NASA's Swift observatory will burn up by December after nearly 2,000 gamma-ray bursts

A pulse that lasts milliseconds is hard to detect and harder to locate on the sky ^[4]. The Vela satellites the United States launched in the late 1960s to watch for banned nuclear tests in space could triangulate a gamma-ray flash to an approximate source and no further. Every flash they found appeared to come from deep space, with a position that could not be pinned down ^[5]. Thirty more years passed before the Dutch-Italian satellite BeppoSAX localized a burst to a specific patch of sky. Ground telescopes then found a fading glow there, sitting on top of a distant galaxy ^[6]. Swift, designed by the late American astronomer Neil Gehrels, searched about a sixth of the sky at a time and then turned to put two onboard telescopes on the afterglow for exact coordinates ^[7]. Those coordinates went to Earth within seconds and out to telescopes across the planet before the light dimmed to invisibility ^[8]. The name was a nod to the bird that changes direction to snag insects in flight, not an acronym ^[13].

The energies involved are why the follow-up mattered. In seconds a burst can emit as much energy as the sun does over its entire 12-billion-year lifetime, and can be detected from across most of the observable universe ^[10].

Nearly 2,000 bursts over nearly 22 years averages about 91 a year, or about 1.7 a week ^[14]. Scientific American also reports that once routine operations began, Swift saw several gamma-ray bursts per week on average ^[9]. Both figures hold only if a large share of detections never entered the catalogue of nearly 2,000. What the catalogue number leaves out is how many of those bursts got positions precise enough, and fast enough, for a ground telescope to reach the afterglow while it was still there.

Swift launched in November 2004 and orbited about 600 kilometres up, losing height as it collided with the thin molecules of the upper atmosphere, a weak force that accumulates ^[9][11]. Over the past few years, unusually large solar magnetic storms puffed the atmosphere up and increased its density at Swift's altitude. The spacecraft dropped faster than projected. By 2025 it was clear that something had to be done or the mission would be lost ^[12]. Scientific American introduces a private company, Katalyst Space, at that point in the story ^[15].

The account names no instrument now in orbit that takes over the seconds-level alert role. Whether one exists is a question it leaves open ^[16]. For nearly 22 years the trigger that the ground follow-up network worked from came from a single spacecraft. That spacecraft is coming down.