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ILLUSTRATION BY JAMES VAUGHAN

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Portal to the Universe

Engineers are building a powerful telescope that could launch a new era in astronomy

ESSENTIAL QUESTION: What challenges might be involved in building a giant space telescope?

Nearly three decades ago, NASA began working on plans for a massive space telescope that would provide views of our universe unlike anything ever seen before. Now, the James Webb Space Telescope’s construction is nearing completion. When launched in 2021, “it will be the largest telescope ever sent into space,” says Matt Mountain, president of the Association of Universities for Research in Astronomy and a scientist working on the telescope.

Webb’s developers have faced many challenges designing and testing the gargantuan telescope—including figuring out how to get it into space. The two-story observatory is too big to fit on any rocket, so it needs to be launched folded up. As it flies toward its destination, about 1.5 million kilometers (1 million miles) away, it will unfold in an intricate series of steps. 

Once in position, Webb will orbit, or circle, the sun in lockstep with Earth. If the mission succeeds, scientists will be rewarded with an unprecedented look at galaxies, planets orbiting distant stars, and our own solar system.

NASA started plans for a huge space telescope almost three decades ago. It would provide views of our universe like nothing ever seen before. Now the James Webb Space Telescope is almost finished. It will launch in 2021, and “it will be the largest telescope ever sent into space,” says Matt Mountain. He’s president of the Association of Universities for Research in Astronomy and a scientist working on the telescope.

Webb’s developers have faced many challenges as they’ve designed and tested the giant telescope. One was finding a way to get it into space. The two-story observatory is too big to fit on any rocket, so it must be folded up to launch. It will fly toward its target, about 1.5 million kilometers (1 million miles) away. Along the way, it will unfold in a complex series of steps.

When it’s in place, Webb will orbit, or circle, the sun at the same rate as Earth. If the mission succeeds, scientists will get a brand-new look at galaxies, planets orbiting far-off stars, and our own solar system.

BEYOND HUBBLE

Scientists started drawing up ideas for the Webb telescope back in 1989, a year before the launch of the Hubble Space Telescope. Hubble was the first major optical telescope in space. Its large mirror gathers and focuses visible light—the kind our eyes can see—onto its cameras.

Earth’s atmosphere can distort a telescope’s view of the cosmos. So Hubble orbits high above it. This allows the telescope to take startlingly clear pictures of space. Its images have revolutionized the field of astronomy (see Hubble’s Greatest Hits). But scientists knew someday they’d need an even more powerful space telescope to see more of our universe.

The light from the farthest and oldest galaxies visible to Hubble took about 13 billion years to reach Earth. Astronomers want to see even more distant objects, looking further back in time—nearly all the way back to the start of the universe, which is estimated to be about 13.8 billion years old. “Hubble can see back to the universe’s teenage years,” says Stefanie Milam, a project scientist for the Webb telescope at NASA’s Goddard Space Flight Center in Maryland. “We want to see its infancy.”

Scientists started drawing up ideas for the Webb telescope in 1989. That was a year before the Hubble Space Telescope launched. Hubble was the first major optical telescope in space. Its large mirror gathers and focuses visible light onto its cameras. That’s the kind of light our eyes can see.

Earth’s atmosphere can distort a telescope’s view of the universe. So Hubble orbits high above it. That way, the telescope can take surprisingly clear pictures of space. Its images have changed the field of astronomy (see Hubble’s Greatest Hits). But scientists wanted to see more of our universe. They knew they’d need an even more powerful space telescope someday.

Hubble can see very old, faraway galaxies. Their light took about 13 billion years to reach Earth. Astronomers want to see objects even farther away. That way, they could look further back in time, almost all the way back to the universe’s beginning. They think that was about 13.8 billion years ago. “Hubble can see back to the universe’s teenage years,” says Stefanie Milam, a project scientist for the Webb telescope at NASA’s Goddard Space Flight Center in Maryland. “We want to see its infancy.” 

NEXT-GEN TELESCOPE

Hubble’s view is limited because the universe is expanding. As ancient galaxies move away from us, their visible light shifts into infrared, a type of light detectable as heat.

Infrared light is invisible to the human eye—and to Hubble. Webb will specialize in detecting infrared, allowing it to see back to the dawn of the universe. Light from distant galaxies is very faint, so Webb needs a giant mirror to gather as much of it as possible. Its 6.5 meter (21 foot)-wide mirror is two-and-a-half times the diameter of Hubble’s (see Anatomy of a Space Telescope). To allow the mirror to collapse to a more compact size for launch, engineers constructed it in 18 hexagonal segments.

Heat interferes with Webb’s ability to detect infrared light. So engineers also had to find a way to keep the telescope cool. They created a shade that unfolds to the size of a tennis court. It will block sunlight to help keep the telescope at a frigid -240ºC (-400ºF).

Hubble can’t see everything because the universe is expanding. As ancient galaxies move away from us, their visible light shifts into infrared. This type of light is detected as heat.

The human eye can’t see infrared light. Hubble can’t either. Webb will focus on detecting infrared, so it can see back to the start of the universe. Light from far-off galaxies is very weak, so Webb needs a giant mirror to gather as much of it as possible. Its mirror is 6.5 meters (21 feet) wide. That’s two-and-a-half times as wide as Hubble’s (see Anatomy of a Space Telescope). The mirror must fold to a smaller size for launch, so engineers built it in 18 six-sided parts.

Heat makes it harder for Webb to detect infrared light. So engineers also had to find a way to keep the telescope cool. They made a shade that unfolds to the size of a tennis court. It will block sunlight to help keep the telescope at a freezing -240ºC (-400ºF). 

PREPARE FOR LAUNCH

The first step was to construct Webb’s mirror and instruments. These components came to Goddard from all over the world. Workers then assembled them and put the observatory through initial tests. They shook it on a vibrating table and blasted it with earsplitting noise from giant speakers, simulating the violent motions and sounds of liftoff.

Next, the telescope was flown in a cargo plane to NASA’s Johnson Space Center in Houston, Texas. Engineers there placed the components in the world’s largest ultra-cold vacuum chamber—a room from which the air can be removed. In conditions simulating the chill and darkness of space, they made sure the telescope focused light as expected. Hubble’s developers had skipped this test, which turned out to be a problem: A flaw in the mirror made early images blurry. Astronauts fixed Hubble while it was in orbit around Earth. But Webb will be beyond the reach of any repair mission. The $9.7 billion telescope must work perfectly on the first try.

The first step was to build Webb’s mirror and instruments. These parts came to Goddard from around the world. Then workers put them together and did the first tests on the observatory. They shook it on a vibrating table and blasted it with booming noise from giant speakers. This imitated the violent movements and sounds of liftoff.

Next, the telescope traveled by cargo plane to NASA’s Johnson Space Center in Houston, Texas. There, engineers placed the parts in the world’s largest ultra-cold vacuum chamber. Air can be removed from such a room. The conditions imitated the chill and darkness of space. The test made sure the telescope focused light as it should. Hubble’s developers had skipped this test, and that was a problem. A flaw in the mirror made early images blurry. Astronauts fixed Hubble while it was in orbit around Earth. But Webb will be too far away for any repair mission. The $9.7 billion telescope must work perfectly on the first try. 

LAURA BETZ/NASA VIA AP PHOTO

After Houston, Webb’s mirror and instruments made one more stop. They traveled to Northrop Grumman Aerospace Systems in Redondo Beach, California, where engineers are currently connecting the telescope’s remaining parts. These include its gigantic shade and its base, which contains the power and communications systems.

The new components are also undergoing testing, including practicing the deployment of the sunshade. But “there’s no test chamber on Earth that doesn’t have gravity,” says Milam, “and the shade will unfold differently in a weightless environment.” So during unfolding trials, teams of engineers support the shade’s weight. Luckily, she says, almost all of the steps involved in unfolding the telescope after launch have backups in case something fails to open properly.

Webb’s mirror and instruments made one more stop after Houston. They traveled to Northrop Grumman Aerospace Systems in Redondo Beach, California. There, engineers are connecting the telescope’s other parts. These include its huge shade and its base, which holds the power and communications systems.

The new parts are also going through tests, including practicing the opening of the sunshade. But “there’s no test chamber on Earth that doesn’t have gravity,” says Milam, “and the shade will unfold differently in a weightless environment.” So teams of engineers support the shade’s weight during unfolding tests. Many steps are involved in unfolding the telescope after launch. Luckily, Milam says, almost all of them have backups in case something doesn’t open properly. 

CHRIS GUNN/NASA

COUNTDOWN TO LIFTOFF

Eventually, the finished Webb telescope will sail to French Guiana in South America for launch. Once the telescope is traveling through space, the communication antenna and solar panels that provide power will deploy automatically. Mission staff in Baltimore, Maryland, will then proceed through each carefully choreographed step of unfolding the mirror, moving its segments into position, and opening the shade.

After Webb has expanded to its full glory, they will switch on and test its instruments. Once it’s operational, astronomers can begin focusing the awesome observatory on objects in space. Among Webb’s first targets: rocky exoplanets outside our solar system. “I’m interested in whether we’ll find liquid water on a planet around another star,” says Mountain. “That could put us on the path to finding life.”

Webb’s most exciting discoveries might end up being things no one ever predicted, says Milam. “We launched Hubble not knowing so much of what it was going to find,” she says. “I think Webb will be the same. We’re about to enter a whole new era.”

When it’s ready, the Webb telescope will sail to French Guiana in South America for launch. After the telescope is in space, the communication antenna will open by itself. So will solar panels that provide power. Then mission staff in Baltimore, Maryland, will go through a series of carefully planned steps. They’ll unfold the mirror, move its segments into position, and open the shade.

After Webb has opened completely, they’ll switch on and test its instruments. When the enormous observatory is ready, astronomers can begin focusing it on objects in space. Some of Webb’s first targets are rocky exoplanets outside our solar system. “I’m interested in whether we’ll find liquid water on a planet around another star,” says Mountain. “That could put us on the path to finding life.”

Webb’s most exciting discoveries might end up being things no one ever expected, says Milam. “We launched Hubble not knowing so much of what it was going to find,” she says. “I think Webb will be the same. We’re about to enter a whole new era.”    

CORE QUESTION: How did engineers address the criteria and constraints involved in developing the Webb telescope?

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