Analyzing missile electric system reliability

Abstract

The performance reliability of a missile electric system may be defined in terms of steady-state values of voltage and frequency applied to the system equipment. This viewpoint stresses the auxiliary function of furnishing electric power as contrasted to the prime functions of electronic equipment such as signal amplification or control response. Other failure-producing parameters such as operational environments, aging, and production differences must be recognized by the definition. Hypothetically at least, these parameters may be classified as secondary factors, thus bringing attention to focus on problems most acute in early design stages. Performance reliability of load equipment is evaluated at the so-called blackbox level. In this process, the prime electric source is connected to the input; performance is measured at the output. The test results from varying input conditions furnish information to describe the input-output relationships. In the discussion, variations on electric input conditions are confined to voltage but may be extended to frequency as well by an identical procedure. From these results, statistical calculations derive values of probable performance for equipments. A similar process gives probable performance of generators or other sources, the output in this case being electric voltage. These tests replace conventional circuit analysis and testing, and account for performance dispersion that cannot be predicted with accuracy in equipment of great complexity. Hence, approximations of performance expected from subsequent production-line equipment may be obtained on breadboard equipment that cannot be submitted to environmental testing. To carry out the method thoroughly requires a single prototype model for each of the equipments that make up the entire system, or at least those that are considered most critical. Such tests do not consider explicitly the individual component parts which make up the equipment package. They are designed to permit determination of performance reliability of over-all complex systems with the least amount of system or equipment breakdown. Finally, under assumptions of statistical independence, equipment reliabilities are serially multiplied to determine over-all system reliability.