Science

The James Webb Space Telescope Has Launched: Now Comes the Hard Part


The relief was as deep as the stakes were high. At 7:20 A.M. (ET), the rocket carrying the largest, most ambitious space telescope in history cleared the launchpad in French Guiana, and the members of mission control at the Space Telescope Science Institute in Baltimore roared their elation.

The suspense was not quite over. Half an hour postlaunch, the telescope still needed to decouple from its host rocket, after which it had to deploy solar panels to partly power its journey. Only after that first deployment proved successful, said a NASA spokesperson in a statement to Scientific American, would “we know we have a mission.” When the announcement of a successful rocket separation and solar-array deployment finally came, it was almost drowned out by cheers.

Astronomers have more riding on the rocket than the James Webb Space Telescope (JWST). Also at risk is the viability of NASA’s vast space-science portfolio if not the future of astronomy itself. As the successor to the Hubble Space Telescope (HST), JWST is one of those once-in-a-generation scientific projects that can strain the patience of government benefactors as well as the responsible agency’s credibility but also define a field for decades to come—and possibly redefine it forever.

“This is a great day—not only for America and our European and Canadian partners, but it’s a great day for Planet Earth…. [JWST is] going to take us back to the very beginnings of the universe,” said NASA administrator Bill Nelson in postlaunch remarks. “We know that in great reward there is great risk. That’s what this business is all about, and that’s why we dare to explore. The James Webb Space Telescope is very much a part of that exploration.”

As JWST separated from its rocket’s upper stage, a video feed showed the now-independent spacecraft gleaming in sunlight, capturing one last close-up look at the observatory before its quest to pierce the veil of cosmic darkness took it inaccessibly far from Earth. “When we look farther, delve deeper, or measure more precisely, we’re bound to find something wondrous,” says Ken Sembach, the Space Telescope Science Institute’s director. “Today we said goodbye to the telescope on the ground and we opened our eyes to the universe.”

Back to the Beginning

The telescope that would become JWST was already under discussion even before HST launched in April 1990. By orbiting Earth, HST would have a line of sight free of the optical distortions endemic to our planet’s atmosphere. It would therefore be able to see farther across the universe (and, given that the speed of light is finite, farther back in time) than any terrestrial telescope.

Even so, HST would be observing primarily in optical wavelengths—the tiny portion of the electromagnetic spectrum that the human eye can detect. The Next Generation Space Telescope (as the future JWST was then known) would be looking at the universe in infrared, the regime into which cosmic expansion would have stretched, or redshifted, visible light emitted more than 13 billion years ago.

Much of the attention leading up to today’s launch has focused on the ability of JWST to peer farther into the past than HST, which has observed infant galaxies as far back as approximately 400 million years after the big bang. At that point in the universe’s history, however, matter had already undergone several generations of evolution—galaxies merging and shredding, supernovae seeding space with additions to (what sentient beings on Earth would one day call) the periodic table of the elements.

JWST, however, will be able to see as far into the past as 100 million years after the big bang, a period when most matter consisted of only the primordial elements and was just beginning to coalesce into stars and galaxies. From the inception of JWST, the primary goal has been to glimpse these phenomena—the first luminous objects in the universe.

A New Search for Life

The other major scientific frontier that JWST will probe is one that has received less attention but might prove to be just as profound in our understanding of the universe. It is a bonus of sorts, a subject of study those 1980s-era visionaries could have scarcely foreseen: exoplanets.

Evidence for planets orbiting stars other than the sun first emerged in the 1990s (a finding that earned some of its discoverers a share of the 2019 Nobel Prize in Physics). Since then, astronomers have found exoplanets by the thousands, with tens of thousands more sure to overflow their catalogs in coming years. Almost all of these discoveries, however, rely on indirect evidence: the regular brightening and dimming of a star as a planet transits across its face, or the wobble in a star’s axis caused by the gravitational pull of a nearby world.

JWST should offer more direct evidence: observations of the planets themselves, a feat only a few other facilities can manage—though none with the promised clarity of this new space telescope. In visible light, the brightness of a star overwhelms any nearby objects, but by observing in the infrared JWST will reduce the contrast so that the planets can pop out from the background stellar glare as tiny blips of light. That reduction in contrast will further help observers to probe the atmospheres of a handful of worlds for potential biosignatures such as oxygen (produced on Earth by photosynthetic plants) as well as tracers of habitability such as water and carbon dioxide.

In short: JWST offers some chance, however slim, to answer an eternal question: Are we alone?

“That’s where the big discoveries will be,” predicts Nicholas Suntzeff, an astronomer at Texas A&M and former vice president of the American Astronomical Society. “Is there other life in the universe? If so, it would have to be the biggest discovery in science ever.”

Near-Death Experiences

But first JWST will have to, you know, work.

Many of the members of the JWST project were not yet born when HST launched in 1990. But what happened next shadows them, just as it haunts all of NASA. Like some “Ghost of Missions Past,” a grim event from the observatory’s early days drags and rattles its chains along the otherwise pristine corridors of the Space Telescope Science Institute—the operations headquarters for HST and now mission control for JWST. Initial observations from HST were out of focus, and engineers soon realized that its mirror had been improperly polished, leading to a ruinous case of cosmic myopia and widespread public ridicule. Although spacewalking astronauts later repaired the mirror (at tremendous expense), the fiasco was a classic instance of “You had only one job…,” threatening to render HST almost useless and leaving NASA vulnerable to congressional oversight bordering on strangulation.

In the case of JWST, similar significant setbacks—technical, political, sociological—have preceded the launch. The original budget estimate was a hazy $1.5 billion to $3 billion, and its similarly nebulous launch date was, oh, let us say 2010. By that deadline, however, not only had costs risen to $5 billion but much of the telescope was still on the drawing board; the development of JWST’s myriad foundational new technologies was proving more intractable than planners had imagined. Only a year later the budget had ballooned by 60 percent to $8 billion—at which point Congress intervened, establishing a cost cap for JWST: $8 billion, or bust.

Would Congress dare to cancel a scientific mission of such ambition? Yes, it would—and once did. In October 1993, President Bill Clinton signed a bill killing the Superconducting Super Collider, which would have been the world’s most powerful particle accelerator. Never mind that the project had already cost $2 billion ($3.15 billion in 2021 dollars). Never mind that underground boring had already cleared nearly 19 of the projected 51 miles of tunnel. Never mind that the particle accelerator promised transformative scientific breakthroughs. Congress deemed the project’s budget to be out of control. The cancellation blew a hole through the heart of the U.S. particle physics community, which, even three decades later, has yet to fully recover.

By 2018, the JWST project was both flirting with the congressional cap and pushing the launch date farther and farther into the future. Behind the scenes, as a Government Accountability Office investigation would later reveal, technical problems were multiplying: Workers at Northrop Grumman, the primary contractor for JWST, discovered that the application of an inappropriate solvent had damaged the observatory’s propulsion valves. A wiring error destroyed the pressure transducers. And during vibration testing, dozens of bolts flew off the spacecraft.

The budget grew by another $800 million, officially exceeding the congressional cap. And the launch date slipped to 2021.

Even the name of the telescope has been a subject of controversy. In 2002, NASA’s then administrator Sean O’Keefe announced that the Next Generation Space Telescope would thereafter be called the James Webb Space Telescope. The practice of replacing generic names for telescopes and observatories with the names of prominent scientists is routine. O’Keefe, however, violated two norms: His choice of honoree was essentially a unilateral decision, and that honoree was not a scientist but a fellow administrator—indeed, one of O’Keefe’s predecessors. James E. Webb had served as NASA’s chief during its race-to-the-moon heyday, from 1961 to 1968.

In recent years, though, the name of the mission has gained another layer of controversy: who Webb was, at heart. Webb’s tenure as the second in command at the Department of State in the late 1940s and early 1950s and then as the head of NASA coincided with what historians now call “the lavender scare”—a search for and purge of LGBTQ employees at these and other federal institutions. Investigations in recent years have turned up scant specific evidence of Webb’s involvement, but the association between bureaucrat and bigotry is close enough that some astronomers insist on referring to the project only as “JWST” and never as “Webb.”

Will It Work?

Minor delays have continued to plague JWST on its path to the launchpad. In recent weeks the launch date has slipped repeatedly, first due to an accidental jostling of the telescope (an inspection revealed no damage) and then to a flaw in a communication cable connecting the telescope to ground systems. Just this past Tuesday, a forecast of high winds for Kourou, the launch site in French Guiana, nudged the timing of liftoff from Christmas Eve to Christmas Day.

Over the next month, JWST will still have to execute nearly 350 potentially fatal maneuvers— or “single points of failure” in NASA’s nomenclature—while prepping for scientific observations. Perhaps trickiest of all will be the deployment of the mirror—or, more accurately, mirrors: 18 hexagonal gold-coated slabs in a honeycomb arrangement. Partly so that the telescope would not be too heavy to launch, engineers chose to make the mirrors out of the relatively lightweight element beryllium. But the weight of the mirrors was not the most difficult design challenge. It was their size.

When the mirrors assume their eventual configuration, they will collectively span more than 21 feet (in contrast to HST’s eight-foot diameter), far too wide for a rocket’s payload fairing. So engineers developed an ingenious solution: dividing the honeycomb into segments that fold up so that they fit inside the rocket on Earth, then unfold, origami-like, in space.

If all goes well, about 30 days after launch JWST will reach its final resting place (so to speak): a region of space that astronomers call the second Lagrange point, or L2, one of five sites in the solar system that the 19th-century Italian-French mathematician Joseph-Louis Lagrange determined would keep pace with Earth in their orbits around the sun. At a Lagrange point, the gravitational balance between the Earth and sun acts as a stabilizing influence, thereby allowing spacecraft to conserve fuel. (Other astronomical projects that have occupied L2 include the Wilkinson Microwave Anisotropy Probe and the Herschel and Planck space observatories.)

In the case of JWST, though, L2 has a further advantage: it is on the side of Earth directly opposite the sun, a position that reduces exposure not only to light but also to heat—an essential concern in an instrument sensitive to infrared wavelengths. Even so, JWST will still need thermal protection so that it can gradually cool down—across several months—to its operational temperature only tens of degrees above absolute zero. Over the first week of its voyage, the telescope will unfurl a tennis-court-sized, five-layered sunshield (SPF one million) to separate its delicate optics and instruments from all the potential heat pollutants. On the telescope side of the shield, the temperature will approach -400 degrees F. On the other side, it may become as hot as 200 degrees F or more.

For all its advantages, though, L2 comes with one significant drawback: it is far from Earth—nearly one million miles, or four times the distance of the moon. HST enjoyed the benefit of human servicing missions—for instance, to fix the flaw in its mirror. But that option will not be available for JWST. If something breaks, it will stay broken.

But if nothing breaks, JWST will start streaming scientific data back to Earth this summer (NASA’s collaborators on the mission, the European Space Agency and the Canadian Space Agency, will receive 15 percent and 5 perfect of observation time, respectively). These telescopic treasures will contain not just new insights into the origins of cosmic structure and the atmospheres of exoplanets but also the secrets of star formation in the Milky Way and the geology of the outer planets in our solar system.

Only then will members of the worldwide JWST community be able to truly relax—and, for those who so wish, celebrate Christmas in July.


Source link

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button