An experimental spy satellite that was deemed "lost" after eluding detection for decades has finally been found. "The S73-7 satellite has been rediscovered after being untracked for 25 years," astrophysicist Jonathan McDowell said in an April 29 post on X, formerly Twitter. He says it reappeared on April 25, citing Space Force data.

The Cold War-era satellite, officially called the Infra-Red Calibration Balloon (S73-7), was just over 2 feet in diameter. The U.S. Air Force's Space Test program launched it on April 10, 1974, with a much larger spy satellite, Gizmodo reported.

According to the outlet, the balloon was supposed to inflate after launch, but something went wrong. After the failure, teams back home lost track of the balloon twice—once in the 1970s and then again for much longer starting in the 1990s when ground-based sensors could no longer detect it.

For a quarter-century, analysts in the 18th Space Defense Squadron, the group responsible for tracking all human-made objects in Earth's orbit, saw nothing of S73-7, Popular Science reported. In the minds of experts, the balloon was now lost in the world of "space junk.