GMT’S first giant mirror segment starts journey south

Publication date
Monday, 25 Sep 2017

The first of seven 27-foot mirrors that together assemble into the world’s largest telescope, the Giant Magellan Telescope, has left the Richard F. Caris Mirror Lab at the University of Arizona, making space for the production of the remaining mirror segments.

At 2:00 a.m. on Sept. 20 the hangar-like doors of the Mirror Lab, located underneath the University’s football stadium, slid open to reveal a custom-made precision shipping container, with the mirror tucked inside, ready to be moved to a temporary storage facility on the outskirts of Tucson AZ, as the first step on its journey towards its ultimate destination in the Chilean Andes.

Once completed, the seven mirror segments will form the heart of the Giant Magellan Telescope, designed to have a resolving power 10 times greater than that of the Hubble Space Telescope.

The Mirror Lab currently houses GMT primary mirror segment numbers 2, 3, and 4 which are in various stages of fabrication. Segment 2 is undergoing its final stage of work – polishing of its reflective surface – while segment 3 is ready for front surface grinding, and segment 4 is ready for rear surface grinding. The 17-ton glass disc for the fifth GMT primary mirror segment will be cast at the Mirror Lab on November 5, 2017.

In the weeks preceding the move, the mirror had been lifted into a transport container inside the Mirror Lab. The mirror was lifted with suction cups attached to its precisely polished front surface. The transport container is a highly sophisticated unit, containing shock absorbers, load-equalizing levers, and heavy insulation capable of keeping the mirror safe until it is delivered to the mountain top site in Chile. The transport container, weighing twice as much as the mirror itself, was fabricated by CAID Industries of Tucson, Az. With the mirror inside, the unit weighs 55 tons.

Safely ensconced in its transport container, the mirror was carefully loaded onto the deck of a 48-wheel transporter. The move by road was undertaken by Precision Heavy Haul Inc. of Phoenix AZ, taking an hour to cover the roughly 8 miles to the storage facility.

GMT segment 1 will remain in storage until it is shipped, by road and sea, to the GMT site at the Carnegie Institution for Science’s Las Campanas Observatory in Chile – one of the world’s premier astronomical sites.

Construction is underway at the GMT site; work on essential infrastructure – roads, power, water, sanitation, communications, and a worker’s residence – is complete. Excavation of the foundations for the telescope and the laboratory where the mirrors will be matched to the telescope is scheduled to begin early next year.

The telescope is expected to see first light in 2023 with four of the Arizona mirrors. The seventh mirror should be in the telescope in 2025.