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28 March 2014 sky & telescope

Megatelescope Mirrors

“With this active correction,” Martin says, “the fi rst

GMT mirror’s shape is nearly perfect, with a typical error

of only 19 nanometers.”

The Giant Magellan Telescope’s Future

With the fi rst mirror complete, the plan is to continue

grinding out mirrors for the next decade. Two more off -

axis mirrors have been cast, one in January 2012 and one

in August 2013, and the polishing of their front surfaces

should begin in 2015 and 2016, respectively.

The current timetable is a bit delayed because the Mir-

ror Lab has contracts to make mirrors for two other tele-

scopes, including the Large Synoptic Survey Telescope in

Chile. Once the Mirror Lab has completed these contracts,

it will devote its operations to making GMT’s remaining

mirrors. By 2017 it should begin churning out mirrors on

a 12- to 14-month cycle.

This schedule, of course, assumes that the GMT

partnership raises the funds to fi nish the telescope. The

consortium includes the Carnegie Institution for Science,

the Smithsonian Institution, and eight other universities

and institutions across the U.S., Australia, and South

Korea. The group to date has raised more than half of the

telescope’s projected $800 million cost.

And the partnership is moving forward, buoyed by the

fi rst mirror’s success. A fi nal design review is planned for

January 2014, and construction of the GMT facility should

begin later in the year.

The three mirrors cast so far are destined for GMT’s

outer ring. The Mirror Lab will then cast and polish

GMT’s central mirror. By 2020, GMT is scheduled to see

fi rst light with just these four mirrors installed; if all goes

well, all seven mirrors will be installed by 2022.

And the odds are good that all will go well. One of the

project’s themes, Martin notes, is taking something they

already know how to do — such as making an 8-meter

telescope — and applying it on a larger scale.

So stay tuned for some spectacularly large-scale

ground-based astronomy coming in the next decade. ✦

S&T contributing editor Robert Zimmerman reports on sci-

ence, astronomy, culture, and history at his website, Behind

the Black, at behindtheblack.com. A new edition of his fi rst

book, Genesis: The Story of Apollo 8, is now available as an

e-book at all e-book sellers.

AT THE MIRROR LAB Buddy Martin stands in front of the

Large Synoptic Survey Telescope’s combined primary and tertiary

mirror. The unique mirror sits below the nine-story tower that

houses four devices for testing surface shape.

GIANT MAGELLAN TELESCOPE / GMTO CORPORATION

ROBERT ZIMMERMAN

GMT Mirror.indd 28 12/24/13 11:46 AM