How Should We Say Goodbye to the Robots That Helped Us Explore the Universe?
NASA's Swift Observatory will burn up this week. And while the agency has a lot of experience losing beloved hardware, it never gets easier.
For years, NASA’s Neil Gehrels Swift Observatory stood out among Earth-orbiting telescopes for its ability to swivel within seconds toward a mysterious flicker in the void of space, like a detective twirling a flashlight at the slightest noise in a dark room. But the more it maneuvered itself toward intriguing phenomena—a burst of gamma rays from beyond the Milky Way, or the afterglow of exploding stars—the faster it sank toward a blazing plunge through the planet’s atmosphere.
In February, its stewards back on Earth halted Swift’s usual science observations, desperately trying to slow its descent with special maneuvers and a last-ditch rescue mission. Swift, which has been orbiting the planet for more than two decades, just had to hold on a little longer.
Given how quickly it had been marshaled together, the rescue operation was a long shot. The Swift team knew this, but that didn’t make the disappointment easier when the attempt failed over the summer. “In my head I understood that, but perhaps not fully in my heart,” says Brad Cenko, an astrophysicist at NASA and the principal investigator for the telescope mission.
Now, Swift is expected to plunge into the atmosphere in the early hours of tomorrow morning. When the telescope perishes, it will join a long line of missions around the solar system that have met dramatic ends. Behind each of these lost explorers is a group of people—engineers, scientists, and others—in charge of shepherding these programs, often from millions of miles away. Spacecraft are tremendously expensive, and often one-of-a-kind, so space agencies don’t take the decision to end or prolong a machine’s life lightly.
And when space robots are lost, their stewards (and the public) sometimes grieve them like loved ones. People have a natural tendency to anthropomorphize autonomous machines that seem to exhibit lifelike behavior. The celestial variety carries an added sheen because they are proxies for our senses, stretching the human experience to a realm that the majority of us will never visit. Their machine hands touch the fine dust of the moon’s surface; their mechanical ears catch the gentle whooshing of a Martian breeze; their lensed eyes bask in the swirling storms of Jupiter; and their robotic noses sniff the frosty plumes erupting from icy moons. They can appear, in their actions, to possess a distinctly human quality: The desire to understand the workings of the universe, and their own place in it.
Perhaps the humanity that people see in the machines they build is part of why unexpected mishaps can be particularly devastating. Last year, one of NASA’s Mars orbiters mysteriously went quiet. The Mars Atmosphere and Volatile Evolution mission (MAVEN) had been circling the red planet since 2014, studying the upper atmosphere and relaying communications between the rovers on the surface and engineers back home. The orbiter team was concerned but remained calm, says Shannon Curry, MAVEN’s principal investigator and a researcher at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. Maybe MAVEN was having trouble syncing frequencies with the Earth-based antennas that regularly converse with far-flung explorers. But after four days of silence, it was “a truly dire situation,” Curry says.
Curry and her colleagues raced to the mission-operations center at Lockheed Martin, MAVEN’s manufacturer, in Colorado. Staff from other robotic missions spanning the solar system, from the moon to Jupiter, assisted the recovery effort, fueled by a steady drip of coffee, donuts, and burritos.
For a totally unrelated experiment, ground stations happened to be recording MAVEN’s radio transmissions on the day the spacecraft fell silent, as part of an experiment analyzing the Martian atmosphere’s effects on radio signals. Engineers dissected that data with forensic intensity, Curry says, and managed to excavate tiny scraps of relevant information. The findings revealed that MAVEN, after years of peacefully winding around Mars, had strayed from its usual trajectory. And the spacecraft was caught in an alarming spin, rotating nearly three times per minute.
Tumbling the way it was, the spacecraft wouldn’t have been able to keep its solar panels aimed at the sun long enough, and its batteries probably drained fast, Curry says. “It’s heartbreaking,” she says, adding that the spacecraft had enough fuel left to keep going for another decade.
Outer space is buzzing with fast-moving, energetic cosmic particles, and one of them, no bigger than a proton, may have zapped through the spacecraft’s electronics and triggered a cascade of anomalies, Curry says . Space weather can fan such particles toward Mars, but the forecast had been clear. MAVEN’s mortal injury was simply a case of cosmically bad luck.
In June, the Curiosity rover, nestled in a crater between the Martian northern plains and southern highlands, dispatched a series of transmissions to MAVEN, bidding farewell to its fellow explorer: “Your amazing support has enabled so much of our roving adventure.” During the recovery effort, Curiosity had pointed its camera skyward, toward where MAVEN was supposed to be. “It would be a bright point of light in the image, like a star,” says Mike Moreau, MAVEN project manager at NASA’s Goddard Space Flight Center. Curiosity didn’t spot its longtime companion, but it will look for the orbiter again in the spring, when there will be less dust in the Martian skies, just in case.
Of all the different types of robotic wanderers, rovers like Curiosity are the easiest to imagine as something more than inanimate machines. Rovers amble across the caramel-colored Martian landscape, gazing through WALL-E-esque eyes. They marvel at funky-looking rocks and pick up the most interesting bits. They take selfies. In 2013, Curiosity marked its first year on Mars by serenading itself with “Happy Birthday,” vibrating its sample-analysis unit at different frequencies to match the song. “It’s almost like having a pet dog that you're watching over, and that you have to feed every day, and see what they've gotten into on that particular day,” says Ray Arvidson, a planetary geologist who served as the deputy principal investigator on the Opportunity rover.
In June 2018, Arvidson was deeply worried about his own cherished companion on Mars. A dust storm had swept across Opportunity’s location in a gravelly valley near the equator. A common occurrence in Martian summer, but this tempest clogged the atmosphere with more dust than Arvidson had ever seen since he began working on Mars missions in the 1970s. In the resulting darkness, Opportunity, a solar-powered being, slipped into a deep sleep.
Engineers dispatched daily commands to the rover, asking Opportunity to beep if it could hear them. After a couple of months with no response, NASA leaders decided that the recovery attempt should wind down in the fall, but engineers at the agency’s Jet Propulsion Laboratory passionately lobbied for more time, Arvidson says. They kept listening until February 2019, relaying all sorts of transmissions to the 14-year-old spacecraft. “We went as far as we could to try to wake her up,” Arvidson says.
NASA mounted a similar campaign a decade earlier for the Spirit rover, on an impact crater on the opposite side of Mars. The spacecraft spent most of its time on the planet driving in reverse after one of its front wheels failed, like a wonky shopping cart, says Arvidson, who worked on the Spirit mission too. In 2009, while dragging the faulty wheel along, the robot’s remaining wheels broke through a crust and into a sandy pit.
Engineers executed a variety of wriggly maneuvers, but the rover only sank deeper. Spirit could no longer prepare for winter by moseying to a sunny slope, where its solar panels could bask in battery-sustaining light. But “it was in a beautiful place scientifically,” Arvidson says. For a few months before the decisive season arrived, Spirit, trapped but alert, used its rock-grinding tool to study the surrounding soil, making the most of its final months as a Martian geologist.
Cosmic murder isn’t out of the question—despite efforts to extend robot lives and make the most of their deaths. Take the Cassini probe, which departed Earth for Saturn in 1997. At the time, mission managers were thinking about all the wonderful things the spacecraft might discover about the ringed planet—not about the possibility that, someday, they would deliberately kill their beloved robot.
Yet the team had a mandate from the beginning to prevent Cassini from colliding with two Saturnian moons, Titan and Enceladus, if it ran out of fuel in orbit. Scientists think these worlds could harbor their own forms of life, and if Cassini crashed into either, it could contaminate the icy moons with Earthly microbes.
When the time came to brainstorm disposal methods, the team considered several options, according to Earl Maize, the program manager for the Cassini mission at JPL. They could use the gravity of Titan, Saturn’s largest moon, to swing the orbiter out of the system and go after some asteroids, and maybe even all the way to Uranus. Cassini could propel itself into a longer orbit, away from any worlds, and spend its final days quietly studying invisible magnetic phenomena. The team settled on perhaps the gnarliest conclusion: Chuck the spacecraft right into Saturn itself, where it would disintegrate in the atmosphere.
Scientists still wanted to make Cassini’s final months really count. They devised a dramatic scheme that involved threading the spacecraft through the unexplored gap between Saturn and its rings nearly a dozen times before its final plunge. When Julie Webster, who served as the spacecraft operations manager, heard the plan, “it was a real WTF moment.” That region might be filled with menacing micrometeoroids. “At the speed you're going, a BB can take out your spacecraft,” Webster says.
They went for it anyway. Over several months in 2017, Cassini skimmed the top of the planet’s atmosphere and nearly brushed the sparkly bands of ice. By the time the spacecraft dipped toward Saturn for good, Maize says, its gas tank was nearly empty. Webster could imagine the demise in vivid detail; after 20 years, she knew Cassini’s responses to various maneuvers, technical idiosyncrasies that felt like a real personality. “I put my heart and soul into Cassini,” she says, and it seemed as if the spacecraft did too. During the plunge, Cassini’s thrusters kept firing, fighting to keep the antenna directed toward Earth to report every detail about the wild journey down.
(A reflection on Cassini's enduring legacy.)
In our own atmosphere, Swift will make a silent plunge; NASA shut down the telescope several weeks ago in preparation for the end. But the push to save it speaks to a certain culture within space agencies, particularly at NASA, that failure is not an option, and the belief that there’s always another fix, one more Hail Mary. Nearly half a century into the mission, engineers are still trying new things to keep the twin Voyager probes alive as they coast through interstellar space, even as Voyager 1 nears a distance record of one light-day from Earth. Just last week, NASA asked commercial companies to submit ideas for a mission that would boost the Hubble Space Telescope, which has been orbiting Earth since 1990, and is experiencing the same atmospheric drag as Swift.
The failed Swift operation was perhaps the most ambitious rescue attempt of an uncrewed mission in space history. The telescope lacks a propulsion system of its own, and recent space weather, courtesy of the sun, has hastened natural atmospheric drag. NASA hired a private spaceflight company called Katalyst to build a craft to grab the telescope and pull it into a higher orbit. Katalyst engineers had just nine months to design, build, and launch the craft—“a crazy, tight schedule,” Cenko says. To buy more time, Swift’s engineers pointed the cylinder-shaped observatory in certain directions to minimize drag, a hack they had figured out could reduce altitude loss.
The savior spacecraft launched in July, but the robot tumbled out of control as it neared the telescope. Attempts to rescue the rescue mission were unsuccessful, and the vehicle burned up in the atmosphere in September. If it had succeeded, the mission would have added another decade to the telescope’s lifetime.
Swift’s death will probably go like this: The telescope crosses the point of no return, toward the atmosphere’s unrelenting friction. Its rapid descent crushes the air particles in the way, creating scorching temperatures and a shockwave. The solar panels, protruding like delicate dragonfly wings from the body of the spacecraft, are likely torn off first. The exterior melts, and the structure buckles, breaking apart from the outside in. “It's like throwing an appliance into a fire,” says Stijn Lemmens, a space-debris analyst at the European Space Agency.
Then it’s a free fall, with nearly every bit of Swift disintegrating, not unlike the cosmic rocks that have rained down on Earth for eons. For a brief time, the dying mission may resemble a meteor streaking across the sky, shimmering like stardust.
