Warping harness actuator for the Thirty Meter Telescope primary mirror segments

Abstract

The Thirty Meter Telescope (TMT) Primary Mirror (M1) is composed of 492 hexagonal aspheric segments. In order to compensate for residual polishing errors, installation errors, gravity effects and parasitic forces in the whiffletree support, each segment is equipped with 21 Warping Harness (WH) mechanisms, which allow low order corrections to the optical surface. The primary mirror segment aberrations after shape corrections with warping harness have been identified as the single largest error term in the Thirty Meter Telescope (TMT) image quality error budget [1]. The WH mechanism consists of a Linear Actuator, Ball Link and a Leaf Spring with strain gauge sensor. The Warping Harness key requirements are: high positioning accuracy, 50 years operational life time with minimum maintenance, low cost, high reliability, high resolution, low hysteresis, high stability in unpowered state, large operational temperature range, low power dissipation, vacuum compatibility and survival of accidental condensing conditions. Smooth motor has developed a robust, low cost linear actuator for the TMT M1 Warping Harness. A WH Accelerated Life Cycle Test with increased temperature extremes was successfully completed. Acceleration factors were calculated with the Coffin-Manson model for temperature. Compliance with the technical requirements for the WH system has been demonstrated.