Dependent failure in multifunctional automatic control systems

The paper considers the components interference of the automated control system. The safety and survivability are investigated. The failure gradation is given. The failure consequences of components and modules of the system that cause failures of other components and modules, the capabilities to prevent these failures are considered. Some probable variants of the dependent failures are provided. It is shown that a possible source of danger can be both module failure and failure of redundant components in these modules. It is assumed that at least the potential danger is not reduced to zero due to the increase in the number of redundant components. The various logical structures of the compound components in the automated control systems (ACS) for spacecraft are discussed. A typical structure of reliability of the automated control system that performs several functions, i.e. a tree structure is presented. The process of failures development in multifunction systems, the mutual influence of components in case of simple linear and branching redundant structures are illustrated. The negative effects of redundancy are considered. An example of the reliability calculation of the system with a parallel connection of the components and their dependent failures caused by these components are given. The conclusion about the necessity of non-redundant methods for improving the reliability and dangerous impact prevention is made.