The Giant Magellan Telescope (GMT): structure design update

Gunnels, Steven M.; Kan, Frank W.; Sarawit, Andrew T.

doi:10.1117/12.789459

Cited by 5 publications

(2 citation statements)

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“…The Gregorian Instrument Rotator (GIR) 8 will be supported on hydrostatic bearings and will be driven to take out field rotation produced by alt-azimuth tracking. Walkways and stairs around the perimeter of the GIR provide service access.…”

Section: Instrument Mountingmentioning

confidence: 99%

Progress on the GMT

Johns

2008

SPIE Proceedings

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The Giant Magellan Telescope (GMT) is being developed by a consortium of major US and international educational and research institutions. The 25 meter next-generation telescope will be located at Las Campanas Observatory in Chile. The project has completed the conceptual design of the telescope and enclosure and is currently in the Design Development Phase leading up to construction. Various refinements have been made to the telescope structure since the Conceptual Design. These include the modification of the upper truss structure to reduce image blur due to wind shake and the design of a 9 meter rotator for large Gregorian instruments. An integral field spectrograph has been added to the candidate list of first-generation instruments. The primary mirror for GMT consists of seven 8.4 meter diameter segments. The first of the six, highly aspheric, off-axis segments has been cast and generated at the University of Arizona SOML with completion of the mirror expected in 2009. The metrology for polishing the segments is currently being installed in the new test tower at SOML. Verification tests that independently measure the mirror figure have been designed and are also being implemented. This paper summarizes the overall design and recent progress in the technical development of GMT and in characterizing the site.

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Section: Instrument Mountingmentioning

confidence: 99%

Progress on the GMT

Johns

2008

SPIE Proceedings

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“…The telescope is housed within a rotating enclosure that protects the telescope during severe weather conditions and shelters the telescope from wind during science operations by adjusting the position of upper and vertical shutters and enclosure wind vents. [1][2][3] The telescope must operate in a relatively high wind speed environment and the enclosure will provide some protection of the telescope from wind buffeting. Ongoing wind tunnel testing and computational fluid dynamics modeling of the enclosure are being conducted to refine the extent of attenuation of the wind velocity around the telescope structure relative to the outside wind environment due to the presence of the enclosure.…”

Section: Introductionmentioning

confidence: 99%

Vibration mitigation for wind-induced jitter for the Giant Magellan Telescope

Glaese

Sheehan

2012

SPIE Proceedings

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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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The Giant Magellan Telescope (GMT): hydrostatic constraints

Gunnels

2010

SPIE Proceedings

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The Giant Magellan Telescope (GMT): structure design update

Cited by 5 publications

References 0 publications

Progress on the GMT

Progress on the GMT

Vibration mitigation for wind-induced jitter for the Giant Magellan Telescope

The Giant Magellan Telescope (GMT): hydrostatic constraints

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