Giant Magellan Telescope

Giant Magellan Telescope (GMT) in an artistic visualization

The Giant Magellan Telescope (GMT) is a planned giant telescope at the Las Campanas Observatory in the highlands of Chile , due to be Template: future / in 5 yearscompleted in 2029 . According to its precise calibration, it should have about ten times the resolution (selectivity) of the Hubble space telescope . Its name suggests the "relationship" with the two Magellan telescopes of the Chilean Las Campanas observatory.

planning

After completion, it will consist of 7 primary mirrors , each with a diameter of 8.4 m. Around a central mirror, with a central opening for the Cassegrain focus , the remaining 6 are mounted close to the periphery, all of which are mounted on a common azimuthal mount . This creates a telescope with an effective mirror diameter of 21.4 m (surface) or 24.5 m (resolution). The Large Binocular Telescope (with two such mirrors) on Mt. Graham in the US state of Arizona is considered to be a model for this construction . The focal length of the primary mirror is extremely short at 18 m for such a device (f / 0.7), which enables a very compact design. (For comparison: the primary mirror of the Hale telescope of the Palomar observatory has a focal length of 17 m with its 5 m mirror.) The effective focal length of the entire system should be 203 m (f / 8.0). The optical design is an aplanatic Gregory telescope . The size of the vignetting-free image field should be 26 arc minutes . (For comparison: the apparent diameter of the full moon is approx. 30 arc minutes.)

The main proponent of the GMT is the American Roger Angel , founder of the Spiegel Laboratory of the Steward Observatory at the University of Arizona . This laboratory - together with Schott & Gen. Mainz - experience in casting “light” giant mirrors with the help of rotating furnaces. The rotation already creates a parabolic mirror surface during casting and significantly reduces the subsequent grinding effort. While the Schott mirrors are thin, deformable meniscuses (like those of the Very Large Telescope ), the mirrors of the laboratory mentioned are rigid, with a honeycomb structure on the back, which is cast together with the mirror from Japanese borosilicate glass (type E6 from Ohara) .

particularities

Las Campanas is currently the favored location

The new thing about GMT is the one from the above. Laboratory carried out grinding and polishing process of the six peripheral primary mirrors, carried out on a vertical portal machining center from Breton, because the mirrors must be asymmetrical. The sponsors have initially released 20 million of the estimated total costs of 400 to 500 million US dollars for the production and testing of an asymmetrical primary mirror and the associated secondary mirror . In addition, optics is studied on a 1: 5 model.

To achieve the best possible resolution (λ / D = 600 nm / 24.5 m ⇒ 0.005 arc seconds , ten times better than the Hubble Space Telescope), the seven thin, deformable secondary mirrors with a diameter of around 1 m are fitted with adaptive optics .

Due to the relatively compact design with the intended focal length, the required dome structure is only slightly larger than that of the Palomar observatory.

organization

The members of the Giant Magellan Telescope Organization (GMTO) are:

completion

The contract for the construction was signed in February 2009. A first primary mirror, cast in 2005 in the Mirror Lab at the University of Arizona , was finished with polishing and testing in October 2012. Of the estimated cost of $ 700 million, 130 million has already been committed. The blank of the second mirror was completed on January 14, 2012, and on March 23, 2012, blasting work began at the telescope site to create a level construction site. At the same time, the seven segments of the primary mirror are made.

Comparison with other large telescopes

Comparison of the mirror surfaces of optical telescopes

Surname	Aperture diameter (m)	Mirror surface (m²)	First light
Extremely Large Telescope (ELT)	39.3	978	2025
Thirty Meter Telescope (TMT)	30th	655	2027
Giant Magellan Telescope (GMT)	24.5	368	2029
Southern African Large Telescope (SALT)	11.1 x 9.8	79	2005
Keck Observatory	10.0	76	1990 , 1996
Gran Telescopio Canarias (GTC)	10.4	74	2007
Very Large Telescope (VLT)	8.2	4 × 50	1998 - 2000

literature

Scientific American. New York 2005.12 (Dec.) pp. 24.25 and May 2006,5 (Mai), pp. 52-59. ISSN 0036-8733
HM Martin u. a .: Manufacture of 8.4 m off-axis segments, a 1/5 scale demonstration. (162 kB) Optical Sciences Center. University of Arizona, Tucson 2004 (?), Accessed 2008 (pdf).