Salyut 6 "double explosion" seen by cosmonaut Kovalyonok (Earth orbit, 1981)

In 1981, during the Soyuz T-4 mission to Salyut 6, commander Vladimir Kovalyonok was running on the station's treadmill when he saw an object moving below them, against the Earth, in the same orbital plane. He called flight engineer Viktor Savinykh to fetch a camera. Before Savinykh could take a picture, the object seemed to shrink inward and burst in two flashes, and seconds later the station passed into Earth's shadow. Later accounts date the sighting to 5 May 1981, which has not been checked against the flight log.

Kovalyonok says he reported it to the State Commission. He has always been careful about it: distances in orbit are impossible to judge, and he thinks it was a man-made object of terrestrial origin, not an alien craft. A rocket stage, a vented cloud or debris close to the window are all possible. No official record, photograph or mission-control transcript of the event has been published.

Sources: Kovalyonok, Russian television interview (Homocosmicus mirror)