Michael A. Stecker

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GMT Casting Event
July, 2005
Giant Magellan Telescope


Approximately 125 astronomers, administrators and guests attended a July 23, 2005 meeting in Tucson, Arizona celebrating the casting of the first of seven 8.4 meter mirrors for the Giant Magellan Telescope (GMT) .  The group responsible for the project are: Carnegie Institution, Harvard University, Smithsonian Astrophysical Observatory, University of Arizona, University of Michigan, Massachusetts Institute of Technology, University of Texas and Texas A&M.  When completed and placed in Chile the instrument will be the largest telescope in the world with resolution "ten times that of the Hubble Space Telescope".

The University of Arizona's Steward Observatory Mirror Lab is building the mirrors in a huge spinning furnace (in order to achieve a meniscus shape to the molten glass).  Twenty tons of E6 borosilicate glass from Ohara Glassworks in Japan is used in the casting of the first 8.4-meter (27-foot) diameter mirror for the GMT.  With this milestone step, the GMT becomes the first extremely large ground-based telescope to start construction.

The completed GMT telescope primary mirror will consist of six 8.4-meter off-axis mirrors surrounding a seventh, on-axis central mirror.  An off-axis mirror focuses light at an angle away from its axis, unlike a symmetrical mirror that focuses light along its axis. This arrangement will give the GMT four-and-one-half times the collecting area of any current optical telescope and the resolving power of a 25.6-meter (84-foot) diameter telescope, or 10 times the resolution of the Hubble Space Telescope.

'Spin-casting' single-piece telescope mirrors that are giant, stiff yet lightweight is an ingenious, awesome process that was conceived and developed by University of Arizona Regents' Professor of Astronomy J. Roger P. Angel. Casting giant monolithic mirrors is accomplished at only one place in the world -- the Steward Observatory Mirror Laboratory.

The casting team installed about 50 cores a day for a total 1,681 cores during seven weeks in April - May. The team bolted each core at precisely measured angles to hearth tile and adjoining cores in this operation. The crew daubed all the glued junctures with blue "smurf" - a concoction the color of the blue smurf cartoon characters -- to prevent glass from sticking to the mold.  At this point, the mold held 17,000 pounds of hearth tiles, 16,000 pounds in fiber tub walls, and 15,000 pounds of cores and pins.  Heating the furnace started on July 18. It takes six days for the glass to reach peak temperature of 2,150 degrees Fahrenheit (1178 Celsius).  The furnace can be supplied with up to 1.1 Megawatts of electricity during casting -- enough to power an average 750 to 1,100 Tucson households, depending on the time of year.  Once heated the furnace will rotate during the "spincasting" in order to give the mirror its concave surface.  The oven's rotation rate determines the depth of the curve spun into the shape of the mirror, or the mirror's focal length. The GMT mirror will spin 5 times a minute because the off-axis GMT mirror is to be a shallower, longer focal-length mirror than symmetric types.

Richard Meserve, president of the Carnegie Institution, said:
"This is a new epoch for astronomy.  The fabrication of the off-axis mirror is a path-breaking event that will advance scientific discovery. Everyone in the eight-member GMT consortium is excited that we're in production."




Ground Breaking -- 2015
edited from: http://www.spacedaily.com/reports/The_Giant_Magellan_Telescope_Organization_Breaks_Ground_in_Chile_999.html

The Giant Magellan Telescope (GMT) is poised to become the world's largest telescope when it begins early operations in 2021. It will produce images ten times sharper than those delivered by the Hubble Space Telescope and will address key questions in cosmology, astrophysics and the study of planets outside our solar system.

The GMT will be located at the Las Campanas Observatory in Chile's Atacama Desert. Construction crews will soon be busy on the site building the roads, power, data, and other infrastructure needed to support the observatory. The unique design of the telescope combines seven of the largest mirrors that can be manufactured, each 8.4 meters (27 feet) across, to create a single telescope effectively 25 meters or 85 feet in diameter. The giant mirrors are being developed at the University of Arizona's Richard F. Caris Mirror Laboratory. Each mirror must be polished to an accuracy of 25 nanometers or one millionth of an inch. One giant mirror has been polished to meet its exacting specifications. Three others are being processed, and production of the additional mirrors will be started at the rate of one per year. The telescope will begin early operations with these first mirrors in 2021, and the telescope is expected to reach full operational capacity within the next decade. Founders come from the U.S., Australia, Brazil, and Korea, with Chile as the host country.

GMT Casting Meeting Photos
mouse click on any of the thumb nail images below for an enlargement

GMTC Crowd


GMT meeting panorama


Cambridge, MA  table


Charles Alcock


Albert & Nancy Boggess


Miguel Roth


Steve Shectman
Michael Gellert


Wendy Freedman


Robert Kirshner



John Huchra


Dan Fabricant


Richard Meserve


Sheldon Ekland-Olson


David Evans


Vera Rubin


Peter Strittmatter


Roger Angel


Paul Schechter


Douglas Richstone
Michael Stecker


Steward Obs. Mirror Lab


mirror overlook


Roger Angel tour


rotating furnace


8.4 meter  honeycomb mirror



mirror close-up


my room at Westward Look Resort


Robert Kirshner & M. Stecker




barrel cactus