Design and Fabrication of Composite Structures in the GMT-Consortium Large Earth Finder (G-CLEF)

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, optical echelle spectrograph that will be a first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general-purpose echelle spectrograph with precision radial velocity (PRV) capability. The radial velocity (RV) precision goal of G-CLEF is 10 cm/sec; necessary for detection of Earth-sized exoplanets orbiting Solar-type stars in their habitable zone. This imposes challenging stability requirements on the optical mounts and spectrograph support structures especially when considering the instrument's operational environment. G-CLEF's accuracy will be influenced by thermal effects, ambient air pressure, vibration, and micro gravity-vector variations caused by normal telescope slewing. The design and fabrication schedule for G-CLEF spectrograph and ancillary systems will lead the GMT telescope by approximately 5 years, therefore, we will design and build an interim installation configuration for G-CLEF at Magellan's 6.5m telescopes. This will allow us to complete and commission the spectrograph. During this period, we will collect at least 5 years of data utilizing G-CLEF at Magellan from roughly 2027 to 2032. We also will also optimize major subsystems including spectrograph optics and mechanics, vacuum, thermal control, and vibration isolation. G-CLEF's challenging technical requirements drove the decision to use low-CTE composites for the optical bench and several optical mounts including its collimator and pupil transfer mirrors and its Echelle Grating Support Structure. This paper discusses the process implemented in designing and procuring the composite structures used in the G-CLEF instrument.