Discovery Channel Telescope

As a part of my tour of Lowell Observatory, I visited the Discovery Channel Telescope out near the Happy Jack Ranger station. It is up around 7700-feet elevation with unobstructed views all-around. The telescope itself is 4.3-meters in diameter utilizing an alt-az mount, both weighing in at some 140-tons. They have already taken first light, although these were more of engineering than scientific value to verify that all systems are nominal. There is even an eyepiece holder at the back of the scope—what I wouldn't do to use it to view Orion's nebula or Whirlpool galaxy using it.

Me. Telescope. Need I write more?
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Telescope with the primary mirror closed off.
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Looking up to the hyperbolic secondary mirror.
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There are 128 pressure actuators that help keep the mirror centered regardless of primary mirror orientation. The primary mirror is meniscus (very thin relative to its diameter), measuring only some 4-inches thick over its 169-inch diameter. This reduction in thickness significantly reduces its mass and its thermal inertia allowing it to come to ambient temperature quickly. And this thinness, as it were, allows the mirror to be flexed into shape, allowing it deflect to counter aberrations in other mirrors and orientation. Contrary to popular thought, these actuators do not support adaptive optics. The decision to not include AO is due to the increased complexity and consequently risk to project schedule that it would introduce. Nevertheless, it may be possible retro-fit the telescope with this capability at some later date by introducing a tertiary mirror to act as active corrector.
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View of the back (or bottom) of the telescope with a portion of the LMI (large monolithic instrument) attached. The telescope is designed to allow a variety of instruments to be attached at various points along the mount, side, and secondary mirror giving it unparalleled flexibility to grow to meet the needs of Lowell's researchers over its 50-year life-span.
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Primary mirror up-close.
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Inside of aluminize autoclave used to re-surface the primary mirror when its reflectivity drops below a defined limit. It generates a vacuum inside the chamber. Then tungsten elements (think light-bulb elements) with aluminum sputtered on it are heated till the aluminum vaporizes. This aluminum is gaseous form eventually finds its way onto the mirror surface to create a surface thickness of only a few angstrom thick. The total amount of aluminum is on the order of a dime's worth (that might be a bad turn of phrase, though).
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Outside of aluminize autoclave used to re-surface the primary mirror when its reflectivity drops below a defined limit.
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Inside of telescope chamber with cabling. The cabling is allowed to rotate with the telescope ensuring it does not get tangled up as it rotates around.
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Discovery Channel Telescope

(May 2012)
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From Arizona

Ward's Pics

Discovery Channel Telescope