NG is the prime contractor for JWST and leads the telescope's overall system design and development effort under contract to NASA's Goddard Space Flight Center in Greenbelt, Md. Ball is developing the Webb's optical elements. The series of intensive tests was performed at the Ball Aerospace facility in Boulder, Colo.

The JWST primary mirror segment assembly underwent three separate tests: two for vibration and one for acoustics. In the first, an ultimate test of strength, the mirror was subjected to the maximum static load it will experience on launch via a burst of vibration.

The second test measured the mirror's response to a random series of vibrations. An accelerometer measured vibration in units of G's, or the acceleration of gravity. During launch, the primary mirror assembly will experience 17 G's or forces 17 times those due to its own weight.

The third test subjected the mirror segment to acoustic noise similar to what it will experience during launch aboard the Ariane 5 launch vehicle.

The test setup consisted of gigantic speakers rented from a rock concert acoustics company arranged in a ring around the mirror in order to blast it with up to 141 decibels of sound, the volume of a very loud rock concert.

To record test results, the team optically measured the surface shape of the mirror prior to, and then again after the tests. Specifications are so stringent that only a variance of 25 nanometers is allowed.

That is slightly more than one 5,000th the thickness of a normal piece of paper. Results confirmed that the mirror surface would not bend, ensuring accurate imaging by the telescope.

With the successful completion of these tests, the mirror segment assembly passed the final milestone to achieve Technology Readiness Level 6. TRL is a measure used by the U.S. government to assess the maturity of evolving technologies; a level six rating means a system has been tested successfully in a relevant operational environment.

"The tests required to meet significant milestones for JWST are challenging, and it's therefore gratifying that the team continues to make excellent progress," said Mark Bergeland, Ball Aerospace JWST program manager.

"By January 2007, all JWST technologies are scheduled to reach TRL 6, more than six years ahead of launch," said Martin Mohan, Northrop Grumman JWST program manager. "This advanced state of development for a program at this stage is unprecedented and dramatically lowers future risk on the program."

JWST is expected to explore far beyond the reach of current telescopes, including the Hubble, peering into the near and mid-infrared at great distances to search for answers to fundamental questions about the birth and evolution of galaxies, the size and shape of the universe and the mysterious life cycle of matter.

Related Links
James Webb Space Telescope
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