The James Webb Space Telescope is NASA’s next generation space based telescope. The Optical Telescope Element (OTE) is an infrared system designed to operate at cryogenic temperatures. Its primary mirror consists of 18 segments; each segment is controlled by a series of actuators mounted on the back of each mirror segment. Mission success depends vitally on the actuators, specifically the critical bearing assembly of each actuator’s gear motor. This paper details the methodology employed by NASA and Ball Aerospace to evaluate the lifetime of the bearings and to design life tests which quantitatively offset risk at the system level, in a cost effective manner. The life prediction methodology utilized the Lundberg-Palmgren rule to estimate life, employing a cryogenic service factor developed from consideration of fracture toughness changes expected at cryogenic temperatures. This approach showed the capacity of the bearing system to have significant margin and reliability necessary to endure the requirements of OTE operations, over the life of JWST, under the estimated loads. Baseline test designs were subsequently developed with targets designed to show adequate risk reduction during life testing. Tests were subsequently executed at cryogenic temperatures and targets were shown to be met for the required system level risk tolerance.

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