This is just an Excerpt from a larger document, click here to view the entire document.Growth Without Testing?
For products such as one-of-a-kind satellites, testing of the types normally associated with reliability growth is seldom possible due to the high cost and limited (if any) availability of test articles. Can reliability growth be achieved for such systems? To answer this question, consider how a design evolves and is finally given form in a prototype model. Generally, iterations of the design are needed because the various performance requirements often conflict; optimizing the design to meet one requirement can result in the design failing to meet another requirement. Balancing the requirements is a demanding task. Iteration is also needed because not all analyses can be done simultaneously. Consequently, the design may be changed as the result of a particular analysis, only to be changed again when the results of a subsequent analysis are available. As iterations take place, the design is refined, and each revised design is (hopefully) an improvement over its predecessor. Some of the analyses conducted during the design process directly address the reliability of the design. So, the reliability of the design improves as successive design changes are made based on analysis.
With the preceding discussion in mind, reliability growth can be broadly defined as:
The process by which the reliability of an initial design is improved. Improvement results as the design is iterated, either on the basis of analytical evaluation and assessment or on test results (failures).
The concept of reliability growth suggested by this broader definition is illustrated in Figure 1. Ideally, when the product enters testing, all deficiencies have been eliminated through design changes made as a result of analyses. In practice, some design changes will be required as the result of undiscovered design deficiencies causing failures during development testing. A specific type of development testing often dedicated to the reliability growth process is the RGT.
Figure 1. Reliability Growth Begins with Design Iteration, Not Test (Click to Zoom)
(Note that the pure design process and the design-test process are not purely separate processes occurring sequentially. They often overlap, although the pure design phase does begin before any testing begins).
Several key points are made in the stated definition, and each one will be addressed separately.