Random Vibration Analysis of the Tip-tilt System in the GMT Fast Steering Secondary Mirror

Abstract

A random vibration analysis was accomplished on the tip-tilt system of the fast steering secondary mirror (FSM) for the Giant Magellan Telescope (GMT). As the FSM was to be mounted on the top end of the secondary truss and disturbed by the winds, dynamic effects of the FSM disturbances on the tip-tilt correction performance was studied. The coupled dynamic responses of the FSM segments were evaluated with a suggested tip-tilt correction modeling. Dynamic equations for the tip-tilt system were derived from the force and moment equilibrium on the segment mirror and the geometric compatibility conditions with four design parameters. Statically stationary responses for the tip-tilt actuations to correct the wind-induced disturbances were studied with two design parameters based on the spectral density function of the star image errors in the frequency domain. Frequency response functions and root mean square values of the dynamic responses and the residual star image errors were numerically calculated for the off-axis and on-axis segments of the FSM. A prototype of on-axis segment of the FSM was developed for tip-tilt actuation tests to confirm the ratio of tip-tilt force to tip-tilt angle calculated from the suggested dynamic equations of the tip-tilt system. Tip-tilt actuation tests were executed at 4, 8 and 12 Hz by measuring displacements of piezoelectric actuators and reaction forces acting on the axial supports. The derived ratios of rms tip-tilt force to rms tip-tilt angle from tests showed a good correlation with the numerical results. The suggested process of random vibration analysis on the tip-tilt system to correct the wind-induced disturbances of the FSM segments would be useful to advance the FSM design and upgrade the capability to achieve the least residual star image errors by understanding the details of dynamics.

Effect of Panel Misalignment Error Distribution on the Radiation Pattern of Leighton Chajnantor Telescope’s Antenna

“…Various factors contribute to the deterioration of panel alignment accuracy, including piston and tip-tilt errors on each panel, gaps between panels, and distortion along panel edges (Yaitskova et al 2003). Among these factors, piston and tip-tilt error are the most prominent ones affecting the characteristics of the segmented reflector antennas (Lee et al 2017;Van Kooten et al 2022). Therefore, this paper will focus on analyzing the effects of panel misalignments caused by piston errors and tip-tilt errors on radiation characteristics.…”

Development of piezoelectric fast steering mirror with tilt error compensation for portable spectroscopic sensor

“…5,6 These fast steering mirrors have been applied to various optical application including the gaze correction and jitter suppression of large telescopes for astronomical application. 7,8 In addition, these are frequently used in the gimbal structure of the aircraft to be applied to the pilot's gaze aiming and stabilization. 9 In the material processing, these have been used as laser scanners with high-power laser 10 and is also used as a laser triangulation sensor for distance measurement.…”