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The Giant Magellan Telescope (GMT) is a planned large terrestrial telescope with a segmented primary mirror with a
24.5 meter overall diameter. Like most terrestrial telescopes, the GMT resides within an enclosure designed to protect
the telescope from the elements and to reduce the effects of wind on the optical performance of the telescope. Wind
impingement on the telescope causes static deformation and vibration in the telescope structure that affects the alignment
and image jitter performance of the telescope. Actively controlled primary mirror segments and a secondary mirror can
correct for the static and low frequency portions of the wind effects, but typically the actuators do not have the
bandwidth to address higher frequency components of the wind environment. Preliminary analyses on the GMT indicate
that the image jitter associated with wind effects meets budgeted allowances but without much margin. Preliminary
models show that the bulk of the residual jitter arises from excitation of a small number of modes in the 9 to 12 Hz
range. Therefore, as a risk mitigation effort to increase the margin on the wind induced jitter, passive and active
vibration mitigation approaches have been examined for the GMT, which will be the focus of this paper. Using a finite
element model of the GMT along with wind loading load cases, several passive and active vibration mitigation
approaches were analyzed. These approaches include passive approaches such as tuned mass dampers targeting the
worst offending modes, and constrained layer damping targeting all of the modes within the troublesome frequency
range. Active approaches evaluated include two active damping approaches, one using several reaction mass actuators
and the other using active strut type actuators. The results of the study show that although all approaches are successful
in reducing the jitter, the active damping approach using reaction mass actuators offers the lightest weight, least
implementation impact, and most adaptability of any of the approaches.
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