Our Millennial Space Telescope Hasn’t Burned Out Yet
The astronomy community is buzzing about the newest space telescope on the block, but Hubble is still going strong.
At this moment, about a million miles from Earth, the world’s most powerful space telescope is making tiny adjustments to its mirrors, aligning the shiny tiles just so. Soon, the starlight will come into focus for the James Webb Space Telescope, and the observatory will begin to make sense of it. Thousands of astronomers are simply buzzing, eager to see the marvels that Webb might pick out of the darkness.
All the anticipation surrounding this shiny new space telescope made me wonder: How’s Hubble doing?
You know, Hubble—that other space telescope, and arguably the most well-known one. For nearly 32 years, Hubble has been perched on high, peering into space, delivering dazzling sights, and making new discoveries. If you’ve ever seen a really good picture of a galaxy, all sparkly and ethereal, it probably came from Hubble.
Space folks at NASA and other space agencies have been keen to point out that Webb is Hubble’s scientific successor, designed to be 100 times more powerful than Hubble, and capable of showing the universe to us in a wavelength that Hubble isn’t built for. With all this talk about the new kid on the block, Hubble starts to sound like a has-been—out of the game, or at least on its way there.
But Hubble is still very much around, still scanning the universe, chugging along like the Millennial space telescope it is. At the beginning of this year, days after Webb departed Earth, Hubble marked its 1-billionth second in space. “It was almost like, after Webb launched and all eyes were on JWST, Hubble’s like, ‘Yeah! I’m still here. I’m still cooking,’” Rachel Osten, the deputy mission head for Hubble at the Space Telescope Science Institute, which oversees both space telescopes, told me.
Like some Millennials, Hubble is a little achier than it used to be. The final astronaut mission to freshen up the telescope was 13 years ago, and Hubble now suffers from, as one astronomer put it to me, “electronic osteoarthritis.” Every once in a while, a part malfunctions, and Hubble slips into safe mode, slumbering until engineers can come up with a fix. But the observatory always reemerges, ready to return to work. Just this week, the Space Telescope Science Institute released a picture Hubble took of two distant galaxies colliding, the flashier of the two dragging so much cosmic dust around that new stars have sparked into existence between them.
We are closer to the end of Hubble’s mission now than we are to its beginning. Someday, probably at the end of this decade, the space telescope will stop working. The people who manage Hubble’s time are already working with astronomers around the world to make sure they make the most of the years left, Jennifer Wiseman, a senior project scientist on the Hubble mission, told me. They’re asking: “What’s important to do with Hubble while we still have Hubble?”
There was a time when Hubble was not beloved. A few weeks after the observatory launched into space in 1990, Richard Griffiths and his fellow astronomers were staring at a computer, wondering why Hubble kept sending home one blurry picture after another. They had expected a fuzzy view as Hubble settled in—as Webb is doing now—but this was something else. “We were really puzzled because it wasn’t in focus,” Griffiths, now a physics professor at the University of Hawaii at Hilo, told me. “We couldn’t figure out why.” It turned out that the company that had manufactured Hubble’s main mirror had accidentally polished it into the wrong shape. When NASA officials went public with their realization, Hubble seemed like a giant flop. Without a working mirror, Hubble couldn’t see the universe.
Unlike Webb, Hubble orbits closer to home, so when NASA figured out that the mirror couldn’t be repaired from afar, they sent astronauts to do it. Even after Hubble’s eyesight was fixed, NASA continued to dispatch astronauts to upgrade the science instruments, patch up any broken components, and even boost the observatory higher into space so that it would feel less atmospheric drag. The visits from space-shuttle crews extended Hubble’s life span, giving astronomers more time to explore everything from the planets and moons in our solar system to distant stars and galaxies.
Astronomers hoped Hubble would last until Webb launched, so that the space telescopes could work together. Webb will study the universe mainly in infrared, while Hubble observes mostly in visible and ultraviolet wavelengths, and in astronomy, the more wavelengths, the merrier. Tandem observations could produce richer portraits of a celestial target, or a better understanding of an astrophysical phenomenon. For example, Hubble can study the radiation of hot, new stars while Webb investigates the cool, dusty regions where stars haven’t yet ignited. Although Hubble can explore a bit in infrared, astronomers have already stretched that small capacity to its limits; Webb will relieve Hubble of those demands. “We actually are excited about this, because that means we will concentrate more on the things Hubble can uniquely observe in ultraviolet and visible light,” Wiseman said. More views of Jupiter’s radiant auroras, of blazing winds whipping around new stars, of glimmering galaxies.
Since the astronauts’ final house call, in 2009, Hubble has developed some wear and tear. It has lost some of its sensitivity. Its detectors have been zapped with cosmic rays, producing permanent “hot pixels” that show up in its imagery and must be edited out. Some computers and hardware have failed, forcing engineers to switch to backup systems. Ever the Millennial, Hubble alerts its stewards to problems via text. “When I get a text message, it tells me that something’s not good,” Jim Jeletic, Hubble’s deputy project manager, says. Last November, Hubble spent a month in safe mode—longer than usual—while the team tried to figure out why its science instruments were spitting out error codes. “We weren’t happy to see it,” Jeletic told me. “But it’s one of those strange errors that occurs every once in a blue moon,” not a “showstopper” problem.
What would take Hubble out for good? The failure of its gyroscopes, the hardware that the telescope uses to move itself in space and point toward observational targets. When astronauts last touched Hubble, the observatory had six beautifully functioning gyroscopes; today, it’s down to three. NASA has figured out how to manage with only two gyroscopes, or even one, a scenario that would involve Hubble using some of Earth’s magnetic field to orient itself, Jeletic said. But when all the gyros go, so will the mission, even if Hubble’s science instruments are still functioning just fine.
There is also the very small but not impossible chance that Hubble could be thwacked by a passing satellite. The observatory has always faced some threat of collision with space debris, but the risk has doubled since the early 2000s as more satellites have arrived where it lives, in low-Earth orbit. NASA recently said that it anticipates more close encounters between SpaceX’s growing fleet of internet satellites and the agency’s own spacecraft in low-Earth orbit too. Hubble can use its gyros to slightly maneuver itself out of the way of satellites, but it’s not built to deftly dodge anything, especially not a moving train of dozens of freshly launched Starlinks (a project which, like so many others from Elon Musk, has generated its share of controversy). “That would be bad, if Hubble got taken out by a Starlink train,” Osten said.
NASA doesn’t have any more servicing missions planned for Hubble—the space shuttles that carried them out stopped flying in 2011—but “we still believe wholeheartedly that we can continue to keep it operating into the late 2020s, if not beyond,” Jeletic said. Hubble is expected to lose enough altitude to begin falling back to Earth some time after that, around 2040; NASA has some fuzzy plans to give the telescope a propulsion system that would either send it down into the Pacific Ocean, far from any populated areas, or higher up, where it could remain in orbit for hundreds of years. Jeletic hopes NASA decides on the latter; he imagines that, maybe, later generations with technology far more advanced than ours might go back for Hubble, bring it home in one piece, and put it in a museum.
By the time Hubble takes its final picture, Webb—if all its final little deployments work—will be producing its own glittering catalog, cementing its place in people’s imagination as the coolest space telescope they know. Hubble launched the year I was born, and I can’t remember when I first heard about the mission or saw one of its images. It was always just there, hanging out in space, producing pictures so pretty that they became ubiquitous not just in scientific circles, but as coffee-table books and computer wallpaper. For people born just before Webb launched, in the middle of a pandemic, this observatory will be the source of a constant stream of wonder, whirring deep in the background—their own way to see the stars.