Moving a Mountain to See the Stars
The Giant Magellan Telescope will have to function as an extremely precise instrument in order to counter the earth’s rotation in 23 hours, 56 minutes and 4.1 seconds. The GMT structure will be anchored firmly to its mountaintop bedrock base to avoid the smallest vibrations. If not firmly anchored, vibrations would make their way up through the steel structure to the mirrors as the 1,100-ton telescope rotates and pivots, shaking the telescope and causing stars’ images to blur.
Months of meticulously planned blasting in 2012 have removed over 90,000 cubic meters of extremely hard bedrock—about the weight of the Empire State Building—from the 8,500-foot peak high in the Atacama Desert. In addition, a geotechnical survey was carried out 200 feet below grade. This is equivalent to getting a “CAT scan” of the mountain peak. The survey and other seismic tests will inform the design and specifications of the foundation and enclosure. The results of the survey and seismic tests are being studied carefully to determine how much concrete and steel will be needed for the foundation of the telescope. GMT engineers now feel confident that their machine will “see” the stars with unprecedented stability and clarity from the Cerro Las Campanas mountain peak.
Blasting … With Care
Removing this much rock in an open pit mine operation would normally be done with three large detonation sequences. But blasting for the GMT site required a more exacting approach to ensure that the bedrock of the site was not fractured below a depth of a few feet. Fortunately, in Chile, highly specialized mining companies know exactly how to do this for many different kinds of rock and conditions. The mining company chosen by GMT utilized computer-assisted design for the blasting. Using a special blend of ANFO (ammonium nitrate fuel oil) explosive, 200 micro-detonations were conducted in a slightly staggered sequence to push the rock in a sideways motion, known as horizontal blasting. The crew of 30 then used bulldozers, excavators, and dump trucks to remove approximately 25,000 tons of rock from from an area the size of three football fields.
The next phase of operation will include constructing the foundations for the telescope and support buildings, and widening the access road to about 40 feet. The width is necessary to accommodate the oversized components of the giant machine, including the enclosure, numerous mounting structures and, of course, the mirrors, each of which is nearly 25 feet across. Stay tuned for more reports as progress continues!
Click the link below to see a video of the site.
GMT Enclosure Passes Critical Test
At over 200 feet tall—the height of a 20-story building—the GMT Enclosure will accommodate one of the largest ground-based telescopes ever built. Its shutters must protect sensitive optics and instruments from winds that can reach 120 mph on a high mountain peak, while delivering high-resolution images from the universe. Is the enclosure design the right approach to meeting science and operational needs and goals? Can it be built with current engineering technology or will new technology need to be developed? Can the enclosure be built within budget parameters?
On January 18th, the GMTO Enclosure and Facilities Group successfully answered all of these questions and many others by passing its Preliminary Design Review (PDR). Now the group moves on to the Construction Document phase, followed by Final Design, and then actual construction.
Lead Mechanical/Structural Engineer Arash Farahani described why the Enclosure team was so elated at the news, “Other groups will need the Enclosure and Facilities to be on site before they can start work; the project completion date would have been affected if the Enclosure design was delayed.”
During science operations, the Enclosure must allow the telescope to operate to its maximum capability, while providing ultimate protection from the sometimes-harsh environment at the summit of Las Campanas peak. The GMTO team found sophisticated solutions to these challenges.
Storms can bring heavy accumulations of snow and ice. Wind buffeting the telescope will result in vibration that causes jitter of the images arriving from the distant universe. When the environment around the telescope cools at night, residual heat from the Enclosure will interfere with the light path, blurring the images. Earthquakes in Chile are very common. Factoring in this seismic activity was also a significant design consideration.
The best way to avoid jittery images caused by residual heat is to provide a high rate of ventilation through the Enclosure. To accomplish this, over 30% of the exterior walls of the Enclosure consist of ventilation doors that can open and close to allow the desired amount of air to pass through. The structure also features large doors (shutters) covering over 85 feet of the roof and one side of the Enclosure. These shutters open to allow the telescope to have a full view of the nighttime sky.
Detailed scaled 3D models of the Enclosure were created specifically to carry out a series of wind tunnel tests and a Computational Fluid Dynamics (CFD) study using a range of Enclosure configurations and wind directions. In high winds or during the day, both the ventilation and shutter doors can be sealed and locked in place to protect the telescope and its instruments. In low winds, the doors can be partially or fully opened for ventilation.
Each design challenge was amplified by the sheer size of the Enclosure. The 40-foot high Enclosure base supports a rotating structure weighing well over 2,000 tons–more than four million pounds. Yet, in the final design, the entire Enclosure will require only 320 horsepower–the equivalent power of a large SUV–to rotate smoothly over rails on just four primary and 11 secondary truck assemblies (the Drive Bogies and Idler Bogies). There will be a total of 76 steel wheels rolling on the rails attached to the base.
The Enclosure and Facilities Group is the first team to pass what will be series of design reviews: Telescope, Adaptive Optics (AO), and Software Controls. With the success of this first PDR, the Enclosure and Facilities team and GMT Project can now look forward to moving ahead with the Construction Document and Final Design phases.
Welcome Bret Schaefer – GMT C.F.O.
He began as a history major at the University of Chicago, and eventually managed international operations financing for one of Silicon Valley’s most successful start-ups. Today, he is overseeing the financial dynamics of building the biggest telescope on Earth. Meet Bret Schaefer – GMT’s new Chief Financial Officer.
What makes Bret an asset to GMT? “I guess one way to think about it is that I bring Fortune 100-level financial and investor relations expertise. What you learn in the start-up world is that you have to have a small team that is very effective and versatile—but also is capable of engaging with the experts that you need in order to deliver the project.”
Bret spent nearly 20 years at Sun Microsystems and later helped several non-profit organizations establish long-term financial planning to sustain and grow their operations. Now Bret looks forward to growing with GMT. “You don’t see opportunities with projects that have this kind of impact very often.”
In addition to a B.A. in History, Bret earned a Master’s in Business Administration in Chicago. He began his career at Price Waterhouse in London and was based there for a couple of years. In 1991, he moved on to Sun Microsystems. “I wanted to work in Silicon Valley because of the opportunities to grow and do new, different and interesting things,” says Bret. At Sun, he developed a keen interest in the advancement of science and technology. “The more I learned, the more I enjoyed it,” he says.
During his decades-long career at Sun Microsystems, Bret rose from Internal Audit Manager to Vice President of Finance for Manufacturing, then Corporate Controller and ultimately, to Senior Vice President for Shareholder Value Finance, supporting a number of billion dollar engineering programs. Bret found that “one of the most interesting things about Sun was working with the senior scientists, engineers and other Ph.D. level staff.” At the GMT Project, he will have plenty of interface with scientists and engineers. Welcome Bret!
GMT’s “Workhorse” Instrument Will See Early Universe
A marvel of engineering and about the weight of a large pickup truck, one of the instruments being designed for early use on the GMT will be located underneath the Giant Magellan Telescope’s central mirror. Each night, it will gather and dissect very faint infrared light to help solve the mysteries of how galaxies and black holes form and grow over billions of years. Known as “GMTIFS”—The GMT Integral Field Spectrograph—it will be one of the key Adaptive Optics (AO) instruments used by the observatory.
GMT recently held a workshop on March 12th and 13th in Pasadena to discuss the current design of the sophisticated instrument and collect valuable input from the international astronomy community as a key step toward finalizing the instrument’s design. Below is a brief video of the meeting:
The Australian National University, a GMT partner, is designing the instrument. GMTIFS will operate in two ways, using only natural guide stars as reference, or using the six artificial guide star constellation provided by powerful lasers launched from within the telescope enclosure. These laser beams illuminate sodium atoms in the mesosphere – some 90 kilometers above the Earth’s surface and create “artificial stars” – reference points for the GMT AO system.
GMTIFS is really two instruments in one: a spectrograph and an imager. The integral field spectrograph will use a series of 45 mirrors, like small window louvers, to slice up regions of the night sky and disperse the light of each slice into a spectrum, which will reveal chemical makeup, distance, and velocity. The imager will take high-resolution pictures in the infrared part of the spectrum, which is well suited to a giant telescope like GMT, and will enhance the fine detail of the spectrograph. GMTIFS will probe both the most and least massive black holes in the universe, billions of light years away to address key questions: how are black holes related to their host galaxy? How do the black holes affect the evolution of a galaxy’s appearance, mass, size, chemical composition, and types of stars? With its ability to examine emission from ionized atoms, GMTIFS will help astronomers understand the mechanisms that enable new stars to form, even in distant galaxies. Closer to home, GMTIFS will be able to record detailed spectra of stars and globular clusters in our Milky Way galaxy.
GMTIFS will push the current technology in several ways. It will be an extremely high-resolution instrument and also one of the most complex ever designed. To do so, it will communicate with the telescope and AO system 1000 times each second in a delicate dance to help control the shape of the seven adaptive secondary mirrors in order to keep the images sharp.
Another important design challenge for GMTIFS is to make the instrument function at peak performance, no matter which direction the telescope is pointed. If this instrument were not properly engineered, changes in gravity could degrade the data. As the data accumulates inside GMTIFS, it will be relayed via fiber optic cable to various locations around the world where astronomers can study the information. GMTIFS may well be the first instrument with these remarkable capabilities used with a high-resolution giant telescope like GMT.