This harmonica is part of the harmonica and bell set was carried by astronauts Walter "Wally" Schirra and Tom Stafford aboard Gemini 6 in December of 1965. The mission was to test the docking and maneuvering capability of the Gemini spacecraft.
Approximately five hours after the successful maneuvering of the two spacecraft to within six inches of each other, astronauts Schirra and Stafford played "Jingle Bells" with these instruments and pretended to be a UFO called Santa Claus.
Ever the test pilot, Schirra reported that before he donated the instrument to the Smithsonian, he had "retested the harmonica and it performs quite well." He gave it to the Museum in 1967.