Headlines > News > James Webb Space Telescope's First Primary Mirror Segment Meets Flight Specifications

James Webb Space Telescope's First Primary Mirror Segment Meets Flight Specifications

Published by Klaus Schmidt on Tue Jan 19, 2010 12:43 pm via: Northrop Grumman
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The first primary mirror segment of NASA’s James Webb Space Telescope has met flight specifications at ambient temperatures, the result of a process that has been six years in the making. Northrop Grumman Corporation is leading the design and development effort for the space agency’s Goddard Space Flight Center.

The mirror segment, an engineering development unit, was successfully polished to an accuracy of less than 20 nanometers, or smaller than a millionth of an inch. The process, called cryo-null figuring, ensures that when the mirror reaches cryogenic temperatures, it will change its shape into the exact optical prescription needed for its mission. The polishing and ambient testing took place at Tinsley Laboratories, Inc. in Richmond, Calif.

The James Webb Space Telescope in orbit. Credits: Northrop Grumman

The James Webb Space Telescope in orbit. Credits: Northrop Grumman

“This milestone marks the culmination of an intensive six-year manufacturing effort,” said Scott Willoughby, Webb telescope Program Manager for Northrop Grumman Aerospace Systems sector. “To produce these unmatched precision optics, the manufacturing team has worked extremely hard, inventing systems and processes along the way to meet tremendously rigorous specifications.”

“This is a tremendously important milestone to the JWST project that bodes well for both our future mirror manufacturing schedule and for the potential performance capabilities of the telescope,” said Lee Feinberg, James Webb Space Telescope Optical Telescope Element Manager at NASA Goddard Space Flight Center, Greenbelt, Md.

The development unit, which will be used as a spare, was sent to Ball Aerospace and Technologies Corp. in Boulder, Colo. where actuators were added. The mirror assembly is now being verified at cryogenic temperatures in the X-ray and Cryogenic Facility (XRCF) at NASA’s Marshall Space Flight Center in Huntsville, Ala. The development mirror will be closely followed by the “A1″ flight mirror, the first of the actual mirror segments that will fly on the telescope. The second batch of three flight mirror segments is due to Tinsley next month.

“In addition to the milestone verification test of an engineering development unit, which is an “A” segment spare, five flight mirror segments will be tested for the first time in the XRCF this month,” said Helen J. Cole, Webb Telescope Activities Project Manager at NASA Marshall. When the primary mirror is integrated, it will include 18 flight segments altogether. There are three different shapes of segments that fit together to make up the primary mirror. Of the 18 segments, 6 are “A” segments, 6 are “B” segments and 6 are “C” segments. The XRCF test will be the first cryogenic test to collect data for all three types of primary segments being fabricated.

Manufacturing began six years ago, led by Northrop Grumman’s principal optical contractor Ball Aerospace. Brush Wellman in Elmore, Ohio, made twenty-one 500-lb. hexagonal mirror blanks from beryllium, an extremely strong, lightweight metal. Axsys Technologies in Cullman, Ala., machined the backside of the beryllium blanks and chemically etched them into an isogrid pattern that reduced mirror mass by 92 percent, from 553 pounds to 46 pounds (250 kg to 21 kg). The front side of the mirror blank was machined to prep the optical surface for high precision grinding, polishing and testing, which is being done by Tinsley. The mirror segments have undergone a series of polishing and cryotesting cycles. Ball incorporates the mirrors into optical assemblies, which are mounted on the telescope structure.

The James Webb Space Telescope is the next-generation premier space observatory, exploring deep space phenomena from distant galaxies to nearby planets and stars. The Webb Telescope will give scientists clues about the formation of the universe and the evolution of our own solar system, from the first light after the Big Bang to the formation of star systems capable of supporting life on planets like Earth. Expected to launch in 2014, the telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.

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