The Giant Magellan Telescope (GMT) - structure design update

The Giant Magellan Telescope (GMT) is a 21.5-meter equivalent aperture optical-infrared ELT to be located in Chile. It is being designed and constructed by a group of U.S. and international universities and research institutions(1). The concept design of the telescope structure was summarized in an earlier SPIE paper(2) and described in greater detail in the GMT Conceptual Design Review document(3). The structure design has matured during the current Design Development Phase. Important among design improvements has been optimization of the secondary truss with the goal of significantly reducing telescope pointing errors due to wind loading. Three detailed structural changes have resulted in calculated pointing error reductions of similar to 30%. The changes and their contributions to the improved performance as well as other tested features are discussed. Additional refinements to the structure include the instrument mounting system, with a stationary folded-instrument platform plus Gregorian Instrument Rotator utilizing hydrostatic bearings. More detailed features, such as revised C-ring bracing to improve instrument access, are described.