at least not in one piece. The 18 mirror segments
can be folded up to fit into the launch vehicle
and then unfold after launch, and once in space
the segments will work together as a single large
mirror.
Putting Webb into position for its observations is
one thing, but getting the giant segmented mirror
to focus on galaxies millions, even billions, of lightyears away is another challenge all together. In
order to ensure Webb achieves a single perfect
focus, engineers will use six tiny mechanical
motors, or actuators, attached to the back of
each mirror piece to capture the images they
expect Webb to produce.
“Aligning the primary mirror segments as though
they are a single large mirror means each mirror
is aligned to 1/10,000th the thickness of a human
its shape at those cryogenic temperatures and is
a good conductor of electricity and heat.
Gold coats the finished mirrors and is used to
improve the mirror’s reflection of infrared light.
ITT (formerly Kodak) will combine the 18
segments into one big mirror at Goddard once
the mirror backing structure, built by ATK in their
facility in Salt Lake City, Utah, is delivered. ITT
will mount the mirror segments onto their proper
place on the backing structure, which holds 12
segments in the middle part of the mirror and has
two wings with three segments each (it’s these
wings that fold back so that the full mirror will fit
into the payload fairing atop the Ariane-5 rocket).
Although the mirrors are not installed onto the
body of the telescope yet, work to install Webb’s
four fragile science instruments began some time
“
Aligning the
primary mirror
segments as
though they are
a single large
mirror means
each mirror
is aligned to
1/10,000th the
thickness of a
human hair.”
– Lee Feinberg
A full-scale JWST sunshield membrane is deployed on the membrane test fixture ready
for a precise measurement of its three dimensional shape.
Image: Northrop Grumman Aerospace Systems
hair,” said Lee Feinberg, Webb Optical Telescope
Element Manager at NASA’s Goddard Space
Flight Center. “What’s even more amazing is that
the engineers and scientists working on the Webb
telescope literally had to invent how to do this.”
Another problem with “traditional” telescope
mirrors is the fact that they are heavy. If Webb’s
mirror was made same as the Hubble, then it
simply could not be launched. To get around this
problem, the team at Northrop Grumman (the
company that is leading the effort to build Webb)
decided to make Webb’s mirrors from Beryllium,
which is a very strong lightweight metal. In order for
the telescope’s instruments to function properly,
the observatory also needs to be kept very cold,
-400 degrees Fahrenheit cold, and Beryllium holds
ago. The telescope’s most sophisticated and
technically challenging instrument – the MidInfrared Instrument (MIRI) – is now integrated into
a large component of the telescope known as
the science instrument payload, or Integrated
Science Instrument Module (ISIM). The install took
four hours to complete because the delicate
operation required a surgical installation
for precision and accuracy – MIRI had to be
positioned to a tolerance of 25 microns, or one
one-thousandth of an inch – which is less than the
width of a human hair.
The ISIM itself acts like a chassis in a car to
provide support and house all four of Webb’s
science instruments - it’s the heart that enables
the whole mission.
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