Sometime soon—no later than December and likely earlier—one of NASA’s most successful astrophysical missions will be destroyed, doomed to burn up in Earth’s atmosphere.
The Neil Gehrels Swift Observatory has spent nearly 22 years orbiting Earth and keeping a watchful eye on the sky to detect gamma-ray bursts (GRBs)—colossal explosions in the distant universe that mark the births of black holes. These neonatal beasts create powerful pulses of high-energy light that can last mere milliseconds, making them extremely difficult not just to detect but also to locate in the sky. Swift’s clever design overcame both of those issues. And over the decades, the observatory has compiled a list of nearly 2,000 GRBs. It’s no exaggeration to say it revolutionized the science of these terrifyingly energetic objects.
The first bursts were detected in the late 1960s, in a discovery that emerged from Cold War tensions. The U.S. and the Soviet Union had agreed not to test nuclear weapons in space, but of course, neither trusted the other. The U.S. launched a series of satellites called Vela that could monitor gamma rays—such as those emitted by a detonating nuke—and triangulate their approximate source. The satellites detected quite a few flashes, but none were from bombs; they all appeared to come from deep space, though their exact positions were impossible to determine.
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It took 30 more years before the Dutch-Italian astronomical satellite BeppoSAX launched and finally saw a GRB it could locate in a specific patch of sky. Follow-up observations with ground-based telescopes saw a fading glow in that region, nailing down its position. Surprisingly, the burst was sitting right on top of a distant galaxy. If we were seeing them from so far away, these explosions must have been immensely powerful, far more luminous than anything ever seen before. It didn’t take long before black holes were at the center of the investigation, and astronomers came to understand that these bursts were their birth announcements.
Still, it wasn’t known how often the bursts occurred, how far away most were and other basic information. We needed a satellite in space that could detect them, rapidly turn to point toward them, determine their precise location and send those data to a network of telescopes on the ground to follow up.
Thus, Swift. The brainchild of the late American astronomer Neil Gehrels, it was designed to search a huge amount of celestial real estate—about 1⁄6 of the entire sky at a time—and then rapidly turn to point a pair of telescopes onboard to watch for the fading afterglow and get exact coordinates for it. Within seconds, the spacecraft would send that information to Earth and distribute it among telescopes across the planet so they could drop what they were doing and examine the fading light before it dimmed to invisibility.
In a rare move, the name for the observatory wasn’t an acronym: “Swift” was a nod to the bird, which catches insects on the fly, rapidly changing direction to snag difficult-to-capture prey.
Swift detected its first GRB less than a month after its November 2004 launch, and once routine operations started, it saw several per week on average. The science of these explosions burgeoned; researchers began to understand the complex physics of GRBs. The unimaginable forces of gravity and magnetism toss around hair-raising amounts of matter and energy—in just seconds, a GRB can emit as much energy as the sun does over its entire 12-billion-year lifetime and be detected from across most of the observable universe.
After its launch, Swift orbited about 600 kilometers above Earth’s surface. This altitude slowly dropped as it collided with ethereally thin molecules in our planet’s atmosphere—a weak force but cumulative over time. Worse, over the past few years, the sun has been erupting with unusually large magnetic storms. They caused spectacular auroras on Earth, but the outbursts also made our planet’s atmosphere puff up, increasing its density at Swift’s height. This effect dropped the spacecraft’s altitude more rapidly than projected, and by 2025, it was clear something had to be done, or else the mission would be lost.
Katalyst Space, a private company, hastily put together a plan to construct a satellite that could rendezvous with Swift and boost it to a higher orbit. NASA funded the mission, and it launched on July 3, 2026. Unfortunately the spacecraft’s orientation couldn’t be controlled, and the vehicle couldn’t meet up with Swift to save it. On August 19 NASA called the mission off, sealing Swift’s fate.
While there are several extant space missions still examining the cosmos in x-rays and gamma rays, none has the same capabilities as Swift, especially not all in one package. There are future missions planned, such as the Ultraviolet Explorer and the Space Variable Objects Monitor, that will match some of its capabilities but not all. When we lose Swift, we’ll lose a critical piece of our ability to keep tabs on the high-energy sky.
In many ways, I owe my science communication career to this mission. In 1999 Lynn Cominsky, education and public outreach (EPO) lead for Swift, hired me to be a part of her team. I left my job working on a Hubble Space Telescope camera and moved to California to join that effort. I learned a tremendous amount about GRBs, writing about them for the Swift education website and creating educational games and lessons for middle school students in which I leveraged the amazing science of gamma-ray bursts to teach basic physics. It was fun, and we reached thousands of children across the country.
Gehrels, Swift’s principal investigator, was a big supporter of our EPO efforts and read the material we posted and provided feedback. He even graciously gave some of his time to review two chapters in my book Death from the Skies!, which dealt with supernovae and GRBs. He passed away in 2017, and I will always remember him fondly.
That is to say, although Swift is a machine designed to look for incomprehensibly huge explosions from mind-crushing distances, it is entirely a human endeavor. People designed Swift, built it, launched it, analyzed its observations and used that information to the betterment of astronomy and the education of the public. The loss of this mission is a blow not just to science but to the hundreds of people involved with it.
But they persevere. I talked to Brad Cenko, current principal investigator for Swift, and to Michael Siegel, instrument lead on Swift’s Ultraviolet and Optical Telescope, and they told me that, even now, as Swift’s orbit decays, the team is working to continue observations while it can, squeezing a bit more science into the narrowing window of time left before the observatory’s demise.
Every mission must eventually end. I’ll be sad to see Swift go, but I’m proud to have been one small part of the team on this amazing mission and content in the knowledge that its legacy of helping us understand the high-energy universe will endure.