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Unformatted text preview: ity assurance engineer's effort should be integrated with the reliability engineer's so that, for example, component failure rate assumptions in the latter's reliability model are achieved or bettered by the actual (flight) hardware. This kind of process harmony and timeliness is not easily realized in a project; it nevertheless remains a goal of systems engineering. 6.2 Reliability Reliability can be defined as the probability that a device, product, or system will not fail for a given period of time under specified operating conditions. Reliability is an inherent system design characteristic. As a principal contributing factor in operations and support costs and in system effectiveness (see Figure 26), reliability plays a key role in determining the system's cost-effectiveness. 6.2.1 Role of the Reliability Engineer Reliability engineering is a major specialty discipline that contributes to the goal of a cost-effective system. This is primarily accomplished in the systems engineering process through an active role in implementing specific design features to ensure that the system can perform in the predicted physical environments throughout the mission, and by making independent predictions of system reliability for design trades and for (test program, operations, and integrated logistics support) planning. The reliability engineer performs several tasks, which are explained in more detail in NHB 5300.4(1A -1), NASA Systems Engineering Handbook Integrating Engineering Specialties Into the Systems Engineering Process Reliability Relationships The system engineer should be familiar with the following reliability parameters and mathematical relationships for continuously operated systems Many reliability analyses assume that failures are random so that λ(t) = λ and the failure probability density follows an exponential distribution. In that case, R(t) = exp (-λt), and the Mean Time To Failure (MTTF) = 1/λ. Another popular assumption that has been shown to apply to many systems is a failure probability density that follows a Weibull distribution; in that case, the hazard rate λ(t) satisfies a simple power law as a function of...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.

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