The unexpected announcement was followed by Stafford and Schirra performing a rendition of Jingle Bells on a harmonica and sleighbells they smuggled into the spacecraft.
The UFO reported by Stafford was, of course, a reference to Santa Clause as the mission took place so close to Christmas.
The astronaut later admitted the prank was planned weeks before the Gemini 6 flight.
He said: “Wally came up with the idea. He could play the harmonica, and we practised two or three times before we took off ... Read even more