Apollo 10 'outer-space music'

Apollo 10 flew in May 1969 as the dress rehearsal for the first Moon landing. Its crew were commander Tom Stafford, command module pilot John Young and lunar module pilot Gene Cernan. A tape recorder inside the command module captured the crew's own conversation, including stretches when the spacecraft was behind the Moon and cut off from radio contact with Earth.

NASA's onboard voice transcript records the exchange at about 102 hours and 13 minutes into the mission. Cernan says: That music even sounds outer-spacy, doesn't it? You hear that? That whistling sound? Young asks, Did you hear that whistling sound, too? and Cernan answers, Sounds like, you know, outer-space-type music. A few minutes later the transcript has the line Nobody will believe us, and later still Cernan says that eerie music is what's bothering me, and the crew discuss whether to tell the ground about it.

The recordings drew wide attention twice. Reports have described the transcripts as kept secret until their release in 2008, and in February 2016 the Science Channel series NASA's Unexplained Files played the audio. NASA said the material had never been classified. CBS News reported that the full transcript had been published in 1973 and later put online; it is now on NASA's own transcript page.

The crew themselves were already guessing at the cause. A few seconds after the 'nobody will believe us' line, Young's next remark, partly garbled in the transcript, mentions the VHF radio. NASA engineers explained the sound as interference between the VHF radios of the command module and the lunar module flying near each other. Michael Collins, who flew Apollo 11 two months later, wrote in his 1974 book Carrying the Fire that he heard the same whistling and had been warned about it in advance.