The mirrors that will fly aboard NASA’s James Webb Space Telescope will allow the telescope to see farther away and further back in
time to detect the light from the very first and most distant stars and galaxies. In this photo, an engineer’s crystal clear reflection is seen
on the surface of one of the primary mirror segments. The image is so clear you can see an expression of concentration in the engineer’s
Photo NASA/Chris Gunn
face. Other engineers use flashlights to inspect the mirror segment.
obscured star formation, molecular hydrogen
emission from previously unthinkable distances,
the physics of protostars, and the sizes of Kuiper
Belt objects and faint comets are all fair game to
the power of the MIRI instrument.
Having the capability of both a spectrometer
and an imager, basically being two instruments in
one, gives MIRI the ability to point at an object
in space to record both its image and spectrum.
MIRI’s capabilities will also allow it to see light
emitted by molecules that reveal a wealth of
physical information and can reveal the presence
of life on other planets, in addition to seeing
through dust which obscures key phenomena such
as star formation. Physical properties of objects
across the universe, including temperature, mass,
and chemical composition of those objects, will
all be studied by the giant telescope thanks to
MIRI, which will hopefully answer long-standing
questions that Hubble and the other great
observatories alone cannot answer themselves.
The instrument will need to be cold – very cold
– in order to operate correctly. MIRI will operate at
a temperature of minus 270 degrees Celsius, and
it will take approximately 200 days after launch to
reach its optimal operating temperature. To ensure
MIRI is protected from excess heat, it is housed in
a thermal shield, which basically resembles foil. To
obtain images and spectra in infrared light that
is invisible to the human eye, the JWST must be
cooled to a very low temperature (-383 F or -230
C) in order to avoid being blinded by their own
infrared emission, and, since MIRI will operate over
longer infrared wavelengths than the other three
instruments, it must be made approximately 35
degrees colder than the rest of the ISIM.
“MIRI will enable Webb to distinguish the oldest
galaxies from more evolved objects that have
undergone several cycles of star birth and death,”
said Matt Greenhouse, ISIM project scientist at
Goddard. “MIRI also will provide a unique window
into the birth places of stars which are typically
enshrouded by dust that shorter wavelength light
cannot penetrate.”
Webb passed its first significant mission
milestone for 2014, a Spacecraft Critical Design
Review (SCDR), several weeks ago. The weeklong review by an independent panel of experts
involved extensive discussions on all aspects of
the spacecraft – details, designs, construction
and testing plans, and the spacecraft’s operating
procedures were all reviewed in an effort to
ensure the plans to finish construction would result
in a vehicle that enables the powerful telescope
and science instruments to deliver their unique
and invaluable views of the universe.
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