Watch the launch of the James Webb Space Telescope—the most powerful space telescope ever made.

This mission is scheduled to lift off at 7:20 a.m. EST (12:20 UTC),

Dec. 25, 2021

NASA’s long-delayed James Webb Space Telescope, a $10 billion marvel of engineering and scientific ambition, is finally poised to rocket into deep space 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, 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.

An Artist Rendering of the James Webb Telescope

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. NASA plans to launch at 7:20 a.m. Saturday — Christmas morning. 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 Flight Control Room at the Space Telescope Science Institute in Baltimore 

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.

Telescope Backplane Pathfinder

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.

Comparison of the NASA ESA Hubble Space Telescope and the NASA ESACSA James Webb Space

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.

James Webb Space Telescope Secondary Mirror

‘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.”