Vibration measurements on a utility wrap test bench for jitter analysis of high-precision telescopes (experience from the GMT project)

The GMT telescope is equipped with three large utility wraps for the main axes. From the very beginning of the design phase, these were considered critical sources of vibration. Since no information was available on the vibration behavior of the utility wraps at low speeds during tracking, a great deal of effort was put into the planning and execution of a test campaign using a 1:1 scale test bench. One of the special features was a novel structure identification technique using unbalanced motors as a cost-effective yet reliable alternative to the commonly used shaker actuators.