Since many materials change shape when they change temperature, a test team from Ball Aerospace worked together with NASA engineers at Marshall’s X-ray and Cryogenic Facility (XRCF) to cool the mirror segments down to the temperature Webb is experiencing in deep space, -400 degrees Fahrenheit (-240 degrees Celsius).
Cryogenic testing of the primary mirror segments began in at Marshall’s XRCF by Ball Aerospace in 2009.
The change in mirror segment shape due to the exposure to these cryogenic temperatures was recorded by Ball Aerospace Engineers using a laser interferometer. This information, together with the mirrors, traveled back to California for final surface polishing at Tinsley. The mirrors’ final polish was completed in June of 2011.
By the end of 2013, all the flight primary mirror segments, as well as the secondary and tertiary mirrors would be at Goddard. The mirrors were stored in special protective canisters in the cleanroom, awaiting the arrival of the flight telescope structure.
Inside a massive clean room at NASA’s Goddard Space Flight Center in Greenbelt, Maryland the James Webb Space Telescope team used a robotic arm to install the last of the telescope’s 18 mirrors onto the telescope structure.
James Webb Space Telescope Mirror Seen in Full Bloom
Once the mirrors were completed, the science instruments were integrated into the telescope. While at Goddard, the telescope also underwent environmental testing – both acoustic and vibration – to ensure it would be able to withstand the rigors of launch. That successfully completed, the telescope was sent off to NASA Johnson in Houston, Texas, for tests of the optics and instruments at cryogenic temperatures. NASA Johnson’s Chamber A is the only thermal vacuum chamber NASA has that is large enough for Webb!
Once the telescope reached orbit, engineers on Earth made adjustments/corrections to the positioning of the Webb telescope’s primary mirror segments to bring them into alignment – to ensure they would produce sharp, focused images.
