Construction of Giant Magellan Telescope advances in Chile

On a visit to Brazil, Robert Shelton, president of GMTO Corporation, highlighted the progress made on the development of the telescope, which is supported by FAPESP. The first 8 m mirror segment is ready.

By Elton Alisson  |  Agência FAPESP – At the end of June 2018, hard rock excavation began at a building site on Las Campanas Peak, over 2,500 meters above sea level in Chile’s Atacama Desert, to prepare the concrete pier and enclosure foundations for the Giant Magellan Telescope (GMT).

Expected to see first light in 2024, the GMT will be part of a new generation of ground-based extremely large telescopes capable of unprecedented clarity and sensitivity in observing astrophysical phenomena such as the origins of the chemical elements and the formation of the first stars and galaxies.

The international consortium established to manage the GMT’s development, construction and operation has faced a number of technological and funding challenges in making the project feasible.

Visiting Brazil this week for meetings with the community of São Paulo State researchers who are participating in the consortium with support from FAPESP, US physicist Robert Shelton, president of the GMTO Corporation (GMTO), delivered a presentation on August 6 at the University of São Paulo’s Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG/USP).

Shelton spoke about the current status of the project and the challenges posed by construction of the observatory.

“The GMT has entered a very exciting stage. At last, some things are starting to materialize, and we have visible manifestations of incredible developments relating to the telescope,” Shelton told Agência FAPESP.

The first mirror is now ready. The GMT will have seven mirror segments, each with a diameter of 8 meters. They will be integrated to form a primary mirror with an effective aperture of 25.4 meters. The second segment is nearing completion and has been polished more quickly than the first.

The third and fourth segments, which will be integrated with the others when the telescope starts operating, should be cast soon. In addition, the glass for the fifth, sixth and seventh segments is now available.

“[The availability of glass for mirror casting] is important because there’s only one supplier of this material in the world. It’s a Japanese firm. We’ve bought 20 tons of this glass and we’ll use about 18 tons to make the seven mirror segments. Being in possession of this material reduces any risk to the completion of the mirror construction stage,” Shelton said.

The entire GMT site has been leveled; the construction of access roads, dormitories and power and water supply stations is complete; and internet service provision is assured.

The consortium is now finishing work on the telescope’s design. The housing will be 61 meters high (equivalent to a 22-story building), and the telescope itself will weigh 1,100 tons.

The second stage of design and construction is scheduled to begin during the current year (2018) and will consist of finalization of the design and the fabrication, testing and installation of the instrument in the Las Campanas observatory.

“There are many complicating factors in the telescope assembly stage, such as seismic activity in Chile. Fortunately or unfortunately, California [where GTMO’s headquarters are located, in Pasadena] is also in a region with seismic activity, and we’ve been able to take advantage of some technologies already used there,” Shelton said.

The solution to be used by the company responsible for designing the GMT to isolate the telescope from ground vibrations will consist of installing flexible bearings known as base isolators below ground in the concrete pier that forms the base of the telescope, so that it moves only a little during an earthquake. 

“The seismic base isolators that will be installed in the GMT’s pier will be similar to those installed in the foundations of Pasadena City Hall to protect it from earthquakes,” Shelton said.

Another challenge posed by the construction of the telescope will be the integration of the seven primary mirror segments, which must be correctly spaced and integrated so that the gaps between them are uniform.

“We’re making great progress with construction of the GMT, but there are still major challenges. One of them is getting sufficient funding for the project,” Shelton said.

Partnership with TMT

The cost of the GMT is estimated at US$1 billion. GMTO has so far raised approximately US$520 million. To win funding from the National Science Foundation (NSF), one of the leading US research funding agencies, GMTO decided in May 2018 to join forces with a rival project, the Thirty Meter Telescope (TMT), scheduled for construction on Mauna Kea in Hawaii.

The partnership, approved by the boards of GMTO and TMT, calls for at least 25% of each telescope’s observing time to be available to the US astrophysics community, including scientists from nonparticipating institutions. Under previous plans, observing time was available only to researchers from nations or institutions that had provided funding.

One of the arguments used by the GMTO and TMT to defend the construction of two extremely large telescopes concomitantly is that they have complementary strengths and that having telescopes in both the northern and southern hemispheres will cover the whole sky, extending the projects’ scientific reach.

“The GMT and TMT have proceeded separately, but they’re both great projects that involve and will benefit the entire astronomy community,” Shelton said.

FAPESP will invest US$40 million in the GMT, or approximately 4% of the total estimated cost. This investment will guarantee 4% of the telescope’s operating time for studies by researchers from São Paulo State.

More information: www.gmto.org.