CRYOGENIC TESTING COMPLETE ON MIRRORS FOR HUBBLE TELESCOPE REPLACEMENT

The following excerpt is from the NASA website:

Dec. 21, 2011
GREENBELT, Md. -- Cryogenic testing is complete for the final six
primary mirror segments and a secondary mirror that will fly on
NASA's James Webb Space Telescope. The milestone represents the
successful culmination of a process that took years and broke new
ground in manufacturing and testing large mirrors.

"The mirror completion means we can build a large, deployable
telescope for space," said Scott Willoughby, vice president and Webb
program manager at Northrop Grumman Aerospace Systems. "We have
proven real hardware will perform to the requirements of the
mission."

The Webb telescope has 21 mirrors, with 18 mirror segments working
together as a large 21.3-foot (6.5-meter) primary mirror. Each
individual mirror segment now has been successfully tested to operate
at 40 Kelvin (-387 Fahrenheit or -233 Celsius).

"Mirrors need to be cold so their own heat does not drown out the very
faint infrared images," said Lee Feinberg, NASA Optical Telescope
Element manager for the Webb telescope at the agency's Goddard Space
Flight Center in Greenbelt, Md. "With the completion of all mirror
cryogenic testing, the toughest challenge since the beginning of the
program is now completely behind us."

Completed at the X-ray and Cryogenic Facility (XRCF) at NASA's
Marshall Space Flight Center in Huntsville, Ala., a ten-week test
series chilled the primary mirror segments to -379 degrees
Fahrenheit. During two test cycles, telescope engineers took
extremely detailed measurements of how each individual mirror's shape
changed as it cooled. Testing verified each mirror changed shape with
temperature as expected and each one will be the correct shape upon
reaching the extremely cold operating temperature after reaching deep
space.

"Achieving the best performance requires conditioning and testing the
mirrors in the XRCF at temperatures just as cold as will be
encountered in space," said Helen Cole, project manager for Webb
Telescope mirror activities at the XRCF. "This testing ensures the
mirrors will focus crisply in space, which will allow us to see new
wonders in our universe."

Ball Aerospace and Technologies Corp. in Boulder, Colo. successfully
completed comparable testing on the secondary mirror. However,
because the secondary mirror is convex (i.e., it has a domed surface
that bulges outward instead of a concave one that dishes inward like
a bowl), it does not converge light to a focus. Testing the mirror
presented a unique challenge involving a special process and more
complex optical measurements.

The Webb telescope is the world's next-generation space observatory
and successor to the Hubble Space Telescope. It will be most powerful
space telescope ever built, provide images of the first galaxies ever
formed, and explore planets around distant stars. It is a joint
project of NASA, the European Space Agency and the Canadian Space
Agency.”