The paper examines the matters of operational dependability of space systems (SS), efficiency of complex systems, use of redundancy in spacecraft (SC) design. It presents methods of predicting the dependability of designed devices, design of devices with desired dependability and comparison of dependability of various SS. For that purpose, the authors set forth the fundamentals of the dependability theory for SS design, methods of collection and processing of data of equipment dependability based on the results of operation and special dependability tests. Methods, mathematical models are developed, the equipment architecture at the stage of design and manufacture is analyzed. The paper also cites the design ratios for various tested types of redundancy, lifetime extension of SC units based on the residual operating life estimation method. The existing methods of dependability analysis are classified and examined. The authors outline the problems of ambiguity of information of the input data in case of classical computing. The effect of nominal deviations of the external effects, irregularity of the failure rate, non-linear nature of the effect of external factors on the dependability are examined. The paper also takes a look at the way the external factors affect the dependability and the degree to which such factors are taken into consideration in the existing methods. It is noted that the qualitative, technical and organizational (design and software) requirements for dependability in the technical specifications for each stage of elements and SS development, shall be observed and confirmed at the respective stage of activities. The paper presents the methods of estimation of technical item operating life with the focus on those based on the physical premises of operating life depletion. Attention is drawn to the importance of the economic aspect in the research dedicated to SS lifetime extension.

The Aim of this paper is to increase the power of statistical tests through their joint application to reduce the requirement for the size of the test sample.

Methods. It is proposed to combine classical statistical tests, i.e. chi square, Cram r-von Mises and Shapiro-Wilk by means of using equivalent artificial neurons. Each neuron compares the input statistics with a precomputed threshold and has two output states. That allows obtaining three bits of binary output code of a network of three artificial neurons.

Results. It is shown that each of such criteria on small samples of biometric data produces high values of errors of the first and second kind in the process of normality hypothesis testing. Neural network integration of three tests under consideration enables a significant reduction of the probabilities of errors of the first and second kind. The paper sets forth the results of neural network integration of pairs, as well as triples of statistical tests under consideration.

Conclusions. Expected probabilities of errors of the first and second kind are predicted for neural network integrations of 10 and 30 classical statistical tests for small samples that contain 21 tests. An important element of the prediction process is the symmetrization of the problem, when the probabilities of errors of the first and second kind are made identical and averaged out. Coefficient modules of pair correlation of output states are averaged out as well by means of artificial neuron adders. Only in this case the connection between the number of integrated tests and the expected probabilities of errors of the first and second kind becomes linear in logarithmic coordinates.

The Aim of this paper is to show that the development, deployment of new diagnostic tools and improvement of the existing diagnostic tools in onboard equipment enables better operational characteristics and reduced probability of transition of intelligent railway systems into a forbidden state.

Method. In the context of intelligent railway systems, the construction of the analytical model of probability evaluation is of principal interest due to the feasibility of demonstrating the factors that are taken into consideration by such a model. Forbidden events that cause inoperability of intelligent railway systems are random; they can be represented as a random process. A random process of system development, transition from an allowed state into a forbidden state, system state changes in time can be described with a semi-Markovian process. When assessing the probability of system transition into a forbidden state, the question arises as to the selection of a method of calculation. The paper shows the feasibility of representation and solution of a semi-Markovian model with the help of a coupled graph model [3, 5] that has a high level of visualization and is a well-formalized method of identification of the probability of a system’s transition into a forbidden state. The set of system states and their connections are represented with a directed state graph with defined topological concepts [3]. In order to identify the effect of the introduction of new diagnostic tools and improvement of the existing diagnostic tools in onboard equipment on the probability of transition of intelligent railway systems into a forbidden state, the authors use the theorem of identification of the probability of system’s transition from the initial unhazardous state into a hazardous state and set forth the formula to calculate this probability.

Results. The graph method implemented in this paper shows that the use of additional diagnostic tools reduces more than twice the probability of a system’s transition into a forbidden state, i.e. a state when the failure will not be detected by the inbuilt or additional diagnostic tools.

The Aim of this paper is to develop the methods of analysis and simulation of the processes of occurrence and development of emergencies at complex railway infrastructure facilities. It cites analysis data on the threats, causes and consequences of sudden emergencies at complex railway infrastructure facilities. For the purpose of ensuring reliable operation of technical objects, as well as timely identification of faults, it is proposed to use the indicator-based approach that allows diagnosing and formally analyzing the processes of occurrence and propagation of malfunctions across the elements of complex technical systems. For the purpose of simulating the processes of propagation of the disturbances (hazards of emergencies) that occur as the result of malfunctions, it is proposed to use the theoretic graph approach that involves model and visual representation of the structure of a technical system under consideration in the form of a directed graph that shows the correlations between its elements. Each node and edge of a graph is assigned certain parameters or functionals that reflect the processes of correlated operation of the elements of the simulated system. The propagation of disturbances within a system is simulated with pulse processes initiated in one or several nodes. The paper refers to the developed formalized models of disturbance propagation in a technical system based on the construction of structural components and correlation matrices. The authors introduce the concept of critical element of a technical system that helps identify the event of its failure. Two basic criteria of technical system failure, i.e. the exclusive (a system is considered to have failed if the disturbance has reached any of the critical elements) and absolute criterion (failure occurs if the disturbance has reached the specified subset of critical elements) are defined. The paper provides an analytical example that illustrates the capabilities of the proposed model of disturbance propagation within the structure of a technical system. For the purpose more efficient diagnostics of the hazard of emergencies in railway infrastructure facilities the paper proposes a model of application of structurally integrated indicators that consists in the integration of indicators within the structure of a technical system that would immediately deliver the required and sufficient information in case of emergency. The main task would be to identify a set of indicators with the primary purpose of reducing the information-related stress and concentration of dispatchers’ or operators’ attention on the processes within a technical system that are most relevant in terms of accident-free and safe operation. Basic criteria are identified for the generation of the set of indicators within a complex technical system: maximum of reliability of the disturbance consequences estimate, maximum of accuracy of emergency causes identification, minimum of emergency identification time, minimum of nonrecurrent and current costs. A modified graph model of disturbance propagation in a complex technical system is provided that is the prerequisite for solving the multicriterion problems of optimal location of indicators within the structure of a technical system in terms of completeness, accuracy and timeliness of detection of failures of various types. Automation of the processes of generation of indicator sets using models of disturbance propagation in technical systems will allow using the proposed methods as part of further development of the URRAN methodology in terms of improvement of the decision support in railway infrastructure facilities management.

Aim. The paper examines the existing definitions of survivability and damage tolerance (operational survivability) of aeronautical structures. An attempt is made to unambiguously define the survivability of aeronautical structures that can subsequently be extended to an aircraft as a whole and other complex technical items. The primary goal of this paper is to clearly distinguish between dependability and survivability. In order to ensure efficient operation and flight safety, an aircraft must possess airworthiness, a comprehensive characteristic of an aircraft that is defined by the implemented design principles and solutions and that allows performing safe flights under expected conditions and under the established methods of operation. The expected operating conditions are described in the Aviation Regulations – Airworthiness Requirements. Despite the fact that compliance with the Airworthiness Requirements ensures a sufficiently high level of flight safety, the most vital structural components are designed in such a way as to remain operable even under extreme conditions beyond the expected operating conditions. But dependability cannot be responsible for operability outside the expected operating conditions. Conclusion suggests itself that under extreme conditions beyond the expected operating conditions operability is to be ensured by another property, i.e. survivability.

Methods. This research was conducted using the logical and probabilistic approaches. The author examined literary sources primarily dedicated to the matters of dependability and survivability of aeronautical structures, as well as other complex technical items. In order to ensure an optimal understanding of the differences and correlation between the concepts of dependability and survivability, the probabilistic approach was used.

Results. Upon the analysis of literary sources, survivability was defined as the property of an item to retain in time the capability to perform the required functions under extreme conditions beyond the expected operating conditions under the specified methods of maintenance, storage and transportation. Additionally, the paper proposes the definition of damage tolerance (operational survivability) as the property of an item to retain in time the capability to perform the required functions under extreme conditions beyond the expected operating conditions depending on the methods of maintenance, storage and transportation. The probabilistic approach to the delimitation of the concepts of dependability and survivability of aeronautical structures was examined using the known indicator of operating efficiency of a transport aircraft that is represented as the mathematical expectation of the efficiency indicator. An aircraft may be either in the expected operating conditions or in extreme conditions beyond the expected operating conditions. No third option exists. Then, the sum of the probabilities of an aircraft encountering such conditions must be equal to one. The probability of no-failure can be calculated by means of the probability of the contrary event, i.e. the probability of failure that can be represented as the product of the probability of an aircraft encountering certain operating conditions and the probability of failure in such conditions. For the case of extreme conditions beyond the expected conditions the well-known concepts of perishability and vulnerability with the author’s improvements can be used.

Conclusions. A definition of survivability was obtained that is clearly different from the concepts of dependability and fail-safety. Additionally, the concept of damage tolerance (operational survivability) was proposed that was introduced similarly to the previously introduced concept of operational dependability.

Aim. The paper is dedicated to the evaluation of the risk of transportation accidents caused by natural emergencies affecting train traffic on a specific line. The ever-growing anthropogenic burden on the environment inevitably causes climate change that, in turn, gives rise to higher numbers of extreme weather events. The latter usually cause industrial accidents and disasters. The assessment of the factors of climate-related risk that quantitatively characterize their effect on the railway infrastructure is the starting point of calamity risk management and adaptation of human activities to the ever-changing climate.

Methods. The authors propose a method of risk assessment that takes into consideration the effect of various natural emergencies that affect rolling stock in motion. The method is based on elements of the probability theory and mathematical statistics. The developed method enables the assessment of the risk of a transportation accident caused by natural emergencies specific to not only a line, but a route on a railway network.

Results. For the Nevinnomysskaya – Tuapse line that includes 6 sections of the North Caucasus Railway, one of which was damaged due to abundant precipitations on October 24 and 25, 2018, the risk of transportation accident caused by the effects of three types of natural emergencies on the sociotechnical system of this line has been calculated:

– flood,

– hurricane with wind strength of over 22 mps,

– heavy rain.

The parameters of such emergencies are characterized by the following factors:

– frequency as compared to other types of emergencies,

– average annual number of natural emergencies,

– characteristic spatial scale of the natural emergency,

– characteristic duration of the natural emergency.

The conditional probabilities of the effects on the railway sociotechnical system of an event that has characteristic spatial scale and duration and has caused a transportation accident involving a train were estimated based on the assumption that a train flow in space follows the normal Erlang distribution of the k-th kind. The risk of transportation accident involving up and down trains travelling along the i-th line of the j-th railway caused by a hazardous effect of a natural emergency of the m-th type is identified subject to the jointness of events. Using the discounting method, an equation was obtained for estimating the mathematical expectation of economic damage by traffic safety disturbances, which allowed estimating the economic component of the risk.

Conclusions. As the result, a method is proposed for estimation of the risk of transportation accidents caused by natural emergencies, an example is provided of such risk estimation, including the economic component, for the Nevinnomysskaya – Tuapse line.