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The most prominent and beautiful
part of NASA’s ... 

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James Webb Space Telescope is
its gold primary mirror with ...

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its smaller, secondary mirror
suspended out in front.

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The Webb Telescope is a
reflecting telescope.

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Technically, it’s an anastigmat
telescope.

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This means that its concave
primary mirror captures ... 


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the light and reflects it to
this secondary, ... 

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, convex mirror, which reflects
the light back to the ... 

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concave rectangular shaped
tertiary mirror, ... 

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then finally to the flat fine
steering mirror which sends ... 

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sends the light through a hole
in the center of the ...

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the primary mirror to focus at
the science instruments ... 

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behind the primary mirror.  

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This type of telescope enables a
wider field of view ... 

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and minimizes optical
distortions.  

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The primary and secondary mirror
form what is called ... 

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a Cassegrain telescope similar
to the ... 

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Hubble Space Telescope.

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It’s this third powered mirror
that makes Webb ... 

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an anastigmatic telescope.


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Webb has the largest primary
mirror ever to fly in space. 

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At 21 feet 3 inches across, or 6
and a half meters, ... 

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it’s built to see the faintest
light coming from ... 

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from the most distant, luminous
objects in the universe.

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Its size presents one of the
biggest ... 

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mission’s challenges: the
primary mirror is larger ... 

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than the fairing of the rocket
lifting it into space. 

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So, Webb’s mirror has to be
segmented and folded ... 

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for launch – and that means it
has to be unfolded, ...

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and focused, in space. 

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Webb’s mirrors are made of a
rare metal called beryllium, ...

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because this chemical element is
very strong, lightweight ... 

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and virtually ceases changing
shape when it gets really cold. 

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Starting from beryllium mines in
Utah, the mirrors ...

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crisscrossed the
country.

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The beryllium was made into a
powder of ...


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microscopic spheres, then fused
by intense pressure ... 

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into solid discs that were
machined and polished.

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Lastly, the mirror segments were
coated with a thin layer

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of pure gold less than 100 atoms
thick to best ... 

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reflect infrared light.


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All of the mirror machining and
polishing was done at ... 

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room temperature,  
because beryllium changes ...

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its shape with temperature and
only becomes stable at ...

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at very cold temperatures, the
mirrors were manufactured ... 

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to precisely the ‘wrong’
prescription at ...

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room temperature so that they
have precisely the ... 

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right shape at operating
temperatures.

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Thats negative 388 degrees
 Fahrenheit, or ...

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negative 233 degrees Celsius.

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That’s colder than the surface
of Pluto. 

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A robot-like system perfectly
mounted each mirror ... 

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onto Webb’s composite backplane
structure.

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Behind each mirror is an
actuator system that can ...

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move each mirror segment
precisely in ... 

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every direction, as well as  
modify each segment’s shape ...

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ever so slightly, so that all 18
segments can be aligned ...

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to form a single, perfect
mirror.

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After Webb is deployed, it takes
several months for the ... 

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instruments to cool to their
operating temperature.  

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During this time engineers on
the ground will use Webb’s ...

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Near Infrared Camera and a
process called ...  

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Wave Front Sensing and Control,
to align Webb’s mirrors.  

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The mirrors will be retuned as
needed during the mission ...

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to maintain Webb’s perfect
vision.

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Once Webb launches, and the
science team aligns those ... 

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extraordinary mirrors, a new
scientific era will begin. 

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