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One hundred and two hours and 12 minutes after leaving the Earth, the crew of Apollo 10 was on the far side of the Moon. Commander Tom Stafford and lunar module pilot Gene Cernan were in the lunar module Snoopy while command module pilot John Young was in his spacecraft, callsign Charlie Brown. During that orbit, the two spacecraft were traveling separately, preparing for the simulated lunar liftoff by firing the lunar module’s ascent stage like later crews would when launching from the Moon. As they plowed ahead with their flight plan and had a bit of a snack, all three men heard some “spacey music” coming in over their headsets.

Featured in the latest season of NASA’s Unexplained Files on the Science Channel, a clip from the episode (above, featuring an uncredited me) went viral over the weekend and suddenly everyone’s curious about this never-berfore-heard eerie space music.

But what really happened on the far side of the Moon that day in 1969? Well, nothing as mysterious as you might hope. A quick read of the transcript (after the video) tells what the episode clip doesn’t.

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Stafford (in the LM Snoopy): You want some more brownies?

Cernan (in the LM Snoopy): No.

Stafford: [Garble] go hungry.

Cernan: That music even sounds outer-spacey, doesn’t it? You hear that? That whistling sound?

Stafford: Yes.

Cernan: Whooooooooooo.

Young (in the CSM Charlie Brown): Did you hear that whistling sound, too?

Cernan: Yeah. Sounds like – you know, outer-space-type music.

Young: I wonder what it is.

Cernan: Hey, Tom. Is your – is your insulation all burned off here, on the front side of your window over here? Right – –

Stafford: Yeah.

Cernan: Mine’s all burned off. isn’t that weird – eerie, John?

Young: Yes, I got it, too. I was going to see who was outside.

Stafford: You mark that set of features, Gene-o. I’m going to fix us some grape juice. OK?

Young: OK man. I’ve got you 269 miles (498 km) over the [garble] Man, that’s [garble] that’s just fabulous.

Cernan: You’ll want the LGC.

Young: Roger. I’m [garble].

Cernan: There’s the one Jack wants a picture of, over there. I’ll get that one for him with this camera, Yes, these pictures that [Lunar] Orbiter took are fantastic.

Stafford: Bet I’m locked on a side lobe.

Cernan: Yes, we sure is getting high.

Young: Yes. 286 miles. Oh, this radar is [garble] great.

Stafford: Yes. I got it.

Young: It’s going to go right out to 310 [nautical] miles. Just like we said.

Cernan: Is it really?

Young: Yes. I’ll tell you when you get to 327 (nautical miles, 605 km). You don’t – you don’t know when AOS is … do you?

Cernan: Yes, I’ve got it written down. AOS [acquisition of signal with Houston] for us is 102:25. (Cough)

Young: It’s 102:21 for me.

Cernan: OK. 40 minutes, babe. I got to connect the ascent batteries.

Stafford: OK.

Cernan: OK. Stand by BAT’s 1 and 3, High Voltage, Off/Reset. Bat’s 1… [Batteries 1 & 3 are in the descent stage, and Cernan is taking them off the bus.]

Stafford: OK.

Cernan: Boy, that sure is weird music. [It’s been about 6 minutes since they first mentioned hearing the music.]

Young: We’re going to have to find out about that. Nobody will believe us.

Cernan: No. It’s a whistling, you know, like an outer space-type thing.

Young: Probably due to the VHF [Very High Frequency radio] ranging, I’d guess.

Cernan: Yes. I wouldn’t believe there’s anyone out there. OK, Tom, I’m going to call up P20… We want to pressurize our APS here. You get your Rendezvous Radar breakers all In?

Cernan and Stafford during Apollo 10’s mission

Cernan and Stafford during Apollo 10’s mission

The crew was obviously curious and maybe just a little weirded out by the eerie sounds coming in through their headsets, enough to mention it to each other. But none of the men was so concerned that he lost focus on the task at hand. The transcript shows their procedural conversation is peppered with a few mentions of the eerie sounds, but they also continued photographing craters on the Moon, checking their flight plan against the upcoming moment they would reacquire communications with Houston, and ate some brownies and grape juice. And Young quickly solves the mystery. He points out to his crew mates that it’s probably nothing more than radio interference between the two spacecraft, which is all that it was. Apollo 10 was the first mission to take two spacecraft each with a radio communication system to the Moon and fly them separately in lunar orbit making them the first to experience the eerie feedback. But they weren’t the last. Apollo 11 command module pilot Mike Collins also heard the strange sounds, but knew from the previous mission that it wasn’t anything alien.

The “eerie music incident” isn’t often discussed when Apollo 10 comes up among space nerds, and it doesn’t even get a mention in John Young’s memoirs. The far more famous (or perhaps infamous) moment of the flight involving a radio is when Cernan cursed over an open channel for the world to hear.

About a half hour after the discussion of space music, it was time for Apollo 10 to “launch” from the lunar module’s descent stage, effectively practicing what later missions would do leaving the Moon. Almost immediately after stage separation, the LM ascent stage started spinning wildly, eliciting a hearty “son of a bitch” from Cernan, which I talked to him about the first time I met him. Post-flight analysis found that a single switch in the wrong position was the culprit. The spacecraft’s Abort Guidance System had two modes: “auto” had it hunt for the command module for docking and “attitude hold” would maintain the spacecraft’s current attitude. The switch was in auto, sending Snoopy spinning trying to find Charlie Brown on the other side of the Moon. But the crew reaction quickly and got the spacecraft under control.

And there were far more fun instances of music on Apollo 10, too, namely the most apt playing of Frank Sinatra’s “Fly Me To the Moon” there ever was!

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Sources: Apollo 10 at the Apollo Lunar Flight Journal; Apollo 10 Timeline; Vintage Space.