Jun 7

The Discovery Channel Telescope (DCT)

Category: Lowell,Work

Recently there was a Lowell Observatory Advisory board meeting.  A couple of my colleagues and myself gave tours of the construction site to  board members.  The discovery channel telescope ( or DCT, so named because of significant funding from that television channel) is being built on a mesa near Happy jack, AZ.

You can see that the building is in an advanced state of construction; the telescope itself is not yet completed and is not yet inside.

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The portion on top that is mostly girders – “the dome” will weigh about 1/3 of a million pounds when complete.  It will be turned by four electric motors.  The telescope is a leviathan that will weigh some 145000 pounds and sit on its own bearing and have its own motors.  The dome and telescope will turn together in separate but synchronized motion.

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The telescope and the interior of the dome must be kept at the same temperature as outside so that there are no thermal disturbances which will mess up the optical seeing.  To do this, the building has many vent doors which can be opened, as well as active liquid cooling that will control the temperature of the telescope’s mirrors.  Also, air will be drawn through the tubular support structure of the telescope as well as the mirror mount.

Here are a couple pictures of me during the tour, taken by Holly.

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Here I am explaining the Active Optics System (AOS).  It is not designed to correct atmospheric distortions, but to control the shape of the main mirror while the telescope moves around. Although the mirror is made of ultra-low-expansion glass, and a chunk of it would seem rigid, you can think of it as a blanket of glass.  It weighs 6,700 lbs is about 4.2 meters – 14 feet – across and only 10 cm thick.  So, as it moves, it wrinkles and sags.  You can not see this with the naked eye, but since the mirror needs to be maintained in shape by only a fraction of a wavelength of light (less than 1 millionth of a meter), it is a problem.  To counteract this, there are mechanical “pushers” around the periphery and underneath the mirror.  These components push, pull and lift the mirror to maintain its shape.  The mirror is not bolted to its mount, because that  would distort the surface to the mirror and thus the resulting image.  It is made to slide around while the mechanical compensators keep it in shape and in the right position.

I am pointing at an engineering drawing of the mirror on its mount.  To my right is a rendering of the telescope which will sit inside the dome.  I’ll really have to get some JPEGS to post here.

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Inside the dome, under construction.

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One of the numerous dome bearings that will support the enormous mass of the dome structure and allow it to turn smoothly.

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View looking up from the mezzanine level.  The temporary wooden structure fills the space that will be occupied by the telescope.

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View of the landscape around the telescope site.  It’s in the coconino national forest north of Phoenix.

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The day’s pictures (including some already shown above):

For “official” photos of the site as well an engineering documents and more, see here.

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