The first six of 18 segments that will form NASA’s James Webb Space Telescope’s primary mirror for space observations have begun final round-the-clock cryogenic testing at the X-ray and Cryogenic Facility at NASA’s Marshall Space Flight Center, Huntsville AL.
The tests will confirm that the mirrors will respond correctly to the extreme temperatures of space prior to integration into the telescope’s permanent housing structure.
The mirror segments measure approximately 4.3 feet in diameter to form the 21.3 foot hexagonal telescope mirror assembly critical for infrared observations. Each of the 18 hexagonal-shaped mirror assemblies weights approximately 88 pounds. The mirrors are made of the light and strong metal beryllium and coated with a microscopically thin coat of gold to enable the mirror to efficiently collect light.
Helen Cole, project manager for Webb activities at Marshall, said, “The six flight mirrors…for cryogenic testing…have been carefully polished to their exact prescriptions,” adding, “It’s taken the entire mirror development team, including all the partners, over eight years of fabrication, polishing and cryogenic testing to get to this point.”
During cryogenic testing, the mirrors are subjected to extreme temperatures dipping to -415F in a 7,600 cubic-foot helium-cooled vacuum chamber. This permits engineers to measure in extreme detail how the shape of the mirror changes as it cools. This simulates the actual processes each mirror will undergo as it changes shape over a range of operational temperatures in space.
“This final cryotest is expected to confirm the exacting processes that have resulted in flight mirrors manufactured to tolerances as tight as 20 nanometers, or less than one millionth of an inch,” according to Scott Texter, Webb optical Telescope element manager at Northrop Grumman, Redondo Beach CA.
A second set of six mirror assemblies will arrive at Marshall in July and the final set of six will arrive during the fall.
The Webb Telescope is NASA’s next-generation space observatory and successor to the Hubble Space Telescope. The most powerful space telescope designed, Webb will observe the most distant objects in the universe, provide images of the very first galaxies ever formed and help identify unexplored planets around distant stars. It will orbit approximately one million miles from Earth.
The telescope is a combined project of NASA, the European Space Agency and the Canadian Space Agency. Prime contractor under NASA’s Goddard Space Flight Center, Greenbelt MD, is Northrop Grumman. Ball Aerospace & Technologies Corp, Boulder CO, is responsible for mirror development. L-3-Tinsley Laboratories Inc., Richmond CA, is responsible for mirror grinding and polishing. Visit www.jwst.nasa.gov.
