Vol 18, No 4 (2019)

In final adjustment of thermally-loaded elements of space structures information on thermal loads (heat fluxes and surface temperatures) for the whole period of flight in the atmosphere is of primary importance. The level of temperature and the processes taking place on the surface of the heat shield do not always allow using conventional methods of measuring thermal loads. In this case determining thermal loads by the results of measuring the temperature at several points of elements of the heat shield structure is an alternative to direct measurements. The aim of this work is to develop and test sensors for measuring heat loading of thermal-protective coating of modern descent vehicles, as well as to test the developed methods of carrying out thermo-physical tests. Heat flux sensors for indestructible composite fibrous materials with a high degree of non-uniformity are described in the paper.

The results of comparative estimation of the accuracy of autonomous navigation of small spacecraft in formation flying are presented. To carry out the research, the “zenith” method and the method of navigation by orbital references were chosen. These methods are based on measurements of the angular position of the Earth and an orbital reference point relative to navigational stars. Assumptions concerning the central terrestrial gravitational field and the normality of errors of the on-board navigation measurements with known constant variability were introduced in the studies. The studies were carried out using the theory of analytical estimation of the accuracy of spacecraft autonomous navigation methods. The use of this theory makes it possible to obtain the covariance error matrix of the required vector of navigation parameters and to estimate the potential (maximum achievable) characteristics of the accuracy of the navigation methods used. A dimensionless navigation error coefficient was chosen as an indicator of the accuracy of small spacecraft navigation method. The coefficient is associated with the elements of the main diagonal of the covariance matrix, it characterizes the precision properties of the method, is integrated by nature and does not depend on the volume and accuracy of the results of navigation measurements. The criterion of expediency of applying the method of determining the parameters of motion of the spacecraft center of mass is based on the comparison of navigation error rates. The presented results allow us to make reasonable choice of the method of autonomous navigation and of the composition of the onboard control of small spacecraft in formation flying.

The results of finite element modeling and experimental evaluation of dynamic characteristics (vibration modes and frequencies) of the composite element of aircraft power plant structures are presented. The aim of the work is to develop effective design and technological schemes for thin-walled complex-geometry composite parts, taking into account the peculiarities of mechanical behavior of polymer composite materials to the fullest extent possible. A method for determining the parameters of natural oscillations of composite parts in a free state using a ping test is developed, which allows excluding the influence of kinematic boundary conditions and obtaining frequency characteristics that depend only on the local characteristics of the material which are primarily determined by the manufacturing technology. According to the results of measurements of the amplitude-frequency parameters of the dynamic response, spectrograms of damped oscillations are obtained the peak values of which correspond to the experimental evaluation of the natural frequencies of the composite part. Verification of the design model was carried out according to the results of the ping test and a method for assessing the quality of technological processes of manufacturing thin-walled carbon fiber structures was proposed.

The article is devoted to one of the most important components of the onboard complex of aircraft equipment - the onboard cable network. The contents of the design documentation for the aircraft onboard cable network are disclosed. The statement of the problem of designing harnesses is defined in general terms. The main stages of designing aircraft onboard cable networks are described on the verbal level, as well as in the form of logical algorithms and graph-algorithms. Some theoretical aspects of designing aircraft onboard cable networks are presented. The concepts of topological space, topological structure, and continuous mapping of the harness structure into the aircraft structure are introduced. Geometric research of an ordinary cable harness of the onboard cable network led to the need to consider the harnesses as a geometric complex in the framework of combinatorial topology. An example of compiling a table of connections of ordinary harnesses for the aircraft onboard system of ultra-short wave communication is given. The rules and requirements for the information content of the table of connections of an ordinary harness to the aircraft on-board system are emphasized. Mention is made of the need to integrate ordinary harnesses into a complex one consisting of tens or even hundreds of ordinary harnesses to simplify the process of installation of the onboard cable network in the aircraft.

Alongside the development of methods of intensifying convective heat transfer inside the blade, development of methods of local improvement of the efficiency of film cooling of the blade’s surface is still of immediate interest. The film is formed on the blade surface in conditions of high-camber shape and low initial velocity of the gas flow in the vicinity of the leading edge with its subsequent abrupt acceleration. The paper presents some data on the peculiarities of film formation on the back and pressure side of the blade in the vicinity of the leading edge. Experimental temperature distribution over the adiabatic wall was obtained with the use of a FLIR-E 64501 thermal imager. It was found that the conditions for the film formation on the blade back are more favorable than those on the pressure side. It manifests itself in the fact that optimal blowing parameters on the blade back are considerably lower than those on the pressure side. The use of V-shaped dimples located on the wall immediately behind the holes for blowing was suggested as a measure for local improvement of film cooling efficiency. The efficiencies of film cooling in the formation of a curtain, without the use and with the use of V-shaped dimples behind the holes for blowing were compared. Local improvement of efficiency and uniformity of film cooling distribution with the use of V-shaped dimples behind the holes for blowing was observed.

A noncoplanar controlled heliocentric flight to Venus of a spacecraft with a non-perfectly reflecting solar sail is considered. The aim of the heliocentric flight is to get a spacecraft into Hill sphere of Venus with zero hyperbolic excess velocity. An algorithm has been developed for applying the locally optimal control laws for the fastest change of the osculating elements. Solar sail orientation is controlled by thin-film control elements arranged along the solar sail surface perimeter. The flight trajectory, the control program and the required width and area of thin-film control elements are obtained as a result of motion simulation.

The article describes an algorithm for optimizing controlled motion of a spacecraft equipped with low-thrust electric propulsion engines maneuvering in the vicinity of an object with an irregular gravitational field (asteroid Eros 433). A mathematical model of the object’s gravitational potential and a model of spacecraft motion are presented. The Pontryagin maximum principle is used to get the time-optimal control program. The formulated boundary value problem is solved numerically by the modified Newton method. The described algorithm can be used to solve similar problems of low-thrust flight dynamics in the vicinity of objects with irregular gravitational fields.

The paper presents the results of analyzing distribution of hydrogen in welded joints obtained by electron beam welding of titanium alloys VT20 and VT23. The distribution of hydrogen in the cross section of welded joints was measured in the area of the weld, in the heat-affected zone and in the base metal by means of spectral analysis using low-voltage pulse discharge on the spectrograph ISP-51. It was established that hydrogen peaks in fixed joints obtained by electron beam welding, unlike argon arc welding, are located not only in the heat-affected area, but also in the сentral part of the welded joint. Chemical analysis of fractures of fixed joints investigated with the aid of a scanning electron microscope Hitachi S-3400N showed that the pores in the welded joints made by electron beam welding occur due to the desorption of capillary-condensed contaminants located in the defects of the edge surface into the melt and due to selective grain boundary fusion because of insufficient temperature conditions of whole grain melting. It was found that emerging variations in hydrogen content, with formation of defects, are influenced by the temperature conditions of heating of the welded edges, the welding rate and the thickness of welded blanks.

The task of optimizing the optimal quantity of technological resources of a hub airport’s functional subsystem, executing an individual process step of ground handling, is considered. This problem is relevant to hub airports. The analysis is limited to limited availability systems in which handling of certain orders can be performed only by certain resources which are used in reference to automated and mechanical equipment, industrial equipment, personnel, etc. The optimization problem is formulated in a probabilistic statement. An approach to solving the problem is described. We suggest using a simulation computer model as an optimization tool. The model takes into account the features of passenger flows and the operating process of a hub airport and includes a fuzzy controller that reflects the logic of the airport operator who controls the ground handling process. The paper describes a model example of solving an optimization problem indicating the possibility and expedience of using a fuzzy controller as a model for the strategy of a human operator. Time dependence of the quantity of technological resources of the functional subsystem is the main result of optimization. This dependence is applicable at the stages of making decisions concerning increase of its capacity rate, operative resource management, planning staff shift work, solving a number of other tasks, especially relevant for hub airports with intense but non-uniform flows of aircraft and passengers.