Following the links in this comment by @Uwe I've found some interesting sources of information on Ham (amateur) radio operators trying to listen in on Apollo transmissions.

At the bottom of Sven Grahn's Tracking Apollo-17 from Florida there is a table of time points and events. Near the bottom is an item for December 12, 1972 at 22:12 UT.

2212    Perfect voice: "The barber pole - it is gray".:

It links to this audio recording of the Apollo-17 transmission received by the amateur station.

Question: What is a barber pole, and what did "it is gray" mean?


2 Answers 2


Here's a closeup of some Apollo CM switches and talkbacks from the Apollo 15 flight journal:

Apollo CM panel switches and talkbacks, highlighted From that page:

The "gray talkback" referred to by Dave Scott is an example of the indicators which were mounted around some of the instrument panels. Each talkback consisted of a small window with a black and white stripe pattern behind it - the "barber pole" often referred to during the mission. A gray flag could move in front of the barber pole stripes to indicate the status of a particular system. The gray flag would be driven by a control signal from the system in question and it told the crew what was going on in that system, therefore the indicator was called a talkback. Gray was essentially a normal or "doing nothing" indication. A barber pole in the talkback usually meant an abnormal or transient status.

This photograph, kindly supplied by Bruce Yarbro, is of the RCS talkbacks in the Apollo 13 Command Module, Odyssey. The two talkbacks to the left are for the Command Module's RCS system, which will not be activated until re-entry. The four talkbacks to the right show half-barber pole in this photo and are the same as those in question.

[A switch is highlighted in purple; that switch's corresponding talkback, currently gray, is highlighted in orange. Another talkback showing "half barberpole" is highlighted in blue.]

Wikipedia gives the mission start time as December 7, 1972, 05:33:00 UTC, so December 12 22:12 UTC should be 5 days, 16 hours, 39 minutes into the mission (or 136 hours, 39 minutes -- some records break out the days, some don't).

I went looking for that particular call in the Apollo 17 transcripts -- no joy on the Command Module onboard recorder transcript, but the air-to-ground recording has it at 5:16:37, I think:

(CMP is Command Module Pilot Evans; CC is Capcom on Earth)



CC: Roger. We got it.

CMP: ...wherever that is.

CMP: Okay. RECORDER is going OFF, not the HEATERS. RADAR is OFF. DATA SYSTEM is ON. Uh-oh. Should have the SM/AC POWER switch up - up there (laughter) at 230, as much as we use it.

CC: Roger. I concur with that one. I thought it would only be in the simulation that it would get to you on that one.

CMP†: (Laughter) Yes. Okay. SM/AC POWER is ON. The old MAPPER's going to STANDBY. IR is going ON. SELF TEST is going to HEATERS. UV is going ON. Now, we're going to open IR and we're going to wait on UV.


CC: We concur with that, Ron.

CMP: Okay.

CC: We'll give you a cue on that UV COVER, OPEN, here.


CMP: Okay, there's the IR. Barber pole. And a gray.

† Incorrectly attributed to CDR; this exchange occurred while the LM was on the surface so it seems unlikely the commander would have jumped into the checklist.

So our ham operator's watch may have been off by a minute or two.

These operations seem to be in reference to scientific instruments carried in the service module SIM bay, including an ultraviolet (UV) spectrometer to study the moon's (extremely tenuous) atmosphere and an infrared (IR) radiometer to study the cooling of the moon's surface soil at night. "Mapper" is probably the laser altimeter.

There are a number of calls of the form "[some control], barberpole... gray" where a crew member is throwing a switch, observing the "in-progress" barberpole indicator, then reporting the operation completed, e.g. this one where Evans is operating the docking probe circuit breaker at 01:10:20 MET:

CMP: DOCKING PROBE, EXTEND/RELEASE; EXTEND/RELEASE until probe extension. Okay, I'm going to hit it real lightly .... barber pole and gray. I hear a - I thought it went bump, didn't it?

There's also a lot of "barberpole plus three" or "plus four" in relation to camera settings; in those cases each throw of the switch would advance one step through a cycle of possible settings, one of which would show barberpole so that the operator would know where in the cycle they were. "Barberpole plus three" would mean toggling the switch as many times as necessary until barberpole appeared, then toggling three more times. (h/t @hobbs for that clarification.)

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    $\begingroup$ As for the last, the SIM bay cameras had some adjustments (like motion compensation) that weren't direct control / readout; there was a button to cycle through the settings one-by-one, and a certain setting would readback as barber pole so you could figure out where in the sequence you were. So "barber pole plus three" is "press the button until you get a barber pole, then three more times." $\endgroup$
    – hobbs
    Commented Dec 24, 2017 at 19:48
  • $\begingroup$ @hobbs Ahhh, thanks! I’ll incorporate that. $\endgroup$ Commented Dec 24, 2017 at 21:46
  • $\begingroup$ This is a great answer! $\endgroup$ Commented Dec 24, 2017 at 22:43

I don't know specifically which one, but I'd lay large odds the quote refers to a "talkback".

Shuttle and Apollo used electromechanical "talkbacks" to provide status indications on the control panels. The talkbacks showed various statuses like ON, OFF, OP, CL, sometimes just gray, etc. If the signals driving them were lost, or in a conflicting state, the talkback would show "barberpole" - a pattern of diagonal black and white stripes.

A gray talkback indicated nominal operating status. Here's a fuel cell procedure from the Orbit Pocket Checklist asking the crew to check that some talkbacks (tb) are gray or barberpole (bp).

enter image description here

Here's are some pictures I took in an orbiter in the OPF a while back. You can see various talkback statuses including a barberpole talkback on the Emergency Oxygen isolation valve.

enter image description here

enter image description here

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    $\begingroup$ Barberpole talkback might also indicate that something was in progress -- an antenna or something moving from one position to another. You'd flip the switch, get barberpole for a second, then gray. $\endgroup$ Commented Dec 23, 2017 at 18:06
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    $\begingroup$ We have 12-Dec-1972 22:12 UTC and the link also says it's Ron Evans. It might be possible to track it down to the specific barber pole. It's slightly historic being a recording made by amateurs. $\endgroup$
    – uhoh
    Commented Dec 23, 2017 at 18:13
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    $\begingroup$ I wouldn't be surprised if it meant the comm link came online so the tb went from bp to gray. But I don't know the Apollo comm system. @RussellBorogove what you describe was common for shuttle mechanical systems - tb would show closed, you hit the switch to open it, tb goes bp because it sees neither the OP or CL indication while the mechanism is moving, then tb shows OP when it gets the open indication. $\endgroup$ Commented Dec 23, 2017 at 18:14
  • $\begingroup$ Ahhh, found it! $\endgroup$ Commented Dec 23, 2017 at 18:36
  • $\begingroup$ Excellent! Nice job. $\endgroup$ Commented Dec 23, 2017 at 18:46

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