Cryogenic Testing Completed For NASA's Webb Telescope Mirrors

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Dec. 21, 2011

Trent J. Perrotto 
Headquarters, Washington      
202-358-0321      
trent.j.perrotto@xxxxxxxx 

Mary Blake 
Northrop Grumman, Redondo Beach, Calif. 
310-812-6291 
mary.blake@xxxxxxx  

RELEASE: 11-424

CRYOGENIC TESTING COMPLETED FOR NASA'S WEBB TELESCOPE MIRRORS

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. 

For images related to this story, visit: 

http://www.nasa.gov/topics/technology/features/webb-mirror-cryo.html  

For more information about the Webb telescope, visit: 

http://jwst.nasa.gov  

	
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