On Christmas Day in 2013, a rocket blasted off from the Russian Federal Space Agency’s Plesetsk Cosmodrome, about 500 miles north of Moscow. The 95-foot-tall, 118-ton Rokot booster—an unarmed version of a Cold War nuclear-tipped missile—lanced into low orbit, shedding spent stages as it climbed. Seventy-five miles above the Earth’s surface, the Rokot’s nose cracked open and its payload spilled out. The rocket carried Rodnik communications satellites, according to Russian officials. It’s customary for Rodnik sats to deploy in threes, but in a notification to the United Nations, Moscow listed four spacecraft inside the Christmas Rokot.

The discrepancy was strange…and got stranger.Rodnik sats, like most orbital spacecraft, don’t have engines and can’t move under their own power. So it came as a shock to some observers on the ground—a group including amateur satellite-spotters with radios and telescopes; radar-equipped civilian researchers; and military officials monitoring banks of high-tech sensors—when the Rokot’s fourth satellite, designated Kosmos-2491, moved, propelling itself into a slightly different orbit. MORE