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Astronomers are starting to breathe again.

Two weeks ago, the most powerful space observatory ever built roared into the sky, carrying the hopes and dreams of a generation of astronomers on a pillar of thin plastic sheets like mirrors, wires, motors, cable clips, and willow in a tightly-wrapped package. smoke and fire.

On Saturday, the James Webb Space Telescope observatory completed a final and crucial step around 10:30 am by opening the last section of its golden, hexagonal mirrors. About three hours later, engineers sent commands to fix these mirrors in place, a step that meant it was fully deployed, according to NASA.

It was the latest in a series of precision maneuvers when traveling too far in space, which the space agency has dubbed 344 “single points of failure.” Now the telescope is almost ready for operation, although there are more tense moments in the future.

Thomas Zurbuchen, NASA’s chief of science, said that all of the telescope’s mirrors eventually snapped into place: “I’m emotional about it. “What an amazing milestone – we see that beautiful pattern in the sky now almost complete.”

The James Webb Space Telescope, named after a former NASA administrator who oversaw the formation years of the Apollo program, is 25 years and $10 billion in construction. It is three times the size of the Hubble Space Telescope and is designed to see more into the past than its famous predecessor, to study the first stars and galaxies to open at the beginning of time.

The launch with the Ariane rocket on the morning of December 25 was flawless; so seamless that the engineers said it saved enough maneuvering fuel to significantly extend the mission’s estimated 10-year lifespan. But the telescope must complete a one-month trip to a point at an altitude of one million miles, called L2, far beyond the orbit of the Moon, where the gravitational fields of the Earth and the sun combine to create the conditions for a stable orbit around the sun.

With a 21-foot-wide primary mirror, Webb was too large to fit in a rocket, and so the mirror was made in 18 gold-plated hexagons folded together that were supposed to snap into place while the telescope was in space.

Another challenge was that telescope instruments had to be sensitive to infrared, or “heat radiation,” a form of electromagnetic radiation invisible to the human eye. Due to the expansion of the universe, the farthest and oldest galaxies are flying away from us so fast that the visible light from these galaxies is shifted to longer infrared wavelengths. As a result, Webb will see the universe in colors no human eye has ever seen.

But to detect infrared radiation from distant sources, the telescope must be very cold, only a few degrees above zero, so that the telescope itself is not involved.

After years of docking tests on Earth, during Webb’s deployment, or “telescope getting to know you phase,” Bill Ochs, an engineer at the Goddard Space Flight Center and a project in space, revealed little surprises. The telescope manager told reporters on Monday.

Mission managers detected high temperatures in an onboard engine used only in the deployment process, so engineers redirected the telescope on Sunday to shield the device from the sun’s heat. Then, Webb’s solar arrays were readjusted when engineers realized that the telescope had smaller-than-expected power reserves.

One of the riskiest moments came with the successful unveiling of a giant tennis court-sized sunscreen on Tuesday. It’s designed to keep the telescope dark and cool enough so that its own heat doesn’t block the perceived heat from distant stars. The display is made of five layers of Kapton-like plastic, which is just as flimsy as Mylar and occasionally tore during rehearsals of its installation.

Actually, the opening went flawlessly this time.

“It went unbelievably smooth. I feel like we were all shocked that there was no drama,” said Hillary Stock, a sun shield placement specialist at Northrop Grumman, the telescope’s prime contractor.

Then on Thursday, the telescope turned on its secondary mirror, which pointed at 18 hexagons and reflected back to its sensors what the telescope saw.

“We’re about 600,000 miles from Earth and we actually have a telescope,” Mr. Ochs said Thursday in the mission operations control room at the Space Telescope Science Institute in Baltimore.

As the telescope grappled with one task after another, astronomers who had been waiting for this telescope for 25 years began to relax.

“Oddly enough, I don’t feel so anxious anymore, my innate optimism (hello optimism bias and anchoring bias) is fully equipped,” Priyamvada Natarajan, a Yale cosmologist, said in an email.

Two days later, the last mirrors were also locked in place, and the mission control team burst into applause, high fives, and punches.

“How does it feel to make history for everyone?” Dr. Zurbuchen asked the mission managers in Baltimore after the latching was complete. “You just did.”

“NASA is a place where the impossible is possible,” said former senator and astronaut Bill Nelson, who is now NASA’s administrator.

Garth Illingworth of the University of California, Santa Cruz said: “I can’t tell you what an incredible feeling it is to have a full mirror. It’s an astonishing achievement for the JWST Team.”

“NASA and the US can still do great things,” Michael Turner, a senior cosmologist at the Kavli Foundation in Los Angeles, said in an email. “I can’t wait for the first light and then the first science. It will be even better than Ted Lasso for our COVID and enigma spirits.”

“This is a reminder of how successful people can be when they work together,” astrophysicist Chanda Prescod Weinstein of the University of New Hampshire wrote in an email. “I’m definitely excited for the team and really excited for what we’re going to learn about the universe.”

While the telescope is considered fully deployed, there is still a lot to complete before making any astronomical observations. The primary mirror segments are not aligned enough to produce a consistent image, which is part of a process that will take about five months.

“But for sure, light, in principle, can now pass through JWST through objects in the universe and Webb’s instruments – albeit at best as 18 very blurry drops until they’re all set!” said Dr., an astronomer. Illingworth.

By the end of January, the telescope will be in its final orbit at L2. Astronomers will spend the next five months fine-tuning the mirrors to bring them into common focus and starting to test and calibrate their instruments.

Then the real science will begin. Astronomers have said that the first image from the Webb telescope will appear in June, but no one can say.

“I don’t know what the goals will be,” Antonella Nota, deputy director of the European Space Agency, said during a NASA webcast on Saturday. “But I know one thing, they’re going to be absolutely gorgeous.”