Vol 14, No 4 (2015)

The bypass factor as the basis for providing Earth remote sensing spacecraft (ERS SC) operability in anomalous flight conditions, related with onboard equipment (OE) faults, is discussed in the paper. In addition, operability as a complex property is decomposed into three particular characteristics: invulnerability, adaptability, and recoverability. Principles of their implementation during the flight are based not only on structural provisions (for example, protective measures), but also on OE technical state control not only by integrated structural reserves, but also by bypasses based on other resources. Provision of ERS SC operability and target operation with the use of minimum additional resources is the purpose of bypass control in anomalous flight situations. It is based mainly on roundabout ways of accomplishing tasks, in other  words, on bypasses produced on the basis of functional, information-analytic, and natural resources (intrinsic to OE) as well as emergent (synergetic) resources formed as a result of purposeful interaction of dissimilar components, in particular, the complex of the SC onboard equipment. The topicality of this problem increases with the decrease of ERS SC weight-dimension characteristics (caused by tightening the restrictions) and the increase of active life duration (Tаl) under relatively strict requirements of efficiency target (ET). Variants of using available OE redundancies for ERS SC bypass flight control, taking into account the change of ET within the set limits, are proposed in the paper. Schemes of numerical estimation of efficiency and operability as vector parameters on the basis of bypasses including those based on parameters and criteria of SC operability are presented. A possibility of forming requirements to onboard equipment to ensure SC operability in anomalous flight conditions with their help is shown.

The problem of delivering payload in the form of a descent capsule using an orbital tether system is discussed in the paper. The dynamic law of controlling the deployment of an orbital tether system in the form of time dependence of the tether tension force is considered. It is shown that if a previously obtained optimal (relay) program of controlling the tether tension force is implemented the speed of tether deployment can reach high values. To reduce the speed of tether deployment a program of controlling the deployment of an orbital tether system, with prescribed limitations on tether deployment speed is obtained. Numerical simulation of orbital tether system deployment is carried out for the program of controlling the tether tension force with limitations on tether deployment speed. It is established that introducing too tight limitations on the speed of tether deployment does not make it possible to deliver the payload – a descent capsule - to the Earth surface. The dispersion of the points of landing of the capsule on the Earth surface caused by introducing limitations on tether deployment speed is analyzed

The efficiency of using the principle of minimum control in solving the task of synthesizing the system of controlling a spacecraft spatial turn by arbitrarily set angles up to 180 degrees is analyzed, with the “Aist-2” small spacecraft taken as an example. The tensor of inertia has the form of a diagonal matrix. Flywheels the rotors of which are parallel to the principal central axes of the spacecraft inertia are used as actuating devices of the system that controls motion round the center of masses. The control moment developed by each flywheel, is proportional to the angular acceleration of its rotor. The energy spent on the control, proportional to the sum of modules of angular accelerations of flywheel rotors is accepted as an index of the optimality of the spacecraft spatial turn. Euler dynamic equations are reduced to finite-difference recurrent relations to model unperturbed spacecraft motion around the center of masses. An auxiliary dynamic system is introduced the parameters of which are chosen on the basis of the solution of the task posed to use the principle of minimum control that ensures minimum costs of control. The results of mathematical modeling confirmed the efficiency of the proposed principle. In comparison with the traditional method of control (acceleration, motion at a constant angular velocity, braking) two-fold economy of electrical power is achieved.

The article focuses on the development of algorithms for controlling the parameters of the orbit of a geostationary satellite with the help of a low- thrust engine. We consider only the control of two-dimensional parameters that define the position of the satellite in the orbital plane, namely, the orbit time, the eccentricity and the point longitude of satellite observation. A two-dimensional problem of geostationary spacecraft terminal control is formulated. It is assumed that the correction maneuver is carried out by creating low transversal acceleration with the help of low-thrust electric propulsion, and the control vector consists of a sequence of durations of powered and unpowered portions. In this regard, the two-dimensional terminal control problem is solved in a discrete setting. For this purpose, a discrete model of the motion of a geostationary spacecraft in the orbital plane under the influence of low transversal acceleration is developed. It is quite difficult to solve the problem posed by using the traditional method of dynamic programming based on the use of the Bellman equation since the resulting discrete model of the satellite motion is a non-linear system of equations. Therefore, an approximate pattern of solving the problem on the basis of a three-step algorithm of the terminal control of the orbit time, eccentricity and point longitude of satellite observation is proposed in the paper. As a result, the plane terminal control problem is solved in an analytical form. Analytical expressions for estimating the costs of characteristic velocity correction maneuver using a three-step algorithm of terminal control are obtained. In modeling the motion of a geostationary satellite under the influence of low transversal acceleration the algorithm showed sufficiently high accuracy.

Theoretical and experimental studies of characteristics of the vortex throttling valve (diode) for steam and water sample conditioning systems are discussed in the paper. Numerical simulation of forward and reverse flows in the vortex throttle channel is carried out with the help of the Ansys CFX software. Flow visualization, flow parameter field distribution, flow rate vs. pressure drop characteristics are obtained. The design characteristics of the throttling valve are consistent with the experimental results with an accuracy of 10%. Geometric parameters of the throttling valve are selected on the basis of a series of calculations to ensure reliable operation of the sample conditioning system.

The performance reliability of aerospace products is directly related to the reliability of each essential part; therefore special attention is paid to establishing the reasons of occurrence of defects and to developing preventive measures during the whole life cycle of a product. The article contains the analysis of the results of investigating the causes of defects occurring in the inner casing of the combustion chamber of NK- 86 gas turbine engine «Meridional cracks on the conical part of the flange». Metallurgical properties of the defective casing are examined in detail. A number of studies aimed at determining residual stresses on the surface of a part of the housing, as well as on specimens cut out from the housings with different hours in service and different surface treatment, including the use of additional thermal and mechanical treatment has been carried out. Diagrams of residual stress distribution for the specimens cut out of the housings with different treatment and subjected to various methods of relieving tensile residual stresses are presented. Endurance tests of one of the housings have been carried out. Conclusions about the influence of residual stresses on the fatigue resistance of the parts under investigation have been made. Measures to eliminate and prevent the defect both for the tested housing of the combustion chamber and for the base members manufactured by similar technologies and operated in similar conditions are proposed.

The influence of preliminary surface plastic deformation on the endurance limit of parts made of steels 40X and 30ХГСА with the thread М16х2 has been examined. The investigation has been carried out by the computational-experimental method using the results of determining residual stresses mechanically on the specimens cut out of smooth workpieces and by modeling threaded specimens using finite-elements models. The method of thermal elasticity has been used for the calculation of the strain-stress state in the PATRAN/NASTRAN environment, whereby the distribution of initial deformations in the hardened layer is replaced by the appropriate temperature field. The graphs of distribution of axial residual stresses across the thread roots are plotted on the basis of the calculation. The increment of the endurance limit for threaded parts has been predicted by the average integral residual stress criterion. The calculation results are compared with the experimental data of testing the specimens. The specimens made of 30ХГСА steel without a nut were tested under the symmetrical cycle according to the pure bending pattern, the specimens made of 40X steel with a nut were tested under the zero-to-tension positive cycle in the case of stretching. Non-propagating fatigue cracks have been found in the specimens that withstood the tests and were destroyed.

The practicability of using ionization probes for the investigation of fuel consumption in a piston engine is proved in the paper. It is shown that in order to expand the functionality, to increase the reliability of operation and accuracy of the processing of the ionization probe signal it is essential to know the influence of the fuel chemical composition and characteristics of turbulent flame propagation (velocity and width). In this connection, the paper presents theoretical and experimental research of the influence of turbulent flame propagation velocity, the width of the turbulent burning zone, the composition of the fuel-air mixture and the content of carbon in it on the indications of the ionization probe – the ion current. The work carried out resulted in obtaining functional dependence of ion current on carbon concentration in the fuel and characteristics of turbulent flame propagation. Experiments on the engine showed that if the excess air factor is in the range of 0.8 to 1.1 the agreement between the design and experimental values of the ion current in the first and second phases of combustion is over 83 per cent. The results of the work can be used to predict and monitor the propagation velocity and the width of the turbulent flame front in the combustion chamber of an internal combustion engine with the help of an ionization probe.

Various types of accelerators of solid particulates of natural and technogenic origin are analyzed in the paper. We consider the structure and principles of operation of micron- and millimeter-scale accelerators with the center of velocity distribution of about 20 km/s: electrostatic, electromagnetic, pulsed, rail electromagnetic, solenoid coil and electric-gas dynamics, combined installations. Light-gas, explosive, gas discharge and electromagnetic accelerators with different principles of action are reviewed. The focus is on the electromagnetic techniques of acceleration that are most promising for acceleration of macrobodies to supervelocities. The advantages and disadvantages of different types of accelerators of solids are pointed out. The usability of different designs of accelerators to simulate collisions of orbital meteorite particles and space debris with the surface of the spacecraft is analyzed. Problems emerging in the construction and operation of accelerators of various types are specified and solutions to these problems are presented. The results of experiments in the acceleration of solid micron- and millimeter-wave solids using accelerators of various types and methods of structural optimization of particle accelerators with a view to increasing their efficiency and the speed of the accelerated body are presented. The evolution of accelerators and the main directions of their further improvement are shown.