The backplane support frame will bring together Webb's center section and wings, secondary mirror support structure, aft optics system and integrated science instrument module, NASA said Friday in a release.
It also will keep the light path aligned inside the telescope during science observations, NASA said.
The frame, measuring 11.5 feet by 9.1 feet by 23.6 feet and weighing 1,102 pounds, is the final segment needed to complete the primary mirror backplane support structure. It will support the observatory's weight during launch and hold its 21-foot-diameter primary mirror virtually still while the Webb observes deep space, NASA said.
"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 in Greenbelt, Md.
ATK of Magna, Utah, finished fabrication under the direction of the observatory's builder, Northrop Grumman Corp.
The assembled primary backplane support structure and backplane support frame will undergo extreme cryogenic thermal testing later this year. They will undergo structural static testing at Northrop Grumman's facilities in Redondo Beach, Calif., in 2014, before being combined with the wing assemblies.
The James Webb Space Telescope, the successor to NASA's Hubble Space Telescope, will be the most powerful space telescope built and has a 2018 launch date. The Webb telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.