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The giant, 40-ft. space telescope resting in the airtight, climate-controlled clean-room at NASA’s Goddard Space Flight Center in Greenbelt, Md., wants nothing to do with the microscopic dust particles clinging to your clothing. So before you enter the room, you first must stand in a chamber that blows high-powered, compressed air at you from head to toe, sweeping you clean. Next you dress up in surgical scrubs—booties, head covering, mask, blouse, and pants—and pass through a series of doors that take you into successively more-sterile ante rooms. Only then, when your dust can pose no danger to the delicate machine in the center of the room, can you join the Nancy Grace Roman Space telescope on the factory floor. There, technicians are busy completing its assembly in preparation for its launch in May 2027 to a spot in space close to 1 million miles from Earth. From there it may transform our understanding of the cosmos.
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“The vast discovery power of this telescope is going to expand our window of knowledge by orders of magnitude,” says Jamie Dunn, the Roman telescope’s project manager. “You’re going to have a tremendous amount of data available to tens of thousands of scientists. It’s just mind-boggling.”
“We [will be able to] move quickly and map out very large areas of the sky,” adds Josh Schlieder, the telescope’s wide-field instrument scientist. “We [will] detect hundreds of millions of galaxies to very high accuracy with very deep imaging.”
Roman will indeed do all that and more. The telescope will be able to look at a patch of sky 100 times larger than both the Hubble Space Telescope and the James Webb Space Telescope can. It will be able to peer up to 13.2 billion light years away, collecting images of the 13.8-billion year old universe when it was just 600 million years old. The 18 detectors in its wide-field infrared imaging camera are equipped with 16 million pixels each, providing exquisite image resolution. And its 5.6 ft. (1.7 m) high-gain antenna will be able to send a firehose of pictures and data back to Earth at unprecedented speed. What’s more, all of this data will be open-source—available to the world.
“Roman will deliver one terabyte of data a day,” says Rob Zellem, deputy project scientist for communications. “That’s the equivalent of one gaming computer a day.”
That gusher of findings will include new observations of exoplanets—or planets orbiting other stars; new surveys of the structure of the Milky Way; and new studies of dark energy, the mysterious, invisible force that causes the universe to expand continuously at an ever-accelerating rate.
“Part of our core science for Roman is to do surveys that allow us to measure the properties of very large numbers of galaxies throughout cosmic history,” says Schlieder, standing just feet from the Roman telescope on the clean-room floor as bunny-suited technicians tend to it. “By measuring their positions, their velocity, how fast they’re moving toward or away from us and their shapes, we’ll be able to place new constraints on the properties of dark energy.”
The telescope has a lot of assembly and other work ahead of it before it finally takes to space atop a SpaceX Falcon Heavy rocket two years down the line and begins to perform that work. It may be getting pampered today but it will be punished before long as it goes through testing—set to begin late this spring—to ensure that it can tolerate the harsh conditions of deep space and the violent, high-energy shaking that the Falcon will subject it to as its 27 engines light, putting out 5 million pounds of thrust.
“The testing includes electrical testing; vibration testing; acoustical testing, to simulate the sound of a launch; and a thermal vacuum test, [in which] we take it in a big chamber, pump out all the air, and go through warm to cold temperatures, to test out all of its components in a real space-like operating environment,” says Schlieder.
Only if the $4 billion telescope survives that pounding will it get its chance to leave the planet. In keeping with the potentially epochal science Roman will perform once it’s in space, NASA has decided to fling its findings and discoveries open to the world. Typically, the data returned and the discoveries made by space observatories like Hubble and the Webb have a period of 6 to 12 months during which they are available only to the astronomers who did the work. Roman’s findings will be made immediately available to the public—lay people and scientists alike—on a universally accessible website. That’s because Roman’s huge field of view will allow many astronomers—and non-astronomers—at once to gather data from uncounted regions of the sky, with no single principal investigator directing the observation.
“We will not have individual teams that get proprietary access to the data,” says Schlieder. “The data will be obtained, it’ll be downloaded to the Earth, it’ll be processed, and it will be posted in an archive for anyone to go grab and do what they want.”
“Every single Roman observation will have huge and broad science return,” adds Julie McEnery, Roman’s senior project scientist. “The Roman surveys are defined collaboratively by the science community and collectively owned by the science community.”
A cosmic namesake
The Nancy Grace Roman space telescope did not always go by such a lyrical name. When it was first proposed, in 2010, it went by a decidedly more arcane, if more descriptive moniker: the Wide Field Infrared Survey Telescope (WFIRST). When cosmic objects move toward the viewer, the wavelength of visible light they produce is compressed like a spring toward the blue end of the spectrum. Objects moving away emit a light that is stretched toward the red end of the spectrum. The universe as a whole is largely red-shifted, since, as the celebrated astronomer Edwin Hubble discovered in 1929, it is forever expanding, with the billions of known galaxies continuously receding from us. The WFIRST telescope, with its 18 infrared eyes, was designed to study that shift. In 2020, when metal was at last being cut on the new telescope, then-NASA administrator Jim Bridenstine announced that it would be renamed in honor of Nancy Grace Roman, NASA’s first chief astronomer—and Roman clearly earned the honor.
Coming to work for NASA in 1959, Roman was tapped to serve as head of observational astronomy, the first woman of such rank at the fledgling agency. In that position, she spent 20 years leading NASA’s efforts to secure funding for a space-based telescope—one that eventually became the Hubble. For her pains, she was affectionately nicknamed “the mother of Hubble.” It was under her decades of leadership that observations made by the telescope helped build on Edwin Hubble’s work, showing that the rate of the universe’s expansion is actually increasing over time, seemingly violating the laws of gravity, which ought to apply a brake on the cosmos’s growth. The engine of the accelerating expansion was said to be a still-unknown force dubbed dark energy, which is believed to make up 68% of the universe.
The theory of dark energy was first promulgated in 1998, 20 years before Roman’s death. The telescope now named for her will help unravel the stubborn mystery surrounding it.
Planetary multitudes
Probing the secrets of galactic motion and dark energy won’t be Roman’s only task. It will also devote considerable attention to individual stars—specifically focusing on the planets that orbit them. Until now, it has been impossible to spot exoplanets directly, since the glare of their parent star washes out the far fainter pinpoint of the nearby planet—much the way a streetlight would blind you to a moth fluttering next to it. Instead, astronomers infer the presence of a planet, either by measuring the slight dimming of the star when the smaller body passes in front of it or the slight wobble the planet’s gravity causes in the star. The Roman telescope will come at things more straightforwardly, thanks to a coronagraph—an array of flexible, piston-mounted mirrors and optical masks that block the light of the star, allowing the planet to pop into view.
“These optical elements allow us to beat down all of that noise in the system,” says Schlieder. “It’s very striking when you look at a star normally, and then you look at a star once it’s gone through the system. In one of them, the star just looks like a big sort of fuzzy blob. And in the other one, it’s blocked out and you see what’s around it.”
Adds Zellem: “You have the masks, the deformable mirrors, and post-processing [imaging] techniques that happen on the ground. You can then remove that star signal and extract that very small planetary signal.”
The coronagraph won’t be the only way Roman will find planets. It will also rely on what’s known as gravitational microlensing. In 1912, Albert Einstein posited that when a foreground star drifts in front of a background star, the background star should briefly brighten, as the gravity of the one in front distorts and magnifies its light. The theory was proven during the total solar eclipse of 1919 when British physicist Sir Arthur Eddington measured the distortion of background stars near the limb of the darkened sun. Contemporary astronomers can make use of lensing to look for exoplanets. If a foreground star has no planets, it will distort the light of a background star in a relatively smooth up-and-down arc as the obstructing star passes by. If it does have planets, those smaller bodies will cause a bit of additional increase in the background light.
“That little planet that’s at the right location will cause a spike in that brightness, and then it will come back down and finish,” says Schlieder.
Roman will have a lot of those little signals to target. Until 1992, astronomers had not discovered any planets beyond the eight in our own solar system. Since then, they have spotted and confirmed more than 5,500, with thousands of other candidate planets that require more observation and examination. Roman will both be looking for its own newly observed exoplanets—mission planners predict it could discover hundreds of thousands of them—and possibly be revisiting some of the ones that are already in the catalog. Much of what they will be investigating will be the chemistry of the planets’ atmospheres, searching for signs of organic activity, especially on small rocky worlds like Earth. Roman will be particularly tuned to pick up the atmospheric wavelength consistent with methane, a molecule closely associated with life, and one that is being studied by NASA’s Mars rovers as well.
The wider view
Roman’s studies of the macro structure of the universe will be more complex, and partly explain why it will be parked in space so far from Earth. In order for the infrared imagers to work—measuring the red-shift of galaxies in the expanding cosmos—the telescope has to be shielded from stray heat, since that would wash out a thermal image the same way stray light would ruin an optical one. Roman, like the James Webb Space Telescope, will thus station-keep at a spot known as a Lagrange point, one of five places in space where the gravity of the Earth and the sun cancel each other out, allowing objects to circle the invisible point as if they were orbiting a solid body like a planet. Roman, like Webb, will be going to Lagrange Point 2, on the opposite side of the Earth from the sun. Out in that distant remove, the temperature drops to about 90 Kelvin, or -298°F.
“That’s a really good operating temperature for our very sensitive infrared detectors,” says Schlieder.
Roman will be looking at the motion of the universe in the visible range too, thanks to what are known as type 1a supernovas—exploding stars that are part of a binary star system. All type 1a stars erupt with equivalent brightness. To the extent that one shines brighter than another it’s only because it’s closer than the other.
“You can think of them being like a standard candle, like a light bulb,” says Schlieder. “If you have a light bulb and you know the wattage, and you take it some distance away, it looks fainter.” Measuring that brightness will allow Roman astronomers to determine the motion and distance of the supernovas, which will also provide clues to the speed of the expansion of the universe, both now and in the past, shedding more light on just what dark energy is and how it works.
Early in its stay in space, Roman will also conduct the most detailed survey of the Milky Way that’s ever been attempted. Our solar system’s region of space lies in the plane of the galaxy, out in one of its spiral arms. Looking toward the galactic center thus amounts to looking at a vast band of stars—which is what the Milky Way looks like to the naked eye in a very dark sky. Roman will stare toward the center of the galaxy for a surveying period that will last about a month, during which it will gather images of about 50 billion stars, in multiple wavelengths, including the infrared—or up to half of the stars in the galaxy. It will be the most extensive mapping of our galaxy ever conducted and will yield data about star formation, the dust in interstellar space, and the gravitational dynamics at the galactic center. The month that the survey will take is actually a breakneck pace—a thousand times faster than Hubble could conduct similar work.
“One month with Roman is about a thousand months with Hubble,” says Schlieder.
Just why the world needs a new, $4 billion telescope only four years after the launch of the $10 billion James Webb telescope is a question that actually has an easy answer. For one thing, Webb does not have the exoplanet coronagraph capability that Roman has. For another, the two telescopes’ image resolutions are very different. Webb’s cameras can see deeper into space than Roman’s can—about 13.6 billion light years distant, or 13.6 billion years in the past, compared to Roman’s 13.2 billion. But Roman’s wide-field gaze is much greater than Webb’s.
“Roman goes wide, Webb goes deep and narrow,” says Zellem. “Roman is context. It’s like a fisheye compared to Webb’s zoom lens.”
It is a good thing that Roman can conduct its surveys fast, because it won’t have all that long to live. The Hubble Space Telescope has been aloft for 35 years and is still at work—thanks in part to the five servicing missions astronauts made to the telescope before the space shuttles were retired in 2011. But Hubble flies in an easy-to-get-to low-Earth orbit. Roman, like Webb, a million miles away, is out of reach of handyman astronauts. As a result, it has a nominal planned mission of just five years, with flight managers not ruling out extending that to 10 years, if the machinery holds up and the hydrazine fuel that powers its positioning thrusters lasts.
“Fuel is the only expenditure now that sort of limits the Roman timeline,” says Dunn. “Perhaps a future NASA robotic mission, which has yet to be planned and is not designed at all, could go out to Roman and refuel it.”
But that’s for the indeterminate future. For now, Roman is still in its assembly phase, with much more work ahead of it. Exiting the clean room and leaving the telescope behind is a little like exiting an operating room, passing back through successively less sterile chambers, doffing mask and outer garments, and rejoining the world of dirt and dust and grit and grime. Roman will barely touch that world, eventually leaving its home in Maryland and traveling as sealed cargo to the Kennedy Space Center for its launch. From there it will go to live in space—where it will dramatically widen humanity’s eye on our universe. “Today,” says Schlieder with a final backward glance at the telescope as he exits the clean-room, “we are making sure that the instrument—as it’s being built, tested, and ready to go—is going to deliver on the science it has to deliver.”
