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Because of the long-time operation (^10,000 hr) required for most space missions, electric propulsion system reliability is a major problem. Since establishment of high-component reliability at high confidence levels is both time-consuming and costly, other methods for increasing propulsion system reliability must be considered. This paper presents a study of the effects of such considerations on the design of the power conditioning equipment and thruster arrays associated with electric propulsion systems. The necessary mathematical model required to compute thruster system reliability is developed. A power conditioning and thruster system reliability optimization study is then performed to determine the degree of redundancy required for power conditioning circuits and the optimum number of ion engine modules and standbys necessary to obtain the requisite system reliability for least increase in system specific weight. The effects of power conditioner and thruster module size and number are evaluated in terms of reliability. It is shown that, by proper application of redundant circuit and component techniques, the reliability of both the power conditioning equipment and the thruster array can be raised to the desired levels without prohibitive increases in propulsion system weight.

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