Imagine a device that helps us determine the birth of the modern universe and gives us a glimpse at an extraterrestrial future.
When the James Webb Space Telescope launches in October 2018, it will—if all goes well—usher in a new phase of human understanding of the universe. Continuing to probe past the limitations of the Hubble Space Telescope, it will enable astronomers to determine the point at which visible light formed some 13.8 billion years ago, and is sensitive enough to detect smaller exoplanets hospitable enough for life.
In praise of this engineering feat, the Discovery Channel will air the documentary Telescope tomorrow, showcasing the challenges of such an undertaking as well as how the telescope's evolution over the centuries constantly reshaped man’s relationship to the cosmos. Twenty years in development, the $8 billion JWST employed the collective efforts of more than 1,000 scientists and engineers from 24 countries in three space agencies—NASA, the Canadian Space Agency, and the European Space Agency. JWST is being built in several facilities across the U.S., with the focus of activities at Northrop Grumman Space Park in Redondo Beach, Calif., and the Goddard Space Flight Center in Greenbelt, Md.
"By making it a human story and following the people building it, they not only describe it, but we’re watching it unfold in real time and sharing in the edge-of-your seat experience, because they also don’t know exactly what’s going to happen," says Nathaniel Kahn, Telescope’s Oscar-nominated director. "Follow the people and get to the technology that way, because, in the end, this is an enormous human endeavor. It’s at the absolute limit of what we are capable of right now."
One of cosmology's biggest mysteries is the point at which the universe transitioned from the "early universe," a state of dark plasma, to the formation of light, stars, and galaxies. "We don't know when those first stars and galaxies turned on, and those are the seeds of everything that we have today, like heavy metals and dust," says Jason Kalirai, an astrophysicist with the Space Telescope Science Institute in Baltimore, the operations center for the Hubble and JWST. "The James Webb Telescope is designed to witness the point in cosmic history when the universe went through this transition. It’s being designed to hit that sweet spot a couple of hundred million years after the universe formed."
In addition to probing the farthest reaches of the universe, the instruments will be able to detect the atmospheric compositions of smaller rocky exoplanets orbiting other stars to gauge whether they might sustain life. Toward the end of its life, our sun will balloon to engulf the nearer planets before collapsing, so the human race will need to leave Earth and the solar system at some point if it is to survive. "It brings us one step closer in finding other Earth-like worlds in detail," says Kalirai.
The Hubble, which orbits 343 to 345 miles above the Earth, has a 7.9-foot foot mirror and instruments that collect data in the near-infrared, visible, and near-ultraviolet spectra. By comparison, the JWST has a roughly 21-foot mirror and deeper infrared sensors, and will reside one million miles from Earth.
When you measure light in a certain wavelength here, you can calibrate how far away your object is. Infrared enables us to see farther into the universe (thus, farther back in time), because the universe is expanding, creating a redshift effect. Objects moving away from us emit longer electromagnetic wavelengths that appear in the red and infrared part of the spectrum. The JWST can peer farther into the infrared spectrum than Hubble, thus sensing farther objects.
Since infrared cameras are more sensitive to radiation (i.e., light, heat), the telescope has to be far enough away from the sun and its reflected light on the Earth and moon, and have a shield that blocks the sun’s rays. But if it's too far away, its orbit would lag behind Earth’s, interfering with communication. It just so happens, there is a point in space called the second Lagrangian point, or L2, discovered by 18th century Italian astronomer Joseph-Louis Lagrange, that is far enough away from the Earth’s reflected light but where the combined gravitational forces of the Earth and sun enable an object there to rotate the sun at the same pace as Earth. That’s where the JWST will live. The downside is that if the JWST needs repairs, like the Hubble did, we’re SOL.
Now comes the hard part . . .
When engineers began considering the JWST in 1996, 10 technologies needed to achieve it didn’t exist. "They included a giant mirror that had to be broken up into 18 individual parts but work as a unit," says Kalirai. "The entire telescope had to be folded up to fit inside a rocket that launches it into space, because it’s bigger than the fairing of the rocket, and programmed to unfold to its full size at its destination, which takes a month to reach. It includes a tennis-court sized sunshield needed to cool the temperature down and block the radiation from the sun that would otherwise heat up the telescope and new generation detectors that are more sensitive than other instruments we’ve built before in astronomy."
"An enormous amount of computer modeling went into exactly how these five membranes will hold up," says Kahn. "It’s one thing to fold up one membrane and make sure it’s being held down during a launch. But to do that with five layers, it has to have pins going through all of those layers to anchor them so they don’t loosen or rip. You can’t have a hole going through all five, so that any photon of light from the sun will get through them all. So the complexity of modeling just the holes and where the holes go took an entire department to figure that stuff out."
Adds Kalirai: "And you also have to model and test it on the ground, where there’s gravity. But when you launch the telescope in space, there’s no gravity, so you have to account for that in the deployments."
The team had to come up with ways to keep the weight down to a svelte 6.6 tons. Instead of much heavier glass, the mirror is made of beryllium, a rare metal that is stronger than steel but lighter than aluminum, and coated in a thin layer of gold, which reflects 98 percent of infrared light.
"What we’re living through now is, every change you make, every problem, you’re always doing the math, asking, 'What’s this doing to the mass?'" says Blake Bullock, Northrop Grumman special assignment director. "You have a very hard limit. You go over your mass, you’re not getting off the Earth. So we’re constantly doing those trades. What’s exciting is you don’t have the answer in the back of the book. You have to invent it."
The JWST mirror will collect the photons of light from distant objects and focus them onto the camera detector, which will digitize the information and beam it to Earth. All the images will be archived in the Space Telescope Science Institute for the science investigation team who wrote the proposal for those images.
The science community will compete for telescope time to look at ojects—whether it’s looking for exoplanets, first light in the universe, distant stars and galaxies, characterizing asteroids, or close-ups of our planets. A committee of astronomers will pick the best science proposals and build those into the telescope’s schedule.
Even before the JWST launches, next generation telescopes are already in the works to determine the level of life on Earth-sized exoplanets. "You can take a rock and evolve it through natural geological processes to create an atmosphere, but there are certain combinations of elements you cannot create if you don't have life on that planet," says Kalirai. "A future goal is to detect biosignatures, like the ratio of oxygen and ozone to methane, to validate whether the planet has life. Oxygen and ozone lines peak in the ultraviolet part of the spectrum, so we'll optimize that telescope for ultraviolet radiation."