Weighing approximately 3,200 pounds (1,452 kg), the observatory was set to tumble out of orbit and disintegrate somewhere over the tropics. According to NASA, any fragments that survived the re-entry were unlikely to pose a threat to populated areas.
NASA said in an online statement that the US Space Force had estimated the probability of the satellite causing harm to anyone on Earth at one in 2,100. NASA initially projected the re-entry to take place at approximately 3:30 a.m. EST (0830 GMT).
However, different estimates pointed to varying re-entry times. The Aerospace Corporation, a nonprofit national security research entity, projected a re-entry window beginning at 5:19 a.m. EST, with a margin of plus or minus two hours.
London-based astrophysicist Jonathan McDowell, an honorary professor at the Durham University Space Research Centre, cited revised US Space Force data indicating that the most likely re-entry time was around 7:45 a.m. EST.
“The satellite is in a very circular orbit, skimming the top of the atmosphere,” McDowell told Reuters by phone on Tuesday night.
“The question is at what point does it heat up enough that it starts breaking up.”
NASA’s Swift Observatory Studied Cosmic Explosions for 22 Years
NASA's prized $500 million Swift satellite, a first-of-its-kind multi-wavelength space observatory, had been studying gamma-ray bursts and other cosmic phenomena since 2004 through its array of three telescopes.
Originally designed for a two-year prime mission, the observatory continued operating far beyond its initial mission timeline. It explored some of the most powerful known explosions in the universe, including bursts of gamma-ray radiation originating from the cores of distant galaxies.
Swift was also used to observe a wide range of cosmic objects, including galaxies powered by supermassive black holes, stars emitting X-ray flares, and comets and asteroids travelling through Earth's own solar system.
The observatory, which does not have an onboard propulsion system of its own, had been gradually drifting towards its expected demise for months while orbiting Earth at approximately 17,000 miles per hour (27,359 kph).
Astronomers had hoped to extend the satellite's operational life by several years through a mission designed to lift it into a higher orbit.
Robotic Spacecraft Rescue Mission Abandoned After Technical Failure
In July, NASA and Arizona-based startup Katalyst launched a specially designed rescue vehicle called LINK to save the ageing observatory.
The mission involved sending the robotic spacecraft to rendezvous with Swift, attach itself to the satellite and pull it into a higher, more sustainable orbit, potentially extending the telescope's operational life by several years.
However, the rescue attempt encountered a major technical problem soon after the spacecraft reached space. LINK began spinning uncontrollably, preventing the mission from proceeding as planned.
By mid-August, mission managers had abandoned the rescue effort, leaving Swift to continue its orbital descent towards an eventual re-entry into Earth's atmosphere.
Failed Rescue Attempt Tested Technology With Military Applications
Despite its failure to save Swift, the LINK mission carried significance beyond the future of the ageing observatory. The aborted operation was the first US mission of its kind and served as a demonstration of orbital grappling technology considered pivotal to the outcome of the US-China space race.
The mission was closely monitored as a test of satellite-maintenance technology with potential dual-use military space applications.
Katalyst described the undertaking as a historic effort, highlighting that the company had designed, built and tested the LINK rescue vehicle within an unprecedented nine-month production schedule.
The project was carried out under a $30 million NASA contract.
Swift's expected atmospheric re-entry marked the end of a mission that had continued for nearly 22 years, far beyond its originally planned operational period. Although the attempt to extend its life through robotic intervention failed, the LINK mission also tested technology intended to demonstrate new possibilities for maintaining and servicing satellites in orbit.
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