In a major milestone for a decades-old project, the Giant Magellan Telescope project recently passed its final design review, locking in the design of the telescope enclosure and clearing the way for an acquisition process that could begin receiving contractor proposals next year.
The telescope, part of the next generation of optical telescopes now being built or developed 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 able to capture images of deep space with much greater clarity and resolution than current telescopes.
Work on the project began in 2003, with an estimated completion date of the mid-2030s. As a not-for-profit operation, hundreds of millions of dollars of the 2,540 budget have already been spent million dollar Giant Magellan Telescope, with support structures and construction of road infrastructure and utilities on site already completed. Located atop a remote mountain in Chile, the 25m diameter telescope will be housed within a 65m high, 60m diameter steel enclosure, the top section of which must be able to rotate 360° in a matter of minutes.
“In terms of conventional building metrics, think of a 22-story building where the top 18 stories of the building rotate,” explains Bruce Bigelow, facility element manager for the Giant Magellan Telescope Complex and the site infrastructure. The upper and movable 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 mobile structure.”
The scale of the mobile structure presents several unusual design challenges. Outside the world of telescopes, Bigelow compares it to the moving eyepiece ceiling at Atlanta’s Mercedes-Benz Stadium. “This is one of the most complicated mobile roofs ever attempted, and they consider operating this roof a few times a year. We anticipate rotating the venue a few times a night, 330 nights a year.”
The designer, IDOM, based in Bilbao, Spain, has expertise in large telescope enclosures, but this new class of telescopes brings new challenges. “This whole structure can rotate 360° in four minutes, and we’re controlling the air [flow] on the telescope during the observation,” says Tom Lorentz, president of IDOM’s North American operations and director of the Giant Magellan Telescope project.
High winds are also a problem at the mountain observatory site. A mobile wind screen can be deployed to protect the telescope as needed, while 92 four-unit vent modules help redirect wind away from the instrument. “It’s a lot of pieces and moving parts,” Lorentz points out. The telescope is also located in a very active seismic zone, leading to an elaborate seismic isolation system to protect the telescope in an earthquake but maintain the rigidity of the enclosure during nighttime observation.
“The telescope mount is a separate structure: it has a base seismic isolation system underneath,” says Lorentz. The dock where it is installed is a concrete cylinder of 22 m in diameter, with its own multi-stage seismic isolation system. “So 24 pendulums, 24 seismic fuses, allow the telescope to remain rigid until a seismic event, [and then] allow the telescope to move freely to avoid damage.” The mobile structure also has a centering system to return it to its place after a seismic event, as well as a hydraulic jack system to lift the entire the set for repairs.
This is a level of concern about seismic risk that was not considered in previous generations of large optical telescopes, Lorentz explains. “Before those of us [are doing] now, these structures were considered to survive earthquakes without additional effort. This was wrong, and some large 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 intensive examination by a panel of external experts from around the world. “The level of analysis of the site, given the mobile structure, wind loads and seismic risk, drove a high level of systems engineering and quality control,” says Bigelow.
