The U.S. Space Force found a balloon that had been lost for a quarter century. The object is S73-7, the Infra-Red Calibration Balloon, cataloged as object 7244. It launched in 1974 as a piggyback on a KH-9 Hexagon spy satellite and was supposed to inflate into a 26-inch calibration target for ground sensors. It did not fully inflate. It became junk. It dropped out of tracking, flickered back in the early 1990s, then vanished again. New two-line elements started appearing on April 25, 2024. Harvard-Smithsonian astrophysicist Jonathan McDowell flagged it on April 29: «Congrats to whichever @18thSDS analyst made the identification.»
The 18th Space Defense Squadron catalogs man-made objects in orbit. There are tens of thousands of them, most of them dead. S73-7 is small, not very metallic, and has a miserable radar cross-section. McDowell noted it might even be a dispenser or a misfiled fragment. Its altitude had dropped only about nine miles from the original near-500-mile orbit, so re-entry is not imminent. Finding it matters because collision avoidance only works if you know what the rocks are.
The AEGIS Alliance covered the other half of the space-communications problem when NASA’s Psyche spacecraft lasered a message home from 140 million miles. For how you eat once you get there, see the Wageningen intercropping tests in fake Martian dirt. More of this beat is in Science. McDowell’s note is here.
