James Webb Space Telescope Backbone Completed
June 15, 2013

Backbone Of The James Webb Space Telescope Complete

April Flowers for redOrbit.com - Your Universe Online

Assembly of the primary mirror backplane support structure for NASA´s James Webb Space Telescope, the backbone of the telescope, is a step closer to completion with the recent addition of the backplane support frame. The fixture will be used to connect all the pieces of the telescope together.

The Webb´s center section and wings, secondary mirror support structure, aft optics system and integrated science instrument module will all be brought together by the backplane. The fabrication was finished by ATK of Magna, Utah, under the direction of the observatory´s builder, Northrup Grumman Corp.

During science observations, the backplane support frame will also keep the light path aligned inside the telescope. The backplane measures 11.5 feet by 9.1 feet by 23.6 feet and weighs 1,102 pounds. It is the final segment required to complete the primary mirror backplane structure, which will support the observatory's weight during its launch from Earth and hold its 18-piece, 21-foot-diameter primary mirror nearly motionless while Webb peers into deep space.

The final integration of the backplane support frame to the backplane center section was completed in April and two backplane wing assemblies were completed in March.

"Fabricating and assembling the backplane support frame of this size and stability is a significant technological step as it is one of the largest cryogenic composite structures ever built," said Lee Feinberg, James Webb Space Telescope optical telescope element manager at NASA's Goddard Space Flight Center.

The frame was built at room temperature, but must operate in space at temperatures ranging from minus 406 degrees to minus 343 degrees Fahrenheit. The frame will undergo extremely cold, or cryogenic, thermal testing at NASA's Marshall Space Flight Center. The team expects the backplane support frame and primary mirror backplane support structure will shrink as they cool down in space. They will use the tests, which will exceed the low temperatures the telescope´s backbone will experience in space, to verify the components will be the right size and operate correctly in space.

More than 10,000 parts make up the primary mirror backplane support structure, all designed, engineered and built by ATK. When fully deployed, the structure will measure about 24 feet tall, 19.5 feet wide and more than 11 feet deep but will weigh only 2,138 pounds with the wing assemblies, center section and backplane support frame attached. The fully populated support structure will support more than 7,300 pounds, more than three times its own weight, when the mission payload and instruments are installed.

To minimize heat distortion, the primary mirror backplane support structure will also meet unprecedented thermal stability requirements. For example, when the telescope is operating at a range of extremely cold temperatures, from minus 406 degrees to minus 343 degrees Fahrenheit, the backplane must not vary more than 38 nanometers, which is approximately 1 one-thousandth the diameter of a human hair. The structure is made of lightweight graphite materials using advanced fabrication techniques. The composite parts are connected with precision metallic fittings made of invar and titanium.

"The ATK team is providing program hardware that is arguably the largest and most advanced cryogenic structure ever built," said Bob Hellekson, ATK's Webb telescope program manager.

Both structures are scheduled for delivery to Marshall later this year for the extreme cryogenic thermal testing, where they will undergo structural static testing at Northrop Grumman's facilities in early 2014, and then be combined with the wing assemblies.