Compiled by Photonics Spectra staff
GREENBELT, Md. – NASA has completed coating 13 of the James Webb Space Telescope’s
18 primary mirror segments, enabling the observatory to see objects as far away
as the first galaxies in the universe.
Mirrors are the most critical part of a telescope and, as such,
the quality of their polishing is crucial. The mirrors were polished at L3 Integrated
Optical Systems – Tinsley in Richmond, Calif., to accuracies of less than
one-millionth of an inch. That accuracy is important for forming the sharpest images
when the mirrors cool to 2240 °C in space.
The four types of mirrors on the Webb space telescope are shown along with an artist’s
conception of the telescope’s optics with its 18 primary mirror segments.
Courtesy of NASA/Ball Aerospace/Tinsley.
The space telescope is composed of four types of mirrors –
primary, secondary, tertiary and fine steering. The telescope’s primary mirror
has an area of approximately 25 sq m, enabling scientists to capture light from
faint, distant objects in the universe faster than previous space observatories
have allowed. Made of beryllium, the mirrors will work together to relay images
of the sky to the telescope’s science cameras.
Once polished, the mirrors are coated with a microscopically thin
layer of gold that enables them to efficiently reflect infrared light. NASA plans
to complete the coating of the remaining five mirrors by early next year. The 18
segments will fit together to make one large mirror that measures 6.5 m across.
Ernie Wright, a NASA engineer, looks on as the first six of 18 primary
mirror segments are prepped to begin final cryogenic testing at NASA’s Marshall
Space Flight Center in Huntsville, Ala. Courtesy of NASA/MSFC/David Higginbotham.
Although many astronomers believed that developing such mirrors
could not be done, the telescope’s prime contractor, Northrop Grumman Corp.
of Redondo Beach, Calif., invented a mirror technology to make it possible for the
Webb telescope to see back in time, said Scott Willoughby, vice president and Webb
Telescope Program manager for Northrop Grumman Aerospace Systems.
Although NASA has made great strides in preparing the mirrors
for the Webb telescope, the House Subcommittee on Commerce, Justice and Related
Agencies voted July 7 to cut its funding. A decision is expected by Sept. 30 to
determine whether funds will be restored.