August 5, 2012
NASA engineer Ernie Wright looks on as the
first six flight ready James Webb Space Telescope’s
primary mirror segments are prepped to begin final cryogenic
testing at NASA’s Marshall Space Flight Center in
Huntsville, Ala. Credit: NASA’s Marshall Space Flight
NASA technology does some amazing things.
Imagine taking one-tenth of an ounce of gold and spreading it so
thin that it completely coats something over four feet in diameter.
That’s what scientists and engineers did for the primary
mirror segments that will fly on NASA’s James Webb Space
The Webb telescope has 18 hexagonal-shaped
mirror segments that make up its primary mirror. Each of the
segments is 1.32 meters (4.3 feet) in diameter, flat to flat. Webb
Telescope’s scientists and engineers determined that a
primary mirror 6.5 meters (21 feet 4 inches) across is what was
needed to measure the light from faint astronomical sources.
To enable the mirrors to most efficiently
reflect the infrared light from say, distant galaxies, a
microscopically-thin gold coating was needed. Because the Webb
telescope is looking at infrared light, gold was the ideal choice
because it reflects infrared light so efficiently, especially
compared to the reflectivity of bare beryllium. The amazing thing
is that Quantum Coating, Inc.’s mirror coating technology
allowed just a tiny amount of gold to cover an entire mirror.
“The thickness of the gold coating on
the mirrors is only 100 nanometers thick, or a tenth of a micron,
which is 1/10,000th of a millimeter,” said Paul Geithner,
Deputy Project Manager - Technical for the Webb telescope at
NASA’s Goddard Space Flight Center in Greenbelt, Md.
“A human hair is roughly 1000 times