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The primary
mirror is the heart of a telescope. Casting the 8.2
meter mirror blank took three years, and polishing
and final processing took another 4 years. The result
is one of the world's smoothest single piece mirrors. |
A map of the surface error of the mirror shows that
the average bump is only 0.014 μm, or about
one in five thousandths of the thickness of a human hair.
If the primary mirror were the size of the Big Island
of Hawaii, the average bump would only have a thickness
of an ordinary sheet of paper.
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The mirror traveled through land and water from New York
where it was cast, to Pennsylvania where it was polished,
and finally to Hawaii.
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261 robotic
fingers fit into the holes drilled into the back of the
mirror to keep it in a perfect shape no matter where
the telescope is pointing in the sky. This technology,
called active optics, makes the building of large
aperture telescopes possible. A mirror that doesn't
have to maintain its shape can be thin, and therefore
relatively light weight and maneuverable. |
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Subaru Telescope
has the strength and rigidity necessary to support
an instrument at prime focus. The telescope, which
weight over 500 metric tons, sits on a thin layer
of oil and is moved by a magnetically impelled linear
motor so that it can move smoothly and accurately
with minimal friction. This design has translated
into superior tracking and pointing accuracy. |
High tracking accuracy cannot be achieved without
a strong foundation. This photograph shows the pier
that supports the telescope after its completion.
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 The
telescope during test assembly in a shipyard in Japan(1995).
Now that the telescope is in the enclosure on the
summit, it is no longer possible to get a full view
of the telescope. Compare the size of the structure
to the person in the foreground.
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Subaru adopted
a cylindrical enclosure design to reduce air turbulence
inside the enclosure. Fluid experiments and computer
simulations show that wind flows smoothly around cylindrical
enclosures and that air in the enclosure can be flushed
efficiently without bringing in turbulence from outside.
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The shape of Subaru's enclosure is unique among telescopes
on the summit of Mauna Kea.
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 Fluid
flow experiments and computer simulations were essential
for determining the design of the telescope enclosure.
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Instrument
exchange is a delicate process in which optical elements
must be carefully aligned and electrical wiring and
hoses for coolant securely attached. In the physically
challenging high altitude environment of the summit,
automation helps engineers accomplish the work quickly
and accurately. |
 The
Cassegrain Instrument Automatic Exchanger can exchange
Cassegrain instruments in two hours.
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 Prime
focus is located at the center of the telescope's
top ring. The Top Unit Exchanger helps exchange prime
focus instruments, such as Suprime-Cam and the secondary
mirrors.
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Maintenance is essential for keeping the telescope in
optimal condition. The telescope incorporates nozzles
that spray dry ice snow onto the surface of the mirror
to remove dust. Every two years or so, re-aluminization
restores the mirror's reflectivity.
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Actuators through the uncoated primary mirror. 
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The surface of the mirror is cleaned with dry ice
snow every two weeks.
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The lower level of the telescope enclosure houses
facilities for re-aluminizing the mirror.
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