability of the classical formula of the single cylindrical probe theory to determining the electron density based on measurements of the currents of a floating probe system in ionospheric conditions. Probe measurements in the ionosphere are modeled using a cylindrical probe and the body of a very small satellite placed transversely in the incident supersonic flow of a collisionless plasma. The ionospheric plasma is considered to be Maxwellian and consists of electrons and singly charged atomic ions of oxygen and hydrogen. A mathematical model of current collection by the floating probe system “probe – plasma – satellite body” was developed based on classical relationships for the electron and ion currents to a thin cylinder placed transversally in the incident flow. To model the collection of the hydrogen ion current by the satellite body, the results of numerical calculations of the ion current to the cylinder using the two-dimensional Vlasov-Poisson model were approximated. The probe bias potential was determined such that, under ionospheric conditions, the electron region of the floating probe system's current-voltage characteristic is closest to that of a single probe. The determination of the electron density using the classical calculation formula of the single-probe theory was simulated for probe current measurements in the low voltage portion of the electron region of the current-voltage characteristic of the floating probe system. The limiting methodological error in determining the electron density under ionospheric conditions within the framework of the probe system model considered was estimated. The effect of probe current measurement errors on the determination of the electron density using the calculation formula of the single-probe theory was studied. The obtained results may be used in the preparation and interpretation of ionospheric plasma diagnostics experiments using ultra-small satellites.
This article presents the results of an experimental study of the parameters of the ST-40M Hall-effect thruster developed by SETS (Space Electric Propulsion Systems) in its operation on xenon and krypton. Electric propulsion systems based on Hall-effect thrusters have found wide application due to their high performance and relative simplicity of design and operation compared to other types of propulsion systems. Traditionally, xenon is used as propellant in Hall-effect thrusters. It is an inert gas with a low ionization energy and a high atomic mass, which makes it possible to achieve a high performance of the electric propulsion system while maintaining operational simplicity. However, the high cost of xenon significantly affects the overall expenses during the testing and operation of the thruster and the propulsion system. Therefore, research is underway on the use of alternative propellants that could reduce operating costs while maintaining the thruster performance at an acceptable level. The most promising alternative to xenon is considered to be krypton. It has a lower cost and ensures operational simplicity, but its higher ionization energy negatively affects the thruster efficiency. The goal of this work was to compare the main parameters of the thruster operating on xenon and krypton under identical conditions. Experimental tests were carried out in a vacuum chamber at discharge voltages ranging from 250 to 500 V and propellant mass flow rates from 1 to 1.78 mg/s for xenon and from 1 to 1.6 mg/s for krypton. A comparative analysis of the thruster parameters in its operation on xenon and krypton at a mass flow rate of 1 mg/s showed that the use of krypton leads to a deterioration in thruster performance. The anode thrust and specific impulse decreased by 25 %–37 %, while the anode efficiency dropped by 15 %–24 %.
Innovative technologies of layer-by-layer product manufacturing by fast 3-D printing open up new opportunities for producing parts of a given shape. But sometimes, during the printing process with the use of specific materials, it is necessary to additionally heat or cool the part with an air flow over it. To improve the part quality, this process must be controlled, but for production safety, 3-D printing with special materials must be unmanned. Thus, it is necessary to develop an automated system for controlling the 3-printing process. This system should include several subsystems, in particular, a system for controlling the material supply through the extruder, a system for controlling the cooling (or heating) temperature of the printing zone, and a system for controlling the printing speed, which affects the part quality. The parameters of all the systems depend on the material characteristics and the printed part shape. This paper presents a mathematical model of a control object: a subsystem for 3-D printing zine air heating control, which is based on experimental data obtained in real conditions, and structural and parametric identification procedures for this subsystem. As a result of the identification, the model parameters were obtained as a function of the control action. The analysis of these relationships showed that the model of this subsystem as an automatic control object is complex with a variable structure and non-stationary parameters that change randomly over a wide range. It was found that the whole range of the control action can be divided into five sections, within which the structure of the control object model does not change and the model parameters change over relatively small ranges. Taking this into account, recommendations were formed regarding the procedure for further synthesis of the subsystem for automatic control of the air blowing temperature. In developing this printing control subsystem, to ensure the quality of the transient process, the control action values must be checked for different model structures with variable parameters over certain ranges. The control system developed must be interfaced with other printing control systems to get a complete finished automatic control system.
One of the most important problems in the current development of the Ukrainian railway transport is to speed up the integration of Ukraine into the European railway service. For cars to operate on the Ukrainian and West-European railways, it is necessary to use gauge-changeable wheelsets, which can automatically change from one gauge to another, and provide wheel-rail contact pair compatibility on the railways of both standards: with R65 rails of cant 1/20 in Ukraine and UIC rails of cant 1/40 in West Europe. To solve this problem, the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine developed wheel profiles for passenger and freight cars: ITM-73EP and ITM-73EC, respectively. The goal of this work was to study the possibility of using one of these profiles as a common wheel profile for passenger and freight cars with prospective trucks to be operated both on the Ukrainian and on the European railways. The study was concerned with passenger cars with 68-7041 trucks and freight cars with 18-7020 (an axle load of 23.5 tf) and 18-9817 (an axle load of 25 tf) trucks. The use of wheels with both profiles was compared in terms of car dynamic stability at service speeds on tangents of the Ukrainian and European railways and wheel-track interaction indices in curves (with account for different degrees of rail side wear). The results of the calculations made it possible to identify the profile expedient to be used as a common one for passenger and freight cars. According to predictive estimates, the use of wheels with this profile will speed up passing between tracks with different gauges and provide a high ride quality and improved indices of wheel-track interaction on both railways.
