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Webb Space Telescope fully deployed after primary mirror unfolds

January 8, 2022

— That's 18 not-so-small steps for a space telescope, one giant deployment for humanity's understanding of the universe.

The James Webb Space Telescope completed its deployment on Saturday (Jan. 8), two weeks after the observatory's launch. While there remains months of work before Webb can begin making astronomical discoveries, Saturday's milestone marked a significant step forward for the world's largest and most powerful space telescope.

"What an amazing milestone!" exclaimed Thomas Zurbuchen, NASA's associate administrator for science, on NASA's live broadcast of the final deployment. "We see that beautiful pattern out there in the sky. One hundred seventy eight (178) out of the 178 actuators had to fire the right way. I'm just so amazed."

"We have a deployed telescope on orbit," Zurbuchen said, addressing the mission operations room at the Space Telescope Science Institute in Baltimore, Maryland. "How does it feel to make history everybody?"

The commands that were sent on Saturday directed the telescope — which was about 665,000 miles (1.07 million km) away — to swing out the starboard (or right side) wing of its primary mirror, bringing forward the last three of its 18 hexagonal segments. The deployment concluded with latches securing the wing in place.

JWST primary mirror deployment. Click to view and enlarge in a new, pop-up window. (NASA)

Now in its final shape, the tennis court-size Webb will continue to travel outwards to its destination, the second Earth-Sun Lagrange Point, commonly referred to as "L2." The following five months will be used to cool the telescope to its operating temperature, fine-tune its mirrors' alignment and calibrate its instruments.

'An audacious feat'

Webb's multi-step deployment was a factor of its launch. No rocket could lift off with the telescope unfolded, but even using the largest fairing available, Webb had to be compacted down from its 70-foot-wide (21.2 m) final configuration to just 15 feet (4.57 m) in diameter so it fit atop its Ariane 5 launch vehicle.

With the exception of the first two autonomous deployments — Webb's power-providing solar array and the telescope's antenna assembly — the remaining 16 components were commanded to unlatch, unfurl or tighten by team members on the ground. Their work was done without visual confirmation that all had worked as they planned.

"Adding cameras to watch an unprecedentedly complicated deployment of such a precious spacecraft as Webb sounds like a no-brainer, but in Webb's case, there's much more to it than meets the eye," Paul Geithner, a deputy project manager for Webb at NASA's Goddard Space Flight Center in Maryland, said in a statement. The sheer size of the telescope and the environment where it is located ruled out even doorbell-like cameras.

Instead, said Geithner, the team relied solely on switches and various mechanical, electrical and temperature sensors to determine their commands were successful.

Of the many steps needed to unfold Webb, key among them was the extension of the sunshield, which will lower and maintain the telescope's temperature, enabling observations in the infrared. Each of the shield's five layers had to be individually tensioned, a process that took about two days to complete.

"The team has accomplished an audacious feat," said Gregory Robinson, Webb's program director at NASA Headquarters, after all of the layers were tightened on Jan. 4. "Unfolding Webb's sunshield in space is an incredible milestone, crucial to the success of the mission."

Forward to first light

With Webb in its larger configuration, attention will now turn to fine adjustments.

The next step will be to individually activate and move each of the 18 segments that make up the telescope's primary mirror. The primary mirror segments and secondary mirror are adjusted using six actuators that are attached to the back of each piece. The earlier also have a seventh actuator at its center that controls its curvature.

Later, once Webb is in orbit, sensors will be used to measure imperfections in the segments' alignment that prevent them from acting as a single, 6.5-meter (21.3-foot) mirror. During this process, 18 out-of-focus images of a star — one from each mirror segment — will be analyzed by computer to determine the overall shape of the primary mirror and determine how each segment is moved to align them.

First up though, a third and final course correction will mark the last step in Webb's launch, placing it into its operational orbit at L2.

Once its commissioning is complete, the James Webb Space Telescope will be used to explore every phase of cosmic history, from within the solar system to the most distant observable galaxies in the early universe and everything in between. Webb is expected to reveal exoplanets with Earth-like atmospheres and improve our understanding of the origins of the universe.


Artist rendering of the fully deployed James Webb Space Telescope (JWST). (NASA GSFC/CIL/Adriana Manrique Gutierrez)

In March 2020, testing teams deployed the James Webb Space Telescope's 21-foot, 4-inch (6.5 meter) primary mirror into the same configuration it now has while in space. (Northrop Grumman)

Graphic showing the James Webb Space Telescope as it proceeds through the major steps of deployment. (Northrop Grumman)

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