Astronomers are breathing again.
Two weeks ago, the most powerful space observatory ever built roared into the sky, carrying the hopes and dreams of a generation of astronomy in a tightly wrapped package of mirrors, wires, motors, cables and thin plastic on a pillar of smoke and fire.
The final step of the observatory was completed by unfolding the last section of its mirrors at 10:30 a.m. Engineers sent commands to put the mirrors in place, which meant that it was fully deployed, according to NASA.
The space agency called it the most recent of a series of delicate maneuvers with what it called The telescope is almost ready for use, but there are still tense moments to come.
Thomas Zurbuchen, NASA's science chief, said he was emotional about the telescope's mirrors finally clicking into place. The beautiful pattern in the sky is almost complete.
25 years and $10 billion is the amount of time it will take for the James Webb Space Telescope to be built. It is three times the size of the Hubble Space Telescope and designed to see further into the past than its celebrated predecessor in order to study the first stars and galaxies to turn on in the dawn of time.
The engineers said that the launch on the Ariane rocket saved enough maneuvering fuel to extend the mission for at least 10 years. The telescope needs to travel a million miles beyond the moon to a spot called L2 where the Earth and sun can mix to produce the conditions for a stable solar system.
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The telescope separated from the Ariane 5 rocket and flew into space.
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The launch, from Europe's spaceport in Kourou, French Guiana, went so well that it saved enough maneuvering fuel to significantly extend the mission's lifetime.
The telescope was too big to fit in a rocket and so the mirror was made in segments, 18 gold-plated hexagons folded together, that would have to pop into position once the telescope was in space.
The telescope had to be sensitive to the form of radiation invisible to the human eye. Because of the expansion of the universe, the most distant and earliest galaxies are flying away from us so fast that visible light from them shifts into the longer wavelength. The universe will be seen in colors no human eye has ever seen.
The telescope has to be very cold, just a few degrees above zero, so that it doesn't interfere with the work.
After years of deployment tests on Earth, small surprises in space have popped up during the "getting-to-know-you phase" of the telescope.
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Engineers celebrated at the Space Telescope Science Institute in Baltimore after the mirrors finished unfolding.
Engineers repointed the telescope on Sunday to protect it from the sun's heat, after mission managers detected high temperatures on an onboard motor used only in the deployment process. The telescope had smaller power reserves than expected and the solar array was adjusted.
On Tuesday, there was a successful unfolding of a giant sunscreen, the size of a tennis court. It was designed to keep the telescope in the dark and cold so that it wouldn't be able to see the heat from distant stars. The screen is made of five layers of plastic called Kapton, which is similar to Mylar, and which had occasionally ripped during rehearsals.
The unfolding went perfectly this time.
It went well. Hillary Stock, a sun shield deployment specialist at the telescope's primary contractor, said she was shocked that there had been no drama.
On Thursday, the telescope's secondary mirror reflected what the telescope saw back to it.
The Space Telescope Science Institute in Baltimore has a telescope that is 600,000 miles from Earth.
Astronomers who had been waiting 25 years for this telescope began to relax as the telescope finished one chore after another.
I don't feel so anxious anymore, my inherent optimism is in full gear, wrote a cosmologist from Yale.
The team at mission control broke into applause and high fives after the last mirrors were locked in place.
How do you feel to make history? After the latched was complete, Dr. Zurbuchen asked the mission's managers in Baltimore. You did it.
Bill Nelson, the former senator and NASA administrator, said that NASA is a place where the impossible becomes possible.
I can't describe how amazing it is to have a full mirror. It is an amazing achievement for the J.W.S.T. Team.
Michael Turner wrote in an email that NASA and the U.S. can still do great things. I cannot wait for the first light and the first science. It will be better for our spirits than Ted Lasso.
The University of New Hampshire astronomer wrote in an email, "This is such a reminder of how successful people can be when they work together." She said she was excited for what the team would learn about the universe.
The telescope is fully deployed, but much remains to be done. It will take about five months to align its primary mirror segments, part of a process that will take a long time.
Light can now go through objects in the universe and into the instruments of J.W.S.T., but at the best it will be 18 fuzzy blobs.
The telescope will be in its final position at L2 by the end of January. The next five months will be spent tweaking the mirrors to bring them into focus and begin to calibrate their instruments.
Real science will begin once that happens. The first picture from the telescope will be visible in June, but nobody will say what it is.
The associate director of the European Space Agency said during the NASA webcast on Saturday that she didn't know what the targets would be. They will be absolutely spectacular.
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The sun shield, made of five delicate layers of Kapton, was being tested.
