NASA’s James Webb Space Telescope will open a new window on the cosmos — if everything goes just right

The successor to the Hubble must evade 344 potential ‘single point failures’ to achieve its ambitious mission

NASA’s long-delayed James Webb Space Telescope, a $10 billion marvel of engineering and scientific ambition, is poised to rocket into deep space this week from a launchpad in French Guiana, on the northeast shoulder of South America. What happens in the following days and weeks will either change our understanding of the universe, or deliver a crushing blow to NASA and the global astronomical community.

The Webb must cruise for 29 days to a unique orbit around the sun that keeps it roughly 1 million miles from Earth, four times the distance to the moon. At launch — scheduled for 7:20 a.m. Saturday, Christmas morning — it will be folded upon itself, a shrouded package inside the cone of the European Space Agency’s Ariane 5 rocket. After it escapes Earth’s gravity, it must begin opening up, blossoming into a functioning telescope.

That starts with the deployment of the solar panels to make the whole thing work. Next comes the unfurling of a tennis-court-size expanse of multilayered foil — the sun shield, akin to a giant umbrella, ideally more reliable than what you would get from a drugstore.

The James Webb Space Telescope will ascend to orbit in the payload section of an Ariane 5 rocket and unfold to its full size once it reaches orbit.

The centerpiece of the telescope is a 21-foot-diameter mirror assembly, nearly three times the size of the mirror aboard the Hubble Space Telescope it’s meant to replace.

Hubble was designed to be delivered to orbit, fully assembled, in the cargo bay of a space shuttle. The assembled Webb telescope would be far too large to be carried by any existing launcher and so must reach space folded.

The Webb telescope’s sensitive instruments must be kept super-cold to function. The telescope is therefore equipped with a large sun shield.

Made of silicon and insulating Kapton foil, it shades the telescope not just from the sun’s heat but from the reflected warmth of the Earth and the moon as well.

The light from distant galaxies will collect in the Webb’s main mirror and then focus on the secondary mirror. The concentrated light will then stream to the telescope’s instrument module to be interpreted.

The processed images will then stream to Earth via the telescope’s Earth-pointed antenna.

Then, the telescope must deploy 18 hexagonal, gold-covered beryllium mirrors, which collectively act as a light bucket 21 feet across, designed to capture ancient light emitted more than 13 billion years ago as the embryonic universe was still learning how to create stars and galaxies.

What could go wrong?

NASA actually has an answer to that question: This mission is vulnerable to, and therefore must avoid, 344 potential “single-point failures,” according to an independent review board.

“If I’m not nervous, I’m not realistic,” said Thomas Zurbuchen, head of science at NASA. “This is a complex mission. There is no way of making this simple.”

The inescapable reality is that the Webb, or the JWST as some prefer to call it, is either going to provide a revolutionary new view of the cosmic firmament or become a very expensive piece of aerospace sculpture a million miles from Earth. There’s not a lot of in-between.

Heidi Hammel, an astronomer who has worked on the Webb for two decades and is guaranteed observing time with it, echoes Zurbuchen’s feelings: “I’m nervous. This is rocket science. We are putting this amazing telescope on top of a really big rocket, and lighting a fuse and sending it into space.”

This is an international endeavor, a partnership among NASA and the space agencies of Europe and Canada. NASA estimates that 10,000 people have worked on the mission, many of them at its Goddard Space Flight Center in Greenbelt, Md. Professional astronomers and amateur space buffs across the planet are emotionally invested in the telescope’s success. The Webb’s scientific potential has made it something more than a NASA project, in the same way the little telescope Galileo employed to discover the moons of Jupiter was more than just an object in Italian history.

NASA is taking no chances with the Webb. It has delayed the launch twice in recent weeks to deal with technical problems. At one point, a huge clamp broke suddenly, shaking the telescope and rattling everyone’s nerves. A close inspection found no sign of damage. Then came a glitch in the communications interface between the launch vehicle and instruments on the ground; a bad cable was deemed at fault and the problem solved.

If something causes a further delay, there will be launch windows every morning, lasting 30 minutes, until Jan. 6, when the moon will cruise into the picture and create a gravitational disruption for a week.

The Webb is nothing if not ambitious. It is an infrared telescope, capturing wavelengths of light that the Hubble Space Telescope can’t see. It is so sensitive it can study the oldest light of the universe, when galaxies were first forming. The ultimate objective is to penetrate the era of first light — a transitional period, less than 300 million years after the big bang, when the expanding, cooling universe was illuminated by the first stars.

Astronomers also want to use the Webb to study the atmospheres of some of the planets detected in recent years around distant stars, including Proxima b, a planet orbiting Proxima Centauri, the star nearest the sun. Those observations could detect the presence of oxygen, methane and other molecules that could be signatures of extraterrestrial life.

And the Webb will look at things closer to home, too. Hammel, the astronomer, plans to use the telescope to examine the Kuiper belt, a region beyond Neptune jammed with cold, icy objects. Pluto is the most famous such object, but the Webb could help bring out of obscurity the dwarf planets Haumea, Makemake, Orcus and Sedna.

This is NASA throwing long. The telescope is not just “a little bit better than Hubble” but rather is “dramatically different,” senior project scientist John C. Mather told The Washington Post in 2018.

Scientific ambitions drove the design of the telescope and pushed the limits of the engineering ingenuity of NASA and its contractors. They needed to make a telescope that could operate far from Earth, in extremely cold temperatures and be completely protected from sunlight. This required a novel design, including the sprawling sun shield.

If certain things go a little wonky in the deployment phase — if the sun shield doesn’t open perfectly, for example — NASA has a couple of contingency maneuvers. It can fire thrusters on the spacecraft to jostle everything. That’s known as a shimmy. NASA can also put the telescope (or more precisely, the “observatory,” which includes the telescope, instruments and spacecraft hardware) into a spin. Or it can temporarily expose alternate sides to the heat from the sun to see if that helps.

“We can twirl it. We can shake it. We can make it warm and cold,” said Begoña Vila, a NASA systems engineer who has spent much of the fall in French Guiana, at the European Space Agency’s spaceport near the city of Kourou, overseeing final preparations for launch.

Beyond the shimmying and twirling, the observatory is not fixable. There is nothing that can be yanked out and replaced with something new.

The only exception is fuel. The observatory uses fuel to maneuver and to point at interesting targets. It has enough fuel to operate for roughly 10 years. In theory, it could be refueled with a robotic spacecraft, which would extend the mission.

Location matters, too. The Hubble was put into low Earth orbit, via the cargo bay of the space shuttle, and is roughly 340 miles above the surface. Not only is it close, it was also designed to be repaired if necessary. Astronauts have done that five times — rocketing to the telescope, swapping out instruments, installing new gyroscopes and keeping it operational for three decades and counting.

For the Webb, repair is not an option. Even if the instruments were designed to be replaced when they got old, who would perform that task? The Webb will orbit the sun near L2, or Lagrange point 2, a gravitationally stable solar orbit that’s roughly 1 million miles from Earth on the opposite side of our planet from the sun.

There is no spaceship that can send astronauts to such a distant place and bring them safely home. To dream up such a mission would be prohibitively costly and risky. It would make more sense to build and launch a new telescope.

‘As good as it gets’

Among those watching the launch will be Garth Illingworth, 74, who has been pondering this telescope, and helping guide it to fruition, for 35 years. He was among a small group of astronomers who, in the second half of the 1980s, began thinking about a successor to the Hubble — even before the Hubble’s 1990 launch.

“We’re in a business where you can’t guarantee perfection and success in space,” Illingworth, an astronomer at the University of California at Santa Cruz, said in a recent interview. But he’s optimistic about the Webb: “I think we have a program here that’s as good as it gets.”

From the start, the people dreaming up what they called the Next Generation Space Telescope wanted something with a mirror larger than the roughly eight-foot-diameter mirror on the Hubble. They also wanted to observe the universe in infrared wavelengths. The Hubble operates primarily at the optical wavelengths that we humans refer to (anthropocentrically) as “visible light.”

Infrared wavelengths have many advantages. Such light can penetrate the dust that pollutes the cosmos. An infrared telescope can look inside a pillar of dust and see stars incubating. And the oldest light in the universe is entirely in the infrared portion of the spectrum: The light has been red-shifted as space itself has expanded, stretching out those wavelengths during the last 13 billion years.

The Webb will do its own version of the Ultra Deep Field, a celebrated observation by the Hubble, in which for two weeks it pointed at a tiny, seemingly empty and unremarkable point in space, discovering in that darkness a swarm of incredibly distant galaxies. The Webb, which is about 100 times as powerful as the Hubble, can perform the same kind of observation in less than a day, according to NASA.

“The whole point of this is to see the unseen universe,” said John M. Grunsfeld, former head of science at NASA and an astronaut who made three repair missions to the Hubble aboard the space shuttle. “James Webb will be able to see phenomena that Hubble can’t see, that ground-based telescopes can’t see. What are we going to discover that we had no idea was there? That’s the real potential of the James Webb Space Telescope.”

Infrared astronomy requires a very cold environment. A mountaintop is good, but space is better, if you can figure out how to block the sun and keep the mirrors cold. Any warm object (a person, a computer, a fancy astronomical instrument) radiates infrared light, which is why soldiers carry night-vision goggles to see the enemy in the dark.

For the Webb to detect at the desired level, it has to be shielded not only from the sun but from the radiation of its own instruments tucked behind the mirrors. Concerns about heat, and the light pollution it would generate, are one reason the Webb’s engineers — after many years of debate — decided against installing cameras. The hardware required for cameras would also have added complexity to an already complex system and increased the number of things that could go wrong.

Along its journey from inspiration to launchpad, the telescope got a new name. In 2002, then-NASA administrator Sean O’Keefe named the telescope after James Webb, one of his predecessors in the top job at the agency. Webb ran NASA in the 1960s, during the space race, and insisted on making science part of the agency’s portfolio.

But telescopes traditionally have been named after scientists like Hubble. NASA is developing another space telescope named for the pioneering astronomer Nancy Grace Roman, the first female executive at NASA and first chief of astronomy.

O’Keefe’s unilateral decision to honor Webb upset some astronomers at the time, but it did not erupt into a full-blown controversy until recently, amid accusations that Webb, both as a State Department official in the 1950s and later as NASA administrator, was complicit in the “Lavender Scare” — a period when government employees suspected of homosexuality were deemed security threats and were terminated. A group of astronomers published an article in Scientific American saying that Webb’s legacy “at best is complicated and at worst reflects complicity in homophobic discrimination in the federal government.”

But after a review by the agency’s history office, NASA Administrator Bill Nelson said the agency found no evidence warranting a name change for the telescope.

The cost of the Webb has also been hugely controversial. When envisioned in the 1990s it was supposed to cost on the order of $500 million. By the early 2000s, the price tag was in the more realistic range of $4 billion. But the project kept getting delayed. Launch was supposed to happen in 2007, then 2011, then 2013, then 2018. The telescope at one point narrowly survived an attempt in Congress to kill it outright.

The mission is so expensive — the figure $9.7 billion is often mentioned, when all the mission costs are factored in — that it has drained money from other NASA science missions. In 2010 the journal Nature ran a story describing the Webb as “the telescope that ate astronomy.”

Weddings, funerals and a telescope

The telescope has been tested in cold chambers and put through shaking tests. But there are no tests that can mimic precisely the conditions of space, which, contrary to appearance, is not empty but rather is saturated with cosmic radiation and micrometeorites, and is basically a really harsh place to do delicate science.

“We’re taking an incredibly demanding piece of equipment, shaking the hell out of it on a rocket, subjecting it to huge amounts of noise and dumping it into a really rough environment,” Illingworth said. “That’s why it costs $10 billion and took 20 years.”

Many of the potential failures involve the sun shield — a kind of contraption that has never been attempted. The Webb’s instruments are designed in such a way that they do their job only if the mirrors remain extremely cold — less than minus-370 degrees Fahrenheit. The sun shield was designed to be sufficiently robust that it has some margin of error — a little hitch here, a tear there won’t keep the Webb from operating. But it can’t get tangled in a knot.

The sun is a fusion reactor about 865,000 miles in diameter and will be radiating directly upon the Webb. The first layer of the sun shield, blasted by sunlight, will be slightly hotter than the boiling temperature of water. But there are five layers, with gaps in between. The system is designed to ratchet down the heat, from very hot to very cold.

Mike Menzel, the NASA engineer who will supervise every element of the telescope’s deployment in space, notes that hundreds of mechanical elements will pull the sun shield into place. The challenge for the engineers is that this process isn’t like deploying a rigid beam. The Kapton foil of the sun shield is flexible. It’s impossible to know precisely how it will behave.

Menzel will be watching the launch from the Space Telescope Science Institute in Baltimore — the facility on the edge of Johns Hopkins University that also operates the Hubble. He does not describe himself as “nervous.” He prefers “focused.”

“Arguably, it’s one of the most complex missions NASA’s ever done,” Menzel said.

It’s also one of the most protracted. Menzel has been working on the Webb for 24 years. There’s a whole community of people who have put in that kind of generational labor on this telescope.

“We’ve watched our kids grow up, we’ve gone to weddings, we’ve gone to funerals. After 24 years, it would not be incorrect to say we’re an extended family,” Menzel said.

How does a NASA engineer, or scientist, or administrator, or even some astronomer on the far side of the world who is invested in this mission get through the gut-churning anxieties of launch and deployment? By trusting the process.

Everyone has been asking Mather, the senior project scientist, if he’s worried in advance of the launch, according to a NASA blog devoted to the Webb.

“My opinion has no effect on the hardware, but we did what it takes to win,” is Mather’s response. “We sketched, we argued, we worried, we analyzed, we made a plan, we wrote down everything, we made checklists, we built the parts, we put them together, we tested as though our lives depend on it.”

NASA has a track record of achieving the nearly impossible with its space science missions. Early this year, the agency landed the Perseverance rover on Mars, a feat that involved what is known as “seven minutes of terror” — a period when the spacecraft had to penetrate the Martian atmosphere, slow down, deploy parachutes, fire thrusters and deposit the rover softly, upright, in precisely the right location.

But deploying the Webb and making it operational is perhaps a greater challenge.

“We have two months of terror, not seven minutes,” said Grunsfeld, the former NASA science administrator.

Hammel, the astronomer, compares this moment to being in an orchestra in the seconds before a performance.

“We’re right now at the moment where we’re all assembled onstage, the conductor has raised the baton,” she said. “We’ve done all the planning we can do, we’ve done all the testing we can do. And we’re ready to play the music.”


A previous version of this article incorrectly said the sun is 865 million miles in diameter. It is about 865,000 miles in diameter. This version has been corrected.

About this story

Graphics by William Neff. Photography by Katherine Frey. Editing by Stephen Smith. Graphics editing by Simon Ducroquet. Design by Gabriel Florit. Copy editing by Jennifer Morehead.

Joel Achenbach covers science and politics for the National desk. He has been a staff writer for The Post since 1990.