Reflective Surfaces Spent Ten Weeks At 379 Degrees Below Zero

The last six primary mirror segments and the secondary mirror that will fly on the James Webb Space Telescope have passed their final cold test. This milestone concludes testing on the telescope's individual mirror segments and represents the successful culmination of a years-long process that broke new ground in manufacturing and testing large space-qualified mirrors.

"The mirror completion signifies that we can build a large, deployable telescope for space - 18 mirrors that operate as one," said Scott Willoughby, vice president and Webb program manager, Northrop Grumman Aerospace Systems, which designed the Webb telescope for NASA. "We have proven that real hardware will perform to the requirements of the mission."

Completed at the X-ray & Cryogenic Facility at NASA's Marshall Space Flight Center in Huntsville, AL, 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 the mirror's shape changes as it cools. Cryotesting verifies that the mirror will respond as expected to the extreme temperatures of space.

Teammate Ball Aerospace performed a comparable test on the secondary mirror, which presented a unique testing challenge because it is the only mirror that is convex, with a surface that curves or bulges outward. It involved a special test and more complex optical measurements.
 
The James Webb Space Telescope is the world's next-generation space observatory and successor to the Hubble Space Telescope. The most powerful space telescope ever built, Webb will observe the most distant objects in the universe, provide images of the very first galaxies ever formed and study planets around distant stars. The Webb Telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.

FMI: www.nasa.gov, www.northropgrumman.com