Actuator Usage and Fault Tolerance of the James Webb Space Telescope Optical Element Mirror Actuators

The James Webb Space Telescope (JWST) telescope's secondary mirror and eighteen primary mirror segments are each actively controlled in rigid body position via six hexapod actuators. The mirrors are stowed to the mirror support structure to survive the launch environment and then must be deployed 12.5 mm to reach the nominally deployed position before the Wavefront Sensing & Control (WFS&C) alignment and phasing process begins. The actuation system is electrically, but not mechanically redundant. Therefore, with the large number of hexapod actuators, the fault tolerance of the OTE architecture and WFS&C alignment process has been carefully considered. The details of the fault tolerance will be discussed, including motor life budgeting, failure signatures, and motor life.