After nearly 22 years in orbit, one of NASA’s most productive space telescopes has fallen silent. The agency announced on October 23 that the Neil Gehrels Swift Observatory has ended its science mission. Swift made its final observation on October 20 and is expected to re-enter Earth’s atmosphere within the next few weeks.
The reason is simple physics. Every satellite in low Earth orbit feels a little drag from the thin upper atmosphere, and strong solar activity this year has made that atmosphere swell. Swift, which has no engine of its own, began to sink faster than planned. A daring commercial rescue, in which a newly built servicing satellite was supposed to grab Swift and push it higher, ended in August without a boost attempt after the rescue craft ran into attitude control problems.
Once Swift dropped below about 275 kilometers, or 171 miles, the drag became too strong for its telescopes to point steadily at their targets. The spacecraft slipped into safe mode, and the operations team at Penn State sent the command that effectively ended its work.
Swift was built for a two-year primary mission. It lasted more than ten times as long. Its specialty was speed: it could swing around within minutes to catch fleeting cosmic events before they faded. Over its lifetime it observed more than 2,000 gamma-ray bursts, the most powerful explosions in the universe, studied more than 1,400 supernovae, watched stars being torn apart by black holes and kept an eye on comets and asteroids closer to home. Its data has fed about 7,000 scientific papers.
The good news is that the science does not end with the spacecraft. Swift leaves behind a public archive of about 12 terabytes, including more than 1.5 million ultraviolet and optical images. Astronomers will be mining it for decades, even as NASA looks for new ways to react quickly when the sky suddenly lights up.
