On Christmas, scientists launched the James Webb Space Telescope and sent it about a million miles from Earth. This summer, the technological marvel will begin collecting never-before-seen images of the cosmos. But between now and then, NASA researchers and their European and Canadian colleagues have their work cut out for them.
They have a many-step process to ensure that the powerful, expensive telescope’s instruments are ready to successfully collect data about everything from faint planets to the distant universe. “Everything’s just about on schedule, but we’re busy people for the next six months. There’s an awful lot to do,” says John Mather, JWST senior project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The hardest part might already be done: The spacecraft launched without a hitch, and over the next couple of weeks it delicately unfurled its huge, kite-shaped sun shield, designed to block heat and light from the sun, moon, and Earth, and moved its 18 hexagonal mirror segments into place. “We’re incredibly excited. It was a nail-biter for the first month, and thankfully the deployments went really smoothly,” says Analyn Schneider, the project manager of JWST’s Mid-Infrared Instrument (MIRI) at NASA’s Jet Propulsion Laboratory in Pasadena, California.
All the while, the telescope was traveling to its special parking spot at the L2 Lagrange point, where it balances the gravitational pull of the sun and Earth. (Other spacecraft, including the European Space Agency’s Planck Telescope, have been deployed to the same area.) Keeping a spacecraft in that position is gravitationally unstable, sort of like balancing a ball on an upturned bowl. Webb will regularly drift away from L2, requiring little bursts of fuel every few weeks to nudge it back. But it should have plenty left, because scientists maneuvered the telescope to conserve fuel on its outbound trip. Now, the JWST team expects it to run much longer than its planned 5- to 10-year mission, perhaps lasting as long as its predecessors, the Hubble and Spitzer space telescopes. “The ballpark is probably 20 years of life. It depends on how good we are at steering our unstable car,” Mather says.
Since the spacecraft’s now so far away, Mather, Schneider, and their team have to send and receive radio signals through NASA’s Deep Space Network, an international array of giant antennas managed by JPL. When a programmer inputs a command and waits for an acknowledgment from the spacecraft, that signal could be relayed through an antenna in California’s Mojave Desert or one in Eastern Australia, for example. But there’s a slight delay, because of the distance. “If something bad happens, we won’t know for five seconds,” Mather says. (That’s still pretty quick for space transmissions. For example, messages to our Martian ambassadors like the Perseverance rover involve a delay of five to 20 minutes.)
Now that everything’s in place, the JWST team has begun the “commissioning” process for the instruments, setting up the complex cameras and detectors and making sure they work as they’re supposed to, Schneider says. Last week, they conducted their first tests with the Near-Infrared Camera (NIRCam), allowing the first photons to hit the camera. It’s not actually capturing images yet, but this is a step toward doing so. Eventually, scientists will use NIRCam to discover new planets and glimpse some of the first galaxies.
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Once they can take real test images, such as of nearby, previously photographed stars, the first batches will be blurry and out of focus. But that’s normal. Those tests will enable the Webb team to gradually align the telescope and adjust the mirror segments until the images look clear.
Unlike Hubble’s cameras, which mostly scan the universe at visible-light wavelengths, Webb’s will be sensitive to infrared light, allowing it to probe the early days of the universe and to penetrate dust clouds. But infrared light is essentially heat radiation, so the detectors can’t be contaminated with any other heat, either from the sun or from the spacecraft itself. JWST’s three near-infrared instruments have to be cooled to about -389 Fahrenheit, while MIRI will come within 7 degrees of absolute zero, or about -447 F. Scientists will eventually use MIRI to study the birthplaces of stars. When possible, they’ll use MIRI’s camera and spectrograph, which break down light into its full spectrum of colors, like a rainbow, to look for signs of water, carbon dioxide, and methane; all are common on Earth and might be signs of life-friendly places elsewhere. NIRCam’s detectors can work when they’re slightly warmer than the others, but to function properly, all of the infrared instruments on board have to be cooled down to extremely frigid temperatures.
Because the instruments are behind the sun shield, they will be cooled by space itself—hundreds of degrees colder than anyplace on Earth—while radiating their heat away. For MIRI, engineers designed a special “cryocooler” to chill it down further. “It’s essentially a refrigerator that’s built up with four stages, each stage cooling the next. None of the components in the cryocooler are life-limited. We expect it to continue chugging along as long as we continue to get power from the solar arrays,” says Konstantin Penanen, a cryocooler specialist at JPL.
That’s a major advantage over Spitzer, whose instruments depended on its supply of cryogen, a liquid helium coolant that ran out in 2009. NASA continued to use the space telescope for a few years after that, during the “warm Spitzer mission,” but its mid-infrared detectors were no longer viable.
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The JWST team has other challenges ahead, though, like making sure that as the spacecraft cools, little droplets of water vapor escape into space rather than condensing and turning into ice on the mirrors or detectors. (That would make images blurrier.) And over time, tiny micrometeorites, smaller than grains of sand, will likely hit parts of the telescope. But NASA prepared for that too, by making the sun shield five layers thick, so it can withstand those little impacts and minimize the damage.
The spacecraft also depends on some mechanical parts that don’t have a backup. “Webb is so much more complex,” says Sean Carey, who was an astronomer at Caltech’s Spitzer Science Center until it closed last September and is now at NASA’s Exoplanet Science Institute. “It has over 1,000 moving parts. Spitzer had four: the aperture cover, which was ejected once and gone; a focus mechanism, which we moved twice at the beginning of the mission and never moved again; the scan mirror for MIPS; and the shutter for IRAC,” the mid- and near-infrared instruments. If JWST encounters a critical problem, it’s too far away for an astronaut with a screwdriver to be dispatched to repair it, as NASA did for Hubble. For now, the next major milestone for the JWST team is to complete the cooling for all the instruments, including MIRI, which will reach its extremely cold temperature range by early April. The long and careful process of aligning the telescope’s mirrors should be done by May. And then it will finally be time for what everyone’s been waiting for: They’ll probably start up the science program—which means actually taking images and data—in June, Mather says.
“I’m thrilled with how well we’re doing," he says. "Nothing has come up that we couldn’t solve.”
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