Last week, engineers designing the Giant Magellan Telescope announced they had solved a major design challenge. In particular, it protects a 22-story rotating observatory and seven of the world’s largest monolithic mirrors from being damaged by earthquakes. The innovative seismic protection design gained key marks from an independent review panel of international experts in early November, paving the way for the next generation in observational design.
“The structures of the next generation of large telescopes are so large, their instruments so sensitive, and the seismic environments in which they are so intense, that there is no way to avoid seismic protection. We need a seismic isolation system to keep the telescope working, ”Dr Bruce Bigelow, site, site and facilities manager for the Giant Magellan Telescope, said in a statement.
The Giant Magellan Telescope is a new 25-meter ground-based telescope under construction at the Las Campanas Observatory in Chile’s Atacama Desert, one of the best places on Earth to see the universe. But while this remote area boasts more than 300 clear nights of the galactic center each year, it is also home to some of the largest, most frequent, and most destructive earthquakes ever recorded. . Large earthquakes in Chile can last longer than three minutes and often exceed seven on a surface wave magnitude scale (M.S.).
Overcoming obstacles
Bigelow tells IndustryWeek, that the biggest challenge in performing this task is to meet seismic protection requirements in a way that still enabled the normal operation of the telescope. “Seismic isolation systems for regular buildings are aimed at protecting the occupants, and most buildings are not usually dynamic structures in their own right. The telescope, by contrast, must be able to move in two angles (azimuth and elevation), and must be able to perform these movements in a regular, precise and continuous manner while the telescope is rotating. keep an eye on things in the air, ”he says. As a result, the SIS must be hard enough to withstand the normal reflexes of the telescope (up to a certain level), and then move smoothly to a flexible position (above the threshold), so that the protect a telescope from strong ground movements. ”
According to Bigelow, “the key to the GMT seismic isolation system is to use a special configuration of commercially available seismic bearings (single breaking pendulums), which have the stiffness and friction properties necessary to support allow the normal operation of the telescope, and move smoothly into a remote action above a certain level of ground motion. “
Another aspect of the design is the pier rendering and inspection system (PRMS), Bigelow explains. “The PRMS is an irrigation system consisting of irrigation cylinders, sensors and a control system, which provides the forces necessary to reposition the telescope and the pier (unified mass of ~ 6200 metric tons, or ~ 14 million pounds). to the “home” situation after a major earthquake, ”he says.
Digging deeper
The seismic protection system – also known as the seismic isolation system – of the Giant Magellan Telescope is unique in the world of telescopes, in terms of size and complexity. Unlike hospitals or large bridges, the seismic isolation system must not only protect the structures from collapse, but also to prevent the structure and the fragile internal optical parts from needing repair. Since the Giant Magellan Telescope seismic isolation system serves as the basis of the telescope, it must be highly reliable. By design, the probability of seismic isolation failure is less than 0.5 percent over the observatory’s 50-year service life. The system is designed to be inactive during minor “disturbance” earthquakes common at Las Campanas Observatory. The system only responds to extreme earthquakes that typically occur on a 1–2-year time scale.
The Giant Magellan Telescope seismic isolation system is made up of two protective lines that keep it safe and allow a return to activity within hours to weeks, depending on the magnitude of a seismic event.
1. Seismic Isolation System: A circular array of 24 single friction flexible isolators that support the telescope and its pier and protect the optical parts of the telescope and instruments from active ground motion caused by a large earthquake.
2. Pier Circulation System: An irrigation system that can return the telescope to its original rest and operating position after a major earthquake.
After a major earthquake, the telescope’s pendulum isolates may not return directly to its normal operating position. “The remote system will return the telescope to its ‘home’ position within two inches, but that is not good enough,” Bigelow said in a statement. “That’s where the filters of the pier’s perimeter system come in, which can move the 6,000 metric tons of telescope and pier and return the telescope to a fraction of an inch from where it was before the quake. . ”