NASA’s Neil Gehrels Swift Observatory is expected to make a fiery return to Earth early Wednesday morning, nearly 22 years after its launch. The spacecraft was sent into orbit to study the most powerful explosions in the universe.

Most of the 3,200 pound observatory is expected to burn up while passing through the thick inner region of Earth’s atmosphere. NASA nevertheless predicts that some pieces of the spacecraft will survive the descent and reach the ground.

“The risk of harm coming to anyone on Earth is unlikely, approximately 1 in 2,100,” NASA said in a statement Monday. The agency has not identified exactly where any surviving debris could land.

NASA expects the debris to fall somewhere between 20.6 degrees south latitude and 20.6 degrees north latitude. That region extends about 1,420 miles, or 2,285 kilometers, below and above the equator.

The projected area includes much of Central and South America, Central Africa, southern India, Southeast Asia and northern Australia. It also covers vast stretches of ocean.

The precise timing of Swift’s descent remains uncertain because prediction models typically have a margin of error of at least several hours. The nonprofit Aerospace Corporation estimated reentry at 5:19 a.m. ET, plus or minus two hours.

A more recent projection from the US Space Force placed reentry at 7:42 a.m. ET with the same margin of error. The forecasts illustrate how difficult it is to determine the exact time and location of an uncontrolled return.

If Swift were launched today, the observatory would likely face much stricter safety requirements for planning its eventual disposal, according to The Aerospace Corporation. The organization is a federally funded research and development center.

Current orbital debris mitigation standards were updated in 2019. They require that “uncontrolled reentries have an expected casualty of less than 1 in 10,000,” according to Parker Wishik, a spokesperson for The Aerospace Corporation.

Wishik said by email that “casualty” in this context means “serious injury or death.” Swift’s estimated risk of harm is approximately 1 in 2,100, according to NASA.

NASA had long known that Swift would probably face an unpredictable plunge to Earth, but the agency hoped a rescue mission launched in July could intervene. The plan called for a spacecraft to latch onto the observatory and lift it as atmospheric drag pulled Swift from its previously stable orbit.

The rescue might have extended Swift’s operating life by a decade or more, but the effort failed. Swift eventually descended to only 171 miles, or 275 kilometers, above Earth and officially stopped gathering scientific data.

“At this point, the spacecraft was no longer able to compensate for the effects of the increased drag and entered safe mode,” NASA said in a news release. Researchers at Penn State, NASA’s partner on the project and home of the Mission Operations Center, sent Swift its final shutdown command on October 20.

An increase in solar activity accelerated the observatory’s decline as the sun reached the peak of its 11 year cycle in 2024. Intense flares and coronal mass ejections caused Earth’s atmosphere to expand, increasing the drag on Swift.

Arizona based Katalyst Space Technologies assembled the rescue effort in nine months and developed a spacecraft called LINK. The vehicle was designed to grapple Swift and return it to a stable orbit, but LINK spun out of control after its July launch and never reached the observatory.

Once Swift’s fate became unavoidable, mission scientists gradually reactivated its instruments to gather observations until the end. Those instruments had been turned off for months to conserve power and reduce how quickly the spacecraft dropped from orbit.

Swift has operated as an astrophysics tool in low Earth orbit since its November 2004 launch, and no established observational replacement is waiting. Named for fast flying birds, it could pivot quickly to observe brief cosmic events including flaring black holes, gamma ray bursts, other cosmic flashes, asteroids and comets.

Despite the failed rescue, NASA may pursue similar efforts for other valuable instruments. The agency requested proposals from commercial companies about extending the Hubble Space Telescope’s life, as NASA analysis shows a 10% chance Hubble will leave orbit by 2032 and a 50% chance by 2033.

Hubble launched in 1990 and has produced some of astronomy’s most recognizable images while transforming scientists’ understanding of the cosmos. According to NASA’s request for proposals, no replacement for Hubble is expected before the 2040s.