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Webb telescope mirrors
The James Webb Space Telescope’s 18 mirrors are fully installed. (Credit: Chris Gunn / NASA)

NASA has put the 18th and final piece of the puzzle into place for the $8.8 billion James Webb Space Telescope’s primary mirror – marking a major milestone on the way to the observatory’s launch in 2018.

The 21.3-foot-wide mirror is so big it couldn’t be fabricated in one piece. Instead, it’s made up of 18 hexagonal segments, each spanning a little more than 4 feet and weighing about 88 pounds. The last segment was carefully laid into place using a clawlike robotic arm at NASA’s Goddard Space Flight Center in Maryland on Wednesday.

“With the mirrors finally complete, we are one step closer to the audacious observations that will unravel the mysteries of the universe,” John Grunsfeld, NASA’s associate administrator for science, said in a news release.

Webb telescope mirror installation
Inside a massive clean room at NASA’s Goddard Space Flight Center in Maryland, the James Webb Space Telescope team used a robotic am to install the last of the telescope’s 18 mirrors onto the telescope structure. (Credit: Chris Gunn / NASA)

The Webb telescope, named after the administrator who led NASA during the buildup to the Apollo moonshots in the 1960s, has been in the works for 20 years.

The telescope has sometimes characterized as a successor to the 26-year-old Hubble Space Telescope, but it’s optimized to make observations in infrared wavelengths. That part of the spectrum is a key hunting ground for signs of extrasolar planets and phenomena at the edge of the observable universe.

Now that the primary mirror is finished, the Webb team will focus on installing other optical components and testing the telescope. The prime contractor is Northrop Grumman, and Ball Aerospace & Technology is the principal subcontractor for the optics. Harris Corp. is the subcontractor in charge of integration and testing.

The telescope is due for launch in October 2018 from French Guiana on a European Ariane 5 rocket. It will be sent to a gravitational balance point a million miles away from Earth, known as Sun-Earth L2.

To learn more about the Webb, check out Scientific American’s feature about the space telescope’s construction. You can keep tabs on the team’s progress via Goddard Space Flight Center’s “WebbCam.”

At noon PT today, you can join a Google Hangout with Webb scientists and engineers. And stay tuned for “Telescope,” a TV documentary that will make its debut on Discovery Channel and Science Channel during the weekend of Feb. 20-21. (Check local listings.)

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