French Guiana does not often get the chance to be the center of the world, to say nothing of the universe—or at least humanity’s understanding of it. But on Dec. 25, at 7:20 AM ET, the small, forested country on the forehead of South America became the center of things indeed, when a European Space Agency Ariane V rocket lifted off with a payload that represents $9.5 billion worth of hardware and 25 years of work, and on which the next generation of research into the origin of the cosmos depends. The spacecraft entrusted to the Ariane 5 was the James Webb Space Telescope (JWST), NASA’s—and the entire astronomical community’s—follow-on to the aging Hubble Space Telescope, which has widely been considered the greatest space observatory ever built—until now, at least.
The Hubble’s work is most powerfully captured in the vast album of dazzling photos it’s sent back in the 31 years it has been flying. But those pictures also reveal its sole shortcoming: Hubble sees in the ultraviolet and visible spectrums, allowing it to peer approximately 13.4 billion years back in time—or just 400 million years after the Big Bang (because light from the cosmos can take a heck of a long time to reach us, looking up at the night sky is effectively looking into the past). A lot happened in those missing early years—galaxies began to form, stars began to flicker on—but the expanding universe and the great distance the light from that epoch is traveling to reach us cause its wavelength to stretch from the visible spectrum and into the infrared, to which Hubble and human eyes are blind.
The infrared, however, is exactly the band in which the Webb was designed to see, pushing its sensitivity another 200 million years back, to 13.6 billion years ago, or just 200 million years after the Big Bang. That comparatively small improvement is enormously significant, opening the door to the universe’s babyhood—a period in which it matured spectacularly quickly.
“The difference between what Hubble and Webb will see is not like comparing someone who’s 70 years old to somebody who’s 71 years old,” says Scott Friedman, commissioning scientist for the Webb team. “It’s like comparing a baby who’s one day told to a baby who’s one year old, and that’s a huge difference.”
Webb had to overcome a lot of hurdles to get as far as it’s come. First proposed in 1995 with a predicted price tag of $500 million and a hoped-for launch date of 2007, it has repeatedly blown past budget limits and deadlines. The telescope had a near-death experience in 2012 when Congress threatened to pull funding, but the last-minute delivery of the mirror persuaded lawmakers to stay their hand, and Webb survived. There have been some last-minute delays, too—it was previously set to launch Dec. 22—and takeoff could be pushed back further still.
Before the telescope can begin its work, it will face technological hurdles, too. Unlike the Hubble, which flies in a snug Earth orbit barely 545 km (338 mi.) above the ground, Webb will have to travel 1.6 million km (one million mi.) from the planet, where it will station-keep in what’s known as a Lagrange point—a spot in space where the gravity of the Earth and the sun cancel each other out, allowing objects to circle around the invisible point as if they were orbiting a solid body like a planet. Also unlike the Hubble, which was small enough to fit comfortably inside a space shuttle’s cargo bay, the Webb is far too big to fit fully extended inside even the biggest rocket now flying, and will thus have to be folded multiple times, loaded aboard the Ariane and then unfold once in space.
“It’s like an origami object,” said Alphonso Stewart, the Webb deployment systems team leader, during a November NASA press conference. “Only we’ll do origami in reverse.”
Very much like the Hubble, however, the Webb promises to make astronomical history, kicking open the door to portions of the cosmos that until now have remained unseen, and revealing secrets about the birth of the universe that were once not just unknown, but unknowable. “There are all of these things that lurk out there that we haven’t even imagined,” says Klaus Pontoppidan, a Webb project scientist. “That is one of the things that makes it really, really exciting.”
It’s quiet now in mission control at the Space Telescope Science Institute on the Baltimore campus of Johns Hopkins University. As mission controls go, this is a small one—a dozen seats at a dozen consoles in a glassed-in room for the lead controllers, and at least an equal number in an auxiliary room. But on Dec. 24, the day before launch, the room filled with astronomers and engineers preparing for the 12-hour shifts they’ll be working once the Webb goes into operation. The first and biggest job they’ll have to do is the one of unfolding. Never mind simple reverse origami, this is a process that will take a full six months before the telescope is at last in place, deployed and ready to go about its work.
The JWST is especially complex due to the designs required for it to peer into the infrared. It’s easy to tell at a glance what the Hubble does, simply because it looks like a telescope—a metallic tube with a wide aperture at one end to admit light and a main mirror inside to gather up inflowing photons. The traditional tube shape serves as a shield, blocking out extraneous light that would flood and obscure the target image. The Webb is a different telescopic beast entirely. Observing in the infrared, it needs protection not from light but heat, which would ruin its vision as surely as light would Hubble’s. For that reason, the JWST has no housing at all. Its mirror flies open in space, atop a sun shield that protects it from solar radiation and the hundreds of degrees of heat to which the hardware would otherwise be exposed.
All by itself, the mirror is an extraordinary piece of engineering. Hubble’s mirror, which measures 2.4 m (7.9 ft) across, is a single, circular piece of highly milled and polished glass that, like the telescope itself, looks exactly like what it is. Webb’s is much more complex—a far larger 6.5 m (21.3 ft) across, and assembled from 18 separate hexagonal segments. The segments are made of beryllium—a metal that functions like glass but can be more highly shaped and polished—and covered in a thin layer of gold for reflectivity. NASA is fond of pointing out that while the gold covers the entire 25 sq. m (269 sq. ft) of the mirror, it is applied in such a thin layer that if it were peeled off and tamped down, it would be little bigger than a golf ball. The beryllium, meanwhile, is polished so smoothly that if it were expanded to the size of the United States, its biggest imperfection would be just a meter high. Each of the mirror segments can move in seven different directions—up, down, left, right, in, out and a diagonal tilt—to focus and refine the infrared energy being captured across the entire mirror surface.
“We have such a large primary mirror because what we want to do is look deep into the universe, so you need a bigger photon bucket,” says NASA associate administrator Thomas Zurbuchen.
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That bucket has to stay cold—one reason the telescope is not in Earth orbit, where it would have to contend with the constant day-night-hot-cold cycle satellites experience as they circle the globe. But the sun still shines at the Lagrange points, and that’s where the Webb’s sunshield comes in. Roughly diamond shaped and as big as a tennis court, the shield is made of five layers of kapton, a foil-like film as thin as a human hair. On the outer layer, the side exposed directly to the sun, the temperature will be about 110º C (230º F, 383 Kelvin). On the inner layer, closest to the mirror, it will be -237º C (-394º F, 36 Kelvin).
“[The sunshield] is going to be irradiated by 200,000 watts of solar radiation and it should allow only about .02 watts through,” said Mike Menzel, the Webb team’s systems engineer, at the NASA press conference. “So if we’re suntan lotion, that would have an SPF of 10 million.” And both the mirror and the sunshield—plus the power-providing solar panel, the onboard computer, the maneuvering system and more—have to fold up small enough to fit into the Ariane 5’s payload bay, which measures less than 5 m (16 ft) across. The engineers designed the telescope so it is indeed neatly stowable, but the unstowing—and unfolding—is another job entirely.
Friedman’s role as the commissioning scientist means he is responsible for opening up and configuring the telescope over the course of the mission’s first six months. He and the rest of his team will have to work exceedingly carefully and exceedingly well. By the engineers’ calculations, the telescope’s unfurling process has a staggering 344 so-called “single point failures”—each involving a hinge, actuator, pulley or other system or procedure that, if it goes awry, could all by itself spell the end of the mission. Just one single point failure is a high-stakes thing with which to fly. More than one can be exponentially worse; 344 of them is flat-out hair-raising.
“There is some redundancy built into the system of release mechanisms,” said Friedman during a recent walkabout with TIME in the mission control building. “They have multiple wires in and only one has to work right. But one way or another, all of the releases do have to fire.”
“Many of these things are actuators that do have back-up systems,” says Zurbuchen. “But make no mistake, I could easily imagine things that we have no fallback on.”
Assuming none of those single point failures does, in fact, fail, there is much the James Webb Space Telescope could do and discover over the decade of work it has ahead of it. The ability to look as far back in time as the Webb can will raise the curtain on a whole range of astronomical objects and phenomena. For starters, it might be able to glimpse, or at least get close to, the universe’s literal let-there-be-light moment—peering back to the point when stars first began to form among the dust and gas clouds that made up all there was to the cosmos just after the Big Bang. Only at that point did the infant universe become illuminated, as the stars acquired enough mass to ignite their fusion engines and begin to burn their hydrogen fuel.
“There was a period of time when the universe wasn’t able to form stars or galaxies yet, so there wasn’t any light yet,” says Pontoppidan. “Then you form galaxies and they form stars and that happens about 100 million years after the Big Bang, but we don’t know for sure.”
Those early stars were not like those that populate the modern-day cosmos. They were huge, for starters—300 times more massive than our sun—and relatively short-lived. But that was a good thing: When the stellar behemoths exploded in massive supernovas, they helped generate the heavy elements that made our modern, elemementally complex universe possible.
Webb could also contribute to the study of gravitational waves—ripples in the fabric of spacetime caused by collisions of massive objects. The first gravitational waves were detected in 2015, proving a theory that Albert Einstein first promulgated a century earlier. Those waves, and others that have been detected since, were caused by pairs of black holes or neutron stars colliding—cosmic crack-ups that would also have produced massive amounts of heat and other radiative energy. If those emissions left infrared signatures, Webb should detect them.คำพูดจาก สล็อตเว็บตรง
Closer to home, the new telescope will conduct observations within our own galaxy, studying the atmospheres of exoplanets—planets circling other stars—looking for signs of biologyคำพูดจาก สล็อตเว็บตรง. Most of the more than 4,000 exoplanets discovered so far were spotted by using the so-called transit method: When an orbiting planet passes in front of its parent star, it blocks a tiny bit of starlight, a change that can be detected by observatories like the Kepler Space Telescope. The amount of dimming gives you a good estimate of the planet’s diameter, and the frequency with which that little flicker repeats tells you how fast the planet is orbiting. But that’s all you can get from the transit method. With Webb, scientists will be able to analyze starlight as it passes through—and gets distorted by—a given planet’s atmosphere. The precise nature of that distortion can reveal the makeup of the atmosphere’s chemistry, including the presence of oxygen, carbon, methane and other elements and compounds that are requirements for—and perhaps fingerprints of—life as we know it. The JWST can conduct similar chemistry measurements on planets and moons with atmospheres in our own solar system, such as Titan, the great, gaseous satellite of Saturn.
“[Webb] won’t find new planets, so much as it will characterize those we already know,” says Pontoppidan, “in particular, smaller exoplanets with rocky surfaces and maybe relatively temperate temperatures.”
For all its potential, Webb is not expected to have anywhere near the lifespan of the venerable Hubble, which launched when the Soviet Union was still a going concern. One risk is that it’s far more vulnerable. Hubble is a closed system, with its metal body shielding the delicate instruments inside from micrometeorites and other threats. Webb has no such protection, and both its mirror and sun shield are expected to get regularly dinged. Webb engineers are surprisingly sanguine about that fact, since NASA has conducted hypervelocity simulations, firing micrometeorite-like ordnance at mirror material, and has found the damage to be minimal.
“Luckily for us, the micrometeorites will put nice little well-defined bullet holes in [the mirror],” said Webb project manager Bill Ochs at the NASA press conference. That, he says, will detract a little bit from the overall mirror’s light collecting area, but not enough to make a meaningful difference. As for the sun shield, its five layers help a lot. Ochs says that micrometeorites are likely to disintegrate on impact with the first layer and may go on to strike the second, but puncturing all five is not likely.
Webb faces other operational challenges, however. Hubble has been kept alive in part through maintenance and servicing runs done by astronauts. Webb’s great distance from Earth makes that kind of house call impossible. What’s more, in order to remain stable at its gravity-balanced Lagrange point, Webb needs a thruster system, and a thruster system requires fuel. The telescope will launch with a full tank, but that will be only enough to keep it operating for a minimum of five years and a maximum of 10. In theory, a refill ought to be possible, and the telescope is actually equipped with a docking target to accommodate an incoming spacecraft that could conduct a refueling and extend the JWST’s life. It’s an appealing idea, especially considering the telescope’s dizzying price tag. That spacecraft, however, does not yet exist, though it could within the next decade.
“At this moment in time, we’re putting tunnel vision focus on getting this launched,” says Zurbuchen. “There is nothing to refuel if it doesn’t deploy. But I think refueling is not out of the realm of possibility, especially considering technological progress.”
No matter how long Webb lives, it will fly for only the tiniest blink of time compared to the age of the cosmos it will be studying. But it will help us learn much in those exceedingly fleeting years. The universe has long kept parts of its earliest epoch hidden from us—but no more. The Webb, says Pontoppidan, will be nothing less than “a discovery machine.”
