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
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
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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