Progress on the structural and mechanical design of the Giant Magellan Telescope

The Giant Magellan Telescope (GMT), one of several next generation Extremely Large Telescopes (ELTs), is a 25.4 meter diameter altitude over azimuth design set to be built at the summit of Cerro Campanas at the Las Campanas Observatory in Chile. The primary mirror consists of 7 individual 8.4 meter diameter segments resulting in an equivalent collecting area of a 21.5 meter diameter single mirror. The telescope structure, optics and instrumentation has a rotating mass of approximately 1250 metric tons and stands approximately 40 meters tall. This paper reports the results of our ongoing preliminary design and development of the GMT structure and its major mechanical and opto-mechanical components. A major recent redesign of the Gregorian Instrument Rotator (GIR) resulted in significant changes to the telescope structure and several mechanisms. Design trade studies of various aspects of the main structure, hydrostatic bearing system, main axes drives, M2 positioner, M3 subsystem and the corrector-ADC subsystem have refined the preliminary design in these areas.