In a major milestone for a decades-long project, the Giant Magellan Telescope project recently passed its final design review, locking in the design for the telescope enclosure and paving the way for a procurement process that could begin taking contractor proposals next year. 

The telescope, part of the next generation of optical telescopes now under construction or development around the world, will be one of the largest optical telescopes ever built when completed. The new class of optical telescopes, known as “Extremely Large Telescopes” will be capable of capturing images of deep space with far greater clarity and resolution than current telescopes.

Work on the project began in 2003, with an estimated completion date of sometime in the mid 2030s. Run as a non-profit operation, hundreds of millions of dollars of the Giant Magellan Telescope’s $2.54-billion budget have already been spent, with support structures and related utility and road infrastructure construction at the site already complete. Located on a remote mountaintop in Chile, the 25-meter-dia telescope will sit within a 65-m-tall, 60-m-dia steel enclosure, the upper section of which needs to be able to rotate a full 360° in a matter of minutes.

“In terms of conventional building metrics, think about a 22-story building where the upper 18 stories of the building rotate,” explains Bruce Bigelow, element manager for Giant Magellan Telescope enclosure facilities and site infrastructure. The top, moveable section of the enclosure above the podium will be about 5,000 metric tons. “And then the doors that open at night are about 14 stories tall, about 500 metric tons each—we’re talking about a massive moveable structure.”

The scale of the moveable structure presents several unusual design challenges. Outside the telescope world, Bigelow likens it to the moveable oculus roof on Mercedes-Benz Stadium in Atlanta. “That’s one of the most complicated moveable roofs ever attempted, and they consider operating that roof a few times a year. We anticipate rotating the enclosure a few times a night, 330 nights a year."

The designer, Bilbao, Spain-based IDOM, has a background in large telescope enclosures, but this new class of telescopes brings fresh challenges. “This entire structure can rotate 360° in four minutes, and we’re controlling the air [flow] over the telescope during observation,” says Tom Lorentz, president of North American operations for IDOM and project principal for the Giant Magellan Telescope. 

High winds are also an issue on the mountaintop observatory site. A moveable wind screen can be deployed to protect the telescope as needed, while 92 modules of four-unit wind vents help redirect the wind away from the instrument. “It’s a lot of moving parts and pieces,” notes Lorentz. The telescope is also located in a highly active seismic zone, leading to an elaborate seismic isolation system to protect the telescope in an earthquake but maintain rigidity of the enclosure during nighttime observation.

“The telescope mount is a separate structure—it has a base seismic isolation system beneath it,” says Lorentz. The pier it sets on is a 22-m-dia concrete cylinder, with its own multi-stage seismic isolation system. “So 24 pendulums, 24 seismic fuses, allow the telescope to stay rigid until a seismic event, [and then] allow the telescope to move freely to avoid damage.” The moveable structure also has a re-centering system to get it back in place after a seismic event, as well as a hydraulic jack system to lift the entire assembly for repairs. 

This is a level of concern for seismic risk that was not considered in previous generations of large optical telescopes, explains Lorentz. “Before the ones we [are doing] now, these structures were perceived to live through earthquakes without extra effort. That was wrong, and some big telescopes in Chile and Hawaii were damaged in seismic events.”

IDOM has worked on the design for two years, completing multiple design reviews along the way, including intense examination by a panel of outside experts from around the world. “The level of analysis for the enclosure, given the moveable structure, wind loads and seismic risk drove a high level of systems engineering and quality control,” says Bigelow.