Decision Making in Systems Engineering and Management, 3rd Edition

Chapter 11System Reliability

There is no finish line when it comes to system reliability and availability, and our efforts to improve performance never cease.

—Source: Marc Benioff, CEO Salesforce

11.1 MODELING SYSTEM RELIABILITY

Modeling and measuring the effectiveness of a proposed system solution is a necessary component for assessing system performance that is specified in various ways within system requirements and reflected in the value measures used within both deterministic and stochastic tradespace analysis. Soban and Mavris [1] define system effectiveness as “a quantification, represented by system level measure, of the intended or expected effect of the system achieved through functional analysis.” [1].

For systems of all types including complex systems, the key system level measures appearing most often in functional and value models are reliability, availability, and capability, because all three address aspects of how well a system can perform its purpose [1, 2].

Definition: System reliability is probability of a system or system element performing its intended function under stated conditions without failure for a given period of time [3].

Definition: System availability is the probability that a repairable system (RS) or system element is operational at a given point in time under a given set of environmental conditions [3].

Definition: System capability is the ability of a system to execute a particular mission or course of action to achieve a desired effect ...