Practical Models for Determining Standby Redundancy Levels

Far reaching decisions on the use of standby redundancy to assure product reliability are typically made in early phases of a project, well before design details required for the usual reliability predictions are available. Three major considerations are: 1) number of standbys to be provided 2) efficacy of the activation process and 3) status of the standbys when not used. These considerations are evaluated specifically for the case in which redundancy is required to achieve high mission reliability when repair cannot be made during the mission and for the case in which the time to failure must be 'stretched' to meet a minimum performance time constraint.